Infomotions, Inc.Darwin and Modern Science / Seward, Albert Charles, Sir, 1863-1941



Author: Seward, Albert Charles, Sir, 1863-1941
Title: Darwin and Modern Science
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Darwin and Modern Science

by A.C. Seward

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DARWIN AND MODERN SCIENCE

ESSAYS IN COMMEMORATION OF THE CENTENARY OF THE BIRTH OF CHARLES DARWIN AND
OF THE FIFTIETH ANNIVERSARY OF THE PUBLICATION OF "THE ORIGIN OF SPECIES"


BY

A.C. SEWARD




"My success as a man of science, whatever this may have amounted to, has
been determined, as far as I can judge, by complex and diversified mental
qualities and conditions.  Of these, the most important have been--the love
of science--unbounded patience in long reflecting over any subject--
industry in observing and collecting facts--and a fair share of invention
as well as of common sense.  With such moderate abilities as I possess, it
is truly surprising that I should have influenced to a considerable extent
the belief of scientific men on some important points."

Autobiography (1881); "The Life and Letters of Charles Darwin", Vol. 1.
page 107.


PREFACE

At the suggestion of the Cambridge Philosophical Society, the Syndics of
the University Press decided in March, 1908, to arrange for the publication
of a series of Essays in commemoration of the Centenary of the birth of
Charles Darwin and of the Fiftieth anniversary of the publication of "The
Origin of Species".  The preliminary arrangements were made by a committee
consisting of the following representatives of the Council of the
Philosophical Society and of the Press Syndicate:  Dr H.K. Anderson, Prof.
Bateson, Mr Francis Darwin, Dr Hobson, Dr Marr, Prof. Sedgwick, Mr David
Sharp, Mr Shipley, Prof. Sorley, Prof. Seward.  In the course of the
preparation of the volume, the original scheme and list of authors have
been modified:  a few of those invited to contribute essays were, for
various reasons, unable to do so, and some alterations have been made in
the titles of articles.  For the selection of authors and for the choice of
subjects, the committee are mainly responsible, but for such share of the
work in the preparation of the volume as usually falls to the lot of an
editor I accept full responsibility.

Authors were asked to address themselves primarily to the educated layman
rather than to the expert.  It was hoped that the publication of the essays
would serve the double purpose of illustrating the far-reaching influence
of Darwin's work on the progress of knowledge and the present attitude of
original investigators and thinkers towards the views embodied in Darwin's
works.

In regard to the interpretation of a passage in "The Origin of Species"
quoted by Hugo de Vries, it seemed advisable to add an editorial footnote;
but, with this exception, I have not felt it necessary to record any
opinion on views stated in the essays.

In reading the essays in proof I have availed myself freely of the willing
assistance of several Cambridge friends, among whom I wish more especially
to thank Mr Francis Darwin for the active interest he has taken in the
preparation of the volume.  Mrs J.A. Thomson kindly undertook the
translation of the essays by Prof. Weismann and Prof. Schwalbe; Mrs James
Ward was good enough to assist me by translating Prof. Bougle's article on
Sociology, and to Mr McCabe I am indebted for the translation of the essay
by Prof. Haeckel.  For the translation of the botanical articles by Prof.
Goebel, Prof. Klebs and Prof. Strasburger, I am responsible; in the
revision of the translation of Prof. Strasburger's essay Madame Errera of
Brussels rendered valuable help.  Mr Wright, the Secretary of the Press
Syndicate, and Mr Waller, the Assistant Secretary, have cordially
cooperated with me in my editorial work; nor can I omit to thank the
readers of the University Press for keeping watchful eyes on my
shortcomings in the correction of proofs.

The two portraits of Darwin are reproduced by permission of Messrs Maull
and Fox and Messrs Elliott and Fry.  The photogravure of the study at Down
is reproduced from an etching by Mr Axel Haig, lent by Mr Francis Darwin;
the coloured plate illustrating Prof. Weismann's essay was originally
published by him in his "Vortrage uber Descendenztheorie" which afterwards
appeared (1904) in English under the title "The Evolution Theory".  Copies
of this plate were supplied by Messrs Fischer of Jena.

The Syndics of the University Press have agreed, in the event of this
volume being a financial success, to hand over the profits to a University
fund for the endowment of biological research.

It is clearly impossible to express adequately in a single volume of Essays
the influence of Darwin's contributions to knowledge on the subsequent
progress of scientific inquiry.  As Huxley said in 1885:  "Whatever be the
ultimate verdict of posterity upon this or that opinion which Mr Darwin has
propounded; whatever adumbrations or anticipations of his doctrines may be
found in the writings of his predecessors; the broad fact remains that,
since the publication and by reason of the publication of "The Origin of
Species" the fundamental conceptions and the aims of the students of living
Nature have been completely changed...But the impulse thus given to
scientific thought rapidly spread beyond the ordinarily recognised limits
of Biology.  Psychology, Ethics, Cosmology were stirred to their
foundations, and 'The Origin of Species' proved itself to be the fixed
point which the general doctrine needed in order to move the world."

In the contributions to this Memorial Volume, some of the authors have more
especially concerned themselves with the results achieved by Darwin's own
work, while others pass in review the progress of research on lines which,
though unknown or but little followed in his day, are the direct outcome of
his work.

The divergence of views among biologists in regard to the origin of species
and as to the most promising directions in which to seek for truth is
illustrated by the different opinions of contributors.  Whether Darwin's
views on the modus operandi of evolutionary forces receive further
confirmation in the future, or whether they are materially modified, in no
way affects the truth of the statement that, by employing his life "in
adding a little to Natural Science," he revolutionised the world of
thought.  Darwin wrote in 1872 to Alfred Russel Wallace:  "How grand is the
onward rush of science:  it is enough to console us for the many errors
which we have committed, and for our efforts being overlaid and forgotten
in the mass of new facts and new views which are daily turning up."  In the
onward rush, it is easy for students convinced of the correctness of their
own views and equally convinced of the falsity of those of their fellow-
workers to forget the lessons of Darwin's life.  In his autobiographical
sketch, he tells us, "I have steadily endeavoured to keep my mind free so
as to give up any hypothesis, however much beloved...as soon as facts are
shown to be opposed to it."  Writing to Mr J. Scott, he says, "It is a
golden rule, which I try to follow, to put every fact which is opposed to
one's preconceived opinion in the strongest light.  Absolute accuracy is
the hardest merit to attain, and the highest merit.  Any deviation is
ruin."

He acted strictly in accordance with his determination expressed in a
letter to Lyell in 1844, "I shall keep out of controversy, and just give my
own facts."  As was said of another son of Cambridge, Sir George Stokes,
"He would no more have thought of disputing about priority, or the
authorship of an idea, than of writing a report for a company promoter." 
Darwin's life affords a striking confirmation of the truth of Hazlitt's
aphorism, "Where the pursuit of truth has been the habitual study of any
man's life, the love of truth will be his ruling passion."  Great as was
the intellect of Darwin, his character, as Huxley wrote, was even nobler
than his intellect.

A.C. SEWARD.

Botany School, Cambridge,
March 20, 1909.


CONTENTS

I.  INTRODUCTORY LETTER TO THE EDITOR from SIR JOSEPH DALTON HOOKER, O.M.

II.  DARWIN'S PREDECESSORS:
  J. ARTHUR THOMSON, Professor of Natural History in the University of
Aberdeen.

III.  THE SELECTION THEORY:
  AUGUST WEISMANN, Professor of Zoology in the University of Freiburg
(Baden).

IV.  VARIATION:
  HUGO DE VRIES, Professor of Botany in the University of Amsterdam.

V.  HEREDITY AND VARIATION IN MODERN LIGHTS:
  W. BATESON, Professor of Biology in the University of Cambridge.

VI.  THE MINUTE STRUCTURE OF CELLS IN RELATION TO HEREDITY:
  EDUARD STRASBURGER, Professor of Botany in the University of Bonn.

VII.  "THE DESCENT OF MAN":
  G. SCHWALBE, Professor of Anatomy in the University of Strassburg.

VIII.  CHARLES DARWIN AS AN ANTHROPOLOGIST:
  ERNST HAECKEL, Professor of Zoology in the University of Jena.

IX.  SOME PRIMITIVE THEORIES OF THE ORIGIN OF MAN:
  J.G. FRAZER, Fellow of Trinity College, Cambridge.

X.  THE INFLUENCE OF DARWIN ON THE STUDY OF ANIMAL EMBRYOLOGY:
  A. SEDGWICK, Professor of Zoology and Comparative Anatomy in the
University of Cambridge.

XI.  THE PALAEONTOLOGICAL RECORD.  I. ANIMALS:
  W.B. SCOTT, Professor of Geology in the University of Princeton.

XII.  THE PALAEONTOLOGICAL RECORD.  II. PLANTS:
  D.H. SCOTT, President of the Linnean Society of London.

XIII.  THE INFLUENCE OF ENVIRONMENT ON THE FORMS OF PLANTS:
  GEORG KLEBS, Professor of Botany in the University of Heidelberg.

XIV.  EXPERIMENTAL STUDY OF THE INFLUENCE OF ENVIRONMENT ON ANIMALS:
  JACQUES LOEB, Professor of Physiology in the University of California.

XV.  THE VALUE OF COLOUR IN THE STRUGGLE FOR LIFE:
  E.B. POULTON, Hope Professor of Zoology in the University of Oxford.

XVI.  GEOGRAPHICAL DISTRIBUTION OF PLANTS:
  SIR WILLIAM THISELTON-DYER.

XVII.  GEOGRAPHICAL DISTRIBUTION OF ANIMALS:
  HANS GADOW, Strickland Curator and Lecturer on Zoology in the University
of Cambridge.

XVIII.  DARWIN AND GEOLOGY:
  J.W. JUDD.

XIX.  DARWIN'S WORK ON THE MOVEMENTS OF PLANTS:
  FRANCIS DARWIN.

XX.  THE BIOLOGY OF FLOWERS:
  K. GOEBEL, Professor of Botany in the University of Munich.

XXI.  MENTAL FACTORS IN EVOLUTION:
  C. LLOYD MORGAN, Professor of Psychology at University College, Bristol.

XXII.  THE INFLUENCE OF THE CONCEPTION OF EVOLUTION ON MODERN PHILOSOPHY:
  H. HOFFDING, Professor of Philosophy in the University of Copenhagen.

XXIII.  DARWINISM AND SOCIOLOGY:
  C. BOUGLE, Professor of Social Philosophy in the University of Toulouse,
and Deputy-Professor at the Sorbonne, Paris.

XXIV.  THE INFLUENCE OF DARWIN UPON RELIGIOUS THOUGHT:
  REV. P.N. WAGGETT.

XXV.  THE INFLUENCE OF DARWINISM ON THE STUDY OF RELIGIONS:
  JANE ELLEN HARRISON, Staff-Lecturer and sometime Fellow of Newnham
College, Cambridge.

XXVI.  EVOLUTION AND THE SCIENCE OF LANGUAGE:
  P. GILES, Reader in Comparative Philology in the University of Cambridge.

XXVII.  DARWINISM AND HISTORY:
  J.B. BURY, Regius Professor of Modern History in the University of
Cambridge.

XXVIII.  THE GENESIS OF DOUBLE STARS:
  SIR GEORGE DARWIN, Plumian Professor of Astronomy and Experimental
Philosophy in the University of Cambridge.

XXIX.  THE EVOLUTION OF MATTER:
  W.C.D. WHETHAM, Fellow of Trinity College, Cambridge.

INDEX.


DATES OF THE PUBLICATION Of CHARLES DARWIN'S BOOKS AND OF THE PRINCIPAL
EVENTS IN HIS LIFE

1809:

Charles Darwin born at Shrewsbury, February 12.

1817:

"At 8 1/2 years old I went to Mr Case's school."  (A day-school at
Shrewsbury kept by the Rev G. Case, Minister of the Unitarian Chapel.)

1818:

"I was at school at Shrewsbury under a great scholar, Dr Butler; I learnt
absolutely nothing, except by amusing myself by reading and experimenting
in Chemistry."

1825:

"As I was doing no good at school, my father wisely took me away at a
rather earlier age than usual, and sent me (Oct. 1825) to Edinburgh
University with my brother, where I stayed for two years."

1828:

Began residence at Christ's College, Cambridge.

"I went to Cambridge early in the year 1828, and soon became acquainted
with Professor Henslow...Nothing could be more simple, cordial and
unpretending than the encouragement which he afforded to all young
naturalists."

"During the three years which I spent at Cambridge my time was wasted, as
far as the academical studies were concerned, as completely as at Edinburgh
and at school."

"In order to pass the B.A. Examination, it was...necessary to get up
Paley's 'Evidences of Christianity,' and his 'Moral Philosophy'...The
careful study of these works, without attempting to learn any part by rote,
was the only part of the academical course which...was of the least use to
me in the education of my mind."

1831:

Passed the examination for the B.A. degree in January and kept the
following terms.

"I gained a good place among the oi polloi or crowd of men who do not go in
for honours."

"I am very busy,...and see a great deal of Henslow, whom I do not know
whether I love or respect most."

Dec. 27.  "Sailed from England on our circumnavigation," in H.M.S.
"Beagle", a barque of 235 tons carrying 6 guns, under Capt. FitzRoy.

"There is indeed a tide in the affairs of men."

1836:

Oct. 4.  "Reached Shrewsbury after absence of 5 years and 2 days."

"You cannot imagine how gloriously delightful my first visit was at home;
it was worth the banishment."

Dec. 13.  Went to live at Cambridge (Fitzwilliam Street).

"The only evil I found in Cambridge was its being too pleasant."

1837:

"On my return home (in the 'Beagle') in the autumn of 1836 I immediately
began to prepare my journal for publication, and then saw how many facts
indicated the common descent of species...In July (1837) I opened my first
note-book for facts in relation to the Origin of Species, about which I had
long reflected, and never ceased working for the next twenty years...Had
been greatly struck from about the month of previous March on character of
South American fossils, and species on Galapagos Archipelago.  These facts
(especially latter), origin of all my views."

"On March 7, 1837 I took lodgings in (36) Great Marlborough Street in
London, and remained there for nearly two years, until I was married."

1838:

"In October, that is fifteen months after I had begun my systematic
enquiry, I happened to read for amusement 'Malthus on Population,' and
being well prepared to appreciate the struggle for existence which
everywhere goes on from long-continued observation of the habits of animals
and plants, it at once struck me that under these circumstances favourable
variations would tend to be preserved, and unfavourable ones to be
destroyed.  The result of this would be the formation of new species.  Here
then I had at last got a theory by which to work; but I was so anxious to
avoid prejudice, that I determined not for some time to write even the
briefest sketch of it."

1839:

Married at Maer (Staffordshire) to his first cousin Emma Wedgwood, daughter
of Josiah Wedgwood.

"I marvel at my good fortune that she, so infinitely my superior in every
single moral quality, consented to be my wife.  She has been my wise
adviser and cheerful comforter throughout life, which without her would
have been during a very long period a miserable one from ill-health.  She
has earned the love of every soul near her" (Autobiography).

Dec. 31.  "Entered 12 Upper Gower street" (now 110 Gower street, London). 
"There never was so good a house for me, and I devoutly trust you (his
future wife) will approve of it equally.  The little garden is worth its
weight in gold."

Published "Journal and Researches", being Vol. III. of the "Narrative of
the Surveying Voyage of H.M.S. 'Adventure' and 'Beagle'"...

Publication of the "Zoology of the Voyage of H.M.S. 'Beagle'", Part II.,
"Mammalia", by G.R. Waterhouse, with a "Notice of their habits and ranges",
by Charles Darwin.

1840:

Contributed Geological Introduction to Part I. ("Fossil Mammalia") of the
"Zoology of the Voyage of H.M.S. 'Beagle'" by Richard Owen.

1842:

"In June 1842 I first allowed myself the satisfaction of writing a very
brief abstract of my (species) theory in pencil in 35 pages; and this was
enlarged during the summer of 1844 into one of 230 pages, which I had
fairly copied out and still (1876) possess."  (The first draft of "The
Origin of Species", edited by Mr Francis Darwin, will be published this
year (1909) by the Syndics of the Cambridge University Press.)

Sept. 14.  Settled at the village of Down in Kent.

"I think I was never in a more perfectly quiet country."

Publication of "The Structure and Distribution of Coral Reefs"; being Part
I. of the "Geology of the Voyage of the Beagle".

1844:

Publication of "Geological Observations on the Volcanic Islands visited
during the Voyage of H.M.S. 'Beagle'"; being Part II. of the "Geology of
the Voyage of the 'Beagle'".

"I think much more highly of my book on Volcanic Islands since Mr Judd, by
far the best judge on the subject in England, has, as I hear, learnt much
from it."  (Autobiography, 1876.)

1845:

Publication of the "Journal of Researches" as a separate book.

1846:

Publication of "Geological Observations on South America"; being Part III.
of the "Geology of the Voyage of the 'Beagle'".

1851:

Publication of a "Monograph of the Fossil Lepadidae" and of a "Monograph of
the sub-class Cirripedia".

"I fear the study of the Cirripedia will ever remain 'wholly unapplied,'
and yet I feel that such study is better than castle-building."

1854:

Publication of Monographs of the Balanidae and Verrucidae.

"I worked steadily on this subject for...eight years, and ultimately
published two thick volumes, describing all the known living species, and
two thin quartos on the extinct species...My work was of considerable use
to me, when I had to discuss in the "Origin of Species" the principles of a
natural classification.  Nevertheless, I doubt whether the work was worth
the consumption of so much time."

"From September 1854 I devoted my whole time to arranging my huge pile of
notes, to observing, and to experimenting in relation to the transmutation
of species."

1856:

"Early in 1856 Lyell advised me to write out my views pretty fully, and I
began at once to do so on a scale three or four times as extensive as that
which was afterwards followed in my 'Origin of Species'."

1858:

Joint paper by Charles Darwin and Alfred Russel Wallace "On the Tendency of
Species to form Varieties; and on the perpetuation of Varieties and Species
by Natural Means of Selection," communicated to the Linnean Society by Sir
Charles Lyell and Sir Joseph Hooker.

"I was at first very unwilling to consent (to the communication of his MS.
to the Society) as I thought Mr Wallace might consider my doing so
unjustifiable, for I did not then know how generous and noble was his
disposition."

"July 20 to Aug. 12 at Sandown (Isle of Wight) began abstract of Species
book."

1859:

Nov. 24.  Publication of "The Origin of Species" (1250 copies).

"Oh, good heavens, the relief to my head and body to banish the whole
subject from my mind!...But, alas, how frequent, how almost universal it is
in an author to persuade himself of the truth of his own dogmas.  My only
hope is that I certainly see many difficulties of gigantic stature."

1860:

Publication of the second edition of the "Origin" (3000 copies).

Publication of a "Naturalist's Voyage".

1861:

Publication of the third edition of the "Origin" (2000 copies).

"I am going to write a little book...on Orchids, and to-day I hate them
worse than everything."

1862:

Publication of the book "On the various contrivances by which Orchids are
fertilised by Insects".

1865:

Read paper before the Linnean Society "On the Movements and Habits of
Climbing plants".  (Published as a book in 1875.)

1866:

Publication of the fourth edition of the "Origin" (1250 copies).

1868:

"I have sent the MS. of my big book, and horridly, disgustingly big it will
be, to the printers."

Publication of the "Variation of Animals and Plants under Domestication".

"About my book, I will give you (Sir Joseph Hooker) a bit of advice.  Skip
the whole of Vol. I, except the last chapter, (and that need only be
skimmed), and skip largely in the 2nd volume; and then you will say it is a
very good book."

"Towards the end of the work I give my well-abused hypothesis of
Pangenesis.  An unverified hypothesis is of little or no value; but if
anyone should hereafter be led to make observations by which some such
hypothesis could be established, I shall have done good service, as an
astonishing number of isolated facts can be thus connected together and
rendered intelligible."

1869:

Publication of the fifth edition of the "Origin".

1871:

Publication of "The Descent of Man".

"Although in the 'Origin of Species' the derivation of any particular
species is never discussed, yet I thought it best, in order that no
honourable man should accuse me of concealing my views, to add that by the
work 'light would be thrown on the origin of man and his history'."

1872:

Publication of the sixth edition of the "Origin".

Publication of "The Expression of the Emotions in Man and Animals".

1874:

Publication of the second edition of "The Descent of Man".

"The new edition of the "Descent" has turned out an awful job.  It took me
ten days merely to glance over letters and reviews with criticisms and new
facts.  It is a devil of a job."

Publication of the second edition of "The Structure and Distribution of
Coral Reefs".

1875:

Publication of "Insectivorous Plants".

"I begin to think that every one who publishes a book is a fool."

Publication of the second edition of "Variation in Animals and Plants".

Publication of "The Movements and Habits of Climbing Plants" as a separate
book.

1876:

Wrote Autobiographical Sketch ("Life and Letters", Vol. I., Chap II.).

Publication of "The Effects of Cross and Self fertilisation".

"I now (1881) believe, however,...that I ought to have insisted more
strongly than I did on the many adaptations for self-fertilisation."

Publication of the second edition of "Observations on Volcanic Islands".

1877:

Publication of "The Different Forms of Flowers on Plants of the same
species".

"I do not suppose that I shall publish any more books...I cannot endure
being idle, but heaven knows whether I am capable of any more good work."

Publication of the second edition of the Orchid book.

1878:

Publication of the second edition of "The Effects of Cross and Self
fertilisation".

1879:

Publication of an English translation of Ernst Krause's "Erasmus Darwin",
with a notice by Charles Darwin.  "I am EXTREMELY glad that you approve of
the little 'Life' of our Grandfather, for I have been repenting that I ever
undertook it, as the work was quite beyond my tether."  (To Mr Francis
Galton, Nov. 14, 1879.)

1880:

Publication of "The Power of Movement in Plants".

"It has always pleased me to exalt plants in the scale of organised
beings."

Publication of the second edition of "The Different Forms of Flowers".

1881:

Wrote a continuation of the Autobiography.

Publication of "The Formation of Vegetable Mould, through the Action of
Worms".

"It is the completion of a short paper read before the Geological Society
more than forty years ago, and has revived old geological thoughts...As far
as I can judge it will be a curious little book."

1882:

Charles Darwin died at Down, April 19, and was buried in Westminster Abbey,
April 26, in the north aisle of the Nave a few feet from the grave of Sir
Isaac Newton.

"As for myself, I believe that I have acted rightly in steadily following
and devoting my life to Science.  I feel no remorse from having committed
any great sin, but have often and often regretted that I have not done more
direct good to my fellow creatures."

The quotations in the above Epitome are taken from the Autobiography and
published Letters:--

"The Life and Letters of Charles Darwin", including an Autobiographical
Chapter.  Edited by his son, Francis Darwin, 3 Vols., London, 1887.

"Charles Darwin":  His life told in an Autobiographical Chapter, and in a
selected series of his published Letters.  Edited by his son, Francis
Darwin, London, 1902.

"More Letters of Charles Darwin".  A record of his work in a series of
hitherto unpublished Letters.  Edited by Francis Darwin and A.C. Seward, 2
Vols., London, 1903.


I.  INTRODUCTORY LETTER

FROM SIR JOSEPH DALTON HOOKER,

O.M., G.C.S.I., C.B., M.D., D.C.L., LL.D., F.R.S., ETC.


The Camp,

near Sunningdale,

January 15, 1909.

Dear Professor Seward,

The publication of a Series of Essays in Commemoration of the century of
the birth of Charles Darwin and of the fiftieth anniversary of the
publication of "The Origin of Species" is assuredly welcome and is a
subject of congratulation to all students of Science.

These Essays on the progress of Science and Philosophy as affected by
Darwin's labours have been written by men known for their ability to
discuss the problems which he so successfully worked to solve.  They cannot
but prove to be of enduring value, whether for the information of the
general reader or as guides to investigators occupied with problems similar
to those which engaged the attention of Darwin.

The essayists have been fortunate in having for reference the five
published volumes of Charles Darwin's Life and Correspondence.  For there
is set forth in his own words the inception in his mind of the problems,
geological, zoological and botanical, hypothetical and theoretical, which
he set himself to solve and the steps by which he proceeded to investigate
them with the view of correlating the phenomena of life with the evolution
of living things.  In his letters he expressed himself in language so lucid
and so little burthened with technical terms that they may be regarded as
models for those who were asked to address themselves primarily to the
educated reader rather than to the expert.

I may add that by no one can the perusal of the Essays be more vividly
appreciated than by the writer of these lines.  It was my privilege for
forty years to possess the intimate friendship of Charles Darwin and to be
his companion during many of his working hours in Study, Laboratory, and
Garden.  I was the recipient of letters from him, relating mainly to the
progress of his researches, the copies of which (the originals are now in
the possession of his family) cover upwards of a thousand pages of
foolscap, each page containing, on an average, three hundred words.

That the editorship of these Essays has been entrusted to a Cambridge
Professor of Botany must be gratifying to all concerned in their production
and in their perusal, recalling as it does the fact that Charles Darwin's
instructor in scientific methods was his lifelong friend the late Rev. J.S.
Henslow at that time Professor of Botany in the University.  It was owing
to his recommendation that his pupil was appointed Naturalist to H.M.S.
"Beagle", a service which Darwin himself regarded as marking the dawn of
his scientific career.

Very sincerely yours,

J.D. HOOKER.


II.  DARWIN'S PREDECESSORS.

By J. ARTHUR THOMSON.
Professor of Natural History in the University of Aberdeen.

In seeking to discover Darwin's relation to his predecessors it is useful
to distinguish the various services which he rendered to the theory of
organic evolution.

(I)  As everyone knows, the general idea of the Doctrine of Descent is that
the plants and animals of the present-day are the lineal descendants of
ancestors on the whole somewhat simpler, that these again are descended
from yet simpler forms, and so on backwards towards the literal "Protozoa"
and "Protophyta" about which we unfortunately know nothing.  Now no one
supposes that Darwin originated this idea, which in rudiment at least is as
old as Aristotle.  What Darwin did was to make it current intellectual
coin.  He gave it a form that commended itself to the scientific and public
intelligence of the day, and he won wide-spread conviction by showing with
consummate skill that it was an effective formula to work with, a key which
no lock refused.  In a scholarly, critical, and pre-eminently fair-minded
way, admitting difficulties and removing them, foreseeing objections and
forestalling them, he showed that the doctrine of descent supplied a modal
interpretation of how our present-day fauna and flora have come to be.

(II)  In the second place, Darwin applied the evolution-idea to particular
problems, such as the descent of man, and showed what a powerful organon it
is, introducing order into masses of uncorrelated facts, interpreting
enigmas both of structure and function, both bodily and mental, and, best
of all, stimulating and guiding further investigation.  But here again it
cannot be claimed that Darwin was original.  The problem of the descent or
ascent of man, and other particular cases of evolution, had attracted not a
few naturalists before Darwin's day, though no one (except Herbert Spencer
in the psychological domain (1855)) had come near him in precision and
thoroughness of inquiry.

(III)  In the third place, Darwin contributed largely to a knowledge of the
factors in the evolution-process, especially by his analysis of what occurs
in the case of domestic animals and cultivated plants, and by his
elaboration of the theory of Natural Selection, which Alfred Russel Wallace
independently stated at the same time, and of which there had been a few
previous suggestions of a more or less vague description.  It was here that
Darwin's originality was greatest, for he revealed to naturalists the many
different forms--often very subtle--which natural selection takes, and with
the insight of a disciplined scientific imagination he realised what a
mighty engine of progress it has been and is.

(IV)  As an epoch-marking contribution, not only to Aetiology but to
Natural History in the widest sense, we rank the picture which Darwin gave
to the world of the web of life, that is to say, of the inter-relations and
linkages in Nature.  For the Biology of the individual--if that be not a
contradiction in terms--no idea is more fundamental than that of the
correlation of organs, but Darwin's most characteristic contribution was
not less fundamental,--it was the idea of the correlation of organisms. 
This, again, was not novel; we find it in the works of naturalist like
Christian Conrad Sprengel, Gilbert White, and Alexander von Humboldt, but
the realisation of its full import was distinctively Darwinian.

AS REGARDS THE GENERAL IDEA OF ORGANIC EVOLUTION.

While it is true, as Prof. H.F. Osborn puts it, that "'Before and after
Darwin' will always be the ante et post urbem conditam of biological
history," it is also true that the general idea of organic evolution is
very ancient.  In his admirable sketch "From the Greeks to Darwin"
("Columbia University Biological Series", Vol. I. New York and London,
1894.  We must acknowledge our great indebtness to this fine piece of
work.), Prof. Osborn has shown that several of the ancient philosophers
looked upon Nature as a gradual development and as still in process of
change.  In the suggestions of Empedocles, to take the best instance, there
were "four sparks of truth,--first, that the development of life was a
gradual process; second, that plants were evolved before animals; third,
that imperfect forms were gradually replaced (not succeeded) by perfect
forms; fourth, that the natural cause of the production of perfect forms
was the extinction of the imperfect."  (Op. cit. page 41.)  But the
fundamental idea of one stage giving origin to another was absent.  As the
blue Aegean teemed with treasures of beauty and threw many upon its shores,
so did Nature produce like a fertile artist what had to be rejected as well
as what was able to survive, but the idea of one species emerging out of
another was not yet conceived.

Aristotle's views of Nature (See G.J. Romanes, "Aristotle as a Naturalist",
"Contemporary Review", Vol. LIX. page 275, 1891; G. Pouchet "La Biologie
Aristotelique", Paris, 1885; E. Zeller, "A History of Greek Philosophy",
London, 1881, and "Ueber die griechischen Vorganger Darwin's", "Abhandl.
Berlin Akad." 1878, pages 111-124.) seem to have been more definitely
evolutionist than those of his predecessors, in this sense, at least, that
he recognised not only an ascending scale, but a genetic series from polyp
to man and an age-long movement towards perfection.  "It is due to the
resistance of matter to form that Nature can only rise by degrees from
lower to higher types."  "Nature produces those things which, being
continually moved by a certain principle contained in themselves, arrive at
a certain end."

To discern the outcrop of evolution-doctrine in the long interval between
Aristotle and Bacon seems to be very difficult, and some of the instances
that have been cited strike one as forced.  Epicurus and Lucretius, often
called poets of evolution, both pictured animals as arising directly out of
the earth, very much as Milton's lion long afterwards pawed its way out. 
Even when we come to Bruno who wrote that "to the sound of the harp of the
Universal Apollo (the World Spirit), the lower organisms are called by
stages to higher, and the lower stages are connected by intermediate forms
with the higher," there is great room, as Prof. Osborn points out (op. cit.
page 81.), for difference of opinion as to how far he was an evolutionist
in our sense of the term.

The awakening of natural science in the sixteenth century brought the
possibility of a concrete evolution theory nearer, and in the early
seventeenth century we find evidences of a new spirit--in the embryology of
Harvey and the classifications of Ray.  Besides sober naturalists there
were speculative dreamers in the sixteenth and seventeenth centuries who
had at least got beyond static formulae, but, as Professor Osborn points
out (op. cit. page 87.), "it is a very striking fact, that the basis of our
modern methods of studying the Evolution problem was established not by the
early naturalists nor by the speculative writers, but by the Philosophers." 
He refers to Bacon, Descartes, Leibnitz, Hume, Kant, Lessing, Herder, and
Schelling.  "They alone were upon the main track of modern thought.  It is
evident that they were groping in the dark for a working theory of the
Evolution of life, and it is remarkable that they clearly perceived from
the outset that the point to which observation should be directed was not
the past but the present mutability of species, and further, that this
mutability was simply the variation of individuals on an extended scale."

Bacon seems to have been one of the first to think definitely about the
mutability of species, and he was far ahead of his age in his suggestion of
what we now call a Station of Experimental Evolution.  Leibnitz discusses
in so many words how the species of animals may be changed and how
intermediate species may once have linked those that now seem
discontinuous.  "All natural orders of beings present but a single
chain"..."All advances by degrees in Nature, and nothing by leaps." 
Similar evolutionist statements are to be found in the works of the other
"philosophers," to whom Prof. Osborn refers, who were, indeed, more
scientific than the naturalists of their day.  It must be borne in mind
that the general idea of organic evolution--that the present is the child
of the past--is in great part just the idea of human history projected upon
the natural world, differentiated by the qualification that the continuous
"Becoming" has been wrought out by forces inherent in the organisms
themselves and in their environment.

A reference to Kant (See Brock, "Die Stellung Kant's zur
Deszendenztheorie," "Biol. Centralbl." VIII. 1889, pages 641-648.  Fritz
Schultze, "Kant und Darwin", Jena, 1875.) should come in historical order
after Buffon, with whose writings he was acquainted, but he seems, along
with Herder and Schelling, to be best regarded as the culmination of the
evolutionist philosophers--of those at least who interested themselves in
scientific problems.  In a famous passage he speaks of "the agreement of so
many kinds of animals in a certain common plan of structure"...an "analogy
of forms" which "strengthens the supposition that they have an actual
blood-relationship, due to derivation from a common parent."  He speaks of
"the great Family of creatures, for as a Family we must conceive it, if the
above-mentioned continuous and connected relationship has a real
foundation."  Prof. Osborn alludes to the scientific caution which led
Kant, biology being what it was, to refuse to entertain the hope "that a
Newton may one day arise even to make the production of a blade of grass
comprehensible, according to natural laws ordained by no intention."  As
Prof. Haeckel finely observes, Darwin rose up as Kant's Newton.  (Mr Alfred
Russel Wallace writes:  "We claim for Darwin that he is the Newton of
natural history, and that, just so surely as that the discovery and
demonstration by Newton of the law of gravitation established order in
place of chaos and laid a sure foundation for all future study of the
starry heavens, so surely has Darwin, by his discovery of the law of
natural selection and his demonstration of the great principle of the
preservation of useful variations in the struggle for life, not only thrown
a flood of light on the process of development of the whole organic world,
but also established a firm foundation for all future study of nature"
("Darwinism", London, 1889, page 9).  See also Prof. Karl Pearson's
"Grammar of Science" (2nd edition), London, 1900, page 32.  See Osborn, op.
cit.  Page 100.))

The scientific renaissance brought a wealth of fresh impressions and some
freedom from the tyranny of tradition, and the twofold stimulus stirred the
speculative activity of a great variety of men from old Claude Duret of
Moulins, of whose weird transformism (1609) Dr Henry de Varigny
("Experimental Evolution".  London, 1892.  Chap. 1. page 14.) gives us a
glimpse, to Lorenz Oken (1799-1851) whose writings are such mixtures of
sense and nonsense that some regard him as a far-seeing prophet and others
as a fatuous follower of intellectual will-o'-the-wisps.  Similarly, for De
Maillet, Maupertuis, Diderot, Bonnet, and others, we must agree with
Professor Osborn that they were not actually in the main Evolution
movement.  Some have been included in the roll of honour on very slender
evidence, Robinet for instance, whose evolutionism seems to us extremely
dubious.  (See J. Arthur Thomson, "The Science of Life".  London, 1899. 
Chap. XVI. "Evolution of Evolution Theory".)

The first naturalist to give a broad and concrete expression to the
evolutionist doctrine of descent was Buffon (1707-1788), but it is
interesting to recall the fact that his contemporary Linnaeus (1707-1778),
protagonist of the counter-doctrine of the fixity of species (See Carus
Sterne (Ernest Krause), "Die allgemeine Weltanschauung in ihrer
historischen Entwickelung".  Stuttgart, 1889.  Chapter entitled
"Bestandigkeit oder Veranderlichkeit der Naturwesen".), went the length of
admitting (in 1762) that new species might arise by intercrossing. 
Buffon's position among the pioneers of the evolution-doctrine is weakened
by his habit of vacillating between his own conclusions and the orthodoxy
of the Sorbonne, but there is no doubt that he had a firm grasp of the
general idea of "l'enchainement des etres."

Erasmus Darwin (1731-1802), probably influenced by Buffon, was another firm
evolutionist, and the outline of his argument in the "Zoonomia" ("Zoonomia,
or the Laws of Organic Life", 2 vols.  London, 1794; Osborn op. cit. page
145.) might serve in part at least to-day.  "When we revolve in our minds
the metamorphoses of animals, as from the tadpole to the frog; secondly,
the changes produced by artificial cultivation, as in the breeds of horses,
dogs, and sheep; thirdly, the changes produced by conditions of climate and
of season, as in the sheep of warm climates being covered with hair instead
of wool, and the hares and partridges of northern climates becoming white
in winter:  when, further, we observe the changes of structure produced by
habit, as seen especially in men of different occupations; or the changes
produced by artificial mutilation and prenatal influences, as in the
crossing of species and production of monsters; fourth, when we observe the
essential unity of plan in all warm-blooded animals,--we are led to
conclude that they have been alike produced from a similar living
filament"..."From thus meditating upon the minute portion of time in which
many of the above changes have been produced, would it be too bold to
imagine, in the great length of time since the earth began to exist,
perhaps millions of years before the commencement of the history of
mankind, that all warm-blooded animals have arisen from one living
filament?"..."This idea of the gradual generation of all things seems to
have been as familiar to the ancient philosophers as to the modern ones,
and to have given rise to the beautiful hieroglyphic figure of the proton
oon, or first great egg, produced by night, that is, whose origin is
involved in obscurity, and animated by Eros, that is, by Divine Love; from
whence proceeded all things which exist."

Lamarck (1744-1829) seems to have become an evolutionist independently of
Erasmus Darwin's influence, though the parallelism between them is
striking.  He probably owed something to Buffon, but he developed his
theory along a different line.  Whatever view be held in regard to that
theory there is no doubt that Lamarck was a thorough-going evolutionist. 
Professor Haeckel speaks of the "Philosophie Zoologique" as "the first
connected and thoroughly logical exposition of the theory of descent." 
(See Alpheus S. Packard, "Lamarck, the Founder of Evolution, His Life and
Work, with Translations of his writings on Organic Evolution".  London,
1901.)

Besides the three old masters, as we may call them, Buffon, Erasmus Darwin,
and Lamarck, there were other quite convinced pre-Darwinian evolutionists. 
The historian of the theory of descent must take account of Treviranus
whose "Biology or Philosophy of Animate Nature" is full of evolutionary
suggestions; of Etienne Geoffroy St Hilaire, who in 1830, before the French
Academy of Sciences, fought with Cuvier, the fellow-worker of his youth, an
intellectual duel on the question of descent; of Goethe, one of the
founders of morphology and the greatest poet of Evolution--who, in his
eighty-first year, heard the tidings of Geoffroy St Hilaire's defeat with
an interest which transcended the political anxieties of the time; and of
many others who had gained with more or less confidence and clearness a new
outlook on Nature.  It will be remembered that Darwin refers to thirty-four
more or less evolutionist authors in his Historical Sketch, and the list
might be added to.  Especially when we come near to 1858 do the numbers
increase, and one of the most remarkable, as also most independent
champions of the evolution-idea before that date was Herbert Spencer, who
not only marshalled the arguments in a very forcible way in 1852, but
applied the formula in detail in his "Principles of Psychology" in 1855. 
(See Edward Clodd, "Pioneers of Evolution", London, page 161, 1897.)

It is right and proper that we should shake ourselves free from all
creationist appreciations of Darwin, and that we should recognise the
services of pre-Darwinian evolutionists who helped to make the time ripe,
yet one cannot help feeling that the citation of them is apt to suggest two
fallacies.  It may suggest that Darwin simply entered into the labours of
his predecessors, whereas, as a matter of fact, he knew very little about
them till after he had been for years at work.  To write, as Samuel Butler
did, "Buffon planted, Erasmus Darwin and Lamarck watered, but it was Mr
Darwin who said 'That fruit is ripe,' and shook it into his lap"...seems to
us a quite misleading version of the facts of the case.  The second fallacy
which the historical citation is a little apt to suggest is that the
filiation of ideas is a simple problem.  On the contrary, the history of an
idea, like the pedigree of an organism, is often very intricate, and the
evolution of the evolution-idea is bound up with the whole progress of the
world.  Thus in order to interpret Darwin's clear formulation of the idea
of organic evolution and his convincing presentation of it, we have to do
more than go back to his immediate predecessors, such as Buffon, Erasmus
Darwin, and Lamarck; we have to inquire into the acceptance of evolutionary
conceptions in regard to other orders of facts, such as the earth and the
solar system (See Chapter IX. "The Genetic View of Nature" in J.T. Merz's
"History of European Thought in the Nineteenth Century", Vol. 2, Edinburgh
and London, 1903.); we have to realise how the growing success of
scientific interpretation along other lines gave confidence to those who
refused to admit that there was any domain from which science could be
excluded as a trespasser; we have to take account of the development of
philosophical thought, and even of theological and religious movements; we
should also, if we are wise enough, consider social changes.  In short, we
must abandon the idea that we can understand the history of any science as
such, without reference to contemporary evolution in other departments of
activity.

While there were many evolutionists before Darwin, few of them were expert
naturalists and few were known outside a small circle; what was of much
more importance was that the genetic view of nature was insinuating itself
in regard to other than biological orders of facts, here a little and there
a little, and that the scientific spirit had ripened since the days when
Cuvier laughed Lamarck out of court.  How was it that Darwin succeeded
where others had failed?  Because, in the first place, he had clear
visions--"pensees de la jeunesse, executees par l'age mur"--which a
University curriculum had not made impossible, which the "Beagle" voyage
made vivid, which an unrivalled British doggedness made real--visions of
the web of life, of the fountain of change within the organism, of the
struggle for existence and its winnowing, and of the spreading genealogical
tree.  Because, in the second place, he put so much grit into the
verification of his visions, putting them to the proof in an argument which
is of its kind--direct demonstration being out of the question--quite
unequalled.  Because, in the third place, he broke down the opposition
which the most scientific had felt to the seductive modal formula of
evolution by bringing forward a more plausible theory of the process than
had been previously suggested.  Nor can one forget, since questions of this
magnitude are human and not merely academic, that he wrote so that all men
could understand.

AS REGARDS THE FACTORS OF EVOLUTION.

It is admitted by all who are acquainted with the history of biology that
the general idea of organic evolution as expressed in the Doctrine of
Descent was quite familiar to Darwin's grandfather, and to others before
and after him, as we have briefly indicated.  It must also be admitted that
some of these pioneers of evolutionism did more than apply the evolution-
idea as a modal formula of becoming, they began to inquire into the factors
in the process.  Thus there were pre-Darwinian theories of evolution, and
to these we must now briefly refer.  (See Prof. W.A. Locy's "Biology and
its Makers".  New York, 1908.  Part II.  "The Doctrine of Organic
Evolution".

In all biological thinking we have to work with the categories Organism--
Function--Environment, and theories of evolution may be classified in
relation to these.  To some it has always seemed that the fundamental fact
is the living organism,--a creative agent, a striving will, a changeful
Proteus, selecting its environment, adjusting itself to it, self-
differentiating and self-adaptive.  The necessity of recognising the
importance of the organism is admitted by all Darwinians who start with
inborn variations, but it is open to question whether the whole truth of
what we might call the Goethian position is exhausted in the postulate of
inherent variability.

To others it has always seemed that the emphasis should be laid on
Function,--on use and disuse, on doing and not doing.  Practice makes
perfect; c'est a force de forger qu'on devient forgeron.  This is one of
the fundamental ideas of Lamarckism; to some extent it met with Darwin's
approval; and it finds many supporters to-day.  One of the ablest of these
--Mr Francis Darwin--has recently given strong reasons for combining a
modernised Lamarckism with what we usually regard as sound Darwinism. 
(Presidential Address to the British Association meeting at Dublin in
1908.)

To others it has always seemed that the emphasis should be laid on the
Environment, which wakes the organism to action, prompts it to change,
makes dints upon it, moulds it, prunes it, and finally, perhaps, kills it.
It is again impossible to doubt that there is truth in this view, for even
if environmentally induced "modifications" be not transmissible,
environmentally induced "variations" are; and even if the direct influence
of the environment be less important than many enthusiastic supporters of
this view--may we call them Buffonians--think, there remains the indirect
influence which Darwinians in part rely on,--the eliminative process.  Even
if the extreme view be held that the only form of discriminate elimination
that counts is inter-organismal competition, this might be included under
the rubric of the animate environment.

In many passages Buffon (See in particular Samuel Butler, "Evolution Old
and New", London, 1879; J.L. de Lanessan, "Buffon et Darwin", "Revue
Scientifique", XLIII. pages 385-391, 425-432, 1889.) definitely suggested
that environmental influences--especially of climate and food--were
directly productive of changes in organisms, but he did not discuss the
question of the transmissibility of the modifications so induced, and it is
difficult to gather from his inconsistent writings what extent of
transformation he really believed in.  Prof. Osborn says of Buffon:  "The
struggle for existence, the elimination of the least-perfected species, the
contest between the fecundity of certain species and their constant
destruction, are all clearly expressed in various passages."  He quotes two
of these (op. cit. page 136.):

"Le cours ordinaire de la nature vivante, est en general toujours constant,
toujours le meme; son mouvement, toujours regulier, roule sur deux points
inebranlables: l'un, la fecondite sans bornes donnee a toutes les especes;
l'autre, les obstacles sans nombre qui reduisent cette fecondite a une
mesure determinee et ne laissent en tout temps qu'a peu pres la meme
quantite d'individus de chaque espece"..."Les especes les moins parfaites,
les plus delicates, les plus pesantes, les moins agissantes, les moins
armees, etc., ont deja disparu ou disparaitront."

Erasmus Darwin (See Ernst Krause and Charles Darwin, "Erasmus Darwin",
London, 1879.) had a firm grip of the "idea of the gradual formation and
improvement of the Animal world," and he had his theory of the process.  No
sentence is more characteristic than this:  "All animals undergo
transformations which are in part produced by their own exertions, in
response to pleasures and pains, and many of these acquired forms or
propensities are transmitted to their posterity."  This is Lamarckism
before Lamarck, as his grandson pointed out.  His central idea is that
wants stimulate efforts and that these result in improvements, which
subsequent generations make better still.  He realised something of the
struggle for existence and even pointed out that this advantageously checks
the rapid multiplication.  "As Dr Krause points out, Darwin just misses the
connection between this struggle and the Survival of the Fittest."  (Osborn
op. cit. page 142.)

Lamarck (1744-1829) (See E. Perrier "La Philosophie Zoologique avant
Darwin", Paris, 1884; A. de Quatrefages, "Darwin et ses Precurseurs
Francais", Paris, 1870; Packard op. cit.; also Claus, "Lamarck als
Begrunder der Descendenzlehre", Wien, 1888; Haeckel, "Natural History of
Creation", English translation London, 1879; Lang "Zur Charakteristik der
Forschungswege von Lamarck und Darwin", Jena, 1889.) seems to have thought
out his theory of evolution without any knowledge of Erasmus Darwin's which
it closely resembled.  The central idea of his theory was the cumulative
inheritance of functional modifications.  "Changes in environment bring
about changes in the habits of animals.  Changes in their wants necessarily
bring about parallel changes in their habits.  If new wants become constant
or very lasting, they form new habits, the new habits involve the use of
new parts, or a different use of old parts, which results finally in the
production of new organs and the modification of old ones."  He differed
from Buffon in not attaching importance, as far as animals are concerned,
to the direct influence of the environment, "for environment can effect no
direct change whatever upon the organisation of animals," but in regard to
plants he agreed with Buffon that external conditions directly moulded
them.

Treviranus (1776-1837) (See Huxley's article "Evolution in Biology",
"Encyclopaedia Britannica" (9th edit.), 1878, pages 744-751, and Sully's
article, "Evolution in Philosophy", ibid. pages 751-772.), whom Huxley
ranked beside Lamarck, was on the whole Buffonian, attaching chief
importance to the influence of a changeful environment both in modifying
and in eliminating, but he was also Goethian, for instance in his idea that
species like individuals pass through periods of growth, full bloom, and
decline.  "Thus, it is not only the great catastrophes of Nature which have
caused extinction, but the completion of cycles of existence, out of which
new cycles have begun."  A characteristic sentence is quoted by Prof.
Osborn:  "In every living being there exists a capability of an endless
variety of form-assumption; each possesses the power to adapt its
organisation to the changes of the outer world, and it is this power, put
into action by the change of the universe, that has raised the simple
zoophytes of the primitive world to continually higher stages of
organisation, and has introduced a countless variety of species into
animate Nature."

Goethe (1749-1832) (See Haeckel, "Die Naturanschauung von Darwin, Goethe
und Lamarck", Jena, 1882.), who knew Buffon's work but not Lamarck's, is
peculiarly interesting as one of the first to use the evolution-idea as a
guiding hypothesis, e.g. in the interpretation of vestigial structures in
man, and to realise that organisms express an attempt to make a compromise
between specific inertia and individual change.  He gave the finest
expression that science has yet known--if it has known it--of the kernel-
idea of what is called "bathmism," the idea of an "inherent growth-force"--
and at the same time he held that "the way of life powerfully reacts upon
all form" and that the orderly growth of form "yields to change from
externally acting causes."

Besides Buffon, Erasmus Darwin, Lamarck, Treviranus, and Goethe, there were
other "pioneers of evolution," whose views have been often discussed and
appraised.  Etienne Geoffroy Saint-Hilaire (1772-1844), whose work Goethe
so much admired, was on the whole Buffonian, emphasising the direct action
of the changeful milieu.  "Species vary with their environment, and
existing species have descended by modification from earlier and somewhat
simpler species."  He had a glimpse of the selection idea, and believed in
mutations or sudden leaps--induced in the embryonic condition by external
influences.  The complete history of evolution-theories will include many
instances of guesses at truth which were afterwards substantiated, thus the
geographer von Buch (1773-1853) detected the importance of the Isolation
factor on which Wagner, Romanes, Gulick and others have laid great stress,
but we must content ourselves with recalling one other pioneer, the author
of the "Vestiges of Creation" (1844), a work which passed through ten
editions in nine years and certainly helped to harrow the soil for Darwin's
sowing.  As Darwin said, "it did excellent service in this country in
calling attention to the subject, in removing prejudice, and in thus
preparing the ground for the reception of analogous views."  ("Origin of
Species" (6th edition), page xvii.)  Its author, Robert Chambers (1802-
1871) was in part a Buffonian--maintaining that environment moulded
organisms adaptively, and in part a Goethian--believing in an inherent
progressive impulse which lifted organisms from one grade of organisation
to another.

AS REGARDS NATURAL SELECTION.

The only thinker to whom Darwin was directly indebted, so far as the theory
of Natural Selection is concerned, was Malthus, and we may once more quote
the well-known passage in the Autobiography:  "In October, 1838, that is,
fifteen months after I had begun my systematic enquiry, I happened to read
for amusement 'Malthus on Population', and being well prepared to
appreciate the struggle for existence which everywhere goes on from long-
continued observation of the habits of animals and plants, it at once
struck me that under these circumstances favourable variations would tend
to be preserved, and unfavourable ones to be destroyed.  The result of this
would be the formation of new species."  ("The Life and Letters of Charles
Darwin", Vol. 1. page 83.  London, 1887.)

Although Malthus gives no adumbration of the idea of Natural Selection in
his exposition of the eliminative processes which go on in mankind, the
suggestive value of his essay is undeniable, as is strikingly borne out by
the fact that it gave to Alfred Russel Wallace also "the long-sought clue
to the effective agent in the evolution of organic species."  (A.R.
Wallace, "My Life, A Record of Events and Opinions", London, 1905, Vol. 1.
page 232.)  One day in Ternate when he was resting between fits of fever,
something brought to his recollection the work of Malthus which he had read
twelve years before.  "I thought of his clear exposition of 'the positive
checks to increase'--disease, accidents, war, and famine--which keep down
the population of savage races to so much lower an average than that of
more civilized peoples.  It then occurred to me that these causes or their
equivalents are continually acting in the case of animals also; and as
animals usually breed much more rapidly than does mankind, the destruction
every year from these causes must be enormous in order to keep down the
numbers of each species, since they evidently do not increase regularly
from year to year, as otherwise the world would long ago have been densely
crowded with those that breed most quickly.  Vaguely thinking over the
enormous and constant destruction which this implied, it occurred to me to
ask the question, Why do some die and some live?  And the answer was
clearly, that on the whole the best fitted live.  From the effects of
disease the most healthy escaped; from enemies the strongest, the swiftest,
or the most cunning; from famine the best hunters or those with the best
digestion; and so on.  Then it suddenly flashed upon me that this self-
acting process would necessarily IMPROVE THE RACE, because in every
generation the inferior would inevitably be killed off and the superior
would remain--that is, THE FITTEST WOULD SURVIVE."  (Ibid. Vol. 1. page
361.)  We need not apologise for this long quotation, it is a tribute to
Darwin's magnanimous colleague, the Nestor of the evolutionist camp,--and
it probably indicates the line of thought which Darwin himself followed. 
It is interesting also to recall the fact that in 1852, when Herbert
Spencer wrote his famous "Leader" article on "The Development Hypothesis"
in which he argued powerfully for the thesis that the whole animate world
is the result of an age-long process of natural transformation, he wrote
for "The Westminster Review" another important essay, "A Theory of
Population deduced from the General Law of Animal Fertility", towards the
close of which he came within an ace of recognising that the struggle for
existence was a factor in organic evolution.  At a time when pressure of
population was practically interesting men's minds, Darwin, Wallace, and
Spencer were being independently led from a social problem to a biological
theory.  There could be no better illustration, as Prof. Patrick Geddes has
pointed out, of the Comtian thesis that science is a "social phenomenon."

Therefore, as far more important than any further ferreting out of vague
hints of Natural Selection in books which Darwin never read, we would
indicate by a quotation the view that the central idea in Darwinism is
correlated with contemporary social evolution.  "The substitution of Darwin
for Paley as the chief interpreter of the order of nature is currently
regarded as the displacement of an anthropomorphic view by a purely
scientific one:  a little reflection, however, will show that what has
actually happened has been merely the replacement of the anthropomorphism
of the eighteenth century by that of the nineteenth.  For the place vacated
by Paley's theological and metaphysical explanation has simply been
occupied by that suggested to Darwin and Wallace by Malthus in terms of the
prevalent severity of industrial competition, and those phenomena of the
struggle for existence which the light of contemporary economic theory has
enabled us to discern, have thus come to be temporarily exalted into a
complete explanation of organic progress."  (P. Geddes, article "Biology",
"Chambers's Encyclopaedia".)  It goes without saying that the idea
suggested by Malthus was developed by Darwin into a biological theory which
was then painstakingly verified by being used as an interpretative formula,
and that the validity of a theory so established is not affected by what
suggested it, but the practical question which this line of thought raises
in the mind is this:  if Biology did thus borrow with such splendid results
from social theory, why should we not more deliberately repeat the
experiment?

Darwin was characteristically frank and generous in admitting that the
principle of Natural Selection had been independently recognised by Dr W.C.
Wells in 1813 and by Mr Patrick Matthew in 1831, but he had no knowledge of
these anticipations when he published the first edition of "The Origin of
Species".  Wells, whose "Essay on Dew" is still remembered, read in 1813
before the Royal Society a short paper entitled "An account of a White
Female, part of whose skin resembles that of a Negro" (published in 1818). 
In this communication, as Darwin said, "he observes, firstly, that all
animals tend to vary in some degree, and, secondly, that agriculturists
improve their domesticated animals by selection; and then, he adds, but
what is done in this latter case 'by art, seems to be done with equal
efficacy, though more slowly, by nature, in the formation of varieties of
mankind, fitted for the country which they inhabit.'"  ("Origin of Species"
(6th edition) page xv.)  Thus Wells had the clear idea of survival
dependent upon a favourable variation, but he makes no more use of the idea
and applies it only to man.  There is not in the paper the least hint that
the author ever thought of generalising the remarkable sentence quoted
above.

Of Mr Patrick Matthew, who buried his treasure in an appendix to a work on
"Naval Timber and Arboriculture", Darwin said that "he clearly saw the full
force of the principle of natural selection."  In 1860 Darwin wrote--very
characteristically--about this to Lyell:  "Mr Patrick Matthew publishes a
long extract from his work on "Naval Timber and Arboriculture", published
in 1831, in which he briefly but completely anticipates the theory of
Natural Selection.  I have ordered the book, as some passages are rather
obscure, but it is certainly, I think, a complete but not developed
anticipation.  Erasmus always said that surely this would be shown to be
the case some day.  Anyhow, one may be excused in not having discovered the
fact in a work on Naval Timber."  ("Life and Letters" II. page 301.)

De Quatrefages and De Varigny have maintained that the botanist Naudin
stated the theory of evolution by natural selection in 1852.  He explains
very clearly the process of artificial selection, and says that in the
garden we are following Nature's method.  "We do not think that Nature has
made her species in a different fashion from that in which we proceed
ourselves in order to make our variations."  But, as Darwin said, "he does
not show how selection acts under nature."  Similarly it must be noted in
regard to several pre-Darwinian pictures of the struggle for existence
(such as Herder's, who wrote in 1790 "All is in struggle...each one for
himself" and so on), that a recognition of this is only the first step in
Darwinism.

Profs. E. Perrier and H.F. Osborn have called attention to a remarkable
anticipation of the selection-idea which is to be found in the speculations
of Etienne Geoffroy St Hilaire (1825-1828) on the evolution of modern
Crocodilians from the ancient Teleosaurs.  Changing environment induced
changes in the respiratory system and far-reaching consequences followed. 
The atmosphere, acting upon the pulmonary cells, brings about
"modifications which are favourable or destructive ('funestes'); these are
inherited, and they influence all the rest of the organisation of the
animal because if these modifications lead to injurious effects, the
animals which exhibit them perish and are replaced by others of a somewhat
different form, a form changed so as to be adapted to (a la convenance) the
new environment."

Prof. E.B. Poulton ("Science Progress", New Series, Vol. I. 1897.  "A
Remarkable Anticipation of Modern Views on Evolution".  See also Chap. VI.
in "Essays on Evolution", Oxford, 1908.) has shown that the anthropologist
James Cowles Prichard (1786-1848) must be included, even in spite of
himself, among the precursors of Darwin.  In some passages of the second
edition of his "Researches into the Physical History of Mankind" (1826), he
certainly talks evolution and anticipates Prof. Weismann in denying the
transmission of acquired characters.  He is, however, sadly self-
contradictory and his evolutionism weakens in subsequent editions--the only
ones that Darwin saw.  Prof. Poulton finds in Prichard's work a recognition
of the operation of Natural Selection.  "After enquiring how it is that
'these varieties are developed and preserved in connection with particular
climates and differences of local situation,' he gives the following very
significant answer:  'One cause which tends to maintain this relation is
obvious.  Individuals and families, and even whole colonies, perish and
disappear in climates for which they are, by peculiarity of constitution,
not adapted.  Of this fact proofs have been already mentioned.'"  Mr
Francis Darwin and Prof. A.C. Seward discuss Prichard's "anticipations" in
"More Letters of Charles Darwin", Vol. I. page 43, and come to the
conclusion that the evolutionary passages are entirely neutralised by
others of an opposite trend.  There is the same difficulty with Buffon.

Hints of the idea of Natural Selection have been detected elsewhere.  James
Watt (See Prof. Patrick Geddes's article "Variation and Selection",
"Encyclopaedia Britannica (9th edition) 1888.), for instance, has been
reported as one of the anticipators (1851).  But we need not prolong the
inquiry further, since Darwin did not know of any anticipations until after
he had published the immortal work of 1859, and since none of those who got
hold of the idea made any use of it.  What Darwin did was to follow the
clue which Malthus gave him, to realise, first by genius and afterwards by
patience, how the complex and subtle struggle for existence works out a
natural selection of those organisms which vary in the direction of fitter
adaptation to the conditions of their life.  So much success attended his
application of the Selection-formula that for a time he regarded Natural
Selection as almost the sole factor in evolution, variations being pre-
supposed; gradually, however, he came to recognise that there was some
validity in the factors which had been emphasized by Lamarck and by Buffon,
and in his well-known summing up in the sixth edition of the "Origin" he
says of the transformation of species:  "This has been effected chiefly
through the natural selection of numerous successive, slight, favourable
variations; aided in an important manner by the inherited effects of the
use and disuse of parts; and in an unimportant manner, that is, in relation
to adaptive structures, whether past or present, by the direct action of
external conditions, and by variations which seem to us in our ignorance to
arise spontaneously."

To sum up:  the idea of organic evolution, older than Aristotle, slowly
developed from the stage of suggestion to the stage of verification, and
the first convincing verification was Darwin's; from being an a priori
anticipation it has become an interpretation of nature, and Darwin is still
the chief interpreter; from being a modal interpretation it has advanced to
the rank of a causal theory, the most convincing part of which men will
never cease to call Darwinism.


III.  THE SELECTION THEORY

By August Weismann.
Professor of Zoology in the University of Freiburg (Baden).

I.  THE IDEA OF SELECTION.

Many and diverse were the discoveries made by Charles Darwin in the course
of a long and strenuous life, but none of them has had so far-reaching an
influence on the science and thought of his time as the theory of
selection.  I do not believe that the theory of evolution would have made
its way so easily and so quickly after Darwin took up the cudgels in favour
of it, if he had not been able to support it by a principle which was
capable of solving, in a simple manner, the greatest riddle that living
nature presents to us,--I mean the purposiveness of every living form
relative to the conditions of its life and its marvellously exact
adaptation to these.

Everyone knows that Darwin was not alone in discovering the principle of
selection, and that the same idea occurred simultaneously and independently
to Alfred Russel Wallace.  At the memorable meeting of the Linnean Society
on 1st July, 1858, two papers were read (communicated by Lyell and Hooker)
both setting forth the same idea of selection.  One was written by Charles
Darwin in Kent, the other by Alfred Wallace in Ternate, in the Malay
Archipelago.  It was a splendid proof of the magnanimity of these two
investigators, that they thus, in all friendliness and without envy, united
in laying their ideas before a scientific tribunal:  their names will
always shine side by side as two of the brightest stars in the scientific
sky.

But it is with Charles Darwin that I am here chiefly concerned, since this
paper is intended to aid in the commemoration of the hundredth anniversary
of his birth.

The idea of selection set forth by the two naturalists was at the time
absolutely new, but it was also so simple that Huxley could say of it
later, "How extremely stupid not to have thought of that."  As Darwin was
led to the general doctrine of descent, not through the labours of his
predecessors in the early years of the century, but by his own
observations, so it was in regard to the principle of selection.  He was
struck by the innumerable cases of adaptation, as, for instance, that of
the woodpeckers and tree-frogs to climbing, or the hooks and feather-like
appendages of seeds, which aid in the distribution of plants, and he said
to himself that an explanation of adaptations was the first thing to be
sought for in attempting to formulate a theory of evolution.

But since adaptations point to CHANGES which have been undergone by the
ancestral forms of existing species, it is necessary, first of all, to
inquire how far species in general are VARIABLE.  Thus Darwin's attention
was directed in the first place to the phenomenon of variability, and the
use man has made of this, from very early times, in the breeding of his
domesticated animals and cultivated plants.  He inquired carefully how
breeders set to work, when they wished to modify the structure and
appearance of a species to their own ends, and it was soon clear to him
that SELECTION FOR BREEDING PURPOSES played the chief part.

But how was it possible that such processes should occur in free nature? 
Who is here the breeder, making the selection, choosing out one individual
to bring forth offspring and rejecting others?  That was the problem that
for a long time remained a riddle to him.

Darwin himself relates how illumination suddenly came to him.  He had been
reading, for his own pleasure, Malthus' book on Population, and, as he had
long known from numerous observations, that every species gives rise to
many more descendants than ever attain to maturity, and that, therefore,
the greater number of the descendants of a species perish without
reproducing, the idea came to him that the decision as to which member of a
species was to perish, and which was to attain to maturity and reproduction
might not be a matter of chance, but might be determined by the
constitution of the individuals themselves, according as they were more or
less fitted for survival.  With this idea the foundation of the theory of
selection was laid.

In ARTIFICIAL SELECTION the breeder chooses out for pairing only such
individuals as possess the character desired by him in a somewhat higher
degree than the rest of the race.  Some of the descendants inherit this
character, often in a still higher degree, and if this method be pursued
throughout several generations, the race is transformed in respect of that
particular character.

NATURAL SELECTION depends on the same three factors as ARTIFICIAL
SELECTION:  on VARIABILITY, INHERITANCE, and SELECTION FOR BREEDING, but
this last is here carried out not by a breeder but by what Darwin called
the "struggle for existence."  This last factor is one of the special
features of the Darwinian conception of nature.  That there are carnivorous
animals which take heavy toll in every generation of the progeny of the
animals on which they prey, and that there are herbivores which decimate
the plants in every generation had long been known, but it is only since
Darwin's time that sufficient attention has been paid to the facts that, in
addition to this regular destruction, there exists between the members of a
species a keen competition for space and food, which limits multiplication,
and that numerous individuals of each species perish because of
unfavourable climatic conditions.  The "struggle for existence," which
Darwin regarded as taking the place of the human breeder in free nature, is
not a direct struggle between carnivores and their prey, but is the assumed
competition for survival between individuals OF THE SAME species, of which,
on an average, only those survive to reproduce which have the greatest
power of resistance, while the others, less favourably constituted, perish
early.  This struggle is so keen, that, within a limited area, where the
conditions of life have long remained unchanged, of every species, whatever
be the degree of fertility, only two, ON AN AVERAGE, of the descendants of
each pair survive; the others succumb either to enemies, or to
disadvantages of climate, or to accident.  A high degree of fertility is
thus not an indication of the special success of a species, but of the
numerous dangers that have attended its evolution.  Of the six young
brought forth by a pair of elephants in the course of their lives only two
survive in a given area; similarly, of the millions of eggs which two
thread-worms leave behind them only two survive.  It is thus possible to
estimate the dangers which threaten a species by its ratio of elimination,
or, since this cannot be done directly, by its fertility.

Although a great number of the descendants of each generation fall victims
to accident, among those that remain it is still the greater or lesser
fitness of the organism that determines the "selection for breeding
purposes," and it would be incomprehensible if, in this competition, it
were not ultimately, that is, on an average, the best equipped which
survive, in the sense of living long enough to reproduce.

Thus the principle of natural selection is THE SELECTION OF THE BEST FOR
REPRODUCTION, whether the "best" refers to the whole constitution, to one
or more parts of the organism, or to one or more stages of development. 
Every organ, every part, every character of an animal, fertility and
intelligence included, must be improved in this manner, and be gradually
brought up in the course of generations to its highest attainable state of
perfection.  And not only may improvement of parts be brought about in this
way, but new parts and organs may arise, since, through the slow and minute
steps of individual or "fluctuating" variations, a part may be added here
or dropped out there, and thus something new is produced.

The principle of selection solved the riddle as to how what was purposive
could conceivably be brought about without the intervention of a directing
power, the riddle which animate nature presents to our intelligence at
every turn, and in face of which the mind of a Kant could find no way out,
for he regarded a solution of it as not to be hoped for.  For, even if we
were to assume an evolutionary force that is continually transforming the
most primitive and the simplest forms of life into ever higher forms, and
the homogeneity of primitive times into the infinite variety of the
present, we should still be unable to infer from this alone how each of the
numberless forms adapted to particular conditions of life should have
appeared PRECISELY AT THE RIGHT MOMENT IN THE HISTORY OF THE EARTH to which
their adaptations were appropriate, and precisely at the proper place in
which all the conditions of life to which they were adapted occurred:  the
humming-birds at the same time as the flowers; the trichina at the same
time as the pig; the bark-coloured moth at the same time as the oak, and
the wasp-like moth at the same time as the wasp which protects it.  Without
processes of selection we should be obliged to assume a "pre-established
harmony" after the famous Leibnitzian model, by means of which the clock of
the evolution of organisms is so regulated as to strike in exact
synchronism with that of the history of the earth!  All forms of life are
strictly adapted to the conditions of their life, and can persist under
these conditions alone.

There must therefore be an intrinsic connection between the conditions and
the structural adaptations of the organism, and, SINCE THE CONDITIONS OF
LIFE CANNOT BE DETERMINED BY THE ANIMAL ITSELF, THE ADAPTATIONS MUST BE
CALLED FORTH BY THE CONDITIONS.

The selection theory teaches us how this is conceivable, since it enables
us to understand that there is a continual production of what is non-
purposive as well as of what is purposive, but the purposive alone
survives, while the non-purposive perishes in the very act of arising. 
This is the old wisdom taught long ago by Empedocles.

II.  THE LAMARCKIAN PRINCIPLE.

Lamarck, as is well known, formulated a definite theory of evolution at the
beginning of the nineteenth century, exactly fifty years before the Darwin-
Wallace principle of selection was given to the world.  This brilliant
investigator also endeavoured to support his theory by demonstrating forces
which might have brought about the transformations of the organic world in
the course of the ages.  In addition to other factors, he laid special
emphasis on the increased or diminished use of the parts of the body,
assuming that the strengthening or weakening which takes place from this
cause during the individual life, could be handed on to the offspring, and
thus intensified and raised to the rank of a specific character.  Darwin
also regarded this LAMARCKIAN PRINCIPLE, as it is now generally called, as
a factor in evolution, but he was not fully convinced of the
transmissibility of acquired characters.

As I have here to deal only with the theory of selection, I need not
discuss the Lamarckian hypothesis, but I must express my opinion that there
is room for much doubt as to the cooperation of this principle in
evolution.  Not only is it difficult to imagine how the transmission of
functional modifications could take place, but, up to the present time,
notwithstanding the endeavours of many excellent investigators, not a
single actual proof of such inheritance has been brought forward.  Semon's
experiments on plants are, according to the botanist Pfeffer, not to be
relied on, and even the recent, beautiful experiments made by Dr Kammerer
on salamanders, cannot, as I hope to show elsewhere, be regarded as proof,
if only because they do not deal at all with functional modifications, that
is, with modifications brought about by use, and it is to these ALONE that
the Lamarckian principle refers.

III.  OBJECTIONS TO THE THEORY OF SELECTION.

(a)  Saltatory evolution.

The Darwinian doctrine of evolution depends essentially on THE CUMULATIVE
AUGMENTATION of minute variations in the direction of utility.  But can
such minute variations, which are undoubtedly continually appearing among
the individuals of the same species, possess any selection-value; can they
determine which individuals are to survive, and which are to succumb; can
they be increased by natural selection till they attain to the highest
development of a purposive variation?

To many this seems so improbable that they have urged a theory of evolution
by leaps from species to species.  Kolliker, in 1872, compared the
evolution of species with the processes which we can observe in the
individual life in cases of alternation of generations.  But a polyp only
gives rise to a medusa because it has itself arisen from one, and there can
be no question of a medusa ever having arisen suddenly and de novo from a
polyp-bud, if only because both forms are adapted in their structure as a
whole, and in every detail to the conditions of their life.  A sudden
origin, in a natural way, of numerous adaptations is inconceivable.  Even
the degeneration of a medusoid from a free-swimming animal to a mere brood-
sac (gonophore) is not sudden and saltatory, but occurs by imperceptible
modifications throughout hundreds of years, as we can learn from the
numerous stages of the process of degeneration persisting at the same time
in different species.

If, then, the degeneration to a simple brood-sac takes place only by very
slow transitions, each stage of which may last for centuries, how could the
much more complex ASCENDING evolution possibly have taken place by sudden
leaps?  I regard this argument as capable of further extension, for
wherever in nature we come upon degeneration, it is taking place by minute
steps and with a slowness that makes it not directly perceptible, and I
believe that this in itself justifies us in concluding that THE SAME MUST
BE TRUE OF ASCENDING evolution.  But in the latter case the goal can seldom
be distinctly recognised while in cases of degeneration the starting-point
of the process can often be inferred, because several nearly related
species may represent different stages.

In recent years Bateson in particular has championed the idea of saltatory,
or so-called discontinuous evolution, and has collected a number of cases
in which more or less marked variations have suddenly appeared.  These are
taken for the most part from among domesticated animals which have been
bred and crossed for a long time, and it is hardly to be wondered at that
their much mixed and much influenced germ-plasm should, under certain
conditions, give rise to remarkable phenomena, often indeed producing forms
which are strongly suggestive of monstrosities, and which would undoubtedly
not survive in free nature, unprotected by man.  I should regard such cases
as due to an intensified germinal selection--though this is to anticipate a
little--and from this point of view it cannot be denied that they have a
special interest.  But they seem to me to have no significance as far as
the transformation of species is concerned, if only because of the extreme
rarity of their occurrence.

There are, however, many variations which have appeared in a sudden and
saltatory manner, and some of these Darwin pointed out and discussed in
detail:  the copper beech, the weeping trees, the oak with "fern-like
leaves," certain garden-flowers, etc.  But none of them have persisted in
free nature, or evolved into permanent types.

On the other hand, wherever enduring types have arisen, we find traces of a
gradual origin by successive stages, even if, at first sight, their origin
may appear to have been sudden.  This is the case with SEASONAL DIMORPHISM,
the first known cases of which exhibited marked differences between the two
generations, the winter and the summer brood.  Take for instance the much
discussed and studied form Vanessa (Araschnia) levana-prorsa.  Here the
differences between the two forms are so great and so apparently
disconnected, that one might almost believe it to be a sudden mutation,
were it not that old transition-stages can be called forth by particular
temperatures, and we know other butterflies, as for instance our Garden
Whites, in which the differences between the two generations are not nearly
so marked; indeed, they are so little apparent that they are scarcely
likely to be noticed except by experts.  Thus here again there are small
initial steps, some of which, indeed, must be regarded as adaptations, such
as the green-sprinkled or lightly tinted under-surface which gives them a
deceptive resemblance to parsley or to Cardamine leaves.

Even if saltatory variations do occur, we cannot assume that these HAVE
EVER LED TO FORMS WHICH ARE CAPABLE OF SURVIVAL UNDER THE CONDITIONS OF
WILD LIFE.  Experience has shown that in plants which have suddenly varied
the power of persistence is diminished.  Korschinksky attributes to them
weaknesses of organisation in general; "they bloom late, ripen few of their
seeds, and show great sensitiveness to cold."  These are not the characters
which make for success in the struggle for existence.

We must briefly refer here to the views--much discussed in the last decade
--of H. de Vries, who believes that the roots of transformation must be
sought for in SALTATORY VARIATIONS ARISING FROM INTERNAL CAUSES, and
distinguishes such MUTATIONS, as he has called them, from ordinary
individual variations, in that they breed true, that is, with strict
inbreeding they are handed on pure to the next generation.  I have
elsewhere endeavoured to point out the weaknesses of this theory ("Vortrage
uber Descendenztheorie", Jena, 1904, II. 269.  English Translation London,
1904, II. page 317.), and I am the less inclined to return to it here that
it now appears (See Poulton, "Essays on Evolution", Oxford, 1908, pages
xix-xxii.) that the far-reaching conclusions drawn by de Vries from his
observations on the Evening Primrose, Oenothera lamarckiana, rest upon a
very insecure foundation.  The plant from which de Vries saw numerous
"species"--his "mutations"--arise was not, as he assumed, a WILD SPECIES
that had been introduced to Europe from America, but was probably a hybrid
form which was first discovered in the Jardin des Plantes in Paris, and
which does not appear to exist anywhere in America as a wild species.

This gives a severe shock to the "Mutation theory," for the other ACTUALLY
WILD species with which de Vries experimented showed no "mutations" but
yielded only negative results.

Thus we come to the conclusion that Darwin ("Origin of Species" (6th
edition), pages 176 et seq.) was right in regarding transformations as
taking place by minute steps, which, if useful, are augmented in the course
of innumerable generations, because their possessors more frequently
survive in the struggle for existence.

(b)  SELECTION-VALUE OF THE INITIAL STEPS.

Is it possible that the significant deviations which we know as "individual
variations" can form the beginning of a process of selection?  Can they
decide which is to perish and which to survive?  To use a phrase of
Romanes, can they have SELECTION-VALUE?

Darwin himself answered this question, and brought together many excellent
examples to show that differences, apparently insignificant because very
small, might be of decisive importance for the life of the possessor.  But
it is by no means enough to bring forward cases of this kind, for the
question is not merely whether finished adaptations have selection-value,
but whether the first beginnings of these, and whether the small, I might
almost say minimal increments, which have led up from these beginnings to
the perfect adaptation, have also had selection-value.  To this question
even one who, like myself, has been for many years a convinced adherent of
the theory of selection, can only reply:  WE MUST ASSUME SO, BUT WE CANNOT
PROVE IT IN ANY CASE.  It is not upon demonstrative evidence that we rely
when we champion the doctrine of selection as a scientific truth; we base
our argument on quite other grounds.  Undoubtedly there are many apparently
insignificant features, which can nevertheless be shown to be adaptations--
for instance, the thickness of the basin-shaped shell of the limpets that
live among the breakers on the shore.  There can be no doubt that the
thickness of these shells, combined with their flat form, protects the
animals from the force of the waves breaking upon them,--but how have they
become so thick?  What proportion of thickness was sufficient to decide
that of two variants of a limpet one should survive, the other be
eliminated?  We can say nothing more than that we infer from the present
state of the shell, that it must have varied in regard to differences in
shell-thickness, and that these differences must have had selection-value,
--no proof therefore, but an assumption which we must show to be
convincing.

For a long time the marvellously complex RADIATE and LATTICE-WORK skeletons
of Radiolarians were regarded as a mere outflow of "Nature's infinite
wealth of form," as an instance of a purely morphological character with no
biological significance.  But recent investigations have shown that these,
too, have an adaptive significance (Hacker).  The same thing has been shown
by Schutt in regard to the lowly unicellular plants, the Peridineae, which
abound alike on the surface of the ocean and in its depths.  It has been
shown that the long skeletal processes which grow out from these organisms
have significance not merely as a supporting skeleton, but also as an
extension of the superficial area, which increases the contact with the
water-particles, and prevents the floating organisms from sinking.  It has
been established that the processes are considerably shorter in the colder
layers of the ocean, and that they may be twelve times as long (Chun,
"Reise der Valdivia", Leipzig, 1904.) in the warmer layers, thus
corresponding to the greater or smaller amount of friction which takes
place in the denser and less dense layers of the water.

The Peridineae of the warmer ocean layers have thus become long-rayed,
those of the colder layers short-rayed, not through the direct effect of
friction on the protoplasm, but through processes of selection, which
favoured the longer rays in warm water, since they kept the organism
afloat, while those with short rays sank and were eliminated.  If we put
the question as to selection-value in this case, and ask how great the
variations in the length of processes must be in order to possess
selection-value; what can we answer except that these variations must have
been minimal, and yet sufficient to prevent too rapid sinking and
consequent elimination?  Yet this very case would give the ideal
opportunity for a mathematical calculation of the minimal selection-value,
although of course it is not feasible from lack of data to carry out the
actual calculation.

But even in organisms of more than microscopic size there must frequently
be minute, even microscopic differences which set going the process of
selection, and regulate its progress to the highest possible perfection.

Many tropical trees possess thick, leathery leaves, as a protection against
the force of the tropical rain drops.  The DIRECT influence of the rain
cannot be the cause of this power of resistance, for the leaves, while they
were still thin, would simply have been torn to pieces.  Their toughness
must therefore be referred to selection, which would favour the trees with
slightly thicker leaves, though we cannot calculate with any exactness how
great the first stages of increase in thickness must have been.  Our
hypothesis receives further support from the fact that, in many such trees,
the leaves are drawn out into a beak-like prolongation (Stahl and
Haberlandt) which facilitates the rapid falling off of the rain water, and
also from the fact that the leaves, while they are still young, hang limply
down in bunches which offer the least possible resistance to the rain. 
Thus there are here three adaptations which can only be interpreted as due
to selection.  The initial stages of these adaptations must undoubtedly
have had selection-value.

But even in regard to this case we are reasoning in a circle, not giving
"proofs," and no one who does not wish to believe in the selection-value of
the initial stages can be forced to do so.  Among the many pieces of
presumptive evidence a particularly weighty one seems to me to be THE
SMALLNESS OF THE STEPS OF PROGRESS which we can observe in certain cases,
as for instance in leaf-imitation among butterflies, and in mimicry
generally.  The resemblance to a leaf, for instance of a particular
Kallima, seems to us so close as to be deceptive, and yet we find in
another individual, or it may be in many others, a spot added which
increases the resemblance, and which could not have become fixed unless the
increased deceptiveness so produced had frequently led to the overlooking
of its much persecuted possessor.  But if we take the selection-value of
the initial stages for granted, we are confronted with the further question
which I myself formulated many years ago:  How does it happen THAT THE
NECESSARY BEGINNINGS OF A USEFUL VARIATION ARE ALWAYS PRESENT?  How could
insects which live upon or among green leaves become all green, while those
that live on bark become brown?  How have the desert animals become yellow
and the Arctic animals white?  Why were the necessary variations always
present?  How could the green locust lay brown eggs, or the privet
caterpillar develop white and lilac-coloured lines on its green skin?

It is of no use answering to this that the question is wrongly formulated
(Plate, "Selektionsprinzip u. Probleme der Artbildung" (3rd edition),
Leipzig, 1908.) and that it is the converse that is true; that the process
of selection takes place in accordance with the variations that present
themselves.  This proposition is undeniably true, but so also is another,
which apparently negatives it:  the variation required has in the majority
of cases actually presented itself.  Selection cannot solve this
contradiction; it does not call forth the useful variation, but simply
works upon it.  The ultimate reason why one and the same insect should
occur in green and in brown, as often happens in caterpillars and locusts,
lies in the fact that variations towards brown presented themselves, and so
also did variations towards green:  THE KERNEL OF THE RIDDLE LIES IN THE
VARYING, and for the present we can only say, that small variations in
different directions present themselves in every species.  Otherwise so
many different kinds of variations could not have arisen.  I have
endeavoured to explain this remarkable fact by means of the intimate
processes that must take place within the germ-plasm, and I shall return to
the problem when dealing with "germinal selection."

We have, however, to make still greater demands on variation, for it is not
enough that the necessary variation should occur in isolated individuals,
because in that case there would be small prospect of its being preserved,
notwithstanding its utility.  Darwin at first believed, that even single
variations might lead to transformation of the species, but later he became
convinced that this was impossible, at least without the cooperation of
other factors, such as isolation and sexual selection.

In the case of the GREEN CATERPILLARS WITH BRIGHT LONGITUDINAL STRIPES,
numerous individuals exhibiting this useful variation must have been
produced to start with.  In all higher, that is, multicellular organisms,
the germ-substance is the source of all transmissible variations, and this
germ-plasm is not a simple substance but is made up of many primary
constituents.  The question can therefore be more precisely stated thus: 
How does it come about that in so many cases the useful variations present
themselves in numbers just where they are required, the white oblique lines
in the leaf-caterpillar on the under surface of the body, the accompanying
coloured stripes just above them?  And, further, how has it come about that
in grass caterpillars, not oblique but longitudinal stripes, which are more
effective for concealment among grass and plants, have been evolved?  And
finally, how is it that the same Hawk-moth caterpillars, which to-day show
oblique stripes, possessed longitudinal stripes in Tertiary times?  We can
read this fact from the history of their development, and I have before
attempted to show the biological significance of this change of colour. 
("Studien zur Descendenz-Theorie" II., "Die Enstehung der Zeichnung bei den
Schmetterlings-raupen," Leipzig, 1876.)

For the present I need only draw the conclusion that one and the same
caterpillar may exhibit the initial stages of both, and that it depends on
the manner in which these marking elements are INTENSIFIED and COMBINED by
natural selection whether whitish longitudinal or oblique stripes should
result.  In this case then the "useful variations" were actually "always
there," and we see that in the same group of Lepidoptera, e.g. species of
Sphingidae, evolution has occurred in both directions according to whether
the form lived among grass or on broad leaves with oblique lateral veins,
and we can observe even now that the species with oblique stripes have
longitudinal stripes when young, that is to say, while the stripes have no
biological significance.  The white places in the skin which gave rise,
probably first as small spots, to this protective marking could be combined
in one way or another according to the requirements of the species.  They
must therefore either have possessed selection-value from the first, or, if
this was not the case at their earliest occurrence, there must have been
SOME OTHER FACTORS which raised them to the point of selection-value.  I
shall return to this in discussing germinal selection.  But the case may be
followed still farther, and leads us to the same alternative on a still
more secure basis.

Many years ago I observed in caterpillars of Smerinthus populi (the poplar
hawk-moth), which also possess white oblique stripes, that certain
individuals showed RED SPOTS above these stripes; these spots occurred only
on certain segments, and never flowed together to form continuous stripes.
In another species (Smerinthus tiliae) similar blood-red spots unite to
form a line-like coloured seam in the last stage of larval life, while in
S. ocellata rust-red spots appear in individual caterpillars, but more
rarely than in S. Populi, and they show no tendency to flow together.

Thus we have here the origin of a new character, arising from small
beginnings, at least in S. tiliae, in which species the coloured stripes
are a normal specific character.  In the other species, S. populi and S.
ocellata, we find the beginnings of the same variation, in one more rarely
than in the other, and we can imagine that, in the course of time, in these
two species, coloured lines over the oblique stripes will arise.  In any
case these spots are the elements of variation, out of which coloured lines
MAY be evolved, if they are combined in this direction through the agency
of natural selection.  In S. populi the spots are often small, but
sometimes it seems as though several had united to form large spots. 
Whether a process of selection in this direction will arise in S. populi
and S. ocellata, or whether it is now going on cannot be determined, since
we cannot tell in advance what biological value the marking might have for
these two species.  It is conceivable that the spots may have no selection-
value as far as these species are concerned, and may therefore disappear
again in the course of phylogeny, or, on the other hand, that they may be
changed in another direction, for instance towards imitation of the rust-
red fungoid patches on poplar and willow leaves.  In any case we may regard
the smallest spots as the initial stages of variation, the larger as a
cumulative summation of these.  Therefore either these initial stages must
already possess selection-value, or, as I said before:  THERE MUST BE SOME
OTHER REASON FOR THEIR CUMULATIVE SUMMATION.  I should like to give one
more example, in which we can infer, though we cannot directly observe, the
initial stages.

All the Holothurians or sea-cucumbers have in the skin calcareous bodies of
different forms, usually thick and irregular, which make the skin tough and
resistant.  In a small group of them--the species of Synapta--the
calcareous bodies occur in the form of delicate anchors of microscopic
size.  Up till 1897 these anchors, like many other delicate microscopic
structures, were regarded as curiosities, as natural marvels.  But a
Swedish observer, Oestergren, has recently shown that they have a
biological significance:  they serve the footless Synapta as auxiliary
organs of locomotion, since, when the body swells up in the act of
creeping, they press firmly with their tips, which are embedded in the
skin, against the substratum on which the animal creeps, and thus prevent
slipping backwards.  In other Holothurians this slipping is made impossible
by the fixing of the tube-feet.  The anchors act automatically, sinking
their tips towards the ground when the corresponding part of the body
thickens, and returning to the original position at an angle of 45 degrees
to the upper surface when the part becomes thin again.  The arms of the
anchor do not lie in the same plane as the shaft, and thus the curve of the
arms forms the outermost part of the anchor, and offers no further
resistance to the gliding of the animal.  Every detail of the anchor, the
curved portion, the little teeth at the head, the arms, etc., can be
interpreted in the most beautiful way, above all the form of the anchor
itself, for the two arms prevent it from swaying round to the side.  The
position of the anchors, too, is definite and significant; they lie
obliquely to the longitudinal axis of the animal, and therefore they act
alike whether the animal is creeping backwards or forwards.  Moreover, the
tips would pierce through the skin if the anchors lay in the longitudinal
direction.  Synapta burrows in the sand; it first pushes in the thin
anterior end, and thickens this again, thus enlarging the hole, then the
anterior tentacles displace more sand, the body is worked in a little
farther, and the process begins anew.  In the first act the anchors are
passive, but they begin to take an active share in the forward movement
when the body is contracted again.  Frequently the animal retains only the
posterior end buried in the sand, and then the anchors keep it in position,
and make rapid withdrawal possible.

Thus we have in these apparently random forms of the calcareous bodies,
complex adaptations in which every little detail as to direction, curve,
and pointing is exactly determined.  That they have selection-value in
their present perfected form is beyond all doubt, since the animals are
enabled by means of them to bore rapidly into the ground and so to escape
from enemies.  We do not know what the initial stages were, but we cannot
doubt that the little improvements, which occurred as variations of the
originally simple slimy bodies of the Holothurians, were preserved because
they already possessed selection-value for the Synaptidae.  For such minute
microscopic structures whose form is so delicately adapted to the role they
have to play in the life of the animal, cannot have arisen suddenly and as
a whole, and every new variation of the anchor, that is, in the direction
of the development of the two arms, and every curving of the shaft which
prevented the tips from projecting at the wrong time, in short, every
little adaptation in the modelling of the anchor must have possessed
selection-value.  And that such minute changes of form fall within the
sphere of fluctuating variations, that is to say, THAT THEY OCCUR is beyond
all doubt.

In many of the Synaptidae the anchors are replaced by calcareous rods bent
in the form of an S, which are said to act in the same way.  Others, such
as those of the genus Ankyroderma, have anchors which project considerably
beyond the skin, and, according to Oestergren, serve "to catch plant-
particles and other substances" and so mask the animal.  Thus we see that
in the Synaptidae the thick and irregular calcareous bodies of the
Holothurians have been modified and transformed in various ways in
adaptation to the footlessness of these animals, and to the peculiar
conditions of their life, and we must conclude that the earlier stages of
these changes presented themselves to the processes of selection in the
form of microscopic variations.  For it is as impossible to think of any
origin other than through selection in this case as in the case of the
toughness, and the "drip-tips" of tropical leaves.  And as these last could
not have been produced directly by the beating of the heavy rain-drops upon
them, so the calcareous anchors of Synapta cannot have been produced
directly by the friction of the sand and mud at the bottom of the sea, and,
since they are parts whose function is PASSIVE the Lamarckian factor of use
and disuse does not come into question.  The conclusion is unavoidable,
that the microscopically small variations of the calcareous bodies in the
ancestral forms have been intensified and accumulated in a particular
direction, till they have led to the formation of the anchor.  Whether this
has taken place by the action of natural selection alone, or whether the
laws of variation and the intimate processes within the germ-plasm have
cooperated will become clear in the discussion of germinal selection.  This
whole process of adaptation has obviously taken place within the time that
has elapsed since this group of sea-cucumbers lost their tube-feet, those
characteristic organs of locomotion which occur in no group except the
Echinoderms, and yet have totally disappeared in the Synaptidae.  And after
all what would animals that live in sand and mud do with tube-feet?

(c)  COADAPTATION.

Darwin pointed out that one of the essential differences between artificial
and natural selection lies in the fact that the former can modify only a
few characters, usually only one at a time, while Nature preserves in the
struggle for existence all the variations of a species, at the same time
and in a purely mechanical way, if they possess selection-value.

Herbert Spencer, though himself an adherent of the theory of selection,
declared in the beginning of the nineties that in his opinion the range of
this principle was greatly over-estimated, if the great changes which have
taken place in so many organisms in the course of ages are to be
interpreted as due to this process of selection alone, since no
transformation of any importance can be evolved by itself; it is always
accompanied by a host of secondary changes.  He gives the familiar example
of the Giant Stag of the Irish peat, the enormous antlers of which required
not only a much stronger skull cap, but also greater strength of the
sinews, muscles, nerves and bones of the whole anterior half of the animal,
if their mass was not to weigh down the animal altogether.  It is
inconceivable, he says, that so many processes of selection should take
place SIMULTANEOUSLY, and we are therefore forced to fall back on the
Lamarckian factor of the use and disuse of functional parts.  And how, he
asks, could natural selection follow two opposite directions of evolution
in different parts of the body at the same time, as for instance in the
case of the kangaroo, in which the forelegs must have become shorter, while
the hind legs and the tail were becoming longer and stronger?

Spencer's main object was to substantiate the validity of the Lamarckian
principle, the cooperation of which with selection had been doubted by
many.  And it does seem as though this principle, if it operates in nature
at all, offers a ready and simple explanation of all such secondary
variations.  Not only muscles, but nerves, bones, sinews, in short all
tissues which function actively, increase in strength in proportion as they
are used, and conversely they decrease when the claims on them diminish. 
All the parts, therefore, which depend on the part that varied first, as
for instance the enlarged antlers of the Irish Elk, must have been
increased or decreased in strength, in exact proportion to the claims made
upon them,--just as is actually the case.

But beautiful as this explanation would be, I regard it as untenable,
because it assumes the TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS (so-
called "acquired" characters), and this is not only undemonstrable, but is
scarcely theoretically conceivable, for the secondary variations which
accompany or follow the first as correlative variations, occur also in
cases in which the animals concerned are sterile and THEREFORE CANNOT
TRANSMIT ANYTHING TO THEIR DESCENDANTS.  This is true of WORKER BEES, and
particularly of ANTS, and I shall here give a brief survey of the present
state of the problem as it appears to me.

Much has been written on both sides of this question since the published
controversy on the subject in the nineties between Herbert Spencer and
myself.  I should like to return to the matter in detail, if the space at
my disposal permitted, because it seems to me that the arguments I advanced
at that time are equally cogent to-day, notwithstanding all the objections
that have since been urged against them.  Moreover, the matter is by no
means one of subordinate interest; it is the very kernel of the whole
question of the reality and value of the principle of selection.  For if
selection alone does not suffice to explain "HARMONIOUS ADAPTATION" as I
have called Spencer's COADAPTATION, and if we require to call in the aid of
the Lamarckian factor it would be questionable whether selection could
explain any adaptations whatever.  In this particular case--of worker bees
--the Lamarckian factor may be excluded altogether, for it can be
demonstrated that here at any rate the effects of use and disuse cannot be
transmitted.

But if it be asked why we are unwilling to admit the cooperation of the
Darwinian factor of selection and the Lamarckian factor, since this would
afford us an easy and satisfactory explanation of the phenomena, I answer: 
BECAUSE THE LAMARCKIAN PRINCIPLE IS FALLACIOUS, AND BECAUSE BY ACCEPTING IT
WE CLOSE THE WAY TOWARDS DEEPER INSIGHT.  It is not a spirit of
combativeness or a desire for self-vindication that induces me to take the
field once more against the Lamarckian principle, it is the conviction that
the progress of our knowledge is being obstructed by the acceptance of this
fallacious principle, since the facile explanation it apparently affords
prevents our seeking after a truer explanation and a deeper analysis.

The workers in the various species of ants are sterile, that is to say,
they take no regular part in the reproduction of the species, although
individuals among them may occasionally lay eggs.  In addition to this they
have lost the wings, and the receptaculum seminis, and their compound eyes
have degenerated to a few facets.  How could this last change have come
about through disuse, since the eyes of workers are exposed to light in the
same way as are those of the sexual insects and thus in this particular
case are not liable to "disuse" at all?  The same is true of the
receptaculum seminis, which can only have been disused as far as its
glandular portion and its stalk are concerned, and also of the wings, the
nerves tracheae and epidermal cells of which could not cease to function
until the whole wing had degenerated, for the chitinous skeleton of the
wing does not function at all in the active sense.

But, on the other hand, the workers in all species have undergone
modifications in a positive direction, as, for instance, the greater
development of brain.  In many species large workers have evolved,--the so-
called SOLDIERS, with enormous jaws and teeth, which defend the colony,--
and in others there are SMALL workers which have taken over other special
functions, such as the rearing of the young Aphides.  This kind of division
of the workers into two castes occurs among several tropical species of
ants, but it is also present in the Italian species, Colobopsis truncata. 
Beautifully as the size of the jaws could be explained as due to the
increased use made of them by the "soldiers," or the enlarged brain as due
to the mental activities of the workers, the fact of the infertility of
these forms is an insurmountable obstacle to accepting such an explanation.
Neither jaws nor brain can have been evolved on the Lamarckian principle.

The problem of coadaptation is no easier in the case of the ant than in the
case of the Giant Stag.  Darwin himself gave a pretty illustration to show
how imposing the difference between the two kinds of workers in one species
would seem if we translated it into human terms.  In regard to the Driver
ants (Anomma) we must picture to ourselves a piece of work, "for instance
the building of a house, being carried on by two kinds of workers, of which
one group was five feet four inches high, the other sixteen feet high." 
("Origin of Species" (6th edition), page 232.)

Although the ant is a small animal as compared with man or with the Irish
Elk, the "soldier" with its relatively enormous jaws is hardly less heavily
burdened than the Elk with its antlers, and in the ant's case, too, a
strengthening of the skeleton, of the muscles, the nerves of the head, and
of the legs must have taken place parallel with the enlargement of the
jaws.  HARMONIOUS ADAPTATION (coadaptation) has here been active in a high
degree, and yet these "soldiers" are sterile!  There thus remains nothing
for it but to refer all their adaptations, positive and negative alike, to
processes of selection which have taken place in the rudiments of the
workers within the egg and sperm-cells of their parents.  There is no way
out of the difficulty except the one Darwin pointed out.  He himself did
not find the solution of the riddle at once.  At first he believed that the
case of the workers among social insects presented "the most serious
special difficulty" in the way of his theory of natural selection; and it
was only after it had become clear to him, that it was not the sterile
insects themselves but their parents that were selected, according as they
produced more or less well adapted workers, that he was able to refer to
this very case of the conditions among ants "IN ORDER TO SHOW THE POWER OF
NATURAL SELECTION" ("Origin of Species", page 233; see also edition 1, page
242.).  He explains his view by a simple but interesting illustration. 
Gardeners have produced, by means of long continued artificial selection, a
variety of Stock, which bears entirely double, and therefore infertile
flowers (Ibid. page 230.).  Nevertheless the variety continues to be
reproduced from seed, because in addition to the double and infertile
flowers, the seeds always produce a certain number of single, fertile
blossoms, and these are used to reproduce the double variety.  These single
and fertile plants correspond "to the males and females of an ant-colony,
the infertile plants, which are regularly produced in large numbers, to the
neuter workers of the colony."

This illustration is entirely apt, the only difference between the two
cases consisting in the fact that the variation in the flower is not a
useful, but a disadvantageous one, which can only be preserved by
artificial selection on the part of the gardener, while the transformations
that have taken place parallel with the sterility of the ants are useful,
since they procure for the colony an advantage in the struggle for
existence, and they are therefore preserved by natural selection.  Even the
sterility itself in this case is not disadvantageous, since the fertility
of the true females has at the same time considerably increased.  We may
therefore regard the sterile forms of ants, which have gradually been
adapted in several directions to varying functions, AS A CERTAIN PROOF that
selection really takes place in the germ-cells of the fathers and mothers
of the workers, and that SPECIAL COMPLEXES OF PRIMORDIA (IDS) are present
in the workers and in the males and females, and these complexes contain
the primordia of the individual parts (DETERMINANTS).  But since all living
entities vary, the determinants must also vary, now in a favourable, now in
an unfavourable direction.  If a female produces eggs, which contain
favourably varying determinants in the worker-ids, then these eggs will
give rise to workers modified in the favourable direction, and if this
happens with many females, the colony concerned will contain a better kind
of worker than other colonies.

I digress here in order to give an account of the intimate processes,
which, according to my view, take place within the germ-plasm, and which I
have called "GERMINAL SELECTION."  These processes are of importance since
they form the roots of variation, which in its turn is the root of natural
selection.  I cannot here do more than give a brief outline of the theory
in order to show how the Darwin-Wallace theory of selection has gained
support from it.

With others, I regard the minimal amount of substance which is contained
within the nucleus of the germ-cells, in the form of rods, bands, or
granules, as the GERM-SUBSTANCE or GERM-PLASM, and I call the individual
granules IDS.  There is always a multiplicity of such ids present in the
nucleus, either occurring individually, or united in the form of rods or
bands (chromosomes).  Each id contains the primary constituents of a WHOLE
individual, so that several ids are concerned in the development of a new
individual.

In every being of complex structure thousands of primary constituents must
go to make up a single id; these I call DETERMINANTS, and I mean by this
name very small individual particles, far below the limits of microscopic
visibility, vital units which feed, grow, and multiply by division.  These
determinants control the parts of the developing embryo,--in what manner
need not here concern us.  The determinants differ among themselves, those
of a muscle are differently constituted from those of a nerve-cell or a
glandular cell, etc., and every determinant is in its turn made up of
minute vital units, which I call BIOPHORS, or the bearers of life. 
According to my view, these determinants not only assimilate, like every
other living unit, but they VARY in the course of their growth, as every
living unit does; they may vary qualitatively if the elements of which they
are composed vary, they may grow and divide more or less rapidly, and their
variations give rise to CORRESPONDING variations of the organ, cell, or
cell-group which they determine.  That they are undergoing ceaseless
fluctuations in regard to size and quality seems to me the inevitable
consequence of their unequal nutrition; for although the germ-cell as a
whole usually receives sufficient nutriment, minute fluctuations in the
amount carried to different parts within the germ-plasm cannot fail to
occur.

Now, if a determinant, for instance of a sensory cell, receives for a
considerable time more abundant nutriment than before, it will grow more
rapidly--become bigger, and divide more quickly, and, later, when the id
concerned develops into an embryo, this sensory cell will become stronger
than in the parents, possibly even twice as strong.  This is an instance of
a HEREDITARY INDIVIDUAL VARIATION, arising from the germ.

The nutritive stream which, according to our hypothesis, favours the
determinant N by chance, that is, for reasons unknown to us, may remain
strong for a considerable time, or may decrease again; but even in the
latter case it is conceivable that the ascending movement of the
determinant may continue, because the strengthened determinant now ACTIVELY
nourishes itself more abundantly,--that is to say, it attracts the
nutriment to itself, and to a certain extent withdraws it from its fellow-
determinants.  In this way, it may--as it seems to me--get into PERMANENT
UPWARD MOVEMENT, AND ATTAIN A DEGREE OF STRENGTH FROM WHICH THERE IS NO
FALLING BACK.  Then positive or negative selection sets in, favouring the
variations which are advantageous, setting aside those which are
disadvantageous.

In a similar manner a DOWNWARD variation of the determinants may take
place, if its progress be started by a diminished flow of nutriment.  The
determinants which are weakened by this diminished flow will have less
affinity for attracting nutriment because of their diminished strength, and
they will assimilate more feebly and grow more slowly, unless chance
streams of nutriment help them to recover themselves.  But, as will
presently be shown, a change of direction cannot take place at EVERY stage
of the degenerative process.  If a certain critical stage of downward
progress be passed, even favourable conditions of food-supply will no
longer suffice permanently to change the direction of the variation.  Only
two cases are conceivable; if the determinant corresponds to a USEFUL
organ, only its removal can bring back the germ-plasm to its former level;
therefore personal selection removes the id in question, with its
determinants, from the germ-plasm, by causing the elimination of the
individual in the struggle for existence.  But there is another conceivable
case; the determinants concerned may be those of an organ which has become
USELESS, and they will then continue unobstructed, but with exceeding
slowness, along the downward path, until the organ becomes vestigial, and
finally disappears altogether.

The fluctuations of the determinants hither and thither may thus be
transformed into a lasting ascending or descending movement; and THIS IS
THE CRUCIAL POINT OF THESE GERMINAL PROCESSES.

This is not a fantastic assumption; we can read it in the fact of the
degeneration of disused parts.  USELESS ORGANS ARE THE ONLY ONES WHICH ARE
NOT HELPED TO ASCEND AGAIN BY PERSONAL SELECTION, AND THEREFORE IN THEIR
CASE ALONE CAN WE FORM ANY IDEA OF HOW THE PRIMARY CONSTITUENTS BEHAVE,
WHEN THEY ARE SUBJECT SOLELY TO INTRA-GERMINAL FORCES.

The whole determinant system of an id, as I conceive it, is in a state of
continual fluctuation upwards and downwards.  In most cases the
fluctuations will counteract one another, because the passive streams of
nutriment soon change, but in many cases the limit from which a return is
possible will be passed, and then the determinants concerned will continue
to vary in the same direction, till they attain positive or negative
selection-value.  At this stage personal selection intervenes and sets
aside the variation if it is disadvantageous, or favours--that is to say,
preserves--it if it is advantageous.  Only THE DETERMINANT OF A USELESS
ORGAN IS UNINFLUENCED BY PERSONAL SELECTION, and, as experience shows, it
sinks downwards; that is, the organ that corresponds to it degenerates very
slowly but uninterruptedly till, after what must obviously be an immense
stretch of time, it disappears from the germ-plasm altogether.

Thus we find in the fact of the degeneration of disused parts the proof
that not all the fluctuations of a determinant return to equilibrium again,
but that, when the movement has attained to a certain strength, it
continues IN THE SAME DIRECTION.  We have entire certainty in regard to
this as far as the downward progress is concerned, and we must assume it
also in regard to ascending variations, as the phenomena of artificial
selection certainly justify us in doing.  If the Japanese breeders were
able to lengthen the tail feathers of the cock to six feet, it can only
have been because the determinants of the tail-feathers in the germ-plasm
had already struck out a path of ascending variation, and this movement was
taken advantage of by the breeder, who continually selected for
reproduction the individuals in which the ascending variation was most
marked.  For all breeding depends upon the unconscious selection of
germinal variations.

Of course these germinal processes cannot be proved mathematically, since
we cannot actually see the play of forces of the passive fluctuations and
their causes.  We cannot say how great these fluctuations are, and how
quickly or slowly, how regularly or irregularly they change.  Nor do we
know how far a determinant must be strengthened by the passive flow of the
nutritive stream if it is to be beyond the danger of unfavourable
variations, or how far it must be weakened passively before it loses the
power of recovering itself by its own strength.  It is no more possible to
bring forward actual proofs in this case than it was in regard to the
selection-value of the initial stages of an adaptation.  But if we consider
that all heritable variations must have their roots in the germ-plasm, and
further, that when personal selection does not intervene, that is to say,
in the case of parts which have become useless, a degeneration of the part,
and therefore also of its determinant must inevitably take place; then we
must conclude that processes such as I have assumed are running their
course within the germ-plasm, and we can do this with as much certainty as
we were able to infer, from the phenomena of adaptation, the selection-
value of their initial stages.  The fact of the degeneration of disused
parts seems to me to afford irrefutable proof that the fluctuations within
the germ-plasm ARE THE REAL ROOT OF ALL HEREDITARY VARIATION, and the
preliminary condition for the occurrence of the Darwin-Wallace factor of
selection.  Germinal selection supplies the stones out of which personal
selection builds her temples and palaces:  ADAPTATIONS.  The importance for
the theory of the process of degeneration of disused parts cannot be over-
estimated, especially when it occurs in sterile animal forms, where we are
free from the doubt as to the alleged LAMARCKIAN FACTOR which is apt to
confuse our ideas in regard to other cases.

If we regard the variation of the many determinants concerned in the
transformation of the female into the sterile worker as having come about
through the gradual transformation of the ids into worker-ids, we shall see
that the germ-plasm of the sexual ants must contain three kinds of ids,
male, female, and worker ids, or if the workers have diverged into soldiers
and nest-builders, then four kinds.  We understand that the worker-ids
arose because their determinants struck out a useful path of variation,
whether upward or downward, and that they continued in this path until the
highest attainable degree of utility of the parts determined was reached. 
But in addition to the organs of positive or negative selection-value,
there were some which were indifferent as far as the success and especially
the functional capacity of the workers was concerned:  wings, ovarian
tubes, receptaculum seminis, a number of the facets of the eye, perhaps
even the whole eye.  As to the ovarian tubes it is possible that their
degeneration was an advantage for the workers, in saving energy, and if so
selection would favour the degeneration; but how could the presence of eyes
diminish the usefulness of the workers to the colony? or the minute
receptaculum seminis, or even the wings?  These parts have therefore
degenerated BECAUSE THEY WERE OF NO FURTHER VALUE TO THE INSECT.  But if
selection did not influence the setting aside of these parts because they
were neither of advantage nor of disadvantage to the species, then the
Darwinian factor of selection is here confronted with a puzzle which it
cannot solve alone, but which at once becomes clear when germinal selection
is added.  For the determinants of organs that have no further value for
the organism, must, as we have already explained, embark on a gradual
course of retrograde development.

In ants the degeneration has gone so far that there are no wing-rudiments
present in ANY species, as is the case with so many butterflies, flies, and
locusts, but in the larvae the imaginal discs of the wings are still laid
down.  With regard to the ovaries, degeneration has reached different
levels in different species of ants, as has been shown by the researches of
my former pupil, Elizabeth Bickford.  In many species there are twelve
ovarian tubes, and they decrease from that number to one; indeed, in one
species no ovarian tube at all is present.  So much at least is certain
from what has been said, that in this case EVERYTHING depends on the
fluctuations of the elements of the germ-plasm.  Germinal selection, here
as elsewhere, presents the variations of the determinants, and personal
selection favours or rejects these, or,--if it be a question of organs
which have become useless,--it does not come into play at all, and allows
the descending variation free course.

It is obvious that even the problem of COADAPTATION IN STERILE ANIMALS can
thus be satisfactorily explained.  If the determinants are oscillating
upwards and downwards in continual fluctuation, and varying more
pronouncedly now in one direction now in the other, useful variations of
every determinant will continually present themselves anew, and may, in the
course of generations, be combined with one another in various ways.  But
there is one character of the determinants that greatly facilitates this
complex process of selection, that, after a certain limit has been reached,
they go on varying in the same direction.  From this it follows that
development along a path once struck out may proceed without the continual
intervention of personal selection.  This factor only operates, so to
speak, at the beginning, when it selects the determinants which are varying
in the right direction, and again at the end, when it is necessary to put a
check upon further variation.  In addition to this, enormously long periods
have been available for all these adaptations, as the very gradual
transition stages between females and workers in many species plainly show,
and thus this process of transformation loses the marvellous and mysterious
character that seemed at the first glance to invest it, and takes rank,
without any straining, among the other processes of selection.  It seems to
me that, from the facts that sterile animal forms can adapt themselves to
new vital functions, their superfluous parts degenerate, and the parts more
used adapt themselves in an ascending direction, those less used in a
descending direction, we must draw the conclusion that harmonious
adaptation here comes about WITHOUT THE COOPERATION OF THE LAMARCKIAN
PRINCIPLE.  This conclusion once established, however, we have no reason to
refer the thousands of cases of harmonious adaptation, which occur in
exactly the same way among other animals or plants, to a principle, the
ACTIVE INTERVENTION OF WHICH IN THE TRANSFORMATION OF SPECIES IS NOWHERE
PROVED.  WE DO NOT REQUIRE IT TO EXPLAIN THE FACTS, AND THEREFORE WE MUST
NOT ASSUME IT.

The fact of coadaptation, which was supposed to furnish the strongest
argument against the principle of selection, in reality yields the clearest
evidence in favour of it.  We MUST assume it, BECAUSE NO OTHER POSSIBILITY
OF EXPLANATION IS OPEN TO US, AND BECAUSE THESE ADAPTATIONS ACTUALLY EXIST,
THAT IS TO SAY, HAVE REALLY TAKEN PLACE.  With this conviction I attempted,
as far back as 1894, when the idea of germinal selection had not yet
occurred to me, to make "harmonious adaptation" (coadaptation) more easily
intelligible in some way or other, and so I was led to the idea, which was
subsequently expounded in detail by Baldwin, and Lloyd Morgan, and also by
Osborn, and Gulick as ORGANIC SELECTION.  It seemed to me that it was not
necessary that all the germinal variations required for secondary
variations should have occurred SIMULTANEOUSLY, since, for instance, in the
case of the stag, the bones, muscles, sinews, and nerves would be incited
by the increasing heaviness of the antlers to greater activity in THE
INDIVIDUAL LIFE, and so would be strengthened.  The antlers can only have
increased in size by very slow degrees, so that the muscles and bones may
have been able to keep pace with their growth in the individual life, until
the requisite germinal variations presented themselves.  In this way a
disharmony between the increasing weight of the antlers and the parts which
support and move them would be avoided, since time would be given for the
appropriate germinal variations to occur, and so to set agoing the
HEREDITARY variation of the muscles, sinews, and bones.  ("The Effect of
External Influences upon Development", Romanes Lecture, Oxford, 1894.)

I still regard this idea as correct, but I attribute less importance to
"organic selection" than I did at that time, in so far that I do not
believe that it ALONE could effect complex harmonious adaptations. 
Germinal selection now seems to me to play the chief part in bringing about
such adaptations.  Something the same is true of the principle I have
called "Panmixia".  As I became more and more convinced, in the course of
years, that the LAMARCKIAN PRINCIPLE ought not to be called in to explain
the dwindling of disused parts, I believed that this process might be
simply explained as due to the cessation of the conservative effect of
natural selection.  I said to myself that, from the moment in which a part
ceases to be of use, natural selection withdraws its hand from it, and then
it must inevitably fall from the height of its adaptiveness, because
inferior variants would have as good a chance of persisting as better ones,
since all grades of fitness of the part in question would be mingled with
one another indiscriminately.  This is undoubtedly true, as Romanes pointed
out ten years before I did, and this mingling of the bad with the good
probably does bring about a deterioration of the part concerned.  But it
cannot account for the steady diminution, which always occurs when a part
is in process of becoming rudimentary, and which goes on until it
ultimately disappears altogether.  The process of dwindling cannot
therefore be explained as due to panmixia alone; we can only find a
sufficient explanation in germinal selection.

IV.  DERIVATIVES OF THE THEORY OF SELECTION.

The impetus in all directions given by Darwin through his theory of
selection has been an immeasurable one, and its influence is still felt. It
falls within the province of the historian of science to enumerate all the
ideas which, in the last quarter of the nineteenth century, grew out of
Darwin's theories, in the endeavour to penetrate more deeply into the
problem of the evolution of the organic world.  Within the narrow limits to
which this paper is restricted, I cannot attempt to discuss any of these.

V.  ARGUMENTS FOR THE REALITY OF THE PROCESSES OF SELECTION.

(a)  SEXUAL SELECTION.

Sexual selection goes hand in hand with natural selection.  From the very
first I have regarded sexual selection as affording an extremely important
and interesting corroboration of natural selection, but, singularly enough,
it is precisely against this theory that an adverse judgment has been
pronounced in so many quarters, and it is only quite recently, and probably
in proportion as the wealth of facts in proof of it penetrates into a wider
circle, that we seem to be approaching a more general recognition of this
side of the problem of adaptation.  Thus Darwin's words in his preface to
the second edition (1874) of his book, "The Descent of Man and Sexual
Selection", are being justified:  "My conviction as to the operation of
natural selection remains unshaken," and further, "If naturalists were to
become more familiar with the idea of sexual selection, it would, I think,
be accepted to a much greater extent, and already it is fully and
favourably accepted by many competent judges."  Darwin was able to speak
thus because he was already acquainted with an immense mass of facts,
which, taken together, yield overwhelming evidence of the validity of the
principle of sexual selection.

NATURAL SELECTION chooses out for reproduction the individuals that are
best equipped for the struggle for existence, and it does so at every stage
of development; it thus improves the species in all its stages and forms. 
SEXUAL SELECTION operates only on individuals that are already capable of
reproduction, and does so only in relation to the attainment of
reproduction.  It arises from the rivalry of one sex, usually the male, for
the possession of the other, usually the female.  Its influence can
therefore only DIRECTLY affect one sex, in that it equips it better for
attaining possession of the other.  But the effect may extend indirectly to
the female sex, and thus the whole species may be modified, without,
however, becoming any more capable of resistance in the struggle for
existence, for sexual selection only gives rise to adaptations which are
likely to give their possessor the victory over rivals in the struggle for
possession of the female, and which are therefore peculiar to the wooing
sex:  the manifold "secondary sexual characters."  The diversity of these
characters is so great that I cannot here attempt to give anything
approaching a complete treatment of them, but I should like to give a
sufficient number of examples to make the principle itself, in its various
modes of expression, quite clear.

One of the chief preliminary postulates of sexual selection is the unequal
number of individuals in the two sexes, for if every male immediately finds
his mate there can be no competition for the possession of the female. 
Darwin has shown that, for the most part, the inequality between the sexes
is due simply to the fact that there are more males than females, and
therefore the males must take some pains to secure a mate.  But the
inequality does not always depend on the numerical preponderance of the
males, it is often due to polygamy; for, if one male claims several
females, the number of females in proportion to the rest of the males will
be reduced.  Since it is almost always the males that are the wooers, we
must expect to find the occurrence of secondary sexual characters chiefly
among them, and to find it especially frequent in polygamous species.  And
this is actually the case.

If we were to try to guess--without knowing the facts--what means the male
animals make use of to overcome their rivals in the struggle for the
possession of the female, we might name many kinds of means, but it would
be difficult to suggest any which is not actually employed in some animal
group or other.  I begin with the mere difference in strength, through
which the male of many animals is so sharply distinguished from the female,
as, for instance, the lion, walrus, "sea-elephant," and others.  Among
these the males fight violently for the possession of the female, who falls
to the victor in the combat.  In this simple case no one can doubt the
operation of selection, and there is just as little room for doubt as to
the selection-value of the initial stages of the variation.  Differences in
bodily strength are apparent even among human beings, although in their
case the struggle for the possession of the female is no longer decided by
bodily strength alone.

Combats between male animals are often violent and obstinate, and the
employment of the natural weapons of the species in this way has led to
perfecting of these, e.g. the tusks of the boar, the antlers of the stag,
and the enormous, antler-like jaws of the stag-beetle.  Here again it is
impossible to doubt that variations in these organs presented themselves,
and that these were considerable enough to be decisive in combat, and so to
lead to the improvement of the weapon.

Among many animals, however, the females at first withdraw from the males;
they are coy, and have to be sought out, and sometimes held by force.  This
tracking and grasping of the females by the males has given rise to many
different characters in the latter, as, for instance, the larger eyes of
the male bee, and especially of the males of the Ephemerids (May-flies),
some species of which show, in addition to the usual compound eyes, large,
so-called turban-eyes, so that the whole head is covered with seeing
surfaces. In these species the females are very greatly in the minority (1-
100), and it is easy to understand that a keen competition for them must
take place, and that, when the insects of both sexes are floating freely in
the air, an unusually wide range of vision will carry with it a decided
advantage.  Here again the actual adaptations are in accordance with the
preliminary postulates of the theory.  We do not know the stages through
which the eye has passed to its present perfected state, but, since the
number of simple eyes (facets) has become very much greater in the male
than in the female, we may assume that their increase is due to a gradual
duplication of the determinants of the ommatidium in the germ-plasm, as I
have already indicated in regard to sense-organs in general.  In this case,
again, the selection-value of the initial stages hardly admits of doubt;
better vision DIRECTLY secures reproduction.

In many cases THE ORGAN OF SMELL shows a similar improvement.  Many lower
Crustaceans (Daphnidae) have better developed organs of smell in the male
sex.  The difference is often slight and amounts only to one or two
olfactory filaments, but certain species show a difference of nearly a
hundred of these filaments (Leptodora).  The same thing occurs among
insects.

We must briefly consider the clasping or grasping organs which have
developed in the males among many lower Crustaceans, but here natural
selection plays its part along with sexual selection, for the union of the
sexes is an indispensable condition for the maintenance of the species, and
as Darwin himself pointed out, in many cases the two forms of selection
merge into each other.  This fact has always seemed to me to be a proof of
natural selection, for, in regard to sexual selection, it is quite obvious
that the victory of the best-equipped could have brought about the
improvement only of the organs concerned, the factors in the struggle, such
as the eye and the olfactory organ.

We come now to the EXCITANTS; that is, to the group of sexual characters
whose origin through processes of selection has been most frequently called
in question.  We may cite the LOVE-CALLS produced by many male insects,
such as crickets and cicadas.  These could only have arisen in animal
groups in which the female did not rapidly flee from the male, but was
inclined to accept his wooing from the first.  Thus, notes like the
chirping of the male cricket serve to entice the females.  At first they
were merely the signal which showed the presence of a male in the
neighbourhood, and the female was gradually enticed nearer and nearer by
the continued chirping.  The male that could make himself heard to the
greatest distance would obtain the largest following, and would transmit
the beginnings, and, later, the improvement of his voice to the greatest
number of descendants.  But sexual excitement in the female became
associated with the hearing of the love-call, and then the sound-producing
organ of the male began to improve, until it attained to the emission of
the long-drawn-out soft notes of the mole-cricket or the maenad-like cry of
the cicadas.  I cannot here follow the process of development in detail,
but will call attention to the fact that the original purpose of the voice,
the announcing of the male's presence, became subsidiary, and the exciting
of the female became the chief goal to be aimed at.  The loudest singers
awakened the strongest excitement, and the improvement resulted as a matter
of course.  I conceive of the origin of bird-song in a somewhat similar
manner, first as a means of enticing, then of exciting the female.

One more kind of secondary sexual character must here be mentioned:  the
odour which emanates from so many animals at the breeding season.  It is
possible that this odour also served at first merely to give notice of the
presence of individuals of the other sex, but it soon became an excitant,
and as the individuals which caused the greatest degree of excitement were
preferred, it reached as high a pitch of perfection as was possible to it. 
I shall confine myself here to the comparatively recently discovered
fragrance of butterflies.  Since Fritz Muller found out that certain
Brazilian butterflies gave off fragrance "like a flower," we have become
acquainted with many such cases, and we now know that in all lands, not
only many diurnal Lepidoptera but nocturnal ones also give off a delicate
odour, which is agreeable even to man.  The ethereal oil to which this
fragrance is due is secreted by the skin-cells, usually of the wing, as I
showed soon after the discovery of the SCENT-SCALES.  This is the case in
the males; the females have no SPECIAL scent-scales recognisable as such by
their form, but they must, nevertheless, give off an extremely delicate
fragrance, although our imperfect organ of smell cannot perceive it, for
the males become aware of the presence of a female, even at night, from a
long distance off, and gather round her.  We may therefore conclude, that
both sexes have long given forth a very delicate perfume, which announced
their presence to others of the same species, and that in many species (NOT
IN ALL) these small beginnings became, in the males, particularly strong
scent-scales of characteristic form (lute, brush, or lyre-shaped).  At
first these scales were scattered over the surface of the wing, but
gradually they concentrated themselves, and formed broad, velvety bands, or
strong, prominent brushes, and they attained their highest pitch of
evolution when they became enclosed within pits or folds of the skin, which
could be opened to let the delicious fragrance stream forth suddenly
towards the female.  Thus in this case also we see that characters, the
original use of which was to bring the sexes together, and so to maintain
the species, have been evolved in the males into means for exciting the
female.  And we can hardly doubt, that the females are most readily enticed
to yield to the butterfly that sends out the strongest fragrance,--that is
to say, that excites them to the highest degree.  It is a pity that our
organs of smell are not fine enough to examine the fragrance of male
Lepidoptera in general, and to compare it with other perfumes which attract
these insects.  (See Poulton, "Essays on Evolution", 1908, pages 316, 317.) 
As far as we can perceive them they resemble the fragrance of flowers, but
there are Lepidoptera whose scent suggests musk.  A smell of musk is also
given off by several plants:  it is a sexual excitant in the musk-deer, the
musk-sheep, and the crocodile.

As far as we know, then, it is perfumes similar to those of flowers that
the male Lepidoptera give off in order to entice their mates, and this is a
further indication that animals, like plants, can to a large extent meet
the claims made upon them by life, and produce the adaptations which are
most purposive,--a further proof, too, of my proposition that the useful
variations, so to speak, are ALWAYS THERE.  The flowers developed the
perfumes which entice their visitors, and the male Lepidoptera developed
the perfumes which entice and excite their mates.

There are many pretty little problems to be solved in this connection, for
there are insects, such as some flies, that are attracted by smells which
are unpleasant to us, like those from decaying flesh and carrion.  But
there are also certain flowers, some orchids for instance, which give forth
no very agreeable odour, but one which is to us repulsive and disgusting;
and we should therefore expect that the males of such insects would give
off a smell unpleasant to us, but there is no case known to me in which
this has been demonstrated.

In cases such as we have discussed, it is obvious that there is no possible
explanation except through selection.  This brings us to the last kind of
secondary sexual characters, and the one in regard to which doubt has been
most frequently expressed,--decorative colours and decorative forms, the
brilliant plumage of the male pheasant, the humming-birds, and the bird of
Paradise, as well as the bright colours of many species of butterfly, from
the beautiful blue of our little Lycaenidae to the magnificent azure of the
large Morphinae of Brazil.  In a great many cases, though not by any means
in all, the male butterflies are "more beautiful" than the females, and in
the Tropics in particular they shine and glow in the most superb colours. 
I really see no reason why we should doubt the power of sexual selection,
and I myself stand wholly on Darwin's side.  Even though we certainly
cannot assume that the females exercise a conscious choice of the
"handsomest" mate, and deliberate like the judges in a court of justice
over the perfections of their wooers, we have no reason to doubt that
distinctive forms (decorative feathers) and colours have a particularly
exciting effect upon the female, just as certain odours have among animals
of so many different groups, including the butterflies.  The doubts which
existed for a considerable time, as a result of fallacious experiments, as
to whether the colours of flowers really had any influence in attracting
butterflies have now been set at rest through a series of more careful
investigations; we now know that the colours of flowers are there on
account of the butterflies, as Sprengel first showed, and that the blossoms
of Phanerogams are selected in relation to them, as Darwin pointed out.

Certainly it is not possible to bring forward any convincing proof of the
origin of decorative colours through sexual selection, but there are many
weighty arguments in favour of it, and these form a body of presumptive
evidence so strong that it almost amounts to certainty.

In the first place, there is the analogy with other secondary sexual
characters. If the song of birds and the chirping of the cricket have been
evolved through sexual selection, if the penetrating odours of male
animals,--the crocodile, the musk-deer, the beaver, the carnivores, and,
finally, the flower-like fragrances of the butterflies have been evolved to
their present pitch in this way, why should decorative colours have arisen
in some other way?  Why should the eye be less sensitive to SPECIFICALLY
MALE colours and other VISIBLE signs ENTICING TO THE FEMALE, than the
olfactory sense to specifically male odours, or the sense of hearing to
specifically male sounds?  Moreover, the decorative feathers of birds are
almost always spread out and displayed before the female during courtship. 
I have elsewhere ("The Evolution Theory", London, 1904, I. page 219.)
pointed out that decorative colouring and sweet-scentedness may replace one
another in Lepidoptera as well as in flowers, for just as some modestly
coloured flowers (mignonette and violet) have often a strong perfume, while
strikingly coloured ones are sometimes quite devoid of fragrance, so we
find that the most beautiful and gaily-coloured of our native Lepidoptera,
the species of Vanessa, have no scent-scales, while these are often
markedly developed in grey nocturnal Lepidoptera.  Both attractions may,
however, be combined in butterflies, just as in flowers.  Of course, we
cannot explain why both means of attraction should exist in one genus, and
only one of them in another, since we do not know the minutest details of
the conditions of life of the genera concerned.  But from the sporadic
distribution of scent-scales in Lepidoptera, and from their occurrence or
absence in nearly related species, we may conclude that fragrance is a
relatively MODERN acquirement,  more recent than brilliant colouring.

One thing in particular that stamps decorative colouring as a product of
selection is ITS GRADUAL INTENSIFICATION by the addition of new spots,
which we can quite well observe, because in many cases the colours have
been first acquired by the males, and later transmitted to the females by
inheritance.  The scent-scales are never thus transmitted, probably for the
same reason that the decorative colours of many birds are often not
transmitted to the females:  because with these they would be exposed to
too great elimination by enemies.  Wallace was the first to point out that
in species with concealed nests the beautiful feathers of the male occurred
in the female also, as in the parrots, for instance, but this is not the
case in species which brood on an exposed nest.  In the parrots one can
often observe that the general brilliant colouring of the male is found in
the female, but that certain spots of colour are absent, and these have
probably been acquired comparatively recently by the male and have not yet
been transmitted to the female.

Isolation of the group of individuals which is in process of varying is
undoubtedly of great value in sexual selection, for even a solitary
conspicuous variation will become dominant much sooner in a small isolated
colony, than among a large number of members of a species.

Anyone who agrees with me in deriving variations from germinal selection
will regard that process as an essential aid towards explaining the
selection of distinctive courtship-characters, such as coloured spots,
decorative feathers, horny outgrowths in birds and reptiles, combs,
feather-tufts, and the like, since the beginnings of these would be
presented with relative frequency in the struggle between the determinants
within the germ-plasm.  The process of transmission of decorative feathers
to the female results, as Darwin pointed out and illustrated by interesting
examples, in the COLOUR-TRANSFORMATION OF A WHOLE SPECIES, and this
process, as the phyletically older colouring of young birds shows, must, in
the course of thousands of years, have repeated itself several times in a
line of descent.

If we survey the wealth of phenomena presented to us by secondary sexual
characters, we can hardly fail to be convinced of the truth of the
principle of sexual selection.  And certainly no one who has accepted
natural selection should reject sexual selection, for, not only do the two
processes rest upon the same basis, but they merge into one another, so
that it is often impossible to say how much of a particular character
depends on one and how much on the other form of selection.

(b)  NATURAL SELECTION.

An actual proof of the theory of sexual selection is out of the question,
if only because we cannot tell when a variation attains to selection-value.
It is certain that a delicate sense of smell is of value to the male moth
in his search for the female, but whether the possession of one additional
olfactory hair, or of ten, or of twenty additional hairs leads to the
success of its possessor we are unable to tell.  And we are groping even
more in the dark when we discuss the excitement caused in the female by
agreeable perfumes, or by striking and beautiful colours.  That these do
make an impression is beyond doubt; but we can only assume that slight
intensifications of them give any advantage, and we MUST assume this SINCE
OTHERWISE SECONDARY SEXUAL CHARACTERS REMAIN INEXPLICABLE.

The same thing is true in regard to natural selection.  It is not possible
to bring forward any actual proof of the selection-value of the initial
stages, and the stages in the increase of variations, as has been already
shown.  But the selection-value of a finished adaptation can in many cases
be statistically determined.  Cesnola and Poulton have made valuable
experiments in this direction.  The former attached forty-five individuals
of the green, and sixty-five of the brown variety of the praying mantis
(Mantis religiosa), by a silk thread to plants, and watched them for
seventeen days.  The insects which were on a surface of a colour similar to
their own remained uneaten, while twenty-five green insects on brown parts
of plants had all disappeared in eleven days.

The experiments of Poulton and Sanders ("Report of the British Association"
(Bristol, 1898), London, 1899, pages 906-909.) were made with 600 pupae of
Vanessa urticae, the "tortoise-shell butterfly."  The pupae were
artificially attached to nettles, tree-trunks, fences, walls, and to the
ground, some at Oxford, some at St Helens in the Isle of Wight.  In the
course of a month 93 per cent of the pupae at Oxford were killed, chiefly
by small birds, while at St Helens 68 per cent perished.  The experiments
showed very clearly that the colour and character of the surface on which
the pupa rests--and thus its own conspicuousness--are of the greatest
importance.  At Oxford only the four pupae which were fastened to nettles
emerged; all the rest--on bark, stones and the like--perished.  At St
Helens the elimination was as follows:  on fences where the pupae were
conspicuous, 92 per cent; on bark, 66 per cent; on walls, 54 per cent; and
among nettles, 57 per cent.  These interesting experiments confirm our
views as to protective coloration, and show further, THAT THE RATIO OF
ELIMINATION IN THE SPECIES IS A VERY HIGH ONE, AND THAT THEREFORE SELECTION
MUST BE VERY KEEN.

We may say that the process of selection follows as a logical necessity
from the fulfilment of the three preliminary postulates of the theory: 
variability, heredity, and the struggle for existence, with its enormous
ratio of elimination in all species.  To this we must add a fourth factor,
the INTENSIFICATION of variations which Darwin established as a fact, and
which we are now able to account for theoretically on the basis of germinal
selection.  It may be objected that there is considerable uncertainty about
this LOGICAL proof, because of our inability to demonstrate the selection-
value of the initial stages and the individual stages of increase.  We have
therefore to fall back on PRESUMPTIVE EVIDENCE.  This is to be found in THE
INTERPRETATIVE VALUE OF THE THEORY.  Let us consider this point in greater
detail.

In the first place, it is necessary to emphasise what is often overlooked,
namely, that the theory not only explains the TRANSFORMATIONS of species,
it also explains THEIR REMAINING THE SAME; in addition to the principle of
varying, it contains within itself that of PERSISTING.  It is part of the
essence of selection, that it not only causes a part to VARY till it has
reached its highest pitch of adaptation, but that it MAINTAINS IT AT THIS
PITCH.  THIS CONSERVING INFLUENCE OF NATURAL SELECTION is of great
importance, and was early recognised by Darwin; it follows naturally from
the principle of the survival of the fittest.

We understand from this how it is that a species which has become fully
adapted to certain conditions of life ceases to vary, but remains
"constant," as long as the conditions of life FOR IT remain unchanged,
whether this be for thousands of years, or for whole geological epochs. 
But the most convincing proof of the power of the principle of selection
lies in the innumerable multitude of phenomena which cannot be explained in
any other way.  To this category belong all structures which are only
PASSIVELY of advantage to the organism, because none of these can have
arisen by the alleged LAMARCKIAN PRINCIPLE.  These have been so often
discussed that we need do no more than indicate them here.  Until quite
recently the sympathetic coloration of animals--for instance, the whiteness
of Arctic animals--was referred, at least in part, to the DIRECT influence
of external factors, but the facts can best be explained by referring them
to the processes of selection, for then it is unnecessary to make the
gratuitous assumption that many species are sensitive to the stimulus of
cold and that others are not.  The great majority of Arctic land-animals,
mammals and birds, are white, and this proves that they were all able to
present the variation which was most useful for them.  The sable is brown,
but it lives in trees, where the brown colouring protects and conceals it
more effectively.  The musk-sheep (Ovibos moschatus) is also brown, and
contrasts sharply with the ice and snow, but it is protected from beasts of
prey by its gregarious habit, and therefore it is of advantage to be
visible from as great a distance as possible.  That so many species have
been able to give rise to white varieties does not depend on a special
sensitiveness of the skin to the influence of cold, but to the fact that
Mammals and Birds have a general tendency to vary towards white.  Even with
us, many birds--starlings, blackbirds, swallows, etc.--occasionally produce
white individuals, but the white variety does not persist, because it
readily falls a victim to the carnivores.  This is true of white fawns,
foxes, deer, etc.  The whiteness, therefore, arises from internal causes,
and only persists when it is useful.  A great many animals living in a
GREEN ENVIRONMENT have become clothed in green, especially insects,
caterpillars, and Mantidae, both persecuted and persecutors.

That it is not the direct effect of the environment which calls forth the
green colour is shown by the many kinds of caterpillar which rest on leaves
and feed on them, but are nevertheless brown.  These feed by night and
betake themselves through the day to the trunk of the tree, and hide in the
furrows of the bark.  We cannot, however, conclude from this that they were
UNABLE to vary towards green, for there are Arctic animals which are white
only in winter and brown in summer (Alpine hare, and the ptarmigan of the
Alps), and there are also green leaf-insects which remain green only while
they are young and difficult to see on the leaf, but which become brown
again in the last stage of larval life, when they have outgrown the leaf.
They then conceal themselves by day, sometimes only among withered leaves
on the ground, sometimes in the earth itself.  It is interesting that in
one genus, Chaerocampa, one species is brown in the last stage of larval
life, another becomes brown earlier, and in many species the last stage is
not wholly brown, a part remaining green.  Whether this is a case of a
double adaptation, or whether the green is being gradually crowded out by
the brown, the fact remains that the same species, even the same
individual, can exhibit both variations.  The case is the same with many of
the leaf-like Orthoptera, as, for instance, the praying mantis (Mantis
religiosa) which we have already mentioned.

But the best proofs are furnished by those often-cited cases in which the
insect bears a deceptive resemblance to another object.  We now know many
such cases, such as the numerous imitations of green or withered leaves,
which are brought about in the most diverse ways, sometimes by mere
variations in the form of the insect and in its colour, sometimes by an
elaborate marking, like that which occurs in the Indian leaf-butterflies,
Kallima inachis.  In the single butterfly-genus Anaea, in the woods of
South America, there are about a hundred species which are all gaily
coloured on the upper surface, and on the reverse side exhibit the most
delicate imitation of the colouring and pattern of a leaf, generally
without any indication of the leaf-ribs, but extremely deceptive
nevertheless.  Anyone who has seen only one such butterfly may doubt
whether many of the insignificant details of the marking can really be of
advantage to the insect.  Such details are for instance the apparent holes
and splits in the apparently dry or half-rotten leaf, which are usually due
to the fact that the scales are absent on a circular or oval patch so that
the colourless wing-membrane lies bare, and one can look through the spot
as through a window.  Whether the bird which is seeking or pursuing the
butterflies takes these holes for dewdrops, or for the work of a devouring
insect, does not affect the question; the mirror-like spot undoubtedly
increases the general deceptiveness, for the same thing occurs in many
leaf-butterflies, though not in all, and in some cases it is replaced in
quite a peculiar manner.  In one species of Anaea (A. divina), the resting
butterfly looks exactly like a leaf out of the outer edge of which a large
semicircular piece has been eaten, possibly by a caterpillar; but if we
look more closely it is obvious that there is no part of the wing absent,
and that the semicircular piece is of a clear, pale yellow colour, while
the rest of the wing is of a strongly contrasted dark brown.

But the deceptive resemblance may be caused in quite a different manner.  I
have often speculated as to what advantage the brilliant white C could give
to the otherwise dusky-coloured "Comma butterfly" (Grapta C. album). 
Poulton's recent observations ("Proc. Ent. Soc"., London, May 6, 1903.)
have shown that this represents the imitation of a crack such as is often
seen in dry leaves, and is very conspicuous because the light shines
through it.

The utility obviously lies in presenting to the bird the very familiar
picture of a broken leaf with a clear shining slit, and we may conclude,
from the imitation of such small details, that the birds are very sharp
observers and that the smallest deviation from the usual arrests their
attention and incites them to closer investigation.  It is obvious that
such detailed--we might almost say such subtle--deceptive resemblances
could only have come about in the course of long ages through the
acquirement from time to time of something new which heightened the already
existing resemblance.

In face of facts like these there can be no question of chance, and no one
has succeeded so far in finding any other explanation to replace that by
selection.  For the rest, the apparent leaves are by no means perfect
copies of a leaf; many of them only represent the torn or broken piece, or
the half or two-thirds of a leaf, but then the leaves themselves frequently
do not present themselves to the eye as a whole, but partially concealed
among other leaves.  Even those butterflies which, like the species of
Kallima and Anaea, represent the whole of a leaf with stalk, ribs, apex,
and the whole breadth, are not actual copies which would satisfy a
botanist; there is often much wanting.  In Kallima the lateral ribs of the
leaf are never all included in the markings; there are only two or three on
the left side and at most four or five on the right, and in many
individuals these are rather obscure, while in others they are
comparatively distinct.  This furnishes us with fresh evidence in favour of
their origin through processes of selection, for a botanically perfect
picture could not arise in this way; there could only be a fixing of such
details as heightened the deceptive resemblance.

Our postulate of origin through selection also enables us to understand why
the leaf-imitation is on the lower surface of the wing in the diurnal
Lepidoptera, and on the upper surface in the nocturnal forms, corresponding
to the attitude of the wings in the resting position of the two groups.

The strongest of all proofs of the theory, however, is afforded by cases of
true "mimicry," those adaptations discovered by Bates in 1861, consisting
in the imitation of one species by another, which becomes more and more
like its model.  The model is always a species that enjoys some special
protection from enemies, whether because it is unpleasant to taste, or
because it is in some way dangerous.

It is chiefly among insects and especially among butterflies that we find
the greatest number of such cases.  Several of these have been minutely
studied, and every detail has been investigated, so that it is difficult to
understand how there can still be disbelief in regard to them.  If the many
and exact observations which have been carefully collected and critically
discussed, for instance by Poulton ("Essays on Evolution", 1889-1907,
Oxford, 1908, passim, e.g. page 269.) were thoroughly studied, the
arguments which are still frequently urged against mimicry would be found
untenable; we can hardly hope to find more convincing proof of the
actuality of the processes of selection than these cases put into our
hands.  The preliminary postulates of the theory of mimicry have been
disputed, for instance, that diurnal butterflies are persecuted and eaten
by birds, but observations specially directed towards this point in India,
Africa, America and Europe have placed it beyond all doubt.  If it were
necessary I could myself furnish an account of my own observations on this
point.

In the same way it has been established by experiment and observation in
the field that in all the great regions of distribution there are
butterflies which are rejected by birds and lizards, their chief enemies,
on account of their unpleasant smell or taste.  These butterflies are
usually gaily and conspicuously coloured and thus--as Wallace first
interpreted it--are furnished with an easily recognisable sign:  a sign of
unpalatableness or WARNING COLOURS.  If they were not thus recognisable
easily and from a distance, they would frequently be pecked at by birds,
and then rejected because of their unpleasant taste; but as it is, the
insect-eaters recognise them at once as unpalatable booty and ignore them.
Such IMMUNE (The expression does not refer to all the enemies of this
butterfly; against ichneumon-flies, for instance, their unpleasant smell
usually gives no protection.) species, wherever they occur, are imitated by
other palatable species, which thus acquire a certain degree of protection.

It is true that this explanation of the bright, conspicuous colours is only
a hypothesis, but its foundations,--unpalatableness, and the liability of
other butterflies to be eaten,--are certain, and its consequences--the
existence of mimetic palatable forms--confirm it in the most convincing
manner.  Of the many cases now known I select one, which is especially
remarkable, and which has been thoroughly investigated, Papilio dardanus
(merope), a large, beautiful, diurnal butterfly which ranges from Abyssinia
throughout the whole of Africa to the south coast of Cape Colony.

The males of this form are everywhere ALMOST the same in colour and in form
of wings, save for a few variations in the sparse black markings on the
pale yellow ground.  But the females occur in several quite different forms
and colourings, and one of these only, the Abyssinian form, is like the
male, while the other three or four are MIMETIC, that is to say, they copy
a butterfly of quite a different family the Danaids, which are among the
IMMUNE forms.  In each region the females have thus copied two or three
different immune species.  There is much that is interesting to be said in
regard to these species, but it would be out of keeping with the general
tenor of this paper to give details of this very complicated case of
polymorphism in P. dardanus.  Anyone who is interested in the matter will
find a full and exact statement of the case in as far as we know it, in
Poulton's "Essays on Evolution" (pages 373-375). (Professor Poulton has
corrected some wrong descriptions which I had unfortunately overlooked in
the Plates of my book "Vortrage uber Descendenztheorie", and which refer to
Papilio dardanus (merope).  These mistakes are of no importance as far as
and understanding of the mimicry-theory is concerned, but I hope shortly to
be able to correct them in a later edition.)  I need only add that three
different mimetic female forms have been reared from the eggs of a single
female in South Africa.  The resemblance of these forms to their immune
models goes so far that even the details of the LOCAL forms of the models
are copied by the mimetic species.

It remains to be said that in Madagascar a butterfly, Papilio meriones,
occurs, of which both sexes are very similar in form and markings to the
non-mimetic male of P. dardanus, so that it probably represents the
ancestor of this latter species.

In face of such facts as these every attempt at another explanation must
fail.  Similarly all the other details of the case fulfil the preliminary
postulates of selection, and leave no room for any other interpretation. 
That the males do not take on the protective colouring is easily explained,
because they are in general more numerous, and the females are more
important for the preservation of the species, and must also live longer in
order to deposit their eggs.  We find the same state of things in many
other species, and in one case (Elymnias undularis) in which the male is
also mimetically coloured, it copies quite a differently coloured immune
species from the model followed by the female.  This is quite intelligible
when we consider that if there were TOO MANY false immune types, the birds
would soon discover that there were palatable individuals among those with
unpalatable warning colours.  Hence the imitation of different immune
species by Papilio dardanus!

I regret that lack of space prevents my bringing forward more examples of
mimicry and discussing them fully.  But from the case of Papilio dardanus
alone there is much to be learnt which is of the highest importance for our
understanding of transformations.  It shows us chiefly what I once called,
somewhat strongly perhaps, THE OMNIPOTENCE OF NATURAL SELECTION in answer
to an opponent who had spoken of its "inadequacy."  We here see that one
and the same species is capable of producing four or five different
patterns of colouring and marking; thus the colouring and marking are not,
as has often been supposed, a necessary outcome of the specific nature of
the species, but a true adaptation, which cannot arise as a direct effect
of climatic conditions, but solely through what I may call the sorting out
of the variations produced by the species, according to their utility. 
That caterpillars may be either green or brown is already something more
than could have been expected according to the old conception of species,
but that one and the same butterfly should be now pale yellow, with black;
now red with black and pure white; now deep black with large, pure white
spots; and again black with a large ochreous-yellow spot, and many small
white and yellow spots; that in one sub-species it may be tailed like the
ancestral form, and in another tailless like its Danaid model,--all this
shows a far-reaching capacity for variation and adaptation that wide never
have expected if we did not see the facts before us.  How it is possible
that the primary colour-variations should thus be intensified and combined
remains a puzzle even now; we are reminded of the modern three-colour
printing,--perhaps similar combinations of the primary colours take place
in this case; in any case the direction of these primary variations is
determined by the artist whom we know as natural selection, for there is no
other conceivable way in which the model could affect the butterfly that is
becoming more and more like it.  The same climate surrounds all four forms
of female; they are subject to the same conditions of nutrition.  Moreover,
Papilio dardanus is by no means the only species of butterfly which
exhibits different kinds of colour-pattern on its wings.  Many species of
the Asiatic genus Elymnias have on the upper surface a very good imitation
of an immune Euploeine (Danainae), often with a steel-blue ground-colour,
while the under surface is well concealed when the butterfly is at rest,--
thus there are two kinds of protective coloration each with a different
meaning!  The same thing may be observed in many non-mimetic butterflies,
for instance in all our species of Vanessa, in which the under side shows a
grey-brown or brownish-black protective coloration, but we do not yet know
with certainty what may be the biological significance of the gaily
coloured upper surface.

In general it may be said that mimetic butterflies are comparatively rare
species, but there are exceptions, for instance Limenitis archippus in
North America, of which the immune model (Danaida plexippus) also occurs in
enormous numbers.

In another mimicry-category the imitators are often more numerous than the
models, namely in the case of the imitation of DANGEROUS INSECTS by
harmless species.  Bees and wasps are dreaded for their sting, and they are
copied by harmless flies of the genera Eristalis and Syrphus, and these
mimics often occur in swarms about flowering plants without damage to
themselves or to their models; they are feared and are therefore left
unmolested.

In regard also to the FAITHFULNESS OF THE COPY the facts are quite in
harmony with the theory, according to which the resemblance must have
arisen and increased BY DEGREES.  We can recognise this in many cases, for
even now the mimetic species show very VARYING DEGREES OF RESEMBLANCE to
their immune model.  If we compare, for instance, the many different
imitators of Danaida chrysippus we find that, with their brownish-yellow
ground-colour, and the position and size, and more or less sharp limitation
of their clear marginal spots, they have reached very different degrees of
nearness to their model.  Or compare the female of Elymnias undularis with
its model Danaida genutia; there is a general resemblance, but the marking
of the Danaida is very roughly imitated in Elymnias.

Another fact that bears out the theory of mimicry is, that even when the
resemblance in colour-pattern is very great, the WING-VENATION,  which is
so constant, and so important in determining the systematic position of
butterflies, is never affected by the variation.  The pursuers of the
butterfly have no time to trouble about entomological intricacies.

I must not pass over a discovery of Poulton's which is of great theoretical
importance--that mimetic butterflies may reach the same effect by very
different means.  ("Journ. Linn. Soc. London (Zool.)", Vol. XXVI. 1898,
pages 598-602.)  Thus the glass-like transparency of the wing of a certain
Ithomiine (Methona) and its Pierine mimic (Dismorphia orise) depends on a
diminution in the size of the scales; in the Danaine genus Ituna it is due
to the fewness of the scales, and in a third imitator, a moth (Castnia
linus var. heliconoides) the glass-like appearance of the wing is due
neither to diminution nor to absence of scales, but to their absolute
colourlessness and transparency, and to the fact that they stand upright.
In another moth mimic (Anthomyza) the arrangement of the transparent scales
is normal.  Thus it is not some unknown external influence that has brought
about the transparency of the wing in these five forms, as has sometimes
been supposed.  Nor is it a hypothetical INTERNAL evolutionary tendency,
for all three vary in a different manner.  The cause of this agreement can
only lie in selection, which preserves and intensifies in each species the
favourable variations that present themselves.  The great faithfulness of
the copy is astonishing in these cases, for it is not THE WHOLE wing which
is transparent; certain markings are black in colour, and these contrast
sharply with the glass-like ground.  It is obvious that the pursuers of
these butterflies must be very sharp-sighted, for otherwise the agreement
between the species could never have been pushed so far.  The less the
enemies see and observe, the more defective must the imitation be, and if
they had been blind, no visible resemblance between the species which
required protection could ever have arisen.

A seemingly irreconcilable contradiction to the mimicry theory is presented
in the following cases, which were known to Bates, who, however, never
succeeded in bringing them into line with the principle of mimicry.

In South America there are, as we have already said, many mimics of the
immune Ithomiinae (or as Bates called them Heliconidae).  Among these there
occur not merely species which are edible, and thus require the protection
of a disguise, but others which are rejected on account of their
unpalatableness.  How could the Ithomiine dress have developed in their
case, and of what use is it, since the species would in any case be immune?
In Eastern Brazil, for instance, there are four butterflies, which bear a
most confusing resemblance to one another in colour, marking, and form of
wing, and all four are unpalatable to birds.  They belong to four different
genera and three sub-families, and we have to inquire:  Whence came this
resemblance and what end does it serve?  For a long time no satisfactory
answer could be found, but Fritz Muller (In "Kosmos", 1879, page 100.), 
seventeen years after Bates, offered a solution to the riddle, when he
pointed out that young birds could not have an instinctive knowledge of the
unpalatableness of the Ithomiines, but must learn by experience which
species were edible and which inedible.  Thus each young bird must have
tasted at least one individual of each inedible species and discovered its
unpalatability, before it learnt to avoid, and thus to spare the species. 
But if the four species resemble each other very closely the bird will
regard them all as of the same kind, and avoid them all.  Thus there
developed a process of selection which resulted in the survival of the
Ithomiine-like individuals, and in so great an increase of resemblance
between the four species, that they are difficult to distinguish one from
another even in a collection.  The advantage for the four species, living
side by side as they do e.g. in Bahia, lies in the fact that only one
individual from the MIMICRY-RING ("inedible association") need be tasted by
a young bird, instead of at least four individuals, as would otherwise be
the case.  As the number of young birds is great, this makes a considerable
difference in the ratio of elimination.

These interesting mimicry-rings (trusts), which have much significance for
the theory, have been the subject of numerous and careful investigations,
and at least their essential features are now fully established.  Muller
took for granted, without making any investigations, that young birds only
learn by experience to distinguish between different kinds of victims.  But
Lloyd Morgan's ("Habit and Instinct", London, 1896.) experiments with young
birds proved that this is really the case, and at the same time furnished
an additional argument against the LAMARCKIAN PRINCIPLE.

In addition to the mimicry-rings first observed in South America, others
have been described from Tropical India by Moore, and by Poulton and Dixey
from Africa, and we may expect to learn many more interesting facts in this
connection.  Here again the preliminary postulates of the theory are
satisfied.  And how much more that would lead to the same conclusion might
be added!

As in the case of mimicry many species have come to resemble one another
through processes of selection, so we know whole classes of phenomena in
which plants and animals have become adapted to one another, and have thus
been modified to a considerable degree.  I refer particularly to the
relation between flowers and insects; but as there is an article on "The
Biology of Flowers" in this volume, I need not discuss the subject, but
will confine myself to pointing out the significance of these remarkable
cases for the theory of selection.  Darwin has shown that the originally
inconspicuous blossoms of the phanerogams were transformed into flowers
through the visits of insects, and that, conversely, several large orders
of insects have been gradually modified by their association with flowers,
especially as regards the parts of their body actively concerned.  Bees and
butterflies in particular have become what they are through their relation
to flowers.  In this case again all that is apparently contradictory to the
theory can, on closer investigation, be beautifully interpreted in
corroboration of it.  Selection can give rise only to what is of use to the
organism actually concerned, never to what is of use to some other
organism, and we must therefore expect to find that in flowers only
characters of use to THEMSELVES have arisen, never characters which are of
use to insects only, and conversely that in the insects characters useful
to them and not merely to the plants would have originated.  For a long
time it seemed as if an exception to this rule existed in the case of the
fertilisation of the yucca blossoms by a little moth, Pronuba yuccasella. 
This little moth has a sickle-shaped appendage to its mouth-parts which
occurs in no other Lepidopteron, and which is used for pushing the yellow
pollen into the opening of the pistil, thus fertilising the flower.  Thus
it appears as if a new structure, which is useful only to the plant, has
arisen in the insect.  But the difficulty is solved as soon as we learn
that the moth lays its eggs in the fruit-buds of the Yucca, and that the
larvae, when they emerge, feed on the developing seeds.  In effecting the
fertilisation of the flower the moth is at the same time making provision
for its own offspring, since it is only after fertilisation that the seeds
begin to develop.  There is thus nothing to prevent our referring this
structural adaptation in Pronuba yuccasella to processes of selection,
which have gradually transformed the maxillary palps of the female into the
sickle-shaped instrument for collecting the pollen, and which have at the
same time developed in the insect the instinct to press the pollen into the
pistil.

In this domain, then, the theory of selection finds nothing but
corroboration, and it would be impossible to substitute for it any other
explanation, which, now that the facts are so well known, could be regarded
as a serious rival to it.  That selection is a factor, and a very powerful
factor in the evolution of organisms, can no longer be doubted.  Even
although we cannot bring forward formal proofs of it IN DETAIL, cannot
calculate definitely the size of the variations which present themselves,
and their selection-value, cannot, in short, reduce the whole process to a
mathematical formula, yet we must assume selection, because it is the only
possible explanation applicable to whole classes of phenomena, and because,
on the other hand, it is made up of factors which we know can be proved
actually to exist, and which, IF they exist, must of logical necessity
cooperate in the manner required by the theory.  WE MUST ACCEPT IT BECAUSE
THE PHENOMENA OF EVOLUTION AND ADAPTATION MUST HAVE A NATURAL BASIS, AND
BECAUSE IT IS THE ONLY POSSIBLE EXPLANATION OF THEM.  (This has been
discussed in many of my earlier works.  See for instance "The All-
Sufficiency of Natural Selection, a reply to Herbert Spencer", London,
1893.)

Many people are willing to admit that selection explains adaptations, but
they maintain that only a part of the phenomena are thus explained, because
everything does not depend upon adaptation.  They regard adaptation as, so
to speak, a special effort on the part of Nature, which she keeps in
readiness to meet particularly difficult claims of the external world on
organisms.  But if we look at the matter more carefully we shall find that
adaptations are by no means exceptional, but that they are present
everywhere in such enormous numbers, that it would be difficult in regard
to any structure whatever, to prove that adaptation had NOT played a part
in its evolution.

How often has the senseless objection been urged against selection that it
can create nothing, it can only reject.  It is true that it cannot create
either the living substance or the variations of it; both must be given. 
But in rejecting one thing it preserves another, intensifies it, combines
it, and in this way CREATES what is new.  EVERYTHING in organisms depends
on adaptation; that is to say, everything must be admitted through the
narrow door of selection, otherwise it can take no part in the building up
of the whole.  But, it is asked, what of the direct effect of external
conditions, temperature, nutrition, climate and the like?  Undoubtedly
these can give rise to variations, but they too must pass through the door
of selection, and if they cannot do this they are rejected, eliminated from
the constitution of the species.

It may, perhaps, be objected that such external influences are often of a
compelling power, and that every animal MUST submit to them, and that thus
selection has no choice and can neither select nor reject.  There may be
such cases; let us assume for instance that the effect of the cold of the
Arctic regions was to make all the mammals become black; the result would
be that they would all be eliminated by selection, and that no mammals
would be able to live there at all.  But in most cases a certain percentage
of animals resists these strong influences, and thus selection secures a
foothold on which to work, eliminating the unfavourable variation, and
establishing a useful colouring, consistent with what is required for the
maintenance of the species.

Everything depends upon adaptation!  We have spoken much of adaptation in
colouring, in connection with the examples brought into prominence by
Darwin, because these are conspicuous, easily verified, and at the same
time convincing for the theory of selection.  But is it only desert and
polar animals whose colouring is determined through adaptation?  Or the
leaf-butterflies, and the mimetic species, or the terrifying markings, and
"warning-colours" and a thousand other kinds of sympathetic colouring?  It
is, indeed, never the colouring alone which makes up the adaptation; the
structure of the animal plays a part, often a very essential part, in the
protective disguise, and thus MANY variations may cooperate towards ONE
common end.  And it is to be noted that it is by no means only external
parts that are changed; internal parts are ALWAYS modified at the same
time--for instance, the delicate elements of the nervous system on which
depend the INSTINCT of the insect to hold its wings, when at rest, in a
perfectly definite position, which, in the leaf-butterfly, has the effect
of bringing the two pieces on which the marking occurs on the anterior and
posterior wing into the same direction, and thus displaying as a whole the
fine curve of the midrib on the seeming leaf. But the wing-holding instinct
is not regulated in the same way in all leaf-butterflies; even our
indigenous species of Vanessa, with their protective ground-colouring, have
quite a distinctive way of holding their wings so that the greater part of
the anterior wing is covered by the posterior when the butterfly is at
rest.  But the protective colouring appears on the posterior wing and on
the tip of the anterior, TO PRECISELY THE DISTANCE TO WHICH IT IS LEFT
UNCOVERED.  This occurs, as Standfuss has shown, in different degree in our
two most nearly allied species, the uncovered portion being smaller in V.
urticae than in V. polychloros.  In this case, as in most leaf-butterflies,
the holding of the wing was probably the primary character; only after that
was thoroughly established did the protective marking develop.  In any
case, the instinctive manner of holding the wings is associated with the
protective colouring, and must remain as it is if the latter is to be
effective.  How greatly instincts may change, that is to say, may be
adapted, is shown by the case of the Noctuid "shark" moth, Xylina vetusta. 
This form bears a most deceptive resemblance to a piece of rotten wood, and
the appearance is greatly increased by the modification of the innate
impulse to flight common to so many animals, which has here been
transformed into an almost contrary instinct.  This moth does not fly away
from danger, but "feigns death," that is, it draws antennae, legs and wings
close to the body, and remains perfectly motionless.  It may be touched,
picked up, and thrown down again, and still it does not move.  This
remarkable instinct must surely have developed simultaneously with the
wood-colouring; at all events, both cooperating variations are now present,
and prove that both the external and the most minute internal structure
have undergone a process of adaptation.

The case is the same with all structural variations of animal parts, which
are not absolutely insignificant.  When the insects acquired wings they
must also have acquired the mechanism with which to move them--the
musculature, and the nervous apparatus necessary for its automatic
regulation.  All instincts depend upon compound reflex mechanisms and are
just as indispensable as the parts they have to set in motion, and all may
have arisen through processes of selection if the reasons which I have
elsewhere given for this view are correct.  ("The Evolution Theory",
London, 1904, page 144.)

Thus there is no lack of adaptations within the organism, and particularly
in its most important and complicated parts, so that we may say that there
is no actively functional organ that has not undergone a process of
adaptation relative to its function and the requirements of the organism. 
Not only is every gland structurally adapted, down to the very minutest
histological details, to its function, but the function is equally minutely
adapted to the needs of the body.  Every cell in the mucous lining of the
intestine is exactly regulated in its relation to the different nutritive
substances, and behaves in quite a different way towards the fats, and
towards nitrogenous substances, or peptones.

I have elsewhere called attention to the many adaptations of the whale to
the surrounding medium, and have pointed out--what has long been known, but
is not universally admitted, even now--that in it a great number of
important organs have been transformed in adaptation to the peculiar
conditions of aquatic life, although the ancestors of the whale must have
lived, like other hair-covered mammals, on land.  I cited a number of these
transformations--the fish-like form of the body, the hairlessness of the
skin, the transformation of the fore-limbs to fins, the disappearance of
the hind-limbs and the development of a tail fin, the layer of blubber
under the skin, which affords the protection from cold necessary to a warm-
blooded animal, the disappearance of the ear-muscles and the auditory
passages, the displacement of the external nares to the forehead for the
greater security of the breathing-hole during the brief appearance at the
surface, and certain remarkable changes in the respiratory and circulatory
organs which enable the animal to remain for a long time under water.  I
might have added many more, for the list of adaptations in the whale to
aquatic life is by no means exhausted; they are found in the histological
structure and in the minutest combinations in the nervous system.  For it
is obvious that a tail-fin must be used in quite a different way from a
tail, which serves as a fly-brush in hoofed animals, or as an aid to
springing in the kangaroo or as a climbing organ; it will require quite
different reflex-mechanisms and nerve-combinations in the motor centres.

I used this example in order to show how unnecessary it is to assume a
special internal evolutionary power for the phylogenesis of species, for
this whole order of whales is, so to speak, MADE UP OF ADAPTATIONS; it
deviates in many essential respects from the usual mammalian type, and all
the deviations are adaptations to aquatic life.  But if precisely the most
essential features of the organisation thus depend upon adaptation, what is
left for a phyletic force to do, since it is these essential features of
the structure it would have to determine?  There are few people now who
believe in a phyletic evolutionary power, which is not made up of the
forces known to us--adaptation and heredity--but the conviction that EVERY
part of an organism depends upon adaptation has not yet gained a firm
footing.  Nevertheless, I must continue to regard this conception as the
correct one, as I have long done.

I may be permitted one more example.  The feather of a bird is a marvellous
structure, and no one will deny that as a whole it depends upon adaptation.
But what part of it DOES NOT depend upon adaptation?  The hollow quill, the
shaft with its hard, thin, light cortex, and the spongy substance within
it, its square section compared with the round section of the quill, the
flat barbs, their short, hooked barbules which, in the flight-feathers,
hook into one another with just sufficient firmness to resist the pressure
of the air at each wing-beat, the lightness and firmness of the whole
apparatus, the elasticity of the vane, and so on.  And yet all this belongs
to an organ which is only passively functional, and therefore can have
nothing to do with the LAMARCKIAN PRINCIPLE.  Nor can the feather have
arisen through some magical effect of temperature, moisture, electricity,
or specific nutrition, and thus selection is again our only anchor of
safety.

But--it will be objected--the substance of which the feather consists, this
peculiar kind of horny substance, did not first arise through selection in
the course of the evolution of the birds, for it formed the covering of the
scales of their reptilian ancestors.  It is quite true that a similar
substance covered the scales of the Reptiles, but why should it not have
arisen among them through selection?  Or in what other way could it have
arisen, since scales are also passively useful parts?  It is true that if
we are only to call adaptation what has been acquired by the species we
happen to be considering, there would remain a great deal that could not be
referred to selection; but we are postulating an evolution which has
stretched back through aeons, and in the course of which innumerable
adaptations took place, which had not merely ephemeral persistence in a
genus, a family or a class, but which was continued into whole Phyla of
animals, with continual fresh adaptations to the special conditions of each
species, family, or class, yet with persistence of the fundamental
elements.  Thus the feather, once acquired, persisted in all birds, and the
vertebral column, once gained by adaptation in the lowest forms, has
persisted in all the Vertebrates, from Amphioxus upwards, although with
constant readaptation to the conditions of each particular group.  Thus
everything we can see in animals is adaptation, whether of to-day, or of
yesterday, or of ages long gone by; every kind of cell, whether glandular,
muscular, nervous, epidermic, or skeletal, is adapted to absolutely
definite and specific functions, and every organ which is composed of these
different kinds of cells contains them in the proper proportions, and in
the particular arrangement which best serves the function of the organ; it
is thus adapted to its function.

All parts of the organism are tuned to one another, that is, THEY ARE
ADAPTED TO ONE ANOTHER, and in the same way THE ORGANISM AS A WHOLE IS
ADAPTED TO THE CONDITIONS OF ITS LIFE, AND IT IS SO AT EVERY STAGE OF ITS
EVOLUTION.

But all adaptations CAN be referred to selection; the only point that
remains doubtful is whether they all MUST be referred to it.

However that may be, whether the LAMARCKIAN PRINCIPLE is a factor that has
cooperated with selection in evolution, or whether it is altogether
fallacious, the fact remains, that selection is the cause of a great part
of the phyletic evolution of organisms on our earth.  Those who agree with
me in rejecting the LAMARCKIAN PRINCIPLE will regard selection as the only
GUIDING factor in evolution, which creates what is new out of the
transmissible variations, by ordering and arranging these, selecting them
in relation to their number and size, as the architect does his building-
stones so that a particular style must result.  ("Variation under
Domestication", 1875 II. pages 426, 427.)  But the building-stones
themselves, the variations, have their basis in the influences which cause
variation in those vital units which are handed on from one generation to
another, whether, taken together they form the WHOLE organism, as in
Bacteria and other low forms of life, or only a germ-substance, as in
unicellular and multicellular organisms.  (The Author and Editor are
indebted to Professor Poulton for kindly assisting in the revision of the
proof of this Essay.)


IV.  VARIATION. 

By HUGO DE VRIES,
Professor of Botany in the University of Amsterdam.

I.  DIFFERENT KINDS OF VARIABILITY.

Before Darwin, little was known concerning the phenomena of variability. 
The fact, that hardly two leaves on a tree were exactly the same, could not
escape observation:  small deviations of the same kind were met with
everywhere, among individuals as well as among the organs of the same
plant.  Larger aberrations, spoken of as monstrosities, were for a long
time regarded as lying outside the range of ordinary phenomena.  A special
branch of inquiry, that of Teratology, was devoted to them, but it
constituted a science by itself, sometimes connected with morphology, but
having scarcely any bearing on the processes of evolution and heredity.

Darwin was the first to take a broad survey of the whole range of
variations in the animal and vegetable kingdoms.  His theory of Natural
Selection is based on the fact of variability.  In order that this
foundation should be as strong as possible he collected all the facts,
scattered in the literature of his time, and tried to arrange them in a
scientific way.  He succeeded in showing that variations may be grouped
along a line of almost continuous gradations, beginning with simple
differences in size and ending with monstrosities.  He was struck by the
fact that, as a rule, the smaller the deviations, the more frequently they
appear, very abrupt breaks in characters being of rare occurrence.

Among these numerous degrees of variability Darwin was always on the look
out for those which might, with the greatest probability, be considered as
affording material for natural selection to act upon in the development of
new species.  Neither of the extremes complied with his conceptions.  He
often pointed out, that there are a good many small fluctuations, which in
this respect must be absolutely useless.  On the other hand, he strongly
combated the belief, that great changes would be necessary to explain the
origin of species.  Some authors had propounded the idea that highly
adapted organs, e.g. the wings of a bird, could not have been developed in
any other way than by a comparatively sudden modification of a well defined
and important kind.  Such a conception would allow of great breaks or
discontinuity in the evolution of highly differentiated animals and plants,
shortening the time for the evolution of the whole organic kingdom and
getting over numerous difficulties inherent in the theory of slow and
gradual progress.  It would, moreover, account for the genetic relation of
the larger groups of both animals and plants.  It would, in a word,
undoubtedly afford an easy means of simplifying the problem of descent with
modification.

Darwin, however, considered such hypotheses as hardly belonging to the
domain of science; they belong, he said, to the realm of miracles.  That
species have a capacity for change is admitted by all evolutionists; but
there is no need to invoke modifications other than those represented by
ordinary variability.  It is well known that in artificial selection this
tendency to vary has given rise to numerous distinct races, and there is no
reason for denying that it can do the same in nature, by the aid of natural
selection.  On both lines an advance may be expected with equal
probability.

His main argument, however, is that the most striking and most highly
adapted modifications may be acquired by successive variations.  Each of
these may be slight, and they may affect different organs, gradually
adapting them to the same purpose.  The direction of the adaptations will
be determined by the needs in the struggle for life, and natural selection
will simply exclude all such changes as occur on opposite or deviating
lines.  In this way, it is not variability itself which is called upon to
explain beautiful adaptations, but it is quite sufficient to suppose that
natural selection has operated during long periods in the same way. 
Eventually, all the acquired characters, being transmitted together, would
appear to us, as if they had all been simultaneously developed.

Correlations must play a large part in such special evolutions:  when one
part is modified, so will be other parts.  The distribution of nourishment
will come in as one of the causes, the reactions of different organs to the
same external influences as another.  But no doubt the more effective cause
is that of the internal correlations, which, however, are still but dimly
understood.  Darwin repeatedly laid great stress on this view, although a
definite proof of its correctness could not be given in his time.  Such
proof requires the direct observation of a mutation, and it should be
stated here that even the first observations made in this direction have
clearly confirmed Darwin's ideas.  The new evening primroses which have
sprung in my garden from the old form of Oenothera Lamarckiana, and which
have evidently been derived from it, in each case, by a single mutation, do
not differ from their parent species in one character only, but in almost
all their organs and qualities.  Oenothera gigas, for example, has stouter
stems and denser foliage; the leaves are larger and broader; its thick
flower-buds produce gigantic flowers, but only small fruits with large
seeds.  Correlative changes of this kind are seen in all my new forms, and
they lend support to the view that in the gradual development of highly
adapted structures, analogous correlations may have played a large part. 
They easily explain large deviations from an original type, without
requiring the assumption of too many steps.

Monstrosities, as their name implies, are widely different in character
from natural species; they cannot, therefore, be adduced as evidence in the
investigation of the origin of species.  There is no doubt that they may
have much in common as regards their manner of origin, and that the origin
of species, once understood, may lead to a better understanding of the
monstrosities.  But the reverse is not true, at least not as regards the
main lines of development.  Here, it is clear, monstrosities cannot have
played a part of any significance.

Reversions, or atavistic changes, would seem to give a better support to
the theory of descent through modifications.  These have been of paramount
importance on many lines of evolution of the animal as well as of the
vegetable kingdom.  It is often assumed that monocotyledons are descended
from some lower group of dicotyledons, probably allied to that which
includes the buttercup family.  On this view the monocotyledons must be
assumed to have lost the cambium and all its influence on secondary growth,
the differentiation of the flower into calyx and corolla, the second
cotyledon or seed-leaf and several other characters.  Losses of characters
such as these may have been the result of abrupt changes, but this does not
prove that the characters themselves have been produced with equal
suddenness.  On the contrary, Darwin shows very convincingly that a
modification may well be developed by a series of steps, and afterwards
suddenly disappear.  Many monstrosities, such as those represented by
twisted stems, furnish direct proofs in support of this view, since they
are produced by the loss of one character and this loss implies secondary
changes in a large number of other organs and qualities.

Darwin criticises in detail the hypothesis of great and abrupt changes and
comes to the conclusion that it does not give even a shadow of an
explanation of the origin of species.  It is as improbable as it is
unnecessary.

Sports and spontaneous variations must now be considered.  It is well known
that they have produced a large number of fine horticultural varieties. 
The cut-leaved maple and many other trees and shrubs with split leaves are
known to have been produced at a single step; this is true in the case of
the single-leaf strawberry plant and of the laciniate variety of the
greater celandine:  many white flowers, white or yellow berries and
numerous other forms had a similar origin.  But changes such as these do
not come under the head of adaptations, as they consist for the most part
in the loss of some quality or organ belonging to the species from which
they were derived.  Darwin thinks it impossible to attribute to this cause
the innumerable structures, which are so well adapted to the habits of life
of each species.  At the present time we should say that such adaptations
require progressive modifications, which are additions to the stock of
qualities already possessed by the ancestors, and cannot, therefore, be
explained on the ground of a supposed analogy with sports, which are for
the most part of a retrogressive nature.

Excluding all these more or less sudden changes, there remains a long
series of gradations of variability, but all of these are not assumed by
Darwin to be equally fit for the production of new species.  In the first
place, he disregards all mere temporary variations, such as size, albinism,
etc.; further, he points out that very many species have almost certainly
been produced by steps, not greater, and probably not very much smaller,
than those separating closely related varieties.  For varieties are only
small species.  Next comes the question of polymorphic species:  their
occurrence seems to have been a source of much doubt and difficulty in
Darwin's mind, although at present it forms one of the main supports of the
prevailing explanation of the origin of new species.  Darwin simply states
that this kind of variability seems to be of a peculiar nature; since
polymorphic species are now in a stable condition their occurrence gives no
clue as to the mode of origin of new species.  Polymorphic species are the
expression of the result of previous variability acting on a large scale;
but they now simply consist of more or less numerous elementary species,
which, as far as we know, do not at present exhibit a larger degree of
variability than any other more uniform species.  The vernal whitlow-grass
(Draba verna) and the wild pansy are the best known examples; both have
spread over almost the whole of Europe and are split up into hundreds of
elementary forms.  These sub-species show no signs of any extraordinary
degree of variability, when cultivated under conditions necessary for the
exclusion of inter-crossing.  Hooker has shown, in the case of some ferns
distributed over still wider areas, that the extinction of some of the
intermediate forms in such groups would suffice to justify the elevation of
the remaining types to the rank of distinct species.  Polymorphic species
may now be regarded as the link which unites ordinary variability with the
historical production of species.  But it does not appear that they had
this significance for Darwin; and, in fact, they exhibit no phenomena which
could explain the processes by which one species has been derived from
another.  By thus narrowing the limits of the species-producing variability
Darwin was led to regard small deviations as the source from which natural
selection derives material upon which to act.  But even these are not all
of the same type, and Darwin was well aware of the fact.

It should here be pointed out that in order to be selected, a change must
first have been produced.  This proposition, which now seems self-evident,
has, however, been a source of much difference of opinion among Darwin's
followers.  The opinion that natural selection produces changes in useful
directions has prevailed for a long time.  In other words, it was assumed
that natural selection, by the simple means of singling out, could induce
small and useful changes to increase and to reach any desired degree of
deviation from the original type.  In my opinion this view was never
actually held by Darwin.  It is in contradiction with the acknowledged aim
of all his work,--the explanation of the origin of species by means of
natural forces and phenomena only.  Natural selection acts as a sieve; it
does not single out the best variations, but it simply destroys the larger
number of those which are, from some cause or another, unfit for their
present environment.  In this way it keeps the strains up to the required
standard, and, in special circumstances, may even improve them.

Returning to the variations which afford the material for the sieving-
action of natural selection, we may distinguish two main kinds.  It is true
that the distinction between these was not clear at the time of Darwin, and
that he was unable to draw a sharp line between them.  Nevertheless, in
many cases, he was able to separate them, and he often discussed the
question which of the two would be the real source of the differentiation
of species.  Certain variations constantly occur, especially such as are
connected with size, weight, colour, etc.  They are usually too small for
natural selection to act upon, having hardly any influence in the struggle
for life:  others are more rare, occurring only from time to time, perhaps
once or twice in a century, perhaps even only once in a thousand years. 
Moreover, these are of another type, not simply affecting size, number or
weight, but bringing about something new, which may be useful or not. 
Whenever the variation is useful natural selection will take hold of it and
preserve it; in other cases the variation may either persist or disappear.

In his criticism of miscellaneous objections brought forward against the
theory of natural selection after the publication of the first edition of
"The Origin of Species", Darwin stated his view on this point very
clearly:--"The doctrine of natural selection or the survival of the
fittest, which implies that when variations or individual differences of a
beneficial nature happen to arise, these will be preserved."  ("Origin of
Species" (6th edition), page 169, 1882.)  In this sentence the words
"HAPPEN TO ARISE" appear to me of prominent significance.  They are
evidently due to the same general conception which prevailed in Darwin's
Pangenesis hypothesis.  (Cf. de Vries, "Intracellulare Pangenesis", page
73, Jena, 1889, and "Die Mutationstheorie", I. page 63.  Leipzig, 1901.)

A distinction is indicated between ordinary fluctuations which are always
present, and such variations as "happen to arise" from time to time.  ((I
think it right to point out that the interpretation of this passage from
the "Origin" by Professor de Vries is not accepted as correct either by Mr
Francis Darwin or by myself.  We do not believe that Darwin intended to
draw any distinction between TWO TYPES of variation; the words "when
variations or individual differences of a beneficial nature happen to
arise" are not in our opinion meant to imply a distinction between ordinary
fluctuations and variations which "happen to arise," but we believe that
"or" is here used in the sense of ALIAS.  With the permission of Professor
de Vries, the following extract is quoted from a letter in which he replied
to the objection raised to his reading of the passage in question:

"As to your remarks on the passage on page 6, I agree that it is now
impossible to see clearly how far Darwin went in his distinction of the
different kinds of variability.  Distinctions were only dimly guessed at by
him.  But in our endeavour to arrive at a true conception of his view I
think that the chapter on Pangenesis should be our leading guide, and that
we should try to interpret the more difficult passages by that chapter.  A
careful and often repeated study of the Pangenesis hypothesis has convinced
me that Darwin, when he wrote that chapter, was well aware that ordinary
variability has nothing to do with evolution, but that other kinds of
variation were necessary.  In some chapters he comes nearer to a clear
distinction than in others.  To my mind the expression 'happen to arise' is
the sharpest indication of his inclining in this direction.  I am quite
convinced that numerous expressions in his book become much clearer when
looked at in this way."

The statement in this passage that "Darwin was well aware that ordinary
variability has nothing to do with evolution, but that other kinds of
variation were necessary" is contradicted by many passages in the "Origin".
A.C.S.))  The latter afford the material for natural selection to act upon
on the broad lines of organic development, but the first do not. 
Fortuitous variations are the species-producing kind, which the theory
requires; continuous fluctuations constitute, in this respect, a useless
type.

Of late, the study of variability has returned to the recognition of this
distinction.  Darwin's variations, which from time to time happen to arise,
are MUTATIONS, the opposite type being commonly designed fluctuations.  A
large mass of facts, collected during the last few decades, has confirmed
this view, which in Darwin's time could only be expressed with much
reserve, and everyone knows that Darwin was always very careful in
statements of this kind.

From the same chapter I may here cite the following paragraph:  "Thus as I
am inclined to believe, morphological differences,...such as the
arrangement of the leaves, the divisions of the flower or of the ovarium,
the position of the ovules, etc.--first appeared in many cases as
fluctuating variations, which sooner or later became constant through the
nature of the organism and of the surrounding conditions...but NOT THROUGH
NATURAL SELECTION (The italics are mine (H. de V.).); for as these
morphological characters do not affect the welfare of the species, any
slight deviation in them could not have been governed or accumulated
through this latter agency."  ("Origin of Species" (6th edition), page
176.)  We thus see that in Darwin's opinion, all small variations had not
the same importance.  In favourable circumstances some could become
constant, but others could not.

Since the appearance of the first edition of "The Origin of Species"
fluctuating variability has been thoroughly studied by Quetelet.  He
discovered the law, which governs all phenomena of organic life falling
under this head.  It is a very simple law, and states that individual
variations follow the laws of probability.  He proved it, in the first
place, for the size of the human body, using the measurements published for
Belgian recruits; he then extended it to various other measurements of
parts of the body, and finally concluded that it must be of universal
validity for all organic beings.  It must hold true for all characters in
man, physical as well as intellectual and moral qualities; it must hold
true for the plant kingdom as well as for the animal kingdom; in short, it
must include the whole living world.

Quetelet's law may be most easily studied in those cases where the
variability relates to measure, number and weight, and a vast number of
facts have since confirmed its exactness and its validity for all kinds of
organisms, organs and qualities.  But if we examine it more closely, we
find that it includes just those minute variations, which, as Darwin
repeatedly pointed out, have often no significance for the origin of
species.  In the phenomena, described by Quetelet's law nothing "happens to
arise"; all is governed by the common law, which states that small
deviations from the mean type are frequent, but that larger aberrations are
rare, the rarer as they are larger.  Any degree of variation will be found
to occur, if only the number of individuals studied is large enough:  it is
even possible to calculate before hand, how many specimens must be compared
in order to find a previously fixed degree of deviation.

The variations, which from time to time happen to appear, are evidently not
governed by this law.  They cannot, as yet, be produced at will:  no
sowings of thousands or even of millions of plants will induce them,
although by such means the chance of their occurring will obviously be
increased.  But they are known to occur, and to occur suddenly and
abruptly.  They have been observed especially in horticulture, where they
are ranged in the large and ill-defined group called sports.  Korschinsky
has collected all the evidence which horticultural literature affords on
this point.  (S. Korschinsky, "Heterogenesis und Evolution", "Flora", Vol.
LXXXIX. pages 240-363, 1901.)  Several cases of the first appearance of a
horticultural novelty have been recorded:  this has always happened in the
same way; it appeared suddenly and unexpectedly without any definite
relation to previously existing variability.  Dwarf types are one of the
commonest and most favourite varieties of flowering plants; they are not
originated by a repeated selection of the smallest specimens, but appear at
once, without intermediates and without any previous indication.  In many
instances they are only about half the height of the original type, thus
constituting obvious novelties.  So it is in other cases described by
Korschinsky:  these sports or mutations are now recognised to be the main
source of varieties of horticultural plants.

As already stated, I do not pretend that the production of horticultural
novelties is the prototype of the origin of new species in nature.  I
assume that they are, as a rule, derived from the parent species by the
loss of some organ or quality, whereas the main lines of the evolution of
the animal and vegetable kingdom are of course determined by progressive
changes.  Darwin himself has often pointed out this difference.  But the
saltatory origin of horticultural novelties is as yet the simplest parallel
for natural mutations, since it relates to forms and phenomena, best known
to the general student of evolution.

The point which I wish to insist upon is this.  The difference between
small and ever present fluctuations and rare and more sudden variations was
clear to Darwin, although the facts known at his time were too meagre to
enable a sharp line to be drawn between these two great classes of
variability.  Since Darwin's time evidence, which proves the correctness of
his view, has accumulated with increasing rapidity.  Fluctuations
constitute one type; they are never absent and follow the law of chance,
but they do not afford the material from which to build new species. 
Mutations, on the other hand, only happen to occur from time to time.  They
do not necessarily produce greater changes than fluctuations, but such as
may become, or rather are from their very nature, constant.  It is this
constancy which is the mark of specific characters, and on this basis every
new specific character may be assumed to have arisen by mutation.

Some authors have tried to show that the theory of mutation is opposed to
Darwin's views.  But this is erroneous.  On the contrary, it is in fullest
harmony with the great principle laid down by Darwin.  In order to be acted
upon by that complex of environmental forces, which Darwin has called
natural selection, the changes must obviously first be there.  The manner
in which they are produced is of secondary importance and has hardly any
bearing on the theory of descent with modification.  ("Life and Letters"
II. 125.)
 
A critical survey of all the facts of variability of plants in nature as
well as under cultivation has led me to the conviction, that Darwin was
right in stating that those rare beneficial variations, which from time to
time happen to arise,--the now so-called mutations--are the real source of
progress in the whole realm of the organic world.

II.  EXTERNAL AND INTERNAL CAUSES OF VARIABILITY.

All phenomena of animal and plant life are governed by two sets of causes;
one of these is external, the other internal.  As a rule the internal
causes determine the nature of a phenomenon--what an organism can do and
what it cannot do.  The external causes, on the other hand, decide when a
certain variation will occur, and to what extent its features may be
developed.

As a very clear and wholly typical instance I cite the cocks-combs
(Celosia).  This race is distinguished from allied forms by its faculty of
producing the well-known broad and much twisted combs.  Every single
individual possesses this power, but all individuals do not exhibit it in
its most complete form.  In some cases this faculty may not be exhibited at
the top of the main stem, although developed in lateral branches:  in
others it begins too late for full development.  Much depends upon
nourishment and cultivation, but almost always the horticulturist has to
single out the best individuals and to reject those which do not come up to
the standard.

The internal causes are of a historical nature.  The external ones may be
defined as nourishment and environment.  In some cases nutrition is the
main factor, as, for instance, in fluctuating variability, but in natural
selection environment usually plays the larger part.

The internal or historical causes are constant during the life-time of a
species, using the term species in its most limited sense, as designating
the so-called elementary species or the units out of which the ordinary
species are built up.  These historical causes are simply the specific
characters, since in the origin of a species one or more of these must have
been changed, thus producing the characters of the new type.  These changes
must, of course, also be due partly to internal and partly to external
causes.

In contrast to these changes of the internal causes, the ordinary
variability which is exhibited during the life-time of a species is called
fluctuating variability.  The name mutations or mutating variability is
then given to the changes in the specific characters.  It is desirable to
consider these two main divisions of variability separately.

In the case of fluctuations the internal causes, as well as the external
ones, are often apparent.  The specific characters may be designated as the
mean about which the observed forms vary.  Almost every character may be
developed to a greater or a less degree, but the variations of the single
characters producing a small deviation from the mean are usually the
commonest.  The limits of these fluctuations may be called wide or narrow,
according to the way we look at them, but in numerous cases the extreme on
the favoured side hardly surpasses double the value of that on the other
side.  The degree of this development, for every individual and for every
organ, is dependent mainly on nutrition.  Better nourishment or an
increased supply of food produces a higher development; only it is not
always easy to determine which direction is the fuller and which is the
poorer one.  The differences among individuals grown from different seeds
are described as examples of individual variability, but those which may be
observed on the same plant, or on cuttings, bulbs or roots derived from one
individual are referred to as cases of partial variability.  Partial
variability, therefore, determines the differences among the flowers,
fruits, leaves or branches of one individual:  in the main, it follows the
same laws as individual variability, but the position of a branch on a
plant also determines its strength, and the part it may take in the
nourishment of the whole.  Composite flowers and umbels therefore have, as
a rule, fewer rays on weak branches than on the strong main ones.  The
number of carpels in the fruits of poppies becomes very small on the weak
lateral branches, which are produced towards the autumn, as well as on
crowded, and therefore on weakened individuals.  Double flowers follow the
same rule, and numerous other instances could easily be adduced.

Mutating variability occurs along three main lines.  Either a character may
disappear, or, as we now say, become latent; or a latent character may
reappear, reproducing thereby a character which was once prominent in more
or less remote ancestors.  The third and most interesting case is that of
the production of quite new characters which never existed in the
ancestors.  Upon this progressive mutability the main development of the
animal and vegetable kingdom evidently depends.  In contrast to this, the
two other cases are called retrogressive and degressive mutability.  In
nature retrogressive mutability plays a large part; in agriculture and in
horticulture it gives rise to numerous varieties, which have in the past
been preserved, either on account of their usefulness or beauty, or simply
as fancy-types.  In fact the possession of numbers of varieties may be
considered as the main character of domesticated animals and cultivated
plants.

In the case of retrogressive and degressive mutability the internal cause
is at once apparent, for it is this which causes the disappearance or
reappearance of some character.  With progressive mutations the case is not
so simple, since the new character must first be produced and then
displayed.  These two processes are theoretically different, but they may
occur together or after long intervals.  The production of the new
character I call premutation, and the displaying mutation.  Both of course
must have their external as well as their internal causes, as I have
repeatedly pointed out in my work on the Mutation Theory.  ("Die
Mutationstheorie", 2 vols., Leipzig, 1901.)

It is probable that nutrition plays as important a part among the external
causes of mutability as it does among those of fluctuating variability. 
Observations in support of this view, however, are too scanty to allow of a
definite judgment.  Darwin assumed an accumulative influence of external
causes in the case of the production of new varieties or species.  The
accumulation might be limited to the life-time of a single individual, or
embrace that of two or more generations.  In the end a degree of
instability in the equilibrium of one or more characters might be attained,
great enough for a character to give way under a small shock produced by
changed conditions of life.  The character would then be thrown over from
the old state of equilibrium into a new one.

Characters which happen to be in this state of unstable equilibrium are
called mutable.  They may be either latent or active, being in the former
case derived from old active ones or produced as new ones (by the process,
designated premutation).  They may be inherited in this mutable condition
during a long series of generations.  I have shown that in the case of the
evening primrose of Lamarck this state of mutability must have existed for
at least half a century, for this species was introduced from Texas into
England about the year 1860, and since then all the strains derived from
its first distribution over the several countries of Europe show the same
phenomena in producing new forms.  The production of the dwarf evening
primrose, or Oenothera nanella, is assumed to be due to one of the factors,
which determines the tall stature of the parent form, becoming latent; this
would, therefore, afford an example of retrogressive mutation.  Most of the
other types of my new mutants, on the other hand, seem to be due to
progressive mutability.

The external causes of this curious period of mutability are as yet wholly
unknown and can hardly be guessed at, since the origin of the Oenothera
Lamarckiana is veiled in mystery.  The seeds, introduced into England about
1860, were said to have come from Texas, but whether from wild or from
cultivated plants we do not know.  Nor has the species been recorded as
having been observed in the wild condition.  This, however, is nothing
peculiar.  The European types of Oenothera biennis and O. muricata are in
the same condition.  The first is said to have been introduced from
Virginia, and the second from Canada, but both probably from plants
cultivated in the gardens of these countries.  Whether the same elementary
species are still growing on those spots is unknown, mainly because the
different sub-species of the species mentioned have not been systematically
studied and distinguished.

The origin of new species, which is in part the effect of mutability, is,
however, due mainly to natural selection.  Mutability provides the new
characters and new elementary species.  Natural selection, on the other
hand, decides what is to live and what to die.  Mutability seems to be
free, and not restricted to previously determined lines.  Selection,
however, may take place along the same main lines in the course of long
geological epochs, thus directing the development of large branches of the
animal and vegetable kingdom.  In natural selection it is evident that
nutrition and environment are the main factors.  But it is probable that,
while nutrition may be one of the main causes of mutability, environment
may play the chief part in the decisions ascribed to natural selection. 
Relations to neighbouring plants and to injurious or useful animals, have
been considered the most important determining factors ever since the time
when Darwin pointed out their prevailing influence.

From this discussion of the main causes of variability we may derive the
proposition that the study of every phenomenon in the field of heredity, of
variability, and of the origin of new species will have to be considered
from two standpoints; on one hand we have the internal causes, on the other
the external ones.  Sometimes the first are more easily detected, in other
cases the latter are more accessible to investigation.  But the complete
elucidation of any phenomenon of life must always combine the study of the
influence of internal with that of external causes.

III.  POLYMORPHIC VARIABILITY IN CEREALS.

One of the propositions of Darwin's theory of the struggle for life
maintains that the largest amount of life can be supported on any area, by
great diversification or divergence in the structure and constitution of
its inhabitants.  Every meadow and every forest affords a proof of this
thesis.  The numerical proportion of the different species of the flora is
always changing according to external influences.  Thus, in a given meadow,
some species will flower abundantly in one year and then almost disappear,
until, after a series of years, circumstances allow them again to multiply
rapidly.  Other species, which have taken their places, will then become
rare.  It follows from this principle, that notwithstanding the constantly
changing conditions, a suitable selection from the constituents of a meadow
will ensure a continued high production.  But, although the principle is
quite clear, artificial selection has, as yet, done very little towards
reaching a really high standard.

The same holds good for cereals.  In ordinary circumstances a field will
give a greater yield, if the crop grown consists of a number of
sufficiently differing types.  Hence it happens that almost all older
varieties of wheat are mixtures of more or less diverging forms.  In the
same variety the numerical composition will vary from year to year, and in
oats this may, in bad years, go so far as to destroy more than half of the
harvest, the wind-oats (Avena fatua), which scatter their grain to the
winds as soon as it ripens, increasing so rapidly that they assume the
dominant place.  A severe winter, a cold spring and other extreme
conditions of life will destroy one form more completely than another, and
it is evident that great changes in the numerical composition of the
mixture may thus be brought about.

This mixed condition of the common varieties of cereals was well known to
Darwin.  For him it constituted one of the many types of variability.  It
is of that peculiar nature to which, in describing other groups, he applies
the term polymorphy.  It does not imply that the single constituents of the
varieties are at present really changing their characters.  On the other
hand, it does not exclude the possibility of such changes.  It simply
states that observation shows the existence of different forms; how these
have originated is a question which it does not deal with.  In his well-
known discussion of the variability of cereals, Darwin is mainly concerned
with the question, whether under cultivation they have undergone great
changes or only small ones.  The decision ultimately depends on the
question, how many forms have originally been taken into cultivation. 
Assuming five or six initial species, the variability must be assumed to
have been very large, but on the assumption that there were between ten and
fifteen types, the necessary range of variability is obviously much
smaller.  But in regard to this point, we are of course entirely without
historical data.

Few of the varieties of wheat show conspicuous differences, although their
number is great.  If we compare the differentiating characters of the
smaller types of cereals with those of ordinary wild species, even within
the same genus or family, they are obviously much less marked.  All these
small characters, however, are strictly inherited, and this fact makes it
very probable that the less obvious constituents of the mixtures in
ordinary fields must be constant and pure as long as they do not
intercross.  Natural crossing is in most cereals a phenomenon of rare
occurrence, common enough to admit of the production of all possible hybrid
combinations, but requiring the lapse of a long series of years to reach
its full effect.

Darwin laid great stress on this high amount of variability in the plants
of the same variety, and illustrated it by the experience of Colonel Le
Couteur ("On the Varieties, Properties, and Classification of Wheat",
Jersey, 1837.) on his farm on the isle of Jersey, who cultivated upwards of
150 varieties of wheat, which he claimed were as pure as those of any other
agriculturalist.  But Professor La Gasca of Madrid, who visited him, drew
attention to aberrant ears, and pointed out, that some of them might be
better yielders than the majority of plants in the crop, whilst others
might be poor types.  Thence he concluded that the isolation of the better
ones might be a means of increasing his crops.  Le Couteur seems to have
considered the constancy of such smaller types after isolation as
absolutely probable, since he did not even discuss the possibility of their
being variable or of their yielding a changeable or mixed progeny.  This
curious fact proves that he considered the types, discovered in his fields
by La Gasca to be of the same kind as his other varieties, which until that
time he had relied upon as being pure and uniform.  Thus we see, that for
him, the variability of cereals was what we now call polymorphy.  He looked
through his fields for useful aberrations, and collected twenty-three new
types of wheat.  He was, moreover, clear about one point, which, on being
rediscovered after half a century, has become the starting-point for the
new Swedish principle of selecting agricultural plants.  It was the
principle of single-ear sowing, instead of mixing the grains of all the
selected ears together.  By sowing each ear on a separate plot he intended
not only to multiply them, but also to compare their value.  This
comparison ultimately led him to the choice of some few valuable sorts, one
of which, the "Bellevue de Talavera," still holds its place among the
prominent sorts of wheat cultivated in France.  This variety seems to be
really a uniform type, a quality very useful under favourable conditions of
cultivation, but which seems to have destroyed its capacity for further
improvement by selection.

The principle of single-ear sowing, with a view to obtain pure and uniform
strains without further selection, has, until a few years ago, been almost
entirely lost sight of.  Only a very few agriculturists have applied it: 
among these are Patrick Shirreff ("Die Verbesserung der Getreide-Arten",
translated by R. Hesse, Halle, 1880.) in Scotland and Willet M. Hays
("Wheat, varieties, breeding, cultivation", Univ. Minnesota, Agricultural
Experimental Station, Bull. no. 62, 1899.) in Minnesota.  Patrick Shirreff
observed the fact, that in large fields of cereals, single plants may from
time to time be found with larger ears, which justify the expectation of a
far greater yield.  In the course of about twenty-five years he isolated in
this way two varieties of wheat and two of oats.  He simply multiplied them
as fast as possible, without any selection, and put them on the market.

Hays was struck by the fact that the yield of wheat in Minnesota was far
beneath that in the neighbouring States.  The local varieties were Fife and
Blue Stem.  They gave him, on inspection, some better specimens,
"phenomenal yielders" as he called them.  These were simply isolated and
propagated, and, after comparison with the parent-variety and with some
other selected strains of less value, were judged to be of sufficient
importance to be tested by cultivation all over the State of Minnesota. 
They have since almost supplanted the original types, at least in most
parts of the State, with the result that the total yield of wheat in
Minnesota is said to have been increased by about a million dollars yearly.

Definite progress in the method of single-ear sowing has, however, been
made only recently.  It had been foreshadowed by Patrick Shirreff, who
after the production of the four varieties already mentioned, tried to
carry out his work on a larger scale, by including numerous minor
deviations from the main type.  He found by doing so that the chances of
obtaining a better form were sufficiently increased to justify the trial. 
But it was Nilsson who discovered the almost inexhaustible polymorphy of
cereals and other agricultural crops and made it the starting-point for a
new and entirely trustworthy method of the highest utility.  By this means
he has produced during the last fifteen years a number of new and valuable
races, which have already supplanted the old types on numerous farms in
Sweden and which are now being introduced on a large scale into Germany and
other European countries.

It is now twenty years since the station at Svalof was founded.  During the
first period of its work, embracing about five years, selection was
practised on the principle which was then generally used in Germany.  In
order to improve a race a sample of the best ears was carefully selected
from the best fields of the variety.  These ears were considered as
representatives of the type under cultivation, and it was assumed that by
sowing their grains on a small plot a family could be obtained, which could
afterwards be improved by a continuous selection.  Differences between the
collected ears were either not observed or disregarded.  At Svalof this
method of selection was practised on a far larger scale than on any German
farm, and the result was, broadly speaking, the same.  This may be stated
in the following words:  improvement in a few cases, failure in all the
others.  Some few varieties could be improved and yielded excellent new
types, some of which have since been introduced into Swedish agriculture
and are now prominent races in the southern and middle parts of the
country.  But the station had definite aims, and among them was the
improvement of the Chevalier barley.  This, in Middle Sweden, is a fine
brewer's barley, but liable to failure during unfavourable summers on
account of its slender stems.  It was selected with a view of giving it
stiffer stems, but in spite of all the care and work bestowed upon it no
satisfactory result was obtained.

This experience, combined with a number of analogous failures, could not
fail to throw doubt upon the whole method.  It was evident that good
results were only exceptions, and that in most cases the principle was not
one that could be relied upon.  The exceptions might be due to unknown
causes, and not to the validity of the method; it became therefore of much
more interest to search for the causes than to continue the work along
these lines.

In the year 1892 a number of different varieties of cereals were cultivated
on a large scale and a selection was again made from them.  About two
hundred samples of ears were chosen, each apparently constituting a
different type.  Their seeds were sown on separate plots and manured and
treated as much as possible in the same manner.  The plots were small and
arranged in rows so as to facilitate the comparison of allied types. 
During the whole period of growth and during the ripening of the ears the
plots were carefully studied and compared:  they were harvested separately;
ears and kernels were counted and weighed, and notes were made concerning
layering, rust and other cereal pests.

The result of this experiment was, in the main, no distinct improvement. 
Nilsson was especially struck by the fact that the plots, which should
represent distinct types, were far from uniform.  Many of them were as
multiform as the fields from which the parent-ears were taken.  Others
showed variability in a less degree, but in almost all of them it was clear
that a pure race had not been obtained.  The experiment was a fair one,
inasmuch as it demonstrated the polymorphic variability of cereals beyond
all doubt and in a degree hitherto unsuspected; but from the standpoint of
the selectionist it was a failure.  Fortunately there were, however, one or
two exceptions.  A few lots showed a perfect uniformity in regard to all
the stalks and ears:  these were small families.  This fact suggested the
idea that each might have been derived from a single ear.  During the
selection in the previous summer, Nilsson had tried to find as many ears as
possible of each new type which he recognised in his fields.  But the
variability of his crops was so great, that he was rarely able to include
more than two or three ears in the same group, and, in a few cases, he
found only one representative of the supposed type.  It might, therefore,
be possible that those small uniform plots were the direct progeny of ears,
the grains of which had not been mixed with those from other ears before
sowing.  Exact records had, of course, been kept of the chosen samples, and
the number of ears had been noted in each case.  It was, therefore,
possible to answer the question and it was found that those plots alone
were uniform on which the kernels of one single ear only had been sown. 
Nilsson concluded that the mixture of two or more ears in a single sowing
might be the cause of the lack of uniformity in the progeny.  Apparently
similar ears might be different in their progeny.

Once discovered, this fact was elevated to the rank of a leading principle
and tested on as large a scale as possible.  The fields were again
carefully investigated and every single ear, which showed a distinct
divergence from the main type in one character or another, was selected.  A
thousand samples were chosen, but this time each sample consisted of one
ear only.  Next year, the result corresponded to the expectation. 
Uniformity prevailed almost everywhere; only a few lots showed a
discrepancy, which might be ascribed to the accidental selection of hybrid
ears.  It was now clear that the progeny of single ears was, as a rule,
pure, whereas that of mixed ears was impure.  The single-ear selection or
single-ear sowing, which had fallen into discredit in Germany and elsewhere
in Europe, was rediscovered.  It proved to be the only trustworthy
principle of selection.  Once isolated, such single-parent races are
constant from seed and remain true to their type.  No further selection is
needed; they have simply to be multiplied and their real value tested.

Patrick Shirreff, in his early experiments, Le Couteur, Hays and others had
observed the rare occurrence of exceptionally good yielders and the value
of their isolation to the agriculturist.  The possibility of error in the
choice of such striking specimens and the necessity of judging their value
by their progeny were also known to these investigators, but they had not
the slightest idea of all the possibilities suggested by their principle. 
Nilsson, who is a botanist as well as an agriculturist, discovered that,
besides these exceptionably good yielders, every variety of a cereal
consists of hundreds of different types, which find the best conditions for
success when grown together, but which, after isolation, prove to be
constant.  Their preference for mixed growth is so definite, that once
isolated, their claims on manure and treatment are found to be much higher
than those of the original mixed variety.  Moreover, the greatest care is
necessary to enable them to retain their purity, and as soon as they are
left to themselves they begin to deteriorate through accidental crosses and
admixtures and rapidly return to the mixed condition.

Reverting now to Darwin's discussion of the variability of cereals, we may
conclude that subsequent investigation has proved it to be exactly of the
kind which he describes.  The only difference is that in reality it reaches
a degree, quite unexpected by Darwin and his contemporaries.  But it is
polymorphic variability in the strictest sense of the word.  How the single
constituents of a variety originate we do not see.  We may assume, and
there can hardly be a doubt about the truth of the assumption, that a new
character, once produced, will slowly but surely be combined through
accidental crosses with a large number of previously existing types, and so
will tend to double the number of the constituents of the variety.  But
whether it first appears suddenly or whether it is only slowly evolved we
cannot determine.  It would, of course, be impossible to observe either
process in such a mixture.  Only cultures of pure races, of single-parent
races as we have called them, can afford an opportunity for this kind of
observation.  In the fields of Svalof new and unexpected qualities have
recently been seen, from time to time, to appear suddenly.  These
characters are as distinct as the older ones and appear to be constant from
the moment of their origin.

Darwin has repeatedly insisted that man does not cause variability.  He
simply selects the variations given to him by the hand of nature.  He may
repeat this process in order to accumulate different new characters in the
same family, thus producing varieties of a higher order.  This process of
accumulation would, if continued for a longer time, lead to the
augmentation of the slight differences characteristic of varieties into the
greater differences characteristic of species and genera.  It is in this
way that horticultural and agricultural experience contribute to the
problem of the conversion of varieties into species, and to the explanation
of the admirable adaptations of each organism to its complex conditions of
life.  In the long run new forms, distinguished from their allies by quite
a number of new characters, would, by the extermination of the older
intermediates, become distinct species.

Thus we see that the theory of the origin of species by means of natural
selection is quite independent of the question, how the variations to be
selected arise.  They may arise slowly, from simple fluctuations, or
suddenly, by mutations; in both cases natural selection will take hold of
them, will multiply them if they are beneficial, and in the course of time
accumulate them, so as to produce that great diversity of organic life,
which we so highly admire.

Darwin has left the decision of this difficult and obviously subordinate
point to his followers.  But in his Pangenesis hypothesis he has given us
the clue for a close study and ultimate elucidation of the subject under
discussion.


V.  HEREDITY AND VARIATION IN MODERN LIGHTS.

By W. BATESON, M.A., F.R.S.

Professor of Biology in the University of Cambridge.

Darwin's work has the property of greatness in that it may be admired from
more aspects than one.  For some the perception of the principle of Natural
Selection stands out as his most wonderful achievement to which all the
rest is subordinate.  Others, among whom I would range myself, look up to
him rather as the first who plainly distinguished, collected, and
comprehensively studied that new class of evidence from which hereafter a
true understanding of the process of Evolution may be developed.  We each
prefer our own standpoint of admiration; but I think that it will be in
their wider aspect that his labours will most command the veneration of
posterity.

A treatise written to advance knowledge may be read in two moods.  The
reader may keep his mind passive, willing merely to receive the impress of
the writer's thought; or he may read with his attention strained and alert,
asking at every instant how the new knowledge can be used in a further
advance, watching continually for fresh footholds by which to climb higher
still.  Of Shelley it has been said that he was a poet for poets:  so
Darwin was a naturalist for naturalists.  It is when his writings are used
in the critical and more exacting spirit with which we test the outfit for
our own enterprise that we learn their full value and strength.  Whether we
glance back and compare his performance with the efforts of his
predecessors, or look forward along the course which modern research is
disclosing, we shall honour most in him not the rounded merit of finite
accomplishment, but the creative power by which he inaugurated a line of
discovery endless in variety and extension.  Let us attempt thus to see his
work in true perspective between the past from which it grew, and the
present which is its consequence.  Darwin attacked the problem of Evolution
by reference to facts of three classes:  Variation; Heredity; Natural
Selection.  His work was not as the laity suppose, a sudden and unheralded
revelation, but the first fruit of a long and hitherto barren controversy.
The occurrence of variation from type, and the hereditary transmission of
such variation had of course been long familiar to practical men, and
inferences as to the possible bearing of those phenomena on the nature of
specific difference had been from time to time drawn by naturalists. 
Maupertuis, for example, wrote "Ce qui nous reste a examiner, c'est comment
d'un seul individu, il a pu naitre tant d'especes si differentes."  And
again "La Nature contient le fonds de toutes ces varietes:  mais le hasard
ou l'art les mettent en oeuvre.  C'est ainsi que ceux dont l'industrie
s'applique a satisfaire le gout des curieux, sont, pour ainsi dire,
creatures d'especes nouvelles."  ("Venus Physique, contenant deux
Dissertations, l'une sur l'origine des Hommes et des Animaux:  Et l'autre
sur l'origine des Noirs" La Haye, 1746, pages 124 and 129.  For an
introduction to the writings of Maupertuis I am indebted to an article by
Professor Lovejoy in "Popular Sci. Monthly", 1902.)

Such passages, of which many (though few so emphatic) can be found in
eighteenth century writers, indicate a true perception of the mode of
Evolution.  The speculations hinted at by Buffon (For the fullest account
of the views of these pioneers of Evolution, see the works of Samuel
Butler, especially "Evolution, Old and New" (2nd edition) 1882.  Butler's
claims on behalf of Buffon have met with some acceptance; but after reading
what Butler has said, and a considerable part of Buffon's own works, the
word "hinted" seems to me a sufficiently correct description of the part he
played.  It is interesting to note that in the chapter on the Ass, which
contains some of his evolutionary passages, there is a reference to
"plusieurs idees tres-elevees sur la generation" contained in the Letters
of Maupertuis.), developed by Erasmus Darwin, and independently proclaimed
above all by Lamarck, gave to the doctrine of descent a wide renown.  The
uniformitarian teaching which Lyell deduced from geological observation had
gained acceptance.  The facts of geographical distribution (See especially
W. Lawrence, "Lectures on Physiology", London, 1823, pages 213 f.) had been
shown to be obviously inconsistent with the Mosaic legend.  Prichard, and
Lawrence, following the example of Blumenbach, had successfully
demonstrated that the races of Man could be regarded as different forms of
one species, contrary to the opinion up till then received.  These
treatises all begin, it is true, with a profound obeisance to the sons of
Noah, but that performed, they continue on strictly modern lines.  The
question of the mutability of species was thus prominently raised.

Those who rate Lamarck no higher than did Huxley in his contemptuous phrase
"buccinator tantum," will scarcely deny that the sound of the trumpet had
carried far, or that its note was clear.  If then there were few who had
already turned to evolution with positive conviction, all scientific men
must at least have known that such views had been promulgated; and many
must, as Huxley says, have taken up his own position of "critical
expectancy."  (See the chapter contributed to the "Life and Letters of
Charles Darwin" II. page 195.  I do not clearly understand the sense in
which Darwin wrote (Autobiography, ibid. I. page 87):  "It has sometimes
been said that the success of the "Origin" proved 'that the subject was in
the air,' or 'that men's minds were prepared for it.'  I do not think that
this is strictly true, for I occasionally sounded not a few naturalists,
and never happened to come across a single one who seemed to doubt about
the permanence of species."  This experience may perhaps have been an
accident due to Darwin's isolation.  The literature of the period abounds
with indications of "critical expectancy."  A most interesting expression
of that feeling is given in the charming account of the "Early Days of
Darwinism" by Alfred Newton, "Macmillan's Magazine", LVII. 1888, page 241. 
He tells how in 1858 when spending a dreary summer in Iceland, he and his
friend, the ornithologist John Wolley, in default of active occupation,
spent their days in discussion.  "Both of us taking a keen interest in
Natural History, it was but reasonable that a question, which in those days
was always coming up wherever two or more naturalists were gathered
together, should be continually recurring.  That question was, 'What is a
species?' and connected therewith was the other question, 'How did a
species begin?'...Now we were of course fairly well acquainted with what
had been published on these subjects."  He then enumerates some of these
publications, mentioning among others T. Vernon Wollaston's "Variation of
Species"--a work which has in my opinion never been adequately appreciated.
He proceeds:  "Of course we never arrived at anything like a solution of
these problems, general or special, but we felt very strongly that a
solution ought to be found, and that quickly, if the study of Botany and
Zoology was to make any great advance."  He then describes how on his
return home he received the famous number of the "Linnean Journal" on a
certain evening.  "I sat up late that night to read it; and never shall I
forget the impression it made upon me.  Herein was contained a perfectly
simple solution of all the difficulties which had been troubling me for
months past...I went to bed satisfied that a solution had been found.")

Why, then, was it, that Darwin succeeded where the rest had failed?  The
cause of that success was two-fold.  First, and obviously, in the principle
of Natural Selection he had a suggestion which would work.  It might not go
the whole way, but it was true as far as it went.  Evolution could thus in
great measure be fairly represented as a consequence of demonstrable
processes.  Darwin seldom endangers the mechanism he devised by putting on
it strains much greater than it can bear.  He at least was under no
illusion as to the omnipotence of Selection; and he introduces none of the
forced pleading which in recent years has threatened to discredit that
principle.

For example, in the latest text of the "Origin" ("Origin", (6th edition
(1882), page 421.) we find him saying:

"But as my conclusions have lately been much misrepresented, and it has
been stated that I attribute the modification of species exclusively to
natural selection, I may be permitted to remark that in the first edition
of this work, and subsequently, I placed in a most conspicuous position--
namely, at the close of the Introduction--the following words:  'I am
convinced that natural selection has been the main but not the exclusive
means of modification.'"

But apart from the invention of this reasonable hypothesis, which may well,
as Huxley estimated, "be the guide of biological and psychological
speculation for the next three or four generations," Darwin made a more
significant and imperishable contribution.  Not for a few generations, but
through all ages he should be remembered as the first who showed clearly
that the problems of Heredity and Variation are soluble by observation, and
laid down the course by which we must proceed to their solution.  (Whatever
be our estimate of the importance of Natural Selection, in this we all
agree.  Samuel Butler, the most brilliant, and by far the most interesting
of Darwin's opponents--whose works are at length emerging from oblivion--in
his Preface (1882) to the 2nd edition of "Evolution, Old and New", repeats
his earlier expression of homage to one whom he had come to regard as an
enemy:  "To the end of time, if the question be asked, 'Who taught people
to believe in Evolution?' the answer must be that it was Mr. Darwin.  This
is true, and it is hard to see what palm of higher praise can be awarded to
any philosopher.")  The moment of inspiration did not come with the reading
of Malthus, but with the opening of the "first note-book on Transmutation
of Species."  ("Life and Letters", I. pages 276 and 83.)  Evolution is a
process of Variation and Heredity.  The older writers, though they had some
vague idea that it must be so, did not study Variation and Heredity. 
Darwin did, and so begat not a theory, but a science.

The extent to which this is true, the scientific world is only beginning to
realise.  So little was the fact appreciated in Darwin's own time that the
success of his writings was followed by an almost total cessation of work
in that special field.  Of the causes which led to this remarkable
consequence I have spoken elsewhere.  They proceeded from circumstances
peculiar to the time; but whatever the causes there is no doubt that this
statement of the result is historically exact, and those who make it their
business to collect facts elucidating the physiology of Heredity and
Variation are well aware that they will find little to reward their quest
in the leading scientific Journals of the Darwinian epoch.

In those thirty years the original stock of evidence current and in
circulation even underwent a process of attrition.  As in the story of the
Eastern sage who first wrote the collected learning of the universe for his
sons in a thousand volumes, and by successive compression and burning
reduced them to one, and from this by further burning distilled the single
ejaculation of the Faith, "There is no god but God and Mohamed is the
Prophet of God," which was all his maturer wisdom deemed essential:--so in
the books of that period do we find the corpus of genetic knowledge dwindle
to a few prerogative instances, and these at last to the brief formula of
an unquestioned creed.

And yet in all else that concerns biological science this period was, in
very truth, our Golden Age, when the natural history of the earth was
explored as never before; morphology and embryology were exhaustively
ransacked; the physiology of plants and animals began to rival chemistry
and physics in precision of method and in the rapidity of its advances; and
the foundations of pathology were laid.

In contrast with this immense activity elsewhere the neglect which befel
the special physiology of Descent, or Genetics as we now call it, is
astonishing.  This may of course be interpreted as meaning that the
favoured studies seemed to promise a quicker return for effort, but it
would be more true to say that those who chose these other pursuits did so
without making any such comparison; for the idea that the physiology of
Heredity and Variation was a coherent science, offering possibilities of
extraordinary discovery, was not present to their minds at all.  In a word,
the existence of such a science was well nigh forgotten.  It is true that
in ancillary periodicals, as for example those that treat of entomology or
horticulture, or in the writings of the already isolated systematists (This
isolation of the systematists is the one most melancholy sequela of
Darwinism.  It seems an irony that we should read in the peroration to the
"Origin" that when the Darwinian view is accepted "Systematists will be
able to pursue their labours as at present; but they will not be
incessantly haunted by the shadowy doubt whether this or that form be a
true species.  This, I feel sure, and I speak after experience, will be no
slight relief.  The endless disputes whether or not some fifty species of
British brambles are good species will cease."  "Origin", 6th edition
(1882), page 425.  True they have ceased to attract the attention of those
who lead opinion, but anyone who will turn to the literature of systematics
will find that they have not ceased in any other sense.  Should there not
be something disquieting in the fact that among the workers who come most
into contact with specific differences, are to be found the only men who
have failed to be persuaded of the unreality of those differences?),
observations with this special bearing were from time to time related, but
the class of fact on which Darwin built his conceptions of Heredity and
Variation was not seen in the highways of biology.  It formed no part of
the official curriculum of biological students, and found no place among
the subjects which their teachers were investigating.

During this period nevertheless one distinct advance was made, that with
which Weismann's name is prominently connected.  In Darwin's genetic scheme
the hereditary transmission of parental experience and its consequences
played a considerable role.  Exactly how great that role was supposed to
be, he with his habitual caution refrained from specifying, for the
sufficient reason that he did not know.  Nevertheless much of the process
of Evolution, especially that by which organs have become degenerate and
rudimentary, was certainly attributed by Darwin to such inheritance, though
since belief in the inheritance of acquired characters fell into disrepute,
the fact has been a good deal overlooked.  The "Origin" without "use and
disuse" would be a materially different book.  A certain vacillation is
discernible in Darwin's utterances on this question, and the fact gave to
the astute Butler an opportunity for his most telling attack.  The
discussion which best illustrates the genetic views of the period arose in
regard to the production of the rudimentary condition of the wings of many
beetles in the Madeira group of islands, and by comparing passages from the
"Origin" (6th edition pages 109 and 401.  See Butler, "Essays on Life, Art,
and Science", page 265, reprinted 1908, and "Evolution, Old and New",
chapter XXII. (2nd edition), 1882.) Butler convicts Darwin of saying first
that this condition was in the main the result of Selection, with disuse
aiding, and in another place that the main cause of degeneration was
disuse, but that Selection had aided.  To Darwin however I think the point
would have seemed one of dialectics merely.  To him the one paramount
purpose was to show that somehow an Evolution by means of Variation and
Heredity might have brought about the facts observed, and whether they had
come to pass in the one way or the other was a matter of subordinate
concern.


To us moderns the question at issue has a diminished significance.  For
over all such debates a change has been brought by Weismann's challenge for
evidence that use and disuse have any transmitted effects at all.  Hitherto
the transmission of many acquired characteristics had seemed to most
naturalists so obvious as not to call for demonstration.  (W. Lawrence was
one of the few who consistently maintained the contrary opinion.  Prichard,
who previously had expressed himself in the same sense, does not, I believe
repeat these views in his later writings, and there are signs that he came
to believe in the transmission of acquired habits.  See Lawrence, "Lect.
Physiol." 1823, pages 436-437, 447 Prichard, Edin. Inaug. Disp. 1808 (not
seen by me), quoted ibid. and "Nat. Hist. Man", 1843, pages 34 f.) 
Weismann's demand for facts in support of the main proposition revealed at
once that none having real cogency could be produced.  The time-honoured
examples were easily shown to be capable of different explanations.  A few
certainly remain which cannot be so summarily dismissed, but--though it is
manifestly impossible here to do justice to such a subject--I think no one
will dispute that these residual and doubtful phenomena, whatever be their
true nature, are not of a kind to help us much in the interpretation of any
of those complex cases of adaptation which on the hypothesis of unguided
Natural Selection are especially difficult to understand.  Use and disuse
were invoked expressly to help us over these hard places; but whatever
changes can be induced in offspring by direct treatment of the parents,
they are not of a kind to encourage hope of real assistance from that
quarter.  It is not to be denied that through the collapse of this second
line of argument the Selection hypothesis has had to take an increased and
perilous burden.  Various ways of meeting the difficulty have been
proposed, but these mostly resolve themselves into improbable attempts to
expand or magnify the powers of Natural Selection.

Weismann's interpellation, though negative in purpose, has had a lasting
and beneficial effect, for through his thorough demolition of the old loose
and distracting notions of inherited experience, the ground has been
cleared for the construction of a true knowledge of heredity based on
experimental fact.

In another way he made a contribution of a more positive character, for his
elaborate speculations as to the genetic meaning of cytological appearances
have led to a minute investigation of the visible phenomena occurring in
those divisions by which germ-cells arise.  Though the particular views he
advocated have very largely proved incompatible with the observed facts of
heredity, yet we must acknowledge that it was chiefly through the stimulus
of Weismann's ideas that those advances in cytology were made; and though
the doctrine of the continuity of germ-plasm cannot be maintained in the
form originally propounded, it is in the main true and illuminating.  (It
is interesting to see how nearly Butler was led by natural penetration, and
from absolutely opposite conclusions, back to this underlying truth:  "So
that each ovum when impregnate should be considered not as descended from
its ancestors, but as being a continuation of the personality of every ovum
in the chain of its ancestry, which every ovum IT ACTUALLY IS quite as
truly as the octogenarian IS the same identity with the ovum from which he
has been developed.  This process cannot stop short of the primordial cell,
which again will probably turn out to be but a brief resting-place.  We
therefore prove each one of us to BE ACTUALLY the primordial cell which
never died nor dies, but has differentiated itself into the life of the
world, all living beings whatever, being one with it and members one of
another," "Life and Habit", 1878, page 86.)  Nevertheless in the present
state of knowledge we are still as a rule quite unable to connect
cytological appearances with any genetic consequence and save in one
respect (obviously of extreme importance--to be spoken of later) the two
sets of phenomena might, for all we can see, be entirely distinct.

I cannot avoid attaching importance to this want of connection between the
nuclear phenomena and the features of bodily organisation.  All attempts to
investigate Heredity by cytological means lie under the disadvantage that
it is the nuclear changes which can alone be effectively observed. 
Important as they must surely be, I have never been persuaded that the rest
of the cell counts for nothing.  What we know of the behaviour and
variability of chromosomes seems in my opinion quite incompatible with the
belief that they alone govern form, and are the sole agents responsible in
heredity.  (This view is no doubt contrary to the received opinion.  I am
however interested to see it lately maintained by Driesch ("Science and
Philosophy of the Organism", London, 1907, page 233), and from the recent
observations of Godlewski it has received distinct experimental support.)

If, then, progress was to be made in Genetics, work of a different kind was
required.  To learn the laws of Heredity and Variation there is no other
way than that which Darwin himself followed, the direct examination of the
phenomena.  A beginning could be made by collecting fortuitous observations
of this class, which have often thrown a suggestive light, but such
evidence can be at best but superficial and some more penetrating
instrument of research is required.  This can only be provided by actual
experiments in breeding.

The truth of these general considerations was becoming gradually clear to
many of us when in 1900 Mendel's work was rediscovered.  Segregation, a
phenomenon of the utmost novelty, was thus revealed.  From that moment not
only in the problem of the origin of species, but in all the great problems
of biology a new era began.  So unexpected was the discovery that many
naturalists were convinced it was untrue, and at once proclaimed Mendel's
conclusions as either altogether mistaken, or if true, of very limited
application.  Many fantastic notions about the workings of Heredity had
been asserted as general principles before:  this was probably only another
fancy of the same class.

Nevertheless those who had a preliminary acquaintance with the facts of
Variation were not wholly unprepared for some such revelation.  The
essential deduction from the discovery of segregation was that the
characters of living things are dependent on the presence of definite
elements or factors, which are treated as units in the processes of
Heredity.  These factors can thus be recombined in various ways.  They act
sometimes separately, and sometimes they interact in conjunction with each
other, producing their various effects.  All this indicates a definiteness
and specific order in heredity, and therefore in variation.  This order
cannot by the nature of the case be dependent on Natural Selection for its
existence, but must be a consequence of the fundamental chemical and
physical nature of living things.  The study of Variation had from the
first shown that an orderliness of this kind was present.  The bodies and
the properties of living things are cosmic, not chaotic.  No matter how low
in the scale we go, never do we find the slightest hint of a diminution in
that all-pervading orderliness, nor can we conceive an organism existing
for a moment in any other state.  Moreover not only does this order prevail
in normal forms, but again and again it is to be seen in newly-sprung
varieties, which by general consent cannot have been subjected to a
prolonged Selection.  The discovery of Mendelian elements admirably
coincided with and at once gave a rationale of these facts.  Genetic
Variation is then primarily the consequence of additions to, or omissions
from, the stock of elements which the species contains.  The further
investigation of the species-problem must thus proceed by the analytical
method which breeding experiments provide.

In the nine years which have elapsed since Mendel's clue became generally
known, progress has been rapid.  We now understand the process by which a
polymorphic race maintains its polymorphism.  When a family consists of
dissimilar members, given the numerical proportions in which these members
are occurring, we can represent their composition symbolically and state
what types can be transmitted by the various members.  The difficulty of
the "swamping effects of intercrossing" is practically at an end.  Even the
famous puzzle of sex-limited inheritance is solved, at all events in its
more regular manifestations, and we know now how it is brought about that
the normal sisters of a colour-blind man can transmit the colour-blindness
while his normal brothers cannot transmit it.

We are still only on the fringe of the inquiry.  It can be seen extending
and ramifying in many directions.  To enumerate these here would be
impossible.  A whole new range of possibilities is being brought into view
by study of the interrelations between the simple factors.  By following up
the evidence as to segregation, indications have been obtained which can
only be interpreted as meaning that when many factors are being
simultaneously redistributed among the germ-cells, certain of them exert
what must be described as a repulsion upon other factors.  We cannot
surmise whither this discovery may lead.

In the new light all the old problems wear a fresh aspect.  Upon the
question of the nature of Sex, for example, the bearing of Mendelian
evidence is close.  Elsewhere I have shown that from several sets of
parallel experiments the conclusion is almost forced upon us that, in the
types investigated, of the two sexes the female is to be regarded as
heterozygous in sex, containing one unpaired dominant element, while the
male is similarly homozygous in the absence of that element.  (In other
words, the ova are each EITHER female, OR male (i.e. non-female), but the
sperms are all non-female.)  It is not a little remarkable that on this
point--which is the only one where observations of the nuclear processes of
gameto-genesis have yet been brought into relation with the visible
characteristics of the organisms themselves--there should be diametrical
opposition between the results of breeding experiments and those derived
from cytology.

Those who have followed the researches of the American school will be aware
that, after it had been found in certain insects that the spermatozoa were
of two kinds according as they contained or did not contain the accessory
chromosome, E.B. Wilson succeeded in proving that the sperms possessing
this accessory body were destined to form FEMALES on fertilisation, while
sperms without it form males, the eggs being apparently indifferent. 
Perhaps the most striking of all this series of observations is that lately
made by T.H. Morgan (Morgan, "Proc. Soc. Exp. Biol. Med." V. 1908, and von
Baehr, "Zool. Anz." XXXII. page 507, 1908.), since confirmed by von Baehr,
that in a Phylloxeran two kinds of spermatids are formed, respectively with
and without an accessory (in this case, DOUBLE) chromosome.  Of these, only
those possessing the accessory body become functional spermatozoa, the
others degenerating.  We have thus an elucidation of the puzzling fact that
in these forms fertilisation results in the formation of FEMALES only.  How
the males are formed--for of course males are eventually produced by the
parthenogenetic females--we do not know.

If the accessory body is really to be regarded as bearing the factor for
femaleness, then in Mendelian terms female is DD and male is DR.  The eggs
are indifferent and the spermatozoa are each male, OR female.  But
according to the evidence derived from a study of the sex-limited descent
of certain features in other animals the conclusion seems equally clear
that in them female must be regarded as DR and male as RR.  The eggs are
thus each either male or female and the spermatozoa are indifferent.  How
this contradictory evidence is to be reconciled we do not yet know.  The
breeding work concerns fowls, canaries, and the Currant moth (Abraxas
grossulariata).  The accessory chromosome has been now observed in most of
the great divisions of insects (As Wilson has proved, the unpaired body is
not a universal feature even in those orders in which it has been observed.
Nearly allied types may differ.  In some it is altogether unpaired.  In
others it is paired with a body of much smaller size, and by selection of
various types all gradations can be demonstrated ranging to the condition
in which the members of the pair are indistinguishable from each other.),
except, as it happens, Lepidoptera.  At first sight it seems difficult to
suppose that a feature apparently so fundamental as sex should be
differently constituted in different animals, but that seems at present the
least improbable inference.  I mention these two groups of facts as
illustrating the nature and methods of modern genetic work.  We must
proceed by minute and specific analytical investigation.  Wherever we look
we find traces of the operation of precise and specific rules.

In the light of present knowledge it is evident that before we can attack
the Species-problem with any hope of success there are vast arrears to be
made up.  He would be a bold man who would now assert that there was no
sense in which the term Species might not have a strict and concrete
meaning in contradistinction to the term Variety.  We have been taught to
regard the difference between species and variety as one of degree.  I
think it unlikely that this conclusion will bear the test of further
research.  To Darwin the question, What is a variation? presented no
difficulties.  Any difference between parent and offspring was a variation.
Now we have to be more precise.  First we must, as de Vries has shown,
distinguish real, genetic, variation from FLUCTUATIONAL variations, due to
environmental and other accidents, which cannot be transmitted.  Having
excluded these sources of error the variations observed must be expressed
in terms of the factors to which they are due before their significance can
be understood.  For example, numbers of the variations seen under
domestication, and not a few witnessed in nature, are simply the
consequence of some ingredient being in an unknown way omitted from the
composition of the varying individual.  The variation may on the contrary
be due to the addition of some new element, but to prove that it is so is
by no means an easy matter.  Casual observation is useless, for though
these latter variations will always be dominants, yet many dominant
characteristics may arise from another cause, namely the meeting of
complementary factors, and special study of each case in two generations at
least is needed before these two phenomena can be distinguished.

When such considerations are fully appreciated it will be realised that
medleys of most dissimilar occurrences are all confused together under the
term Variation.  One of the first objects of genetic analysis is to
disentangle this mass of confusion.

To those who have made no study of heredity it sometimes appears that the
question of the effect of conditions in causing variation is one which we
should immediately investigate, but a little thought will show that before
any critical inquiry into such possibilities can be attempted, a knowledge
of the working of heredity under conditions as far as possible uniform must
be obtained.  At the time when Darwin was writing, if a plant brought into
cultivation gave off an albino variety, such an event was without
hesitation ascribed to the change of life.  Now we see that albino GAMETES,
germs, that is to say, which are destitute of the pigment-forming factor,
may have been originally produced by individuals standing an indefinite
number of generations back in the ancestry of the actual albino, and it is
indeed almost certain that the variation to which the appearance of the
albino is due cannot have taken place in a generation later than that of
the grandparents.  It is true that when a new DOMINANT appears we should
feel greater confidence that we were witnessing the original variation, but
such events are of extreme rarity, and no such case has come under the
notice of an experimenter in modern times, as far as I am aware.  That they
must have appeared is clear enough.  Nothing corresponding to the Brown-
breasted Game fowl is known wild, yet that colour is a most definite
dominant, and at some moment since Gallus bankiva was domesticated, the
element on which that special colour depends must have at least once been
formed in the germ-cell of a fowl; but we need harder evidence than any
which has yet been produced before we can declare that this novelty came
through over-feeding, or change of climate, or any other disturbance
consequent on domestication.  When we reflect on the intricacies of genetic
problems as we must now conceive them there come moments when we feel
almost thankful that the Mendelian principles were unknown to Darwin.  The
time called for a bold pronouncement, and he made it, to our lasting profit
and delight.  With fuller knowledge we pass once more into a period of
cautious expectation and reserve.

In every arduous enterprise it is pleasanter to look back at difficulties
overcome than forward to those which still seem insurmountable, but in the
next stage there is nothing to be gained by disguising the fact that the
attributes of living things are not what we used to suppose.  If they are
more complex in the sense that the properties they display are throughout
so regular (I have in view, for example, the marvellous and specific
phenomena of regeneration, and those discovered by the students of
"Entwicklungsmechanik".  The circumstances of its occurrence here preclude
any suggestion that this regularity has been brought about by the workings
of Selection.  The attempts thus to represent the phenomena have resulted
in mere parodies of scientific reasoning.) that the Selection of minute
random variations is an unacceptable account of the origin of their
diversity, yet by virtue of that very regularity the problem is limited in
scope and thus simplified.

To begin with, we must relegate Selection to its proper place.  Selection
permits the viable to continue and decides that the non-viable shall
perish; just as the temperature of our atmosphere decides that no liquid
carbon shall be found on the face of the earth:  but we do not suppose that
the form of the diamond has been gradually achieved by a process of
Selection.  So again, as the course of descent branches in the successive
generations, Selection determines along which branch Evolution shall
proceed, but it does not decide what novelties that branch shall bring
forth.  "La Nature contient le fonds de toutes ces varietes, mais le hazard
ou l'art les mettent en oeuvre," as Maupertuis most truly said.

Not till knowledge of the genetic properties of organisms has attained to
far greater completeness can evolutionary speculations have more than a
suggestive value.  By genetic experiment, cytology and physiological
chemistry aiding, we may hope to acquire such knowledge.  In 1872 Nathusius
wrote ("Vortrage uber Viehzucht und Rassenerkenntniss", page 120, Berlin,
1872.):  "Das Gesetz der Vererbung ist noch nicht erkannt; der Apfel ist
noch nicht vom Baum der Erkenntniss gefallen, welcher, der Sage nach,
Newton auf den rechten Weg zur Ergrundung der Gravitationsgesetze fuhrte." 
We cannot pretend that the words are not still true, but in Mendelian
analysis the seeds of that apple-tree at last are sown.

If we were asked what discovery would do most to forward our inquiry, what
one bit of knowledge would more than any other illuminate the problem, I
think we may give the answer without hesitation.  The greatest advance that
we can foresee will be made when it is found possible to connect the
geometrical phenomena of development with the chemical.  The geometrical
symmetry of living things is the key to a knowledge of their regularity,
and the forces which cause it.  In the symmetry of the dividing cell the
basis of that resemblance we call Heredity is contained.  To imitate the
morphological phenomena of life we have to devise a system which can
divide.  It must be able to divide, and to segment as--grossly--a vibrating
plate or rod does, or as an icicle can do as it becomes ribbed in a
continuous stream of water; but with this distinction, that the
distribution of chemical differences and properties must simultaneously be
decided and disposed in orderly relation to the pattern of the
segmentation.  Even if a model which would do this could be constructed it
might prove to be a useful beginning.

This may be looking too far ahead.  If we had to choose some one piece of
more proximate knowledge which we would more especially like to acquire, I
suppose we should ask for the secret of interracial sterility.  Nothing has
yet been discovered to remove the grave difficulty, by which Huxley in
particular was so much oppressed, that among the many varieties produced
under domestication--which we all regard as analogous to the species seen
in nature--no clear case of interracial sterility has been demonstrated. 
The phenomenon is probably the only one to which the domesticated products
seem to afford no parallel.  No solution of the difficulty can be offered
which has positive value, but it is perhaps worth considering the facts in
the light of modern ideas.  It should be observed that we are not
discussing incompatibility of two species to produce offspring (a totally
distinct phenomenon), but the sterility of the offspring which many of them
do produce.

When two species, both perfectly fertile severally, produce on crossing a
sterile progeny, there is a presumption that the sterility is due to the
development in the hybrid of some substance which can only be formed by the
meeting of two complementary factors.  That some such account is correct in
essence may be inferred from the well-known observation that if the hybrid
is not totally sterile but only partially so, and thus is able to form some
good germ-cells which develop into new individuals, the sterility of these
daughter-individuals is sensibly reduced or may be entirely absent.  The
fertility once re-established, the sterility does not return in the later
progeny, a fact strongly suggestive of segregation.  Now if the sterility
of the cross-bred be really the consequence of the meeting of two
complementary factors, we see that the phenomenon could only be produced
among the divergent offspring of one species by the acquisition of at least
TWO new factors; for if the acquisition of a single factor caused sterility
the line would then end.  Moreover each factor must be separately acquired
by distinct individuals, for if both were present together, the possessors
would by hypothesis be sterile.  And in order to imitate the case of
species each of these factors must be acquired by distinct breeds.  The
factors need not, and probably would not, produce any other perceptible
effects; they might, like the colour-factors present in white flowers, make
no difference in the form or other characters.  Not till the cross was
actually made between the two complementary individuals would either factor
come into play, and the effects even then might be unobserved until an
attempt was made to breed from the cross-bred.

Next, if the factors responsible for sterility were acquired, they would in
all probability be peculiar to certain individuals and would not readily be
distributed to the whole breed.  Any member of the breed also into which
BOTH the factors were introduced would drop out of the pedigree by virtue
of its sterility.  Hence the evidence that the various domesticated breeds
say of dogs or fowls can when mated together produce fertile offspring, is
beside the mark.  The real question is, Do they ever produce sterile
offspring?  I think the evidence is clearly that sometimes they do, oftener
perhaps than is commonly supposed.  These suggestions are quite amenable to
experimental tests.  The most obvious way to begin is to get a pair of
parents which are known to have had any sterile offspring, and to find the
proportions in which these steriles were produced.  If, as I anticipate,
these proportions are found to be definite, the rest is simple.

In passing, certain other considerations may be referred to.  First, that
there are observations favouring the view that the production of totally
sterile cross-breds is seldom a universal property of two species, and that
it may be a matter of individuals, which is just what on the view here
proposed would be expected.  Moreover, as we all know now, though
incompatibility may be dependent to some extent on the degree to which the
species are dissimilar, no such principle can be demonstrated to determine
sterility or fertility in general.  For example, though all our Finches can
breed together, the hybrids are all sterile.  Of Ducks some species can
breed together without producing the slightest sterility; others have
totally sterile offspring, and so on.  The hybrids between several genera
of Orchids are perfectly fertile on the female side, and some on the male
side also, but the hybrids produced between the Turnip (Brassica napus) and
the Swede (Brassica campestris), which, according to our estimates of
affinity should be nearly allied forms, are totally sterile.  (See Sutton,
A.W., "Journ. Linn. Soc." XXXVIII. page 341, 1908.)  Lastly, it may be
recalled that in sterility we are almost certainly considering a meristic
phenomenon.  FAILURE TO DIVIDE is, we may feel fairly sure, the immediate
"cause" of the sterility.  Now, though we know very little about the
heredity of meristic differences, all that we do know points to the
conclusion that the less-divided is dominant to the more-divided, and we
are thus justified in supposing that there are factors which can arrest or
prevent cell-division.  My conjecture therefore is that in the case of
sterility of cross-breds we see the effect produced by a complementary pair
of such factors.  This and many similar problems are now open to our
analysis.

The question is sometimes asked, Do the new lights on Variation and
Heredity make the process of Evolution easier to understand?  On the whole
the answer may be given that they do.  There is some appearance of loss of
simplicity, but the gain is real.  As was said above, the time is not ripe
for the discussion of the origin of species.  With faith in Evolution
unshaken--if indeed the word faith can be used in application to that which
is certain--we look on the manner and causation of adapted differentiation
as still wholly mysterious.  As Samuel Butler so truly said:  "To me it
seems that the 'Origin of Variation,' whatever it is, is the only true
'Origin of Species'" ("Life and Habit", London, page 263, 1878.), and of
that Origin not one of us knows anything.  But given Variation--and it is
given:  assuming further that the variations are not guided into paths of
adaptation--and both to the Darwinian and to the modern school this
hypothesis appears to be sound if unproven--an evolution of species
proceeding by definite steps is more, rather than less, easy to imagine
than an evolution proceeding by the accumulation of indefinite and
insensible steps.  Those who have lost themselves in contemplating the
miracles of Adaptation (whether real or spurious) have not unnaturally
fixed their hopes rather on the indefinite than on the definite changes. 
The reasons are obvious.  By suggesting that the steps through which an
adaptative mechanism arose were indefinite and insensible, all further
trouble is spared.  While it could be said that species arise by an
insensible and imperceptible process of variation, there was clearly no use
in tiring ourselves by trying to perceive that process.  This labour-saving
counsel found great favour.  All that had to be done to develop evolution-
theory was to discover the good in everything, a task which, in the
complete absence of any control or test whereby to check the truth of the
discovery, is not very onerous.  The doctrine "que tout est au mieux" was
therefore preached with fresh vigour, and examples of that illuminating
principle were discovered with a facility that Pangloss himself might have
envied, till at last even the spectators wearied of such dazzling
performances.

But in all seriousness, why should indefinite and unlimited variation have
been regarded as a more probable account of the origin of Adaptation? 
Only, I think, because the obstacle was shifted one plane back, and so
looked rather less prominent.  The abundance of Adaptation, we all grant,
is an immense, almost an unsurpassable difficulty in all non-Lamarckian
views of Evolution; but if the steps by which that adaptation arose were
fortuitous, to imagine them insensible is assuredly no help.  In one most
important respect indeed, as has often been observed, it is a
multiplication of troubles.  For the smaller the steps, the less could
Natural Selection act upon them.  Definite variations--and of the
occurrence of definite variations in abundance we have now the most
convincing proof--have at least the obvious merit that they can make and
often do make a real difference in the chances of life.

There is another aspect of the Adaptation problem to which I can only
allude very briefly.  May not our present ideas of the universality and
precision of Adaptation be greatly exaggerated?  The fit of organism to its
environment is not after all so very close--a proposition unwelcome
perhaps, but one which could be illustrated by very copious evidence. 
Natural Selection is stern, but she has her tolerant moods.

We have now most certain and irrefragable proof that much definiteness
exists in living things apart from Selection, and also much that may very
well have been preserved and so in a sense constituted by Selection.  Here
the matter is likely to rest.  There is a passage in the sixth edition of
the "Origin" which has I think been overlooked.  On page 70 Darwin says
"The tuft of hair on the breast of the wild turkey-cock cannot be of any
use, and it is doubtful whether it can be ornamental in the eyes of the
female bird."  This tuft of hair is a most definite and unusual structure,
and I am afraid that the remark that it "cannot be of any use" may have
been made inadvertently; but it may have been intended, for in the first
edition the usual qualification was given and must therefore have been
deliberately excised.  Anyhow I should like to think that Darwin did throw
over that tuft of hair, and that he felt relief when he had done so. 
Whether however we have his great authority for such a course or not, I
feel quite sure that we shall be rightly interpreting the facts of nature
if we cease to expect to find purposefulness wherever we meet with definite
structures or patterns.  Such things are, as often as not, I suspect rather
of the nature of tool-marks, mere incidents of manufacture, benefiting
their possessor not more than the wire-marks in a sheet of paper, or the
ribbing on the bottom of an oriental plate renders those objects more
attractive in our eyes.

If Variation may be in any way definite, the question once more arises, may
it not be definite in direction?  The belief that it is has had many
supporters, from Lamarck onwards, who held that it was guided by need, and
others who, like Nageli, while laying no emphasis on need, yet were
convinced that there was guidance of some kind.  The latter view under the
name of "Orthogenesis," devised I believe by Eimer, at the present day
commends itself to some naturalists.  The objection to such a suggestion is
of course that no fragment of real evidence can be produced in its support. 
On the other hand, with the experimental proof that variation consists
largely in the unpacking and repacking of an original complexity, it is not
so certain as we might like to think that the order of these events is not
pre-determined.  For instance the original "pack" may have been made in
such a way that at the nth division of the germ-cells of a Sweet Pea a
colour-factor might be dropped, and that at the n plus n prime division the
hooded variety be given off, and so on.  I see no ground whatever for
holding such a view, but in fairness the possibility should not be
forgotten, and in the light of modern research it scarcely looks so
absurdly improbable as before.

No one can survey the work of recent years without perceiving that
evolutionary orthodoxy developed too fast, and that a great deal has got to
come down; but this satisfaction at least remains, that in the experimental
methods which Mendel inaugurated, we have means of reaching certainty in
regard to the physiology of Heredity and Variation upon which a more
lasting structure may be built.


VI.  THE MINUTE STRUCTURE OF CELLS IN RELATION TO HEREDITY.

By EDUARD STRASBURGER,
Professor of Botany in the University of Bonn.

Since 1875 an unexpected insight has been gained into the internal
structure of cells.  Those who are familiar with the results of
investigations in this branch of Science are convinced that any modern
theory of heredity must rest on a basis of cytology and cannot be at
variance with cytological facts.  Many histological discoveries, both such
as have been proved correct and others which may be accepted as probably
well founded, have acquired a fundamental importance from the point of view
of the problems of heredity.

My aim is to describe the present position of our knowledge of Cytology. 
The account must be confined to essentials and cannot deal with far-
reaching and controversial questions.  In cases where difference of opinion
exists, I adopt my own view for which I hold myself responsible.  I hope to
succeed in making myself intelligible even without the aid of
illustrations:  in order to convey to the uninitiated an adequate idea of
the phenomena connected with the life of a cell, a greater number of
figures would be required than could be included within the scope of this
article.

So long as the most eminent investigators (As for example the illustrious
Wilhelm Hofmeister in his "Lehre von der Pflanzenzelle" (1867).) believed
that the nucleus of a cell was destroyed in the course of each division and
that the nuclei of the daughter-cells were produced de novo, theories of
heredity were able to dispense with the nucleus.  If they sought, as did
Charles Darwin, who showed a correct grasp of the problem in the
enunciation of his Pangenesis hypothesis, for histological connecting
links, their hypotheses, or at least the best of them, had reference to the
cell as a whole.  It was known to Darwin that the cell multiplied by
division and was derived from a similar pre-existing cell.  Towards 1870 it
was first demonstrated that cell-nuclei do not arise de novo, but are
invariably the result of division of pre-existing nuclei.  Better methods
of investigation rendered possible a deeper insight into the phenomena
accompanying cell and nuclear divisions and at the same time disclosed the
existence of remarkable structures.  The work of O. Butschli, O. Hertwig,
W. Flemming H. Fol and of the author of this article (For further reference
to literature, see my article on "Die Ontogenie der Zelle seit 1875", in
the "Progressus Rei Botanicae", Vol. I. page 1, Jena, 1907.), have
furnished conclusive evidence in favour of these facts.  It was found that
when the reticular framework of a nucleus prepares to divide, it separates
into single segments.  These then become thicker and denser, taking up with
avidity certain stains, which are used as aids to investigation, and
finally form longer or shorter, variously bent, rodlets of uniform
thickness.  In these organs which, on account of their special property of
absorbing certain stains, were styled Chromosomes (By W. Waldeyer in
1888.), there may usually be recognised a separation into thicker and
thinner discs; the former are often termed Chromomeres.  (Discovered by W.
Pfitzner in 1880.)  In the course of division of the nucleus, the single
rows of chromomeres in the chromosomes are doubled and this produces a
band-like flattening and leads to the longitudinal splitting by which each
chromosome is divided into two exactly equal halves.  The nuclear membrane
then disappears and fibrillar cell-plasma or cytoplasm invades the nuclear
area.  In animal cells these fibrillae in the cytoplasm centre on definite
bodies (Their existence and their multiplication by fission were
demonstrated by E. van Beneden and Th. Boveri in 1887.), which it is
customary to speak of as Centrosomes.  Radiating lines in the adjacent
cell-plasma suggest that these bodies constitute centres of force.  The
cells of the higher plants do not possess such individualised centres; they
have probably disappeared in the course of phylogenetic development:  in
spite of this, however, in the nuclear division-figures the fibrillae of
the cell-plasma are seen to radiate from two opposite poles.  In both
animal and plant cells a fibrillar bipolar spindle is formed, the fibrillae
of which grasp the longitudinally divided chromosomes from two opposite
sides and arrange them on the equatorial plane of the spindle as the so-
called nuclear or equatorial plate.  Each half-chromosome is connected with
one of the spindle poles only and is then drawn towards that pole.  (These
important facts, suspected by W. Flemming in 1882, were demonstrated by E.
Heuser, L. Guignard, E. van Beneden, M. Nussbaum, and C. Rabl.)

The formation of the daughter-nuclei is then effected.  The changes which
the daughter-chromosomes undergo in the process of producing the daughter-
nuclei repeat in the reverse order the changes which they went through in
the course of their progressive differentiation from the mother-nucleus. 
The division of the cell-body is completed midway between the two daughter-
nuclei.  In animal cells, which possess no chemically differentiated
membrane, separation is effected by simple constriction, while in the case
of plant cells provided with a definite wall, the process begins with the
formation of a cytoplasmic separating layer.

The phenomena observed in the course of the division of the nucleus show
beyond doubt that an exact halving of its substance is of the greatest
importance.  (First shown by W. Roux in 1883.)  Compared with the method of
division of the nucleus, that of the cytoplasm appears to be very simple. 
This led to the conception that the cell-nucleus must be the chief if not
the sole carrier of hereditary characters in the organism.  It is for this
reason that the detailed investigation of fertilisation phenomena
immediately followed researches into the nucleus.  The fundamental
discovery of the union of two nuclei in the sexual act was then made (By O.
Hertwig in 1875.) and this afforded a new support for the correct
conception of the nuclear functions.  The minute study of the behaviour of
the other constituents of sexual cells during fertilisation led to the
result, that the nucleus alone is concerned with handing on hereditary
characters (This was done by O. Hertwig and the author of this essay
simultaneously in 1884.) from one generation to another.  Especially
important, from the point of view of this conclusion, is the study of
fertilisation in Angiosperms (Flowering plants); in these plants the male
sexual cells lose their cell-body in the pollen-tube and the nucleus only--
the sperm-nucleus--reaches the egg.  The cytoplasm of the male sexual cell
is therefore not necessary to ensure a transference of hereditary
characters from parents to offspring.  I lay stress on the case of the
Angiosperms because researches recently repeated with the help of the
latest methods failed to obtain different results.  As regards the
descendants of angiospermous plants, the same laws of heredity hold good as
for other sexually differentiated organisms; we may, therefore, extend to
the latter what the Angiosperms so clearly teach us.

The next advance in the hitherto rapid progress in our knowledge of nuclear
division was delayed, because it was not at once recognised that there are
two absolutely different methods of nuclear division.  All such nuclear
divisions were united under the head of indirect or mitotic divisions;
these were also spoken of as karyo-kineses, and were distinguished from the
direct or amitotic divisions which are characterised by a simple
constriction of the nuclear body.  So long as the two kinds of indirect
nuclear division were not clearly distinguished, their correct
interpretation was impossible.  This was accomplished after long and
laborious research, which has recently been carried out and with results
which should, perhaps, be regarded as provisional.

Soon after the new study of the nucleus began, investigators were struck by
the fact that the course of nuclear division in the mother-cells, or more
correctly in the grandmother-cells, of spores, pollen-grains, and embryo-
sacs of the more highly organised plants and in the spermatozoids and eggs
of the higher animals, exhibits similar phenomena, distinct from those
which occur in the somatic cells.

In the nuclei of all those cells which we may group together as gonotokonts
(At the suggestion of J.P. Lotsy in 1904.) (i.e. cells concerned in
reproduction) there are fewer chromosomes than in the adjacent body-cells
(somatic cells).  It was noticed also that there is a peculiarity
characteristic of the gonotokonts, namely the occurrence of two nuclear
divisions rapidly succeeding one another.  It was afterwards recognised
that in the first stage of nuclear division in the gonotokonts the
chromosomes unite in pairs:  it is these chromosome-pairs, and not the two
longitudinal halves of single chromosomes, which form the nuclear plate in
the equatorial plane of the nuclear spindle.  It has been proposed to call
these pairs gemini.  (J.E.S. Moore and A.L. Embleton, "Proc. Roy. Soc."
London, Vol. LXXVII. page 555, 1906; V. Gregoire, 1907.)  In the course of
this division the spindle-fibrillae attach themselves to the gemini, i.e.
to entire chromosomes and direct them to the points where the new daughter-
nuclei are formed, that is to those positions towards which the
longitudinal halves of the chromosomes travel in ordinary nuclear
divisions.  It is clear that in this way the number of chromosomes which
the daughter-nuclei contain, as the result of the first stage in division
in the gonotokonts, will be reduced by one half, while in ordinary
divisions the number of chromosomes always remains the same.  The first
stage in the division of the nucleus in the gonotokonts has therefore been
termed the reduction division.  (In 1887 W. Flemming termed this the
heterotypic form of nuclear division.)  This stage in division determines
the conditions for the second division which rapidly ensues.  Each of the
paired chromosomes of the mother-nucleus has already, as in an ordinary
nuclear division, completed the longitudinal fission, but in this case it
is not succeeded by the immediate separation of the longitudinal halves and
their allotment to different nuclei.  Each chromosome, therefore, takes its
two longitudinal halves into the same daughter-nucleus.  Thus, in each
daughter-nucleus the longitudinal halves of the chromosomes are present
ready for the next stage in the division; they only require to be arranged
in the nuclear plate and then distributed among the granddaughter-nuclei.
This method of division, which takes place with chromosomes already split,
and which have only to provide for the distribution of their longitudinal
halves to the next nuclear generation, has been called homotypic nuclear
division.  (The name was proposed by W. Flemming in 1887; the nature of
this type of division was, however, not explained until later.)

Reduction division and homotypic nuclear division are included together
under the term allotypic nuclear division and are distinguished from the
ordinary or typical nuclear division.  The name Meiosis (By J. Bretland
Farmer and J.E.S. Moore in 1905.) has also been proposed for these two
allotypic nuclear divisions.  The typical divisions are often spoken of as
somatic.

Observers who were actively engaged in this branch of recent histological
research soon noticed that the chromosomes of a given organism are
differentiated in definite numbers from the nuclear network in the course
of division.  This is especially striking in the gonotokonts, but it
applies also to the somatic tissues.  In the latter, one usually finds
twice as many chromosomes as in the gonotokonts.  Thus the conclusion was
gradually reached that the doubling of chromosomes, which necessarily
accompanies fertilisation, is maintained in the product of fertilisation,
to be again reduced to one half in the gonotokonts at the stage of
reduction-division.  This enabled us to form a conception as to the essence
of true alternation of generations, in which generations containing single
and double chromosomes alternate with one another.

The single-chromosome generation, which I will call the HAPLOID, must have
been the primitive generation in all organisms; it might also persist as
the only generation.  Every sexual differentiation in organisms, which
occurred in the course of phylogenetic development, was followed by
fertilisation and therefore by the creation of a diploid or double-
chromosome product.  So long as the germination of the product of
fertilisation, the zygote, began with a reducing process, a special DIPLOID
generation was not represented.  This, however, appeared later as a product
of the further evolution of the zygote, and the reduction division was
correspondingly postponed.  In animals, as in plants, the diploid
generation attained the higher development and gradually assumed the
dominant position.  The haploid generation suffered a proportional
reduction, until it finally ceased to have an independent existence and
became restricted to the role of producing the sexual products within the
body of the diploid generation.  Those who do not possess the necessary
special knowledge are unable to realise what remains of the first haploid
generation in a phanerogamic plant or in a vertebrate animal.  In
Angiosperms this is actually represented only by the short developmental
stages which extend from the pollen mother-cells to the sperm-nucleus of
the pollen-tube, and from the embryo-sac mother-cell to the egg and the
endosperm tissue.  The embryo-sac remains enclosed in the diploid ovule,
and within this from the fertilised egg is formed the embryo which
introduces the new diploid generation.  On the full development of the
diploid embryo of the next generation, the diploid ovule of the preceding
diploid generation is separated from the latter as a ripe seed.  The
uninitiated sees in the more highly organised plants only a succession of
diploid generations.  Similarly all the higher animals appear to us as
independent organisms with diploid nuclei only.  The haploid generation is
confined in them to the cells produced as the result of the reduction
division of the gonotokonts; the development of these is completed with the
homotypic stage of division which succeeds the reduction division and
produces the sexual products.

The constancy of the numbers in which the chromosomes separate themselves
from the nuclear network during division gave rise to the conception that,
in a certain degree, chromosomes possess individuality.  Indeed the most
careful investigations (Particularly those of V. Gregoire and his pupils.)
have shown that the segments of the nuclear network, which separate from
one another and condense so as to produce chromosomes for a new division,
correspond to the segments produced from the chromosomes of the preceding
division.  The behaviour of such nuclei as possess chromosomes of unequal
size affords confirmatory evidence of the permanence of individual
chromosomes in corresponding sections of an apparently uniform nuclear
network.  Moreover at each stage in division chromosomes with the same
differences in size reappear.  Other cases are known in which thicker
portions occur in the substance of the resting nucleus, and these agree in
number with the chromosomes.  In this network, therefore, the individual
chromosomes must have retained their original position.  But the
chromosomes cannot be regarded as the ultimate hereditary units in the
nuclei, as their number is too small.  Moreover, related species not
infrequently show a difference in the number of their chromosomes, whereas
the number of hereditary units must approximately agree.  We thus picture
to ourselves the carriers of hereditary characters as enclosed in the
chromosomes; the transmitted fixed number of chromosomes is for us only the
visible expression of the conception that the number of hereditary units
which the chromosomes carry must be also constant.  The ultimate hereditary
units may, like the chromosomes themselves, retain a definite position in
the resting nucleus.  Further, it may be assumed that during the separation
of the chromosomes from one another and during their assumption of the rod-
like form, the hereditary units become aggregated in the chromomeres and
that these are characterised by a constant order of succession.  The
hereditary units then grow, divide into two and are uniformly distributed
by the fission of the chromosomes between their longitudinal halves.

As the contraction and rod-like separation of the chromosomes serve to
isnure the transmission of all hereditary units in the products of division
of a nucleus, so, on the other hand, the reticular distension of each
chromosome in the so-called resting nucleus may effect a separation of the
carriers of hereditary units from each other and facilitate the specific
activity of each of them.

In the stages preliminary to their division, the chromosomes become denser
and take up a substance which increases their staining capacity; this is
called chromatin.  This substance collects in the chromomeres and may form
the nutritive material for the carriers of hereditary units which we now
believe to be enclosed in them.  The chromatin cannot itself be the
hereditary substance, as it afterwards leaves the chromosomes, and the
amount of it is subject to considerable variation in the nucleus, according
to its stage of development.  Conjointly with the materials which take part
in the formation of the nuclear spindle and other processes in the cell,
the chromatin accumulates in the resting nucleus to form the nucleoli.

Naturally connected with the conclusion that the nuclei are the carriers of
hereditary characters in the organism, is the question whether enucleate
organisms can also exist.  Phylogenetic considerations give an affirmative
answer to this question.  The differentiation into nucleus and cytoplasm
represents a division of labour in the protoplast.  A study of organisms
which belong to the lowest class of the organic world teaches us how this
was accomplished.  Instead of well-defined nuclei, scattered granules have
been described in the protoplasm of several of these organisms (Bacteria,
Cyanophyceae, Protozoa.), characterised by the same reactions as nuclear
material, provided also with a nuclear network, but without a limiting
membrane.  (This is the result of the work of R. Hertwig and of the most
recently published investigations.)  Thus the carriers of hereditary
characters may originally have been distributed in the common protoplasm,
afterwards coming together and eventually assuming a definite form as
special organs of the cell.  It may be also assumed that in the protoplasm
and in the primitive types of nucleus, the carriers of the same hereditary
unit were represented in considerable quantity; they became gradually
differentiated to an extent commensurate with newly acquired characters. 
It was also necessary that, in proportion as this happened, the mechanism
of nuclear division must be refined.  At first processes resembling a
simple constriction would suffice to provide for the distribution of all
hereditary units to each of the products of division, but eventually in
both organic kingdoms nuclear division, which alone insured the qualitative
identity of the products of division, became a more marked feature in the
course of cell-multiplication.

Where direct nuclear division occurs by constriction in the higher
organisms, it does not result in the halving of hereditary units.  So far
as my observations go, direct nuclear division occurs in the more highly
organised plants only in cells which have lost their specific functions. 
Such cells are no longer capable of specific reproduction.  An interesting
case in this connection is afforded by the internodal cells of the
Characeae, which possess only vegetative functions.  These cells grow
vigorously and their cytoplasm increases, their growth being accompanied by
a correspondingly direct multiplication of the nuclei.  They serve chiefly
to nourish the plant, but, unlike the other cells, they are incapable of
producing any offspring.  This is a very instructive case, because it
clearly shows that the nuclei are not only carriers of hereditary
characters, but that they also play a definite part in the metabolism of
the protoplasts.

Attention was drawn to the fact that during the reducing division of nuclei
which contain chromosomes of unequal size, gemini are constantly produced
by the pairing of chromosomes of the same size.  This led to the conclusion
that the pairing chromosomes are homologous, and that one comes from the
father, the other from the mother.  (First stated by T.H. Montgomery in
1901 and by W.S. Sutton in 1902.)  This evidently applies also to the
pairing of chromosomes in those reduction-divisions in which differences in
size do not enable us to distinguish the individual chromosomes.  In this
case also each pair would be formed by two homologous chromosomes, the one
of paternal, the other of maternal origin.  When the separation of these
chromosomes and their distribution to both daughter-nuclei occur a
chromosome of each kind is provided for each of these nuclei.  It would
seem that the components of each pair might pass to either pole of the
nuclear spindle, so that the paternal and maternal chromosomes would be
distributed in varying proportion between the daughter-nuclei; and it is
not impossible that one daughter-nucleus might occasionally contain
paternal chromosomes only and its sister-nucleus exclusively maternal
chromosomes.

The fact that in nuclei containing chromosomes of various sizes, the
chromosomes which pair together in reduction-division are always of equal
size, constitutes a further and more important proof of their qualitative
difference.  This is supported also by ingenious experiments which led to
an unequal distribution of chromosomes in the products of division of a
sea-urchin's egg, with the result that a difference was induced in their
further development.  (Demonstrated by Th. Boveri in 1902.)

The recently discovered fact that in diploid nuclei the chromosomes are
arranged in pairs affords additional evidence in favour of the unequal
value of the chromosomes.  This is still more striking in the case of
chromosomes of different sizes.  It has been shown that in the first
division-figure in the nucleus of the fertilised egg the chromosomes of
corresponding size form pairs.  They appear with this arrangement in all
subsequent nuclear divisions in the diploid generation.  The longitudinal
fissions of the chromosomes provide for the unaltered preservation of this
condition.  In the reduction nucleus of the gonotokonts the homologous
chromosomes being near together need not seek out one another; they are
ready to form gemini.  The next stage is their separation to the haploid
daughter-nuclei, which have resulted from the reduction process.

Peculiar phenomena in the reduction nucleus accompany the formation of
gemini in both organic kingdoms.  (This has been shown more particularly by
the work of L. Guignard, M. Mottier, J.B. Farmer, C.B. Wilson, V. Hacker
and more recently by V. Gregoire and his pupil C.A. Allen, by the
researches conducted in the Bonn Botanical Institute, and by A. and K.E.
Schreiner.)  Probably for the purpose of entering into most intimate
relation, the pairs are stretched to long threads in which the chromomeres
come to lie opposite one another.  (C.A. Allen, A. and K.E. Schreiner, and
Strasburger.)  It seems probable that these are homologous chromomeres, and
that the pairs afterwards unite for a short time, so that an exchange of
hereditary units is rendered possible.  (H. de Vries and Strasburger.) 
This cannot be actually seen, but certain facts of heredity point to the
conclusion that this occurs.  It follows from these phenomena that any
exchange which may be effected must be one of homologous carriers of
hereditary units only.  These units continue to form exchangeable segments
after they have undergone unequal changes; they then constitute
allelotropic pairs.  We may thus calculate what sum of possible
combinations the exchange of homologous hereditary units between the
pairing chromosomes provides for before the reduction division and the
subsequent distribution of paternal and maternal chromosomes in the haploid
daughter-nuclei.  These nuclei then transmit their characters to the sexual
cells, the conjugation of which in fertilization again produces the most
varied combinations.  (A.  Weismann gave the impulse to these ideas in his
theory on "Amphimixis".)  In this way all the cooperations which the
carriers of hereditary characters are capable of in a species are produced;
this must give it an appreciable advantage in the struggle for life.

The admirers of Charles Darwin must deeply regret that he did not live to
see the results achieved by the new Cytology.  What service would they have
been to him in the presentation of his hypothesis of Pangenesis; what an
outlook into the future would they have given to his active mind!

The Darwinian hypothesis of Pangenesis rests on the conception that all
inheritable properties are represented in the cells by small invisible
particles or gemmules and that these gemmules increase by division. 
Cytology began to develop on new lines some years after the publication in
1868 of Charles Darwin's "Provisional hypothesis of Pangenesis" ("Animals
and Plants under Domestication", London, 1868, Chapter XXVII.), and when he
died in 1882 it was still in its infancy.  Darwin would have soon suggested
the substitution of the nuclei for his gemmules.  At least the great
majority of present-day investigators in the domain of cytology have been
led to the conclusion that the nucleus is the carrier of hereditary
characters, and they also believe that hereditary characters are
represented in the nucleus as distinct units.  Such would be Darwin's
gemmules, which in conformity with the name of his hypothesis may be called
pangens (So called by H. de Vries in 1889.):  these pangens multiply by
division.  All recently adopted views may be thus linked on to this part of
Darwin's hypothesis.  It is otherwise with Darwin's conception to which
Pangenesis owes its name, namely the view that all cells continually give
off gemmules, which migrate to other places in the organism, where they
unite to form reproductive cells.  When Darwin foresaw this possibility,
the continuity of the germinal substance was still unknown (Demonstrated by
Nussbaum in 1880, by Sachs in 1882, and by Weismann in 1885.), a fact which
excludes a transference of gemmules.

But even Charles Darwin's genius was confined within finite boundaries by
the state of science in his day.

It is not my province to deal with other theories of development which
followed from Darwin's Pangenesis, or to discuss their histological
probabilities.  We can, however, affirm that Charles Darwin's idea that
invisible gemmules are the carriers of hereditary characters and that they
multiply by division has been removed from the position of a provisional
hypothesis to that of a well-founded theory.  It is supported by histology,
and the results of experimental work in heredity, which are now assuming
extraordinary prominence, are in close agreement with it.


VII.  "THE DESCENT OF MAN"

By G. SCHWALBE.
Professor of Anatomy in the University of Strassburg.

The problem of the origin of the human race, of the descent of man, is
ranked by Huxley in his epoch-making book "Man's Place in Nature", as the
deepest with which biology has to concern itself, "the question of
questions,"--the problem which underlies all others.  In the same brilliant
and lucid exposition, which appeared in 1863, soon after the publication of
Darwin's "Origin of Species", Huxley stated his own views in regard to this
great problem.  He tells us how the idea of a natural descent of man
gradually grew up in his mind, it was especially the assertions of Owen in
regard to the total difference between the human and the simian brain that
called forth strong dissent from the great anatomist Huxley, and he easily
succeeded in showing that Owen's supposed differences had no real
existence; he even established, on the basis of his own anatomical
investigations, the proposition that the anatomical differences between the
Marmoset and the Chimpanzee are much greater than those between the
Chimpanzee and Man.

But why do we thus introduce the study of Darwin's "Descent of Man", which
is to occupy us here, by insisting on the fact that Huxley had taken the
field in defence of the descent of man in 1863, while Darwin's book on the
subject did not appear till 1871?  It is in order that we may clearly
understand how it happened that from this time onwards Darwin and Huxley
followed the same great aim in the most intimate association.

Huxley and Darwin working at the same Problema maximum!  Huxley fiery,
impetuous, eager for battle, contemptuous of the resistance of a dull
world, or energetically triumphing over it.  Darwin calm, weighing every
problem slowly, letting it mature thoroughly,--not a fighter, yet having
the greater and more lasting influence by virtue of his immense mass of
critically sifted proofs.  Darwin's friend, Huxley, was the first to do him
justice, to understand his nature, and to find in it the reason why the
detailed and carefully considered book on the descent of man made its
appearance so late.  Huxley, always generous, never thought of claiming
priority for himself.  In enthusiastic language he tells how Darwin's
immortal work, "The Origin of Species", first shed light for him on the
problem of the descent of man; the recognition of a vera causa in the
transformation of species illuminated his thoughts as with a flash.  He was
now content to leave what perplexed him, what he could not yet solve, as he
says himself, "in the mighty hands of Darwin."  Happy in the bustle of
strife against old and deep-rooted prejudices, against intolerance and
superstition, he wielded his sharp weapons on Darwin's behalf; wearing
Darwin's armour he joyously overthrew adversary after adversary.  Darwin
spoke of Huxley as his "general agent."  ("Life and Letters of Thomas Henry
Huxley", Vol. I. page 171, London, 1900.)  Huxley says of himself "I am
Darwin's bulldog."  (Ibid. page 363.)

Thus Huxley openly acknowledged that it was Darwin's "Origin of Species"
that first set the problem of the descent of man in its true light, that
made the question of the origin of the human race a pressing one.  That
this was the logical consequence of his book Darwin himself had long felt.
He had been reproached with intentionally shirking the application of his
theory to Man.  Let us hear what he says on this point in his
autobiography:  "As soon as I had become, in the year 1837 or 1838,
convinced that species were mutable productions, I could not avoid the
belief that man must come under the same law.  Accordingly I collected
notes on the subject for my own satisfaction, and not for a long time with
any intention of publishing.  Although in the 'Origin of Species' the
derivation of any particular species is never discussed, yet I thought it
best, in order THAT NO HONOURABLE MAN SHOULD ACCUSE ME OF CONCEALING MY
VIEWS (No italics in original.), to add that by the work 'light would be
thrown on the origin of man and his history.'  It would have been useless
and injurious to the success of the book to have paraded, without giving
any evidence, my conviction with respect to his origin."  ("Life and
Letters of Charles Darwin", Vol. 1. page 93.)

In a letter written in January, 1860, to the Rev. L. Blomefield, Darwin
expresses himself in similar terms.  "With respect to man, I am very far
from wishing to obtrude my belief; but I thought it dishonest to quite
conceal my opinion."  (Ibid. Vol. II. page 263.)

The brief allusion in the "Origin of Species" is so far from prominent and
so incidental that it was excusable to assume that Darwin had not touched
upon the descent of man in this work.  It was solely the desire to have his
mass of evidence sufficiently complete, solely Darwin's great
characteristic of never publishing till he had carefully weighed all
aspects of his subject for years, solely, in short, his most fastidious
scientific conscience that restrained him from challenging the world in
1859 with a book in which the theory of the descent of man was fully set
forth.  Three years, frequently interrupted by ill-health, were needed for
the actual writing of the book ("Life and Letters", Vol. I. page 94.):  the
first edition, which appeared in 1871, was followed in 1874 by a much
improved second edition, the preparation of which he very reluctantly
undertook.  (Ibid. Vol. III. page 175.)

This, briefly, is the history of the work, which, with the "Origin of
Species", marks an epoch in the history of biological sciences--the work
with which the cautious, peace-loving investigator ventured forth from his
contemplative life into the arena of strife and unrest, and laid himself
open to all the annoyances that deep-rooted belief and prejudice, and the
prevailing tendency of scientific thought at the time could devise.

Darwin did not take this step lightly.  Of great interest in this
connection is a letter written to Wallace on Dec. 22, 1857 (Ibid. Vol. II.
page 109.), in which he says "You ask whether I shall discuss 'man.'  I
think I shall avoid the whole subject, as so surrounded with prejudices;
though I fully admit that it is the highest and most interesting problem
for the naturalist."  But his conscientiousness compelled him to state
briefly his opinion on the subject in the "Origin of Species" in 1859. 
Nevertheless he did not escape reproaches for having been so reticent. 
This is unmistakably apparent from a letter to Fritz Muller dated February
22 (1869?), in which he says:  "I am thinking of writing a little essay on
the Origin of Mankind, as I have been taunted with concealing my opinions." 
(Ibid. Vol. III. page 112.)

It might be thought that Darwin behaved thus hesitatingly, and was so slow
in deciding on the full publication of his collected material in regard to
the descent of man, because he had religious difficulties to overcome.

But this was not the case, as we can see from his admirable confession of
faith, the publication of which we owe to his son Francis.  (Ibid. Vol. I.
pages 304-317.)  Whoever wishes really to understand the lofty character of
this great man should read these immortal lines in which he unfolds to us
in simple and straightforward words the development of his conception of
the universe.  He describes how, though he was still quite orthodox during
his voyage round the world on board the "Beagle", he came gradually to see,
shortly afterwards (1836-1839) that the Old Testament was no more to be
trusted than the Sacred Books of the Hindoos; the miracles by which
Christianity is supported, the discrepancies between the accounts in the
different Gospels, gradually led him to disbelieve in Christianity as a
divine revelation.  "Thus," he writes ("Life and Letters", Vol. 1. page
309.), "disbelief crept over me at a very slow rate, but was at last
complete.  The rate was so slow that I felt no distress."  But Darwin was
too modest to presume to go beyond the limits laid down by science.  He
wanted nothing more than to be able to go, freely and unhampered by belief
in authority or in the Bible, as far as human knowledge could lead him.  We
learn this from the concluding words of his chapter on religion:  "The
mystery of the beginning of all things is insoluble by us; and I for one
must be content to remain an Agnostic."  (Loc. cit. page 313.)

Darwin was always very unwilling to give publicity to his views in regard
to religion.  In a letter to Asa Gray on May 22, 1860 (Ibid. Vol. II. page
310.), he declares that it is always painful to him to have to enter into
discussion of religious problems.  He had, he said, no intention of writing
atheistically.

Finally, let us cite one characteristic sentence from a letter from Darwin
to C. Ridley (Ibid. Vol. III. page. 236.  ("C. Ridley," Mr Francis Darwin
points out to me, should be H.N. Ridley.  A.C.S.)) (Nov. 28, 1878.)  A
clergyman, Dr Pusey, had asserted that Darwin had written the "Origin of
Species" with some relation to theology.  Darwin writes emphatically, "Many
years ago, when I was collecting facts for the 'Origin', my belief in what
is called a personal God was as firm as that of Dr Pusey himself, and as to
the eternity of matter I never troubled myself about such insoluble
questions."  The expression "many years ago" refers to the time of his
voyage round the world, as has already been pointed out.  Darwin means by
this utterance that the views which had gradually developed in his mind in
regard to the origin of species were quite compatible with the faith of the
Church.

If we consider all these utterances of Darwin in regard to religion and to
his outlook on life (Weltanschauung), we shall see at least so much, that
religious reflection could in no way have influenced him in regard to the
writing and publishing of his book on "The Descent of Man".  Darwin had
early won for himself freedom of thought, and to this freedom he remained
true to the end of his life, uninfluenced by the customs and opinions of
the world around him.

Darwin was thus inwardly fortified and armed against the host of calumnies,
accusations, and attacks called forth by the publication of the "Origin of
Species", and to an even greater extent by the appearance of the "Descent
of Man".  But in his defence he could rely on the aid of a band of
distinguished auxiliaries of the rarest ability.  His faithful confederate,
Huxley, was joined by the botanist Hooker, and, after longer resistance, by
the famous geologist Lyell, whose "conversion" afforded Darwin peculiar
satisfaction.  All three took the field with enthusiasm in defence of the
natural descent of man.  From Wallace, on the other hand, though he shared
with him the idea of natural selection, Darwin got no support in this
matter.  Wallace expressed himself in a strange manner.  He admitted
everything in regard to the morphological descent of man, but maintained,
in a mystic way, that something else, something of a spiritual nature must
have been added to what man inherited from his animal ancestors.  Darwin,
whose esteem for Wallace was extraordinarily high, could not understand how
he could give utterance to such a mystical view in regard to man; the idea
seemed to him so "incredibly strange" that he thought some one else must
have added these sentences to Wallace's paper.

Even now there are thinkers who, like Wallace, shrink from applying to man
the ultimate consequences of the theory of descent.  The idea that man is
derived from ape-like forms is to them unpleasant and humiliating.

So far I have been depicting the development of Darwin's work on the
descent of man.  In what follows I shall endeavour to give a condensed
survey of the contents of the book.

It must at once be said that the contents of Darwin's work fall into two
parts, dealing with entirely different subjects.  "The Descent of Man"
includes a very detailed investigation in regard to secondary sexual
characters in the animal series, and on this investigation Darwin founded a
new theory, that of sexual selection.  With astonishing patience he
gathered together an immense mass of material, and showed, in regard to
Arthropods and Vertebrates, the wide distribution of secondary characters,
which develop almost exclusively in the male, and which enable him, on the
one hand, to get the better of his rivals in the struggle for the female by
the greater perfection of his weapons, and on the other hand, to offer
greater allurements to the female through the higher development of
decorative characters, of song, or of scent-producing glands.  The best
equipped males will thus crowd out the less well-equipped in the matter of
reproduction, and thus the relevant characters will be increased and
perfected through sexual selection.  It is, of course, a necessary
assumption that these secondary sexual characters may be transmitted to the
female, although perhaps in rudimentary form.

As we have said, this theory of sexual selection takes up a great deal of
space in Darwin's book, and it need only be considered here in so far as
Darwin applied it to the descent of man.  To this latter problem the whole
of Part I is devoted, while Part III contains a discussion of sexual
selection in relation to man, and a general summary.  Part II treats of
sexual selection in general, and may be disregarded in our present study.
Moreover, many interesting details must necessarily be passed over in what
follows, for want of space.

The first part of the "Descent of Man" begins with an enumeration of the
proofs of the animal descent of man taken from the structure of the human
body.  Darwin chiefly emphasises the fact that the human body consists of
the same organs and of the same tissues as those of the other mammals; he
shows also that man is subject to the same diseases and tormented by the
same parasites as the apes.  He further dwells on the general agreement
exhibited by young, embryonic forms, and he illustrates this by two figures
placed one above the other, one representing a human embryo, after Eaker,
the other a dog embryo, after Bischoff.  ("Descent of Man" (Popular
Edition, 1901), fig. 1, page 14.)

Darwin finds further proofs of the animal origin of man in the reduced
structures, in themselves extremely variable, which are either absolutely
useless to their possessors, or of so little use that they could never have
developed under existing conditions.  Of such vestiges he enumerates:  the
defective development of the panniculus carnosus (muscle of the skin) so
widely distributed among mammals, the ear-muscles, the occasional
persistence of the animal ear-point in man, the rudimentary nictitating
membrane (plica semilunaris) in the human eye, the slight development of
the organ of smell, the general hairiness of the human body, the frequently
defective development or entire absence of the third molar (the wisdom
tooth), the vermiform appendix, the occasional reappearance of a bony canal
(foramen supracondyloideum) at the lower end of the humerus, the
rudimentary tail of man (the so-called taillessness), and so on.  Of these
rudimentary structures the occasional occurrence of the animal ear-point in
man is most fully discussed.  Darwin's attention was called to this
interesting structure by the sculptor Woolner.  He figures such a case
observed in man, and also the head of an alleged orang-foetus, the
photograph of which he received from Nitsche.

Darwin's interpretation of Woolner's case as having arisen through a
folding over of the free edge of a pointed ear has been fully borne out by
my investigations on the external ear. (G. Schwalbe, "Das Darwin'sche
Spitzohr beim menschlichen Embryo", "Anatom. Anzeiger", 1889, pages 176-
189, and other papers.)  In particular, it was established by these
investigations that the human foetus, about the middle of its embryonic
life, possesses a pointed ear somewhat similar to that of the monkey genus
Macacus.  One of Darwin's statements in regard to the head of the orang-
foetus must be corrected.  A LARGE ear with a point is shown in the
photograph ("Descent of Man", fig.3, page 24.), but it can easily be
demonstrated--and Deniker has already pointed this out--that the figure is
not that of an orang-foetus at all, for that form has much smaller ears
with no point; nor can it be a gibbon-foetus, as Deniker supposes, for the
gibbon ear is also without a point.  I myself regard it as that of a
Macacus-embryo.  But this mistake, which is due to Nitsche, in no way
affects the fact recognised by Darwin, that ear-forms showing the point
characteristic of the animal ear occur in man with extraordinary frequency.

Finally, there is a discussion of those rudimentary structures which occur
only in ONE sex, such as the rudimentary mammary glands in the male, the
vesicula prostatica, which corresponds to the uterus of the female, and
others.  All these facts tell in favour of the common descent of man and
all other vertebrates.  The conclusion of this section is characteristic: 
"IT IS ONLY OUR NATURAL PREJUDICE, AND THAT ARROGANCE WHICH MADE OUR
FOREFATHERS DECLARE THAT THEY WERE DESCENDED FROM DEMI-GODS, WHICH LEADS US
TO DEMUR TO THIS CONCLUSION.  BUT THE TIME WILL BEFORE LONG COME, WHEN IT
WILL BE THOUGHT WONDERFUL THAT NATURALISTS, WHO WERE WELL ACQUAINTED WITH
THE COMPARATIVE STRUCTURE AND DEVELOPMENT OF MAN, AND OTHER MAMMALS, SHOULD
HAVE BELIEVED THAT EACH WAS THE WORK OF A SEPARATE ACT OF CREATION." 
(Ibid. page 36.)

In the second chapter there is a more detailed discussion, again based upon
an extraordinary wealth of facts, of the problem as to the manner in which,
and the causes through which, man evolved from a lower form.  Precisely the
same causes are here suggested for the origin of man, as for the origin of
species in general.  Variability, which is a necessary assumption in regard
to all transformations, occurs in man to a high degree.  Moreover, the
rapid multiplication of the human race creates conditions which necessitate
an energetic struggle for existence, and thus afford scope for the
intervention of natural selection.  Of the exercise of ARTIFICIAL selection
in the human race, there is nothing to be said, unless we cite such cases
as the grenadiers of Frederick William I, or the population of ancient
Sparta.  In the passages already referred to and in those which follow, the
transmission of acquired characters, upon which Darwin does not dwell, is
taken for granted.  In man, direct effects of changed conditions can be
demonstrated (for instance in regard to bodily size), and there are also
proofs of the influence exerted on his physical constitution by increased
use or disuse.  Reference is here made to the fact, established by Forbes,
that the Quechua-Indians of the high plateaus of Peru show a striking
development of lungs and thorax, as a result of living constantly at high
altitudes.

Such special forms of variation as arrests of development (microcephalism)
and reversion to lower forms are next discussed.  Darwin himself felt
("Descent of Man", page 54.) that these subjects are so nearly related to
the cases mentioned in the first chapter, that many of them might as well
have been dealt with there.  It seems to me that it would have been better
so, for the citation of additional instances of reversion at this place
rather disturbs the logical sequence of his ideas as to the conditions
which have brought about the evolution of man from lower forms.  The
instances of reversion here discussed are microcephalism, which Darwin
wrongly interpreted as atavistic, supernumerary mammae, supernumerary
digits, bicornuate uterus, the development of abnormal muscles, and so on.
Brief mention is also made of correlative variations observed in man.

Darwin next discusses the question as to the manner in which man attained
to the erect position from the state of a climbing quadruped.  Here again
he puts the influence of Natural Selection in the first rank.  The
immediate progenitors of man had to maintain a struggle for existence in
which success was to the more intelligent, and to those with social
instincts.  The hand of these climbing ancestors, which had little skill
and served mainly for locomotion, could only undergo further development
when some early member of the Primate series came to live more on the
ground and less among trees.

A bipedal existence thus became possible, and with it the liberation of the
hand from locomotion, and the one-sided development of the human foot.  The
upright position brought about correlated variations in the bodily
structure; with the free use of the hand it became possible to manufacture
weapons and to use them; and this again resulted in a degeneration of the
powerful canine teeth and the jaws, which were then no longer necessary for
defence.  Above all, however, the intelligence immediately increased, and
with it skull and brain.  The nakedness of man, and the absence of a tail
(rudimentariness of the tail vertebrae) are next discussed.  Darwin is
inclined to attribute the nakedness of man, not to the action of natural
selection on ancestors who originally inhabited a tropical land, but to
sexual selection, which, for aesthetic reasons, brought about the loss of
the hairy covering in man, or primarily in woman.  An interesting
discussion of the loss of the tail, which, however, man shares with the
anthropoid apes, some other monkeys and lemurs, forms the conclusion of the
almost superabundant material which Darwin worked up in the second chapter. 
His object was to show that some of the most distinctive human characters
are in all probability directly or indirectly due to natural selection. 
With characteristic modesty he adds ("Descent of Man", page 92.):  "Hence,
if I have erred in giving to natural selection great power, which I am very
far from admitting, or in having exaggerated its power, which is in itself
probable, I have at least, as I hope, done good service in aiding to
overthrow the dogma of separate creations."  At the end of the chapter he
touches upon the objection as to man's helpless and defenceless condition. 
Against this he urges his intelligence and social instincts.

The two following chapters contain a detailed discussion of the objections
drawn from the supposed great differences between the mental powers of men
and animals.  Darwin at once admits that the differences are enormous, but
not that any fundamental difference between the two can be found.  Very
characteristic of him is the following passage:  "In what manner the mental
powers were first developed in the lowest organisms, is as hopeless an
enquiry as how life itself first originated.  These are problems for the
distant future, if they are ever to be solved by man."  (Ibid. page 100.)

After some brief observations on instinct and intelligence, Darwin brings
forward evidence to show that the greater number of the emotional states,
such as pleasure and pain, happiness and misery, love and hate are common
to man and the higher animals.  He goes on to give various examples showing
that wonder and curiosity, imitation, attention, memory and imagination
(dreams of animals), can also be observed in the higher mammals, especially
in apes.  In regard even to reason there are no sharply defined limits.  A
certain faculty of deliberation is characteristic of some animals, and the
more thoroughly we know an animal the more intelligence we are inclined to
credit it with.  Examples are brought forward of the intelligent and
deliberate actions of apes, dogs and elephants.  But although no sharply
defined differences exist between man and animals, there is, nevertheless,
a series of other mental powers which are characteristics usually regarded
as absolutely peculiar to man.  Some of these characteristics are examined
in detail, and it is shown that the arguments drawn from them are not
conclusive.  Man alone is said to be capable of progressive improvement;
but against this must be placed as something analogous in animals, the fact
that they learn cunning and caution through long continued persecution. 
Even the use of tools is not in itself peculiar to man (monkeys use sticks,
stones and twigs), but man alone fashions and uses implements DESIGNED FOR
A SPECIAL PURPOSE.  In this connection the remarks taken from Lubbock in
regard to the origin and gradual development of the earliest flint
implements will be read with interest; these are similar to the
observations on modern eoliths, and their bearing on the development of the
stone-industry.  It is interesting to learn from a letter to Hooker ("Life
and Letters", Vol. II. page 161, June 22, 1859.), that Darwin himself at
first doubted whether the stone implements discovered by Boucher de Perthes
were really of the nature of tools.  With the relentless candour as to
himself which characterised him, he writes four years later in a letter to
Lyell in regard to this view of Boucher de Perthes' discoveries:  "I know
something about his errors, and looked at his book many years ago, and am
ashamed to think that I concluded the whole was rubbish!  Yet he has done
for man something like what Agassiz did for glaciers."  (Ibid. Vol. III.
page 15, March 17, 1863.)

To return to Darwin's further comparisons between the higher mental powers
of man and animals.  He takes much of the force from the argument that man
alone is capable of abstraction and self-consciousness by his own
observations on dogs.  One of the main differences between man and animals,
speech, receives detailed treatment.  He points out that various animals
(birds, monkeys, dogs) have a large number of different sounds for
different emotions, that, further, man produces in common with animals a
whole series of inarticulate cries combined with gestures, and that dogs
learn to understand whole sentences of human speech.  In regard to human
language, Darwin expresses a view contrary to that held by Max Muller
("Descent of Man", page 132.):  "I cannot doubt that language owes its
origin to the imitation and modification of various natural sounds, the
voices of other animals, and man's own instinctive cries, aided by signs
and gestures."  The development of actual language presupposes a higher
degree of intelligence than is found in any kind of ape.  Darwin remarks on
this point (Ibid. pages 136, 137.):  "The fact of the higher apes not using
their vocal organs for speech no doubt depends on their intelligence not
having been sufficiently advanced."

The sense of beauty, too, has been alleged to be peculiar to man.  In
refutation of this assertion Darwin points to the decorative colours of
birds, which are used for display.  And to the last objection, that man
alone has religion, that he alone has a belief in God, it is answered "that
numerous races have existed, and still exist, who have no idea of one or
more gods, and who have no words in their languages to express such an
idea."  (Ibid. page 143.)

The result of the investigations recorded in this chapter is to show that,
great as the difference in mental powers between man and the higher animals
may be, it is undoubtedly only a difference "of degree and not of kind." 
("Descent of Man", page 193.)

In the fourth chapter Darwin deals with the MORAL SENSE or CONSCIENCE,
which is the most important of all differences between man and animals.  It
is a result of social instincts, which lead to sympathy for other members
of the same society, to non-egoistic actions for the good of others. 
Darwin shows that social tendencies are found among many animals, and that
among these love and kin-sympathy exist, and he gives examples of animals
(especially dogs) which may exhibit characters that we should call moral in
man (e.g. disinterested self-sacrifice for the sake of others).  The early
ape-like progenitors of the human race were undoubtedly social.  With the
increase of intelligence the moral sense develops farther; with the
acquisition of speech public opinion arises, and finally, moral sense
becomes habit.  The rest of Darwin's detailed discussions on moral
philosophy may be passed over.

The fifth chapter may be very briefly summarised.  In it Darwin shows that
the intellectual and moral faculties are perfected through natural
selection.  He inquires how it can come about that a tribe at a low level
of evolution attains to a higher, although the best and bravest among them
often pay for their fidelity and courage with their lives without leaving
any descendants.  In this case it is the sentiment of glory, praise and
blame, the admiration of others, which bring about the increase of the
better members of the tribe.  Property, fixed dwellings, and the
association of families into a community are also indispensable
requirements for civilisation.  In the longer second section of the fifth
chapter Darwin acts mainly as recorder.  On the basis of numerous
investigations, especially those of Greg, Wallace, and Galton, he inquires
how far the influence of natural selection can be demonstrated in regard to
civilised nations.  In the final section, which deals with the proofs that
all civilised nations were once barbarians, Darwin again uses the results
gained by other investigators, such as Lubbock and Tylor.  There are two
sets of facts which prove the proposition in question.  In the first place,
we find traces of a former lower state in the customs and beliefs of all
civilised nations, and in the second place, there are proofs to show that
savage races are independently able to raise themselves a few steps in the
scale of civilisation, and that they have thus raised themselves.

In the sixth chapter of the work, Morphology comes into the foreground once
more.  Darwin first goes back, however, to the argument based on the great
difference between the mental powers of the highest animals and those of
man.  That this is only quantitative, not qualitative, he has already
shown.  Very instructive in this connection is the reference to the
enormous difference in mental powers in another class.  No one would draw
from the fact that the cochineal insect (Coccus) and the ant exhibit
enormous differences in their mental powers, the conclusion that the ant
should therefore be regarded as something quite distinct, and withdrawn
from the class of insects altogether.

Darwin next attempts to establish the SPECIFIC genealogical tree of man,
and carefully weighs the differences and resemblances between the different
families of the Primates.  The erect position of man is an adaptive
character, just as are the various characters referable to aquatic life in
the seals, which, notwithstanding these, are ranked as a mere family of the
Carnivores.  The following utterance is very characteristic of Darwin
("Descent of Man", page 231.):  "If man had not been his own classifier, he
would never have thought of founding a separate order for his own
reception."  In numerous characters not mentioned in systematic works, in
the features of the face, in the form of the nose, in the structure of the
external ear, man resembles the apes.  The arrangement of the hair in man
has also much in common with the apes; as also the occurrence of hair on
the forehead of the human embryo, the beard, the convergence of the hair of
the upper and under arm towards the elbow, which occurs not only in the
anthropoid apes, but also in some American monkeys.  Darwin here adopts
Wallace's explanation of the origin of the ascending direction of the hair
in the forearm of the orang,--that it has arisen through the habit of
holding the hands over the head in rain.  But this explanation cannot be
maintained when we consider that this disposition of the hair is widely
distributed among the most different mammals, being found in the dog, in
the sloth, and in many of the lower monkeys.

After further careful analysis of the anatomical characters Darwin reaches
the conclusion that the New World monkeys (Platyrrhine) may be excluded
from the genealogical tree altogether, but that man is an offshoot from the
Old World monkeys (Catarrhine) whose progenitors existed as far back as the
Miocene period.  Among these Old World monkeys the forms to which man shows
the greatest resemblance are the anthropoid apes, which, like him, possess
neither tail nor ischial callosities.  The platyrrhine and catarrhine
monkeys have their primitive ancestor among extinct forms of the Lemuridae. 
Darwin also touches on the question of the original home of the human race
and supposes that it may have been in Africa, because it is there that
man's nearest relatives, the gorilla and the chimpanzee, are found.  But he
regards speculation on this point as useless.  It is remarkable that, in
this connection, Darwin regards the loss of the hair-covering in man as
having some relation to a warm climate, while elsewhere he is inclined to
make sexual selection responsible for it.  Darwin recognises the great gap
between man and his nearest relatives, but similar gaps exist at other
parts of the mammalian genealogical tree:  the allied forms have become
extinct.  After the extermination of the lower races of mankind, on the one
hand, and of the anthropoid apes on the other, which will undoubtedly take
place, the gulf will be greater than ever, since the baboons will then
bound it on the one side, and the white races on the other.  Little weight
need be attached to the lack of fossil remains to fill up this gap, since
the discovery of these depends upon chance.  The last part of the chapter
is devoted to a discussion of the earlier stages in the genealogy of man. 
Here Darwin accepts in the main the genealogical tree, which had meantime
been published by Haeckel, who traces the pedigree back through Monotremes,
Reptiles, Amphibians, and Fishes, to Amphioxus.

Then follows an attempt to reconstruct, from the atavistic characters, a
picture of our primitive ancestor who was undoubtedly an arboreal animal. 
The occurrence of rudiments of parts in one sex which only come to full
development in the other is next discussed.  This state of things Darwin
regards as derived from an original hermaphroditism.  In regard to the
mammary glands of the male he does not accept the theory that they are
vestigial, but considers them rather as not fully developed.

The last chapter of Part I deals with the question whether the different
races of man are to be regarded as different species, or as sub-species of
a race of monophyletic origin.  The striking differences between the races
are first emphasised, and the question of the fertility or infertility of
hybrids is discussed.  That fertility is the more usual is shown by the
excessive fertility of the hybrid population of Brazil.  This, and the
great variability of the distinguishing characters of the different races,
as well as the fact that all grades of transition stages are found between
these, while considerable general agreement exists, tell in favour of the
unity of the races and lead to the conclusion that they all had a common
primitive ancestor.

Darwin therefore classifies all the different races as sub-species of ONE
AND THE SAME SPECIES.  Then follows an interesting inquiry into the reasons
for the extinction of human races.  He recognises as the ultimate reason
the injurious effects of a change of the conditions of life, which may
bring about an increase in infantile mortality, and a diminished fertility.
It is precisely the reproductive system, among animals also, which is most
susceptible to changes in the environment.

The final section of this chapter deals with the formation of the races of
mankind.  Darwin discusses the question how far the direct effect of
different conditions of life, or the inherited effects of increased use or
disuse may have brought about the characteristic differences between the
different races.  Even in regard to the origin of the colour of the skin he
rejects the transmitted effects of an original difference of climate as an
explanation.  In so doing he is following his tendency to exclude
Lamarckian explanations as far as possible.  But here he makes gratuitous
difficulties from which, since natural selection fails, there is no escape
except by bringing in the principle of sexual selection, to which, he
regarded it as possible, skin-colouring, arrangement of hair, and form of
features might be traced.  But with his characteristic conscientiousness he
guards himself thus:  "I do not intend to assert that sexual selection will
account for all the differences between the races."  ("Descent of Man",
page 308.)

I may be permitted a remark as to Darwin's attitude towards Lamarck. 
While, at an earlier stage, when he was engaged in the preliminary labours
for his immortal work, "The Origin of Species", Darwin expresses himself
very forcibly against the views of Lamarck, speaking of Lamarckian
"nonsense," ("Life and Letters", Vol. II. page 23.), and of Lamarck's
"absurd, though clever work" (Loc. cit. page 39.) and expressly declaring,
"I attribute very little to the direct action of climate, etc."  (Loc. cit.
(1856), page 82.) yet in later life he became more and more convinced of
the influence of external conditions.  In 1876, that is, two years after
the appearance of the second edition of "The Descent of Man", he writes
with his usual candid honesty:  "In my opinion the greatest error which I
have committed, has been not allowing sufficient weight to the direct
action of the environment, i.e. food, climate, etc. independently of
natural selection."  (Ibid. Vol. III. page 159.)  It is certain from this
change of opinion that, if he had been able to make up his mind to issue a
third edition of "The Descent of Man", he would have ascribed a much
greater influence to the effect of external conditions in explaining the
different characters of the races of man than he did in the second edition.
He would also undoubtedly have attributed less influence to sexual
selection as a factor in the origin of the different bodily
characteristics, if indeed he would not have excluded it altogether.

In Part III of the "Descent" two additional chapters are devoted to the
discussion of sexual selection in relation to man.  These may be very
briefly referred to.  Darwin here seeks to show that sexual selection has
been operative on man and his primitive progenitor.  Space fails me to
follow out his interesting arguments.  I can only mention that he is
inclined to trace back hairlessness, the development of the beard in man,
and the characteristic colour of the different human races to sexual
selection.  Since bareness of the skin could be no advantage, but rather a
disadvantage, this character cannot have been brought about by natural
selection.  Darwin also rejected a direct influence of climate as a cause
of the origin of the skin-colour.  I have already expressed the opinion,
based on the development of his views as shown in his letters, that in a
third edition Darwin would probably have laid more stress on the influence
of external environment.  He himself feels that there are gaps in his
proofs here, and says in self-criticism:  "The views here advanced, on the
part which sexual selection has played in the history of man, want
scientific precision."  ("Descent of Man", page 924.)  I need here only
point out that it is impossible to explain the graduated stages of skin-
colour by sexual selection, since it would have produced races sharply
defined by their colour and not united to other races by transition stages,
and this, it is well known, is not the case.  Moreover, the fact
established by me ("Die Hautfarbe des Menschen", "Mitteilungen der
Anthropologischen Gesellschaft in Wien", Vol. XXXIV. pages 331-352.), that
in all races the ventral side of the trunk is paler than the dorsal side,
and the inner surface of the extremities paler than the outer side, cannot
be explained by sexual selection in the Darwinian sense.

With this I conclude my brief survey of the rich contents of Darwin's book.
I may be permitted to conclude by quoting the magnificent final words of
"The Descent of Man":  "We must, however, acknowledge, as it seems to me,
that man, with all his noble qualities, with sympathy which feels for the
most debased, with benevolence which extends not only to other men but to
the humblest living creature, with his god-like intellect which has
penetrated into the movements and constitution of the solar system--with
all these exalted powers--Man still bears in his bodily frame the indelible
stamp of his lowly origin."  (Ibid. page 947.)

What has been the fate of Darwin's doctrines since his great achievement? 
How have they been received and followed up by the scientific and lay
world?  And what do the successors of the mighty hero and genius think now
in regard to the origin of the human race?

At the present time we are incomparably more favourably placed than Darwin
was for answering this question of all questions.  We have at our command
an incomparably greater wealth of material than he had at his disposal. 
And we are more fortunate than he in this respect, that we now know
transition-forms which help to fill up the gap, still great, between the
lowest human races and the highest apes.  Let us consider for a little the
more essential additions to our knowledge since the publication of "The
Descent of Man".

Since that time our knowledge of animal embryos has increased enormously.
While Darwin was obliged to content himself with comparing a human embryo
with that of a dog, there are now available the youngest embryos of monkeys
of all possible groups (Orang, Gibbon, Semnopithecus, Macacus), thanks to
Selenka's most successful tour in the East Indies in search of such
material.  We can now compare corresponding stages of the lower monkeys and
of the Anthropoid apes with human embryos, and convince ourselves of their
great resemblance to one another, thus strengthening enormously the armour
prepared by Darwin in defence of his view on man's nearest relatives.  It
may be said that Selenka's material fils up the blanks in Darwin's array of
proofs in the most satisfactory manner.

The deepening of our knowledge of comparative anatomy also gives us much
surer foundations than those on which Darwin was obliged to build.  Just of
late there have been many workers in the domain of the anatomy of apes and
lemurs, and their investigations extend to the most different organs.  Our
knowledge of fossil apes and lemurs has also become much wider and more
exact since Darwin's time:  the fossil lemurs have been especially worked
up by Cope, Forsyth Major, Ameghino, and others.  Darwin knew very little
about fossil monkeys.  He mentions two or three anthropoid apes as
occurring in the Miocene of Europe ("Descent of Man", page 240.), but only
names Dryopithecus, the largest form from the Miocene of France.  It was
erroneously supposed that this form was related to Hylobates.  We now know
not only a form that actually stands near to the gibbon (Pliopithecus), and
remains of other anthropoids (Pliohylobates and the fossil chimpanzee,
Palaeopithecus), but also several lower catarrhine monkeys, of which
Mesopithecus, a form nearly related to the modern Sacred Monkeys (a species
of Semnopithecus) and found in strata of the Miocene period in Greece, is
the most important.  Quite recently, too, Ameghino's investigations have
made us acquainted with fossil monkeys from South America (Anthropops,
Homunculus), which, according to their discoverer, are to be regarded as in
the line of human descent.

What Darwin missed most of all--intermediate forms between apes and man--
has been recently furnished.  (E. Dubois, as is well known, discovered in
1893, near Trinil in Java, in the alluvial deposits of the river Bengawan,
an important form represented by a skull-cap, some molars, and a femur. 
His opinion--much disputed as it has been--that in this form, which he
named Pithecanthropus, he has found a long-desired transition-form is
shared by the present writer.  And although the geological age of these
fossils, which, according to Dubois, belong to the uppermost Tertiary
series, the Pliocene, has recently been fixed at a later date (the older
Diluvium), the MORPHOLOGICAL VALUE of these interesting remains, that is,
the intermediate position of Pithecanthropus, still holds good.  Volz says
with justice ("Das geologische Alter der Pithecanthropus-Schichten bei
Trinil, Ost-Java". "Neues Jahrb. f.Mineralogie".  Festband, 1907.), that
even if Pithecanthropus is not THE missing link, it is undoubtedly _A_
missing link.

As on the one hand there has been found in Pithecanthropus a form which,
though intermediate between apes and man, is nevertheless more closely
allied to the apes, so on the other hand, much progress has been made since
Darwin's day in the discovery and description of the older human remains. 
Since the famous roof of a skull and the bones of the extremities belonging
to it were found in 1856 in the Neandertal near Dusseldorf, the most varied
judgments have been expressed in regard to the significance of the remains
and of the skull in particular.  In Darwin's "Descent of Man" there is only
a passing allusion to them ("Descent of Man", page 82.) in connection with
the discussion of the skull-capacity, although the investigations of
Schaaffhausen, King, and Huxley were then known.  I believe I have shown,
in a series of papers, that the skull in question belongs to a form
different from any of the races of man now living, and, with King and Cope,
I regard it as at least a different species from living man, and have
therefore designated it Homo primigenius.  The form unquestionably belongs
to the older Diluvium, and in the later Diluvium human forms already
appear, which agree in all essential points with existing human races.

As far back as 1886 the value of the Neandertal skull was greatly enhanced
by Fraipont's discovery of two skulls and skeletons from Spy in Belgium. 
These are excellently described by their discoverer ("La race humaine de
Neanderthal ou de Canstatt en Belgique".  "Arch. de Biologie", VII. 1887.),
and are regarded as belonging to the same group of forms as the Neandertal
remains.  In 1899 and the following years came the discovery by Gorjanovic-
Kramberger of different skeletal parts of at least ten individuals in a
cave near Krapina in Croatia.  (Gorjanovic-Kramberger "Der diluviale Mensch
von Krapina in Kroatien", 1906.)  It is in particular the form of the lower
jaw which is different from that of all recent races of man, and which
clearly indicates the lowly position of Homo primigenius, while, on the
other hand, the long-known skull from Gibraltar, which I ("Studien zur
Vorgeschichte des Menschen", 1906, pages 154 ff.) have referred to Homo
primigenius, and which has lately been examined in detail by Sollas ("On
the cranial and facial characters of the Neandertal Race".  "Trans. R.
Soc." London, vol. 199, 1908, page 281.), has made us acquainted with the
surprising shape of the eye-orbit, of the nose, and of the whole upper part
of the face.  Isolated lower jaws found at La Naulette in Belgium, and at
Malarnaud in France, increase our material which is now as abundant as
could be desired.  The most recent discovery of all is that of a skull dug
up in August of this year (1908) by Klaatsch and Hauser in the lower grotto
of the Le Moustier in Southern France, but this skull has not yet been
fully described.  Thus Homo primigenius must also be regarded as occupying
a position in the gap existing between the highest apes and the lowest
human races, Pithecanthropus, standing in the lower part of it, and Homo
primigenius in the higher, near man.  In order to prevent misunderstanding,
I should like here to emphasise that in arranging this structural series--
anthropoid apes, Pithecanthropus, Homo primigenius, Homo sapiens--I have no
intention of establishing it as a direct genealogical series.  I shall have
something to say in regard to the genetic relations of these forms, one to
another, when discussing the different theories of descent current at the
present day.  ((Since this essay was written Schoetensack has discovered
near Heidelberg and briefly described an exceedingly interesting lower jaw
from rocks between the Pliocene and Diluvial beds.  This exhibits
interesting differences from the forms of lower jaw of Homo primigenius. 
(Schoetensack "Der Unterkiefer des Homo heidelbergensis".  Leipzig, 1908.) 
G.S.))

In quite a different domain from that of morphological relationship, namely
in the physiological study of the blood, results have recently been gained
which are of the highest importance to the doctrine of descent.  Uhlenhuth,
Nuttall, and others have established the fact that the blood-serum of a
rabbit which has previously had human blood injected into it, forms a
precipitate with human blood.  This biological reaction was tried with a
great variety of mammalian species, and it was found that those far removed
from man gave no precipitate under these conditions.  But as in other cases
among mammals all nearly related forms yield an almost equally marked
precipitate, so the serum of a rabbit treated with human blood and then
added to the blood of an anthropoid ape gives ALMOST as marked a
precipitate as in human blood; the reaction to the blood of the lower
Eastern monkeys is weaker, that to the Western monkeys weaker still; indeed
in this last case there is only a slight clouding after a considerable time
and no actual precipitate.  The blood of the Lemuridae (Nuttall) gives no
reaction or an extremely weak one, that of the other mammals none whatever.
We have in this not only a proof of the literal blood-relationship between
man and apes, but the degree of relationship with the different main groups
of apes can be determined beyond possibility of mistake.

Finally, it must be briefly mentioned that in regard to remains of human
handicraft also, the material at our disposal has greatly increased of late
years, that, as a result of this, the opinions of archaeologists have
undergone many changes, and that, in particular, their views in regard to
the age of the human race have been greatly influenced.  There is a
tendency at the present time to refer the origin of man back to Tertiary
times.  It is true that no remains of Tertiary man have been found, but
flints have been discovered which, according to the opinion of most
investigators, bear traces either of use, or of very primitive workmanship.
Since Rutot's time, following Mortillet's example, investigators have
called these "eoliths," and they have been traced back by Verworn to the
Miocene of the Auvergne, and by Rutot even to the upper Oligocene. 
Although these eoliths are even nowadays the subject of many different
views, the preoccupation with them has kept the problem of the age of the
human race continually before us.

Geology, too, has made great progress since the days of Darwin and Lyell,
and has endeavoured with satisfactory results to arrange the human remains
of the Diluvial period in chronological order (Penck).  I do not intend to
enter upon the question of the primitive home of the human race; since the
space at my disposal will not allow of my touching even very briefly upon
all the departments of science which are concerned in the problem of the
descent of man.  How Darwin would have rejoiced over each of the
discoveries here briefly outlined!  What use he would have made of the new
and precious material, which would have prevented the discouragement from
which he suffered when preparing the second edition of "The Descent of
Man"!  But it was not granted to him to see this progress towards filling
up the gaps in his edifice of which he was so painfully conscious.

He did, however, have the satisfaction of seeing his ideas steadily gaining
ground, notwithstanding much hostility and deep-rooted prejudice.  Even in
the years between the appearance of "The Origin of Species" and of the
first edition of the "Descent", the idea of a natural descent of man, which
was only briefly indicated in the work of 1859, had been eagerly welcomed
in some quarters.  It has been already pointed out how brilliantly Huxley
contributed to the defence and diffusion of Darwin's doctrines, and how in
"Man's Place in Nature" he has given us a classic work as a foundation for
the doctrine of the descent of man.  As Huxley was Darwin's champion in
England, so in Germany Carl Vogt, in particular, made himself master of the
Darwinian ideas.  But above all it was Haeckel who, in energy, eagerness
for battle, and knowledge may be placed side by side with Huxley, who took
over the leadership in the controversy over the new conception of the
universe.  As far back as 1866, in his "Generelle Morphologie", he had
inquired minutely into the question of the descent of man, and not content
with urging merely the general theory of descent from lower animal forms,
he drew up for the first time genealogical trees showing the close
relationships of the different animal groups; the last of these illustrated
the relationships of Mammals, and among them of all groups of the Primates,
including man.  It was Haeckel's genealogical trees that formed the basis
of the special discussion of the relationships of man, in the sixth chapter
of Darwin's "Descent of Man".

In the last section of this essay I shall return to Haeckel's conception of
the special descent of man, the main features of which he still upholds,
and rightly so.  Haeckel has contributed more than any one else to the
spread of the Darwinian doctrine.

I can only allow myself a few words as to the spread of the theory of the
natural descent of man in other countries.  The Parisian anthropological
school, founded and guided by the genius of Broca, took up the idea of the
descent of man, and made many notable contributions to it (Broca,
Manouvrier, Mahoudeau, Deniker and others).  In England itself Darwin's
work did not die.  Huxley took care of that, for he, with his lofty and
unprejudiced mind, dominated and inspired English biology until his death
on June 29, 1895.  He had the satisfaction shortly before his death of
learning of Dubois' discovery, which he illustrated by a humorous sketch. 
("Life and Letters of Thomas Henry Huxley", Vol. II. page 394.)  But there
are still many followers in Darwin's footsteps in England.  Keane has
worked at the special genealogical tree of the Primates; Keith has inquired
which of the anthropoid apes has the greatest number of characters in
common with man; Morris concerns himself with the evolution of man in
general, especially with his acquisition of the erect position.  The recent
discoveries of Pithecanthropus and Homo primigenius are being vigorously
discussed; but the present writer is not in a position to form an opinion
of the extent to which the idea of descent has penetrated throughout
England generally.

In Italy independent work in the domain of the descent of man is being
produced, especially by Morselli; with him are associated, in the
investigation of related problems, Sergi and Giuffrida-Ruggeri.  From the
ranks of American investigators we may single out in particular the eminent
geologist Cope, who championed with much decision the idea of the specific
difference of Homo neandertalensis (primigenius) and maintained a more
direct descent of man from the fossil Lemuridae.  In South America too, in
Argentina, new life is stirring in this department of science.  Ameghino in
Buenos Ayres has awakened the fossil primates of the Pampas formation to
new life; he even believes that in Tetraprothomo, represented by a femur,
he has discovered a direct ancestor of man.  Lehmann-Nitsche is working at
the other side of the gulf between apes and men, and he describes a
remarkable first cervical vertebra (atlas) from Monte Hermoso as belonging
to a form which may bear the same relation to Homo sapiens in South America
as Homo primigenius does in the Old World.  After a minute investigation he
establishes a human species Homo neogaeus, while Ameghino ascribes this
atlas vertebra to his Tetraprothomo.

Thus throughout the whole scientific world there is arising a new life, an
eager endeavour to get nearer to Huxley's problema maximum, to penetrate
more deeply into the origin of the human race.  There are to-day very few
experts in anatomy and zoology who deny the animal descent of man in
general.  Religious considerations, old prejudices, the reluctance to
accept man, who so far surpasses mentally all other creatures, as descended
from "soulless" animals, prevent a few investigators from giving full
adherence to the doctrine.  But there are very few of these who still
postulate a special act of creation for man.  Although the majority of
experts in anatomy and zoology accept unconditionally the descent of man
from lower forms, there is much diversity of opinion among them in regard
to the special line of descent.

In trying to establish any special hypothesis of descent, whether by the
graphic method of drawing up genealogical trees or otherwise, let us always
bear in mind Darwin's words ("Descent of Man", page 229.) and use them as a
critical guiding line:  "As we have no record of the lines of descent, the
pedigree can be discovered only by observing the degrees of resemblance
between the beings which are to be classed."  Darwin carries this further
by stating "that resemblances in several unimportant structures, in useless
and rudimentary organs, or not now functionally active, or in an
embryological condition, are by far the most serviceable for
classification."  (Loc. cit.)  It has also to be remembered that NUMEROUS
separate points of agreement are of much greater importance than the amount
of similarity or dissimilarity in a few points.

The hypotheses as to descent current at the present day may be divided into
two main groups.  The first group seeks for the roots of the human race not
among any of the families of the apes--the anatomically nearest forms--nor
among their very similar but less specialised ancestral forms, the fossil
representatives of which we can know only in part, but, setting the monkeys
on one side, it seeks for them lower down among the fossil Eocene Pseudo-
lemuridae or Lemuridae (Cope), or even among the primitive pentadactylous
Eocene forms, which may either have led directly to the evolution of man
(Adloff), or have given rise to an ancestral form common to apes and men
(Klaatsch (Klaatsch in his last publications speaks in the main only of an
ancestral form common to men and anthropoid apes.), Giuffrida-Ruggeri). 
The common ancestral form, from which man and apes are thus supposed to
have arisen independently, may explain the numerous resemblances which
actually exist between them.  That is to say, all the characters upon which
the great structural resemblance between apes and man depends must have
been present in their common ancestor.  Let us take an example of such a
common character.  The bony external ear-passage is in general as highly
developed in the lower Eastern monkeys and the anthropoid apes as in man. 
This character must, therefore, have already been present in the common
primitive form.  In that case it is not easy to understand why the Western
monkeys have not also inherited the character, instead of possessing only a
tympanic ring.  But it becomes more intelligible if we assume that forms
with a primitive tympanic ring were the original type, and that from these
were evolved, on the one hand, the existing New World monkeys with
persistent tympanic ring, and on the other an ancestral form common to the
lower Old World monkeys, the anthropoid apes and man.  For man shares with
these the character in question, and it is also one of the "unimportant"
characters required by Darwin.  Thus we have two divergent lines arising
from the ancestral form, the Western monkeys (Platyrrhine) on the one hand,
and an ancestral form common to the lower Eastern monkeys, the anthropoid
apes, and man, on the other.  But considerations similar to those which
showed it to be impossible that man should have developed from an ancestor
common to him and the monkeys, yet outside of and parallel with these, may
be urged also against the likelihood of a parallel evolution of the lower
Eastern monkeys, the anthropoid apes, and man.  The anthropoid apes have in
common with man many characters which are not present in the lower Old
World monkeys.  These characters must therefore have been present in the
ancestral form common to the three groups.  But here, again, it is
difficult to understand why the lower Eastern monkeys should not also have
inherited these characters.  As this is not the case, there remains no
alternative but to assume divergent evolution from an indifferent form. 
The lower Eastern monkeys are carrying on the evolution in one direction--I
might almost say towards a blind alley--while anthropoids and men have
struck out a progressive path, at first in common, which explains the many
points of resemblance between them, without regarding man as derived
directly from the anthropoids.  Their many striking points of agreement
indicate a common descent, and cannot be explained as phenomena of
convergence.

I believe I have shown in the above sketch that a theory which derives man
directly from lower forms without regarding apes as transition-types leads
ad absurdum.  The close structural relationship between man and monkeys can
only be understood if both are brought into the same line of evolution.  To
trace man's line of descent directly back to the old Eocene mammals,
alongside of, but with no relation to these very similar forms, is to
abandon the method of exact comparison, which, as Darwin rightly
recognised, alone justifies us in drawing up genealogical trees on the
basis of resemblances and differences.  The farther down we go the more
does the ground slip from beneath our feet.  Even the Lemuridae show very
numerous divergent conditions, much more so the Eocene mammals (Creodonta,
Condylarthra), the chief resemblance of which to man consists in the
possession of pentadactylous hands and feet!  Thus the farther course of
the line of descent disappears in the darkness of the ancestry of the
mammals.  With just as much reason we might pass by the Vertebrates
altogether, and go back to the lower Invertebrates, but in that case it
would be much easier to say that man has arisen independently, and has
evolved, without relation to any animals, from the lowest primitive form to
his present isolated and dominant position.  But this would be to deny all
value to classification, which must after all be the ultimate basis of a
genealogical tree.  We can, as Darwin rightly observed, only infer the line
of descent from the degree of resemblance between single forms.  If we
regard man as directly derived from primitive forms very far back, we have
no way of explaining the many points of agreement between him and the
monkeys in general, and the anthropoid apes in particular.  These must
remain an inexplicable marvel.

I have thus, I trust, shown that the first class of special theories of
descent, which assumes that man has developed, parallel with the monkeys,
but without relation to them, from very low primitive forms cannot be
upheld, because it fails to take into account the close structural affinity
of man and monkeys.  I cannot but regard this hypothesis as lamentably
retrograde, for it makes impossible any application of the facts that have
been discovered in the course of the anatomical and embryological study of
man and monkeys, and indeed prejudges investigations of that class as
pointless.  The whole method is perverted; an unjustifiable theory of
descent is first formulated with the aid of the imagination, and then we
are asked to declare that all structural relations between man and monkeys,
and between the different groups of the latter, are valueless,--the fact
being that they are the only true basis on which a genealogical tree can be
constructed.

So much for this most modern method of classification, which has probably
found adherents because it would deliver us from the relationship to apes
which many people so much dislike.  In contrast to it we have the second
class of special hypotheses of descent, which keeps strictly to the nearest
structural relationships.  This is the only basis that justifies the
drawing up of a special hypothesis of descent.  If this fundamental
proposition be recognised, it will be admitted that the doctrine of special
descent upheld by Haeckel, and set forth in Darwin's "Descent of Man", is
still valid to-day.  In the genealogical tree, man's place is quite close
to the anthropoid apes; these again have as their nearest relatives the
lower Old World monkeys, and their progenitors must be sought among the
less differentiated Platyrrhine monkeys, whose most important characters
have been handed on to the present day New World monkeys.  How the
different genera are to be arranged within the general scheme indicated
depends in the main on the classificatory value attributed to individual
characters.  This is particularly true in regard to Pithecanthropus, which
I consider as the root of a branch which has sprung from the anthropoid ape
root and has led up to man; the latter I have designated the family of the
Hominidae.

For the rest, there are, as we have said, various possible ways of
constructing the narrower genealogy within the limits of this branch
including men and apes, and these methods will probably continue to change
with the accumulation of new facts.  Haeckel himself has modified his
genealogical tree of the Primates in certain details since the publication
of his "Generelle Morphologie" in 1866, but its general basis remains the
same.  (Haeckel's latest genealogical tree is to be found in his most
recent work, "Unsere Ahnenreihe".  Jena, 1908.)  All the special
genealogical trees drawn up on the lines laid down by Haeckel and Darwin--
and that of Dubois may be specially mentioned--are based, in general, on
the close relationship of monkeys and men, although they may vary in
detail.  Various hypotheses have been formulated on these lines, with
special reference to the evolution of man.  "Pithecanthropus" is regarded
by some authorities as the direct ancestor of man, by others as a side-
track failure in the attempt at the evolution of man.  The problem of the
monophyletic or polyphyletic origin of the human race has also been much
discussed.  Sergi (Sergi G. "Europa", 1908.) inclines towards the
assumption of a polyphyletic origin of the three main races of man, the
African primitive form of which has given rise also to the gorilla and
chimpanzee, the Asiatic to the Orang, the Gibbon, and Pithecanthropus. 
Kollmann regards existing human races as derived from small primitive races
(pigmies), and considers that Homo primigenius must have arisen in a
secondary and degenerative manner.

But this is not the place, nor have I the space to criticise the various
special theories of descent.  One, however, must receive particular notice.
According to Ameghino, the South American monkeys (Pitheculites) from the
oldest Tertiary of the Pampas are the forms from which have arisen the
existing American monkeys on the one hand, and on the other, the extinct
South American Homunculidae, which are also small forms.  From these last,
anthropoid apes and man have, he believes, been evolved.  Among the
progenitors of man, Ameghino reckons the form discovered by him
(Tetraprothomo), from which a South American primitive man, Homo pampaeus,
might be directly evolved, while on the other hand all the lower Old World
monkeys may have arisen from older fossil South American forms
(Clenialitidae), the distribution of which may be explained by the bridge
formerly existing between South America and Africa, as may be the
derivation of all existing human races from Homo pampaeus.  (See Ameghino's
latest paper, "Notas preliminares sobre el Tetraprothomo argentinus", etc. 
"Anales del Museo nacional de Buenos Aires", XVI. pages 107-242, 1907.) 
The fossil forms discovered by Ameghino deserve the most minute
investigation, as does also the fossil man from South America of which
Lehmann-Nitsche ("Nouvelles recherches sur la formation pampeenne et
l'homme fossile de la Republique Argentine".  "Rivista del Museo de la
Plata", T. XIV. pages 193-488.) has made a thorough study.

It is obvious that, notwithstanding the necessity for fitting man's line of
descent into the genealogical tree of the Primates, especially the apes,
opinions in regard to it differ greatly in detail.  This could not be
otherwise, since the different Primate forms, especially the fossil forms,
are still far from being exhaustively known.  But one thing remains
certain,--the idea of the close relationship between man and monkeys set
forth in Darwin's "Descent of Man".  Only those who deny the many points of
agreement, the sole basis of classification, and thus of a natural
genealogical tree, can look upon the position of Darwin and Haeckel as
antiquated, or as standing on an insufficient foundation.  For such a
genealogical tree is nothing more than a summarised representation of what
is known in regard to the degree of resemblance between the different
forms.

Darwin's work in regard to the descent of man has not been surpassed; the
more we immerse ourselves in the study of the structural relationships
between apes and man, the more is our path illumined by the clear light
radiating from him, and through his calm and deliberate investigation,
based on a mass of material in the accumulation of which he has never had
an equal.  Darwin's fame will be bound up for all time with the
unprejudiced investigation of the question of all questions, the descent of
the human race.


VIII.  CHARLES DARWIN AS AN ANTHROPOLOGIST.

By ERNST HAECKEL.
Professor of Zoology in the University of Jena.

The great advance that anthropology has made in the second half of the
nineteenth century is due in the first place, to Darwin's discovery of the
origin of man.  No other problem in the whole field of research is so
momentous as that of "Man's place in nature," which was justly described by
Huxley (1863) as the most fundamental of all questions.  Yet the scientific
solution of this problem was impossible until the theory of descent had
been established.

It is now a hundred years since the great French biologist Jean Lamarck
published his "Philosophie Zoologique".  By a remarkable coincidence the
year in which that work was issued, 1809, was the year of the birth of his
most distinguished successor, Charles Darwin.  Lamarck had already
recognised that the descent of man from a series of other Vertebrates--that
is, from a series of Ape-like Primates--was essentially involved in the
general theory of transformation which he had erected on a broad inductive
basis; and he had sufficient penetration to detect the agencies that had
been at work in the evolution of the erect bimanous man from the arboreal
and quadrumanous ape.  He had, however, few empirical arguments to advance
in support of his hypothesis, and it could not be established until the
further development of the biological sciences--the founding of comparative
embryology by Baer (1828) and of the cell-theory by Schleiden and Schwann
(1838), the advance of physiology under Johannes Muller (1833), and the
enormous progress of palaeontology and comparative anatomy between 1820 and
1860--provided this necessary foundation.  Darwin was the first to
coordinate the ample results of these lines of research.  With no less
comprehensiveness than discrimination he consolidated them as a basis of a
modified theory of descent, and associated with them his own theory of
natural selection, which we take to be distinctive of "Darwinism" in the
stricter sense.  The illuminating truth of these cumulative arguments was
so great in every branch of biology that, in spite of the most vehement
opposition, the battle was won within a single decade, and Darwin secured
the general admiration and recognition that had been denied to his
forerunner, Lamarck, up to the hour of his death (1829).

Before, however, we consider the momentous influence that Darwinism has had
in anthropology, we shall find it useful to glance at its history in the
course of the last half century, and notice the various theories that have
contributed to its advance.  The first attempt to give extensive expression
to the reform of biology by Darwin's work will be found in my "Generelle
Morphologie" (1866) ("Generelle Morphologie der Organismen", 2 vols.,
Berlin, 1866.) which was followed by a more popular treatment of the
subject in my "Naturliche Schopfungsgeschichte (1868) (English translation;
"The History of Creation", London, 1876.), a compilation from the earlier
work.  In the first volume of the "Generelle Morphologie" I endeavoured to
show the great importance of evolution in settling the fundamental
questions of biological philosophy, especially in regard to comparative
anatomy.  In the second volume I dealt broadly with the principle of
evolution, distinguishing ontogeny and phylogeny as its two coordinate main
branches, and associating the two in the Biogenetic Law.  The Law may be
formulated thus: "Ontogeny (embryology or the development of the
individual) is a concise and compressed recapitulation of phylogeny (the
palaeontological or genealogical series) conditioned by laws of heredity
and adaptation."  The "Systematic introduction to general evolution," with
which the second volume of the "Generelle Morphologie" opens, was the first
attempt to draw up a natural system of organisms (in harmony with the
principles of Lamarck and Darwin) in the form of a hypothetical pedigree,
and was provisionally set forth in eight genealogical tables.

In the nineteenth chapter of the "Generelle Morphologie"--a part of which
has been republished, without any alteration, after a lapse of forty years
--I made a critical study of Lamarck's theory of descent and of Darwin's
theory of selection, and endeavoured to bring the complex phenomena of
heredity and adaptation under definite laws for the first time.  Heredity I
divided into conservative and progressive:  adaptation into indirect (or
potential) and direct (or actual).  I then found it possible to give some
explanation of the correlation of the two physiological functions in the
struggle for life (selection), and to indicate the important laws of
divergence (or differentiation) and complexity (or division of labour),
which are the direct and inevitable outcome of selection.  Finally, I
marked off dysteleology as the science of the aimless (vestigial, abortive,
atrophied, and useless) organs and parts of the body.  In all this I worked
from a strictly monistic standpoint, and sought to explain all biological
phenomena on the mechanical and naturalistic lines that had long been
recognised in the study of inorganic nature.  Then (1866), as now, being
convinced of the unity of nature, the fundamental identity of the agencies
at work in the inorganic and the organic worlds, I discarded vitalism,
teleology, and all hypotheses of a mystic character.

It was clear from the first that it was essential, in the monistic
conception of evolution, to distinguish between the laws of conservative
and progressive heredity.  Conservative heredity maintains from generation
to generation the enduring characters of the species.  Each organism
transmits to its descendants a part of the morphological and physiological
qualities that it has received from its parents and ancestors.  On the
other hand, progressive heredity brings new characters to the species--
characters that were not found in preceding generations.  Each organism may
transmit to its offspring a part of the morphological and physiological
features that it has itself acquired, by adaptation, in the course of its
individual career, through the use or disuse of particular organs, the
influence of environment, climate, nutrition, etc.  At that time I gave the
name of "progressive heredity" to this inheritance of acquired characters,
as a short and convenient expression, but have since changed the term to
"transformative heredity" (as distinguished from conservative).  This term
is preferable, as inherited regressive modifications (degeneration,
retrograde metamorphisis, etc.) come under the same head.

Transformative heredity--or the transmission of acquired characters--is one
of the most important principles in evolutionary science.  Unless we admit
it most of the facts of comparative anatomy and physiology are
inexplicable.  That was the conviction of Darwin no less than of Lamarck,
of Spencer as well as Virchow, of Huxley as well as Gegenbaur, indeed of
the great majority of speculative biologists.  This fundamental principle
was for the first time called in question and assailed in 1885 by August
Weismann of Freiburg, the eminent zoologist to whom the theory of evolution
owes a great deal of valuable support, and who has attained distinction by
his extension of the theory of selection.  In explanation of the phenomena
of heredity he introduced a new theory, the "theory of the continuity of
the germ-plasm."  According to him the living substance in all organisms
consists of two quite distinct kinds of plasm, somatic and germinal.  The
permanent germ-plasm, or the active substance of the two germ-cells (egg-
cell and sperm-cell), passes unchanged through a series of generations, and
is not affected by environmental influences.  The environment modifies only
the soma-plasm, the organs and tissues of the body.  The modifications that
these parts undergo through the influence of the environment or their own
activity (use and habit), do not affect the germ-plasm, and cannot
therefore be transmitted.

This theory of the continuity of the germ-plasm has been expounded by
Weismann during the last twenty-four years in a number of able volumes, and
is regarded by many biologists, such as Mr Francis Galton, Sir E. Ray
Lankester, and Professor J. Arthur Thomson (who has recently made a
thoroughgoing defence of it in his important work "Heredity" (London,
1908.)), as the most striking advance in evolutionary science.  On the
other hand, the theory has been rejected by Herbert Spencer, Sir W. Turner,
Gegenbaur, Kolliker, Hertwig, and many others.  For my part I have, with
all respect for the distinguished Darwinian, contested the theory from the
first, because its whole foundation seems to me erroneous, and its
deductions do not seem to be in accord with the main facts of comparative
morphology and physiology.  Weismann's theory in its entirety is a finely
conceived molecular hypothesis, but it is devoid of empirical basis.  The
notion of the absolute and permanent independence of the germ-plasm, as
distinguished from the soma-plasm, is purely speculative; as is also the
theory of germinal selection.  The determinants, ids, and idants, are
purely hypothetical elements.  The experiments that have been devised to
demonstrate their existence really prove nothing.

It seems to me quite improper to describe this hypothetical structure as
"Neodarwinism."  Darwin was just as convinced as Lamarck of the
transmission of acquired characters and its great importance in the scheme
of evolution.  I had the good fortune to visit Darwin at Down three times
and discuss with him the main principles of his system, and on each
occasion we were fully agreed as to the incalculable importance of what I
call transformative inheritance.  It is only proper to point out that
Weismann's theory of the germ-plasm is in express contradiction to the
fundamental principles of Darwin and Lamarck.  Nor is it more acceptable in
what one may call its "ultradarwinism"--the idea that the theory of
selection explains everything in the evolution of the organic world.  This
belief in the "omnipotence of natural selection" was not shared by Darwin
himself.  Assuredly, I regard it as of the utmost value, as the process of
natural selection through the struggle for life affords an explanation of
the mechanical origin of the adapted organisation.  It solves the great
problem:  how could the finely adapted structure of the animal or plant
body be formed unless it was built on a preconceived plan?  It thus enables
us to dispense with the teleology of the metaphysician and the dualist, and
to set aside the old mythological and poetic legends of creation.  The idea
had occurred in vague form to the great Empedocles 2000 years before the
time of Darwin, but it was reserved for modern research to give it ample
expression.  Nevertheless, natural selection does not of itself give the
solution of all our evolutionary problems.  It has to be taken in
conjunction with the transformism of Lamarck, with which it is in complete
harmony.

The monumental greatness of Charles Darwin, who surpasses every other
student of science in the nineteenth century by the loftiness of his
monistic conception of nature and the progressive influence of his ideas,
is perhaps best seen in the fact that not one of his many successors has
succeeded in modifying his theory of descent in any essential point or in
discovering an entirely new standpoint in the interpretation of the organic
world.  Neither Nageli nor Weismann, neither De Vries nor Roux, has done
this.  Nageli, in his "Mechanisch-Physiologische Theorie der
Abstammungslehre" (Munich, 1884.), which is to a great extent in agreement
with Weismann, constructed a theory of the idioplasm, that represents it
(like the germ-plasm) as developing continuously in a definite direction
from internal causes.  But his internal "principle of progress" is at the
bottom just as teleological as the vital force of the Vitalists, and the
micellar structure of the idioplasm is just as hypothetical as the
"dominant" structure of the germ-plasm.  In 1889 Moritz Wagner sought to
explain the origin of species by migration and isolation, and on that basis
constructed a special "migration-theory."  This, however, is not out of
harmony with the theory of selection.  It merely elevates one single factor
in the theory to a predominant position.  Isolation is only a special case
of selection, as I had pointed out in the fifteenth chapter of my "Natural
history of creation".  The "mutation-theory" of De Vries ("Die
Mutationstheorie", Leipzig, 1903.), that would explain the origin of
species by sudden and saltatory variations rather than by gradual
modification, is regarded by many botanists as a great step in advance, but
it is generally rejected by zoologists.  It affords no explanation of the
facts of adaptation, and has no causal value.

Much more important than these theories is that of Wilhelm Roux ("Der Kampf
der Theile im Organismus", Leipzig, 1881.) of "the struggle of parts within
the organism, a supplementation of the theory of mechanical adaptation." 
He explains the functional autoformation of the purposive structure by a
combination of Darwin's principle of selection with Lamarck's idea of
transformative heredity, and applies the two in conjunction to the facts of
histology.  He lays stress on the significance of functional adaptation,
which I had described in 1866, under the head of cumulative adaptation, as
the most important factor in evolution.  Pointing out its influence in the
cell-life of the tissues, he puts "cellular selection" above "personal
selection," and shows how the finest conceivable adaptations in the
structure of the tissue may be brought about quite mechanically, without
preconceived plan.  This "mechanical teleology" is a valuable extension of
Darwin's monistic principle of selection to the whole field of cellular
physiology and histology, and is wholly destructive of dualistic vitalism.

The most important advance that evolution has made since Darwin and the
most valuable amplification of his theory of selection is, in my opinion,
the work of Richard Semon:  "Die Mneme als erhaltendes Prinzip im Wechsel
des organischen Geschehens" (Leipzig, 1904.).  He offers a psychological
explanation of the facts of heredity by reducing them to a process of
(unconscious) memory.  The physiologist Ewald Hering had shown in 1870 that
memory must be regarded as a general function of organic matter, and that
we are quite unable to explain the chief vital phenomena, especially those
of reproduction and inheritance, unless we admit this unconscious memory.
In my essay "Die Perigenesis der Plastidule" (Berlin, 1876.) I elaborated
this far-reaching idea, and applied the physical principle of transmitted
motion to the plastidules, or active molecules of plasm.  I concluded that
"heredity is the memory of the plastidules, and variability their power of
comprehension."  This "provisional attempt to give a mechanical explanation
of the elementary processes of evolution" I afterwards extended by showing
that sensitiveness is (as Carl Nageli, Ernst Mach, and Albrecht Rau express
it) a general quality of matter.  This form of panpsychism finds its
simplest expression in the "trinity of substance."

To the two fundamental attributes that Spinoza ascribed to substance--
Extension (matter as occupying space) and Cogitation (energy, force)--we
now add the third fundamental quality of Psychoma (sensitiveness, soul).  I
further elaborated this trinitarian conception of substance in the
nineteenth chapter of my "Die Lebenswunder" (1904) ("Wonders of Life",
London, 1904.), and it seems to me well calculated to afford a monistic
solution of many of the antitheses of philosophy.

This important Mneme-theory of Semon and the luminous physiological
experiments and observations associated with it not only throw considerable
light on transformative inheritance, but provide a sound physiological
foundation for the biogenetic law.  I had endeavoured to show in 1874, in
the first chapter of my "Anthropogenie" (English translation; "The
Evolution of Man", 2 volumes, London, 1879 and 1905.), that this
fundamental law of organic evolution holds good generally, and that there
is everywhere a direct causal connection between ontogeny and phylogeny. 
"Phylogenesis is the mechanical cause of ontogenesis"; in other words, "The
evolution of the stem or race is--in accordance with the laws of heredity
and adaptation--the real cause of all the changes that appear, in a
condensed form, in the development of the individual organism from the
ovum, in either the embryo or the larva."

It is now fifty years since Charles Darwin pointed out, in the thirteenth
chapter of his epoch-making "Origin of Species", the fundamental importance
of embryology in connection with his theory of descent:

"The leading facts in embryology, which are second to none in importance,
are explained on the principle of variations in the many descendants from
some one ancient progenitor, having appeared at a not very early period of
life, and having been inherited at a corresponding period."  ("Origin of
Species" (6th edition), page 396.)

He then shows that the striking resemblance of the embryos and larvae of
closely related animals, which in the mature stage belong to widely
different species and genera, can only be explained by their descent from a
common progenitor.  Fritz Muller made a closer study of these important
phenomena in the instructive instance of the Crustacean larva, as given in
his able work "Fur Darwin" (1864).  (English translation; "Facts and
Arguments for Darwin", London, 1869.)  I then, in 1872, extended the range
so as to include all animals (with the exception of the unicellular
Protozoa) and showed, by means of the theory of the Gastraea, that all
multicellular, tissue-forming animals--all the Metazoa--develop in
essentially the same way from the primary germ-layers.  I conceived the
embryonic form, in which the whole structure consists of only two layers of
cells, and is known as the gastrula, to be the ontogenetic recapitulation,
maintained by tenacious heredity, of a primitive common progenitor of all
the Metazoa, the Gastraea.  At a later date (1895) Monticelli discovered
that this conjectural ancestral form is still preserved in certain
primitive Coelenterata--Pemmatodiscus, Kunstleria, and the nearly-related
Orthonectida.

The general application of the biogenetic law to all classes of animals and
plants has been proved in my "Systematische Phylogenie".  (3 volumes,
Berlin, 1894-96.)  It has, however, been frequently challenged, both by
botanists and zoologists, chiefly owing to the fact that many have failed
to distinguish its two essential elements, palingenesis and cenogenesis. 
As early as 1874 I had emphasised, in the first chapter of my "Evolution of
Man", the importance of discriminating carefully between these two sets of
phenomena:

"In the evolutionary appreciation of the facts of embryology we must take
particular care to distinguish sharply and clearly between the primary,
palingenetic evolutionary processes and the secondary, cenogenetic
processes.  The palingenetic phenomena, or embryonic RECAPITULATIONS, are
due to heredity, to the transmission of characters from one generation to
another.  They enable us to draw direct inferences in regard to
corresponding structures in the development of the species (e.g. the chorda
or the branchial arches in all vertebrate embryos).  The cenogenetic
phenomena, on the other hand, or the embryonic VARIATIONS, cannot be traced
to inheritance from a mature ancestor, but are due to the adaptation of the
embryo or the larva to certain conditions of its individual development
(e.g. the amnion, the allantois, and the vitelline arteries in the embryos
of the higher vertebrates).  These cenogenetic phenomena are later
additions; we must not infer from them that there were corresponding
processes in the ancestral history, and hence they are apt to mislead."

The fundamental importance of these facts of comparative anatomy, atavism,
and the rudimentary organs, was pointed out by Darwin in the first part of
his classic work, "The Descent of Man and Selection in Relation to Sex"
(1871).  ("Descent of Man" (Popular Edition), page 927.)  In the "General
summary and conclusion" (chapter XXI.) he was able to say, with perfect
justice:  "He who is not content to look, like a savage, at the phenomena
of nature as disconnected, cannot any longer believe that man is the work
of a separate act of creation.  He will be forced to admit that the close
resemblance of the embryo of man to that, for instance, of a dog--the
construction of his skull, limbs, and whole frame on the same plan with
that of other mammals, independently of the uses to which the parts may be
put--the occasional reappearance of various structures, for instance of
several muscles, which man does not normally possess, but which are common
to the Quadrumana--and a crowd of analogous facts--all point in the
plainest manner to the conclusion that man is the co-descendant with other
mammals of a common progenitor."

These few lines of Darwin's have a greater scientific value than hundreds
of those so-called "anthropological treatises," which give detailed
descriptions of single organs, or mathematical tables with series of
numbers and what are claimed to be "exact analyses," but are devoid of
synoptic conclusions and a philosophical spirit.

Charles Darwin is not generally recognised as a great anthropologist, nor
does the school of modern anthropologists regard him as a leading
authority.  In Germany, especially, the great majority of the members of
the anthropological societies took up an attitude of hostility to him from
the very beginning of the controversy in 1860.  "The Descent of Man" was
not merely rejected, but even the discussion of it was forbidden on the
ground that it was "unscientific."

The centre of this inveterate hostility for thirty years--especially after
1877--was Rudolph Virchow of Berlin, the leading investigator in
pathological anatomy, who did so much for the reform of medicine by his
establishment of cellular pathology in 1858.  As a prominent representative
of "exact" or "descriptive" anthropology, and lacking a broad equipment in
comparative anatomy and ontogeny, he was unable to accept the theory of
descent.  In earlier years, and especially during his splendid period of
activity at Wurzburg (1848-1856), he had been a consistent free-thinker,
and had in a number of able articles (collected in his "Gesammelte
Abhandlungen") ("Gesammelte Abhandlungen zur wissenschaftlichen Medizin",
Berlin, 1856.) upheld the unity of human nature, the inseparability of body
and spirit.  In later years at Berlin, where he was more occupied with
political work and sociology (especially after 1866), he abandoned the
positive monistic position for one of agnosticism and scepticism, and made
concessions to the dualistic dogma of a spiritual world apart from the
material frame.

In the course of a Scientific Congress at Munich in 1877 the conflict of
these antithetic views of nature came into sharp relief.  At this memorable
Congress I had undertaken to deliver the first address (September 18th) on
the subject of "Modern evolution in relation to the whole of science."  I
maintained that Darwin's theory not only solved the great problem of the
origin of species, but that its implications, especially in regard to the
nature of man, threw considerable light on the whole of science, and on
anthropology in particular.  The discovery of the real origin of man by
evolution from a long series of mammal ancestors threw light on his place
in nature in every aspect, as Huxley had already shown in his excellent
lectures of 1863.  Just as all the organs and tissues of the human body had
originated from those of the nearest related mammals, certain ape-like
forms, so we were bound to conclude that his mental qualities also had been
derived from those of his extinct primate ancestor.

This monistic view of the origin and nature of man, which is now admitted
by nearly all who have the requisite acquaintance with biology, and
approach the subject without prejudice, encountered a sharp opposition at
that time.  The opposition found its strongest expression in an address
that Virchow delivered at Munich four days afterwards (September 22nd), on
"The freedom of science in the modern State."  He spoke of the theory of
evolution as an unproved hypothesis, and declared that it ought not to be
taught in the schools, because it was dangerous to the State.  "We must
not," he said, "teach that man has descended from the ape or any other
animal."  When Darwin, usually so lenient in his judgment, read the English
translation of Virchow's speech, he expressed his disapproval in strong
terms.  But the great authority that Virchow had--an authority well founded
in pathology and sociology--and his prestige as President of the German
Anthropological Society, had the effect of preventing any member of the
Society from raising serious opposition to him for thirty years.  Numbers
of journals and treatises repeated his dogmatic statement:  "It is quite
certain that man has descended neither from the ape nor from any other
animal."  In this he persisted till his death in 1902.  Since that time the
whole position of German anthropology has changed.  The question is no
longer whether man was created by a distinct supernatural act or evolved
from other mammals, but to which line of the animal hierarchy we must look
for the actual series of ancestors.  The interested reader will find an
account of this "battle of Munich" (1877) in my three Berlin lectures
(April, 1905) ("Der Kampf um die Entwickelungs-Gedanken".  (English
translation; "Last Words on Evolution", London, 1906.)

The main points in our genealogical tree were clearly recognised by Darwin
in the sixth chapter of the "Descent of Man".  Lowly organised fishes, like
the lancelet (Amphioxus), are descended from lower invertebrates resembling
the larvae of an existing Tunicate (Appendicularia).  From these primitive
fishes were evolved higher fishes of the ganoid type and others of the type
of Lepidosiren (Dipneusta).  It is a very small step from these to the
Amphibia:

"In the class of mammals the steps are not difficult to conceive which led
from the ancient Monotremata to the ancient Marsupials; and from these to
the early progenitors of the placental mammals.  We may thus ascend to the
Lemuridae; and the interval is not very wide from these to the Simiadae. 
The Simiadae then branched off into two great stems, the New World and Old
World monkeys; and from the latter, at a remote period, Man, the wonder and
glory of the Universe, proceeded."  ("Descent of Man" (Popular Edition),
page 255.)

In these few lines Darwin clearly indicated the way in which we were to
conceive our ancestral series within the vertebrates.  It is fully
confirmed by all the arguments of comparative anatomy and embryology, of
palaeontology and physiology; and all the research of the subsequent forty
years has gone to establish it.  The deep interest in geology which Darwin
maintained throughout his life and his complete knowledge of palaeontology
enabled him to grasp the fundamental importance of the palaeontological
record more clearly than anthropologists and zoologists usually do.

There has been much debate in subsequent decades whether Darwin himself
maintained that man was descended from the ape, and many writers have
sought to deny it.  But the lines I have quoted verbatim from the
conclusion of the sixth chapter of the "Descent of Man" (1871) leave no
doubt that he was as firmly convinced of it as was his great precursor Jean
Lamarck in 1809.  Moreover, Darwin adds, with particular explicitness, in
the "general summary and conclusion" (chapter XXI.) of that standard work
("Descent of Man", page 930.):

"By considering the embryological structure of man--the homologies which he
presents with the lower animals,--the rudiments which he retains,--and the
reversions to which he is liable, we can partly recall in imagination the
former condition of our early progenitors; and can approximately place them
in their proper place in the zoological series.  We thus learn that man is
descended from a hairy, tailed quadruped, probably arboreal in its habits,
and an inhabitant of the Old World.  This creature, if its whole structure
had been examined by a naturalist, would have been classed amongst the
Quadrumana, as surely as the still more ancient progenitor of the Old and
New World monkeys."

These clear and definite lines leave no doubt that Darwin--so critical and
cautious in regard to important conclusions--was quite as firmly convinced
of the descent of man from the apes (the Catarrhinae, in particular) as
Lamarck was in 1809 and Huxley in 1863.

It is to be noted particularly that, in these and other observations on the
subject, Darwin decidedly assumes the monophyletic origin of the mammals,
including man.  It is my own conviction that this is of the greatest
importance.  A number of difficult questions in regard to the development
of man, in respect of anatomy, physiology, psychology, and embryology, are
easily settled if we do not merely extend our progonotaxis to our nearest
relatives, the anthropoid apes and the tailed monkeys from which these have
descended, but go further back and find an ancestor in the group of the
Lemuridae, and still further back to the Marsupials and Monotremata.  The
essential identity of all the Mammals in point of anatomical structure and
embryonic development--in spite of their astonishing differences in
external appearance and habits of life--is so palpably significant that
modern zoologists are agreed in the hypothesis that they have all sprung
from a common root, and that this root may be sought in the earlier
Palaeozoic Amphibia.

The fundamental importance of this comparative morphology of the Mammals,
as a sound basis of scientific anthropology, was recognised just before the
beginning of the nineteenth century, when Lamarck first emphasised (1794)
the division of the animal kingdom into Vertebrates and Invertebrates. 
Even thirteen years earlier (1781), when Goethe made a close study of the
mammal skeleton in the Anatomical Institute at Jena, he was intensely
interested to find that the composition of the skull was the same in man as
in the other mammals.  His discovery of the os intermaxillare in man
(1784), which was contradicted by most of the anatomists of the time, and
his ingenious "vertebral theory of the skull," were the splendid fruit of
his morphological studies.  They remind us how Germany's greatest
philosopher and poet was for many years ardently absorbed in the
comparative anatomy of man and the mammals, and how he divined that their
wonderful identity in structure was no mere superficial resemblance, but
pointed to a deep internal connection.  In my "Generelle Morphologie"
(1866), in which I published the first attempts to construct phylogenetic
trees, I have given a number of remarkable theses of Goethe, which may be
called "phyletic prophecies."  They justify us in regarding him as a
precursor of Darwin.

In the ensuing forty years I have made many conscientious efforts to
penetrate further along that line of anthropological research that was
opened up by Goethe, Lamarck, and Darwin.  I have brought together the many
valuable results that have constantly been reached in comparative anatomy,
physiology, ontogeny, and palaeontology, and maintained the effort to
reform the classification of animals and plants in an evolutionary sense.
The first rough drafts of pedigrees that were published in the "Generelle
Morphologie" have been improved time after time in the ten editions of my
"Naturaliche Schopfungsgeschichte" (1868-1902).  (English translation; "The
History of Creation", London, 1876.)  A sounder basis for my phyletic
hypotheses, derived from a discriminating combination of the three great
records--morphology, ontogeny, and palaeontology--was provided in the three
volumes of my "Systematische Phylogenie (Berlin, 1894-96.) (1894 Protists
and Plants, 1895 Vertebrates, 1896 Invertebrates).  In my "Anthropogenie"
(Leipzig, 1874, 5th edition 1905.  English translation; "The Evolution of
Man", London, 1905.) I endeavoured to employ all the known facts of
comparative ontogeny (embryology) for the purpose of completing my scheme
of human phylogeny (evolution).  I attempted to sketch the historical
development of each organ of the body, beginning with the most elementary
structures in the germ-layers of the Gastraea.  At the same time I drew up
a corrected statement of the most important steps in the line of our
ancestral series.

At the fourth International Congress of Zoology at Cambridge (August 26th,
1898) I delivered an address on "Our present knowledge of the Descent of
Man."  It was translated into English, enriched with many valuable notes
and additions, by my friend and pupil in earlier days Dr Hans Gadow
(Cambridge), and published under the title:  "The Last Link; our present
knowledge of the Descent of Man".  (London, 1898.)  The determination of
the chief animal forms that occur in the line of our ancestry is there
restricted to thirty types, and these are distributed in six main groups.

The first half of this "Progonotaxis hominis," which has no support from
fossil evidence, comprises three groups:  (i) Protista (unicellular
organisms, 1-5:  (ii) Invertebrate Metazoa (Coelenteria 6-8, Vermalia 9-
11):  (iii) Monorrhine Vertebrates (Acrania 12-13, Cyclostoma 14-15).  The
second half, which is based on fossil records, also comprises three groups: 
(iv) Palaeozoic cold-blooded Craniota (Fishes 16-18, Amphibia 19, Reptiles
20:  (v) Mesozoic Mammals (Monotrema 21, Marsupialia 22, Mallotheria 23): 
(vi) Cenozoic Primates (Lemuridae 24-25, Tailed Apes 26-27, Anthropomorpha
28-30).  An improved and enlarged edition of this hypothetic "Progonotaxis
hominis" was published in 1908, in my essay "Unsere Ahnenreihe". 
("Festschrift zur 350-jahrigen Jubelfeier der Thuringer Universitat Jena". 
Jena, 1908.)

If I have succeeded in furthering, in some degree, by these anthropological
works, the solution of the great problem of Man's place in nature, and
particularly in helping to trace the definite stages in our ancestral
series, I owe the success, not merely to the vast progress that biology has
made in the last half century, but largely to the luminous example of the
great investigators who have applied themselves to the problem, with so
much assiduity and genius, for a century and a quarter--I mean Goethe and
Lamarck, Gegenbaur and Huxley, but, above all, Charles Darwin.  It was the
great genius of Darwin that first brought together the scattered material
of biology and shaped it into that symmetrical temple of scientific
knowledge, the theory of descent.  It was Darwin who put the crown on the
edifice by his theory of natural selection.  Not until this broad inductive
law was firmly established was it possible to vindicate the special
conclusion, the descent of man from a series of other Vertebrates.  By his
illuminating discovery Darwin did more for anthropology than thousands of
those writers, who are more specifically titled anthropologists, have done
by their technical treatises.  We may, indeed, say that it is not merely as
an exact observer and ingenious experimenter, but as a distinguished
anthropologist and far-seeing thinker, that Darwin takes his place among
the greatest men of science of the nineteenth century.

To appreciate fully the immortal merit of Darwin in connection with
anthropology, we must remember that not only did his chief work, "The
Origin of Species", which opened up a new era in natural history in 1859,
sustain the most virulent and widespread opposition for a lengthy period,
but even thirty years later, when its principles were generally recognised
and adopted, the application of them to man was energetically contested by
many high scientific authorities.  Even Alfred Russel Wallace, who
discovered the principle of natural selection independently in 1858, did
not concede that it was applicable to the higher mental and moral qualities
of man.  Dr Wallace still holds a spiritualist and dualist view of the
nature of man, contending that he is composed of a material frame
(descended from the apes) and an immortal immaterial soul (infused by a
higher power).  This dual conception, moreover, is still predominant in the
wide circles of modern theology and metaphysics, and has the general and
influential adherence of the more conservative classes of society.

In strict contradiction to this mystical dualism, which is generally
connected with teleology and vitalism, Darwin always maintained the
complete unity of human nature, and showed convincingly that the
psychological side of man was developed, in the same way as the body, from
the less advanced soul of the anthropoid ape, and, at a still more remote
period, from the cerebral functions of the older vertebrates.  The eighth
chapter of the "Origin of Species", which is devoted to instinct, contains
weighty evidence that the instincts of animals are subject, like all other
vital processes, to the general laws of historic development.  The special
instincts of particular species were formed by adaptation, and the
modifications thus acquired were handed on to posterity by heredity; in
their formation and preservation natural selection plays the same part as
in the transformation of every other physiological function.  The higher
moral qualities of civilised man have been derived from the lower mental
functions of the uncultivated barbarians and savages, and these in turn
from the social instincts of the mammals.  This natural and monistic
psychology of Darwin's was afterwards more fully developed by his friend
George Romanes in his excellent works "Mental Evolution in Animals" and
"Mental Evolution in Man".  (London, 1885; 1888.)

Many valuable and most interesting contributions to this monistic
psychology of man were made by Darwin in his fine work on "The Descent of
Man and Selection in Relation to Sex", and again in his supplementary work,
"The Expression of the Emotions in Man and Animals".  To understand the
historical development of Darwin's anthropology one must read his life and
the introduction to "The Descent of Man".  From the moment that he was
convinced of the truth of the principle of descent--that is to say, from
his thirtieth year, in 1838--he recognised clearly that man could not be
excluded from its range.  He recognised as a logical necessity the
important conclusion that "man is the co-descendant with other species of
some ancient, lower, and extinct form."  For many years he gathered notes
and arguments in support of this thesis, and for the purpose of showing the
probable line of man's ancestry.  But in the first edition of "The Origin
of Species" (1859) he restricted himself to the single line, that by this
work "light would be thrown on the origin of man and his history."  In the
fifty years that have elapsed since that time the science of the origin and
nature of man has made astonishing progress, and we are now fairly agreed
in a monistic conception of nature that regards the whole universe,
including man, as a wonderful unity, governed by unalterable and eternal
laws.  In my philosophical book "Die Weltratsel" (1899) ("The Riddle of the
Universe", London, 1900.) and in the supplementary volume "Die
Lebenswunder" (1904) "The Wonders of Life", London, 1904.), I have
endeavoured to show that this pure monism is securely established, and that
the admission of the all-powerful rule of the same principle of evolution
throughout the universe compels us to formulate a single supreme law--the
all-embracing "Law of Substance," or the united laws of the constancy of
matter and the conservation of energy.  We should never have reached this
supreme general conception if Charles Darwin--a "monistic philosopher" in
the true sense of the word--had not prepared the way by his theory of
descent by natural selection, and crowned the great work of his life by the
association of this theory with a naturalistic anthropology.


IX.  SOME PRIMITIVE THEORIES OF THE ORIGIN OF MAN.

By J.G. FRAZER.
Fellow of Trinity College, Cambridge.

On a bright day in late autumn a good many years ago I had ascended the
hill of Panopeus in Phocis to examine the ancient Greek fortifications
which crest its brow.  It was the first of November, but the weather was
very hot; and when my work among the ruins was done, I was glad to rest
under the shade of a clump of fine holly-oaks, to inhale the sweet
refreshing perfume of the wild thyme which scented all the air, and to
enjoy the distant prospects, rich in natural beauty, rich too in memories
of the legendary and historic past.  To the south the finely-cut peak of
Helicon peered over the low intervening hills.  In the west loomed the
mighty mass of Parnassus, its middle slopes darkened by pine-woods like
shadows of clouds brooding on the mountain-side; while at its skirts
nestled the ivy-mantled walls of Daulis overhanging the deep glen, whose
romantic beauty accords so well with the loves and sorrows of Procne and
Philomela, which Greek tradition associated with the spot.  Northwards,
across the broad plain to which the hill of Panopeus descends, steep and
bare, the eye rested on the gap in the hills through which the Cephissus
winds his tortuous way to flow under grey willows, at the foot of barren
stony hills, till his turbid waters lose themselves, no longer in the vast
reedy swamps of the now vanished Copaic Lake, but in the darkness of a
cavern in the limestone rock.  Eastward, clinging to the slopes of the
bleak range of which the hill of Panopeus forms part, were the ruins of
Chaeronea, the birthplace of Plutarch; and out there in the plain was
fought the disastrous battle which laid Greece at the feet of Macedonia. 
There, too, in a later age East and West met in deadly conflict, when the
Roman armies under Sulla defeated the Asiatic hosts of Mithridates.  Such
was the landscape spread out before me on one of those farewell autumn days
of almost pathetic splendour, when the departing summer seems to linger
fondly, as if loth to resign to winter the enchanted mountains of Greece. 
Next day the scene had changed:  summer was gone.  A grey November mist
hung low on the hills which only yesterday had shone resplendent in the
sun, and under its melancholy curtain the dead flat of the Chaeronean
plain, a wide treeless expanse shut in by desolate slopes, wore an aspect
of chilly sadness befitting the battlefield where a nation's freedom was
lost.

But crowded as the prospect from Panopeus is with memories of the past, the
place itself, now so still and deserted, was once the scene of an event
even more ancient and memorable, if Greek story-tellers can be trusted. 
For here, they say, the sage Prometheus created our first parents by
fashioning them, like a potter, out of clay.  (Pausanias X. 4.4.  Compare
Apollodorus, "Bibliotheca", I. 7. 1; Ovid, "Metamorph." I. 82 sq.; Juvenal,
"Sat". XIV. 35.  According to another version of the tale, this creation of
mankind took place not at Panopeus, but at Iconium in Lycaonia.  After the
original race of mankind had been destroyed in the great flood of
Deucalion, the Greek Noah, Zeus commanded Prometheus and Athena to create
men afresh by moulding images out of clay, breathing the winds into them,
and making them live.  See "Etymologicum Magnum", s.v. "'Ikonion", pages
470 sq.  It is said that Prometheus fashioned the animals as well as men,
giving to each kind of beast its proper nature.  See Philemon, quoted by
Stobaeus, "Florilegium" II. 27.  The creation of man by Prometheus is
figured on ancient works of art.  See J. Toutain, "Etudes de Mythologie et
d'Histoire des Religions Antiques" (Paris, 1909), page 190.  According to
Hesiod ("Works and Days", 60 sqq.) it was Hephaestus who at the bidding of
Zeus moulded the first woman out of moist earth.)  The very spot where he
did so can still be seen.  It is a forlorn little glen or rather hollow
behind the hill of Panopeus, below the ruined but still stately walls and
towers which crown the grey rocks of the summit.  The glen, when I visited
it that hot day after the long drought of summer, was quite dry; no water
trickled down its bushy sides, but in the bottom I found a reddish
crumbling earth, a relic perhaps of the clay out of which the potter
Prometheus moulded the Greek Adam and Eve.  In a volume dedicated to the
honour of one who has done more than any other in modern times to shape the
ideas of mankind as to their origin it may not be out of place to recall
this crude Greek notion of the creation of the human race, and to compare
or contrast it with other rudimentary speculations of primitive peoples on
the same subject, if only for the sake of marking the interval which
divides the childhood from the maturity of science.

The simple notion that the first man and woman were modelled out of clay by
a god or other superhuman being is found in the traditions of many peoples. 
This is the Hebrew belief recorded in Genesis:  "The Lord God formed man of
the dust of the ground, and breathed into his nostrils the breath of life;
and man became a living soul."  (Genesis ii.7.)  To the Hebrews this
derivation of our species suggested itself all the more naturally because
in their language the word for "ground" (adamah) is in form the feminine of
the word for man (adam).  (S.R. Driver and W.H.Bennett, in their
commentaries on Genesis ii. 7.)  From various allusions in Babylonian
literature it would seem that the Babylonians also conceived man to have
been moulded out of clay.  (H. Zimmern, in E. Schrader's "Die
Keilinschriften und das Alte Testament"3 (Berlin, 1902), page 506.) 
According to Berosus, the Babylonian priest whose account of creation has
been preserved in a Greek version, the god Bel cut off his own head, and
the other gods caught the flowing blood, mixed it with earth, and fashioned
men out of the bloody paste; and that, they said, is why men are so wise,
because their mortal clay is tempered with divine blood.  (Eusebius,
"Chronicon", ed. A. Schoene, Vol. I. (Berlin, 1875), col. 16.)  In Egyptian
mythology Khnoumou, the Father of the gods, is said to have moulded men out
of clay.  (G. Maspero, "Histoire Ancienne des Peuples de l'Orient
Classique", I. (Paris, 1895), page 128.)  We cannot doubt that such crude
conceptions of the origin of our race were handed down to the civilised
peoples of antiquity by their savage or barbarous forefathers.  Certainly
stories of the same sort are known to be current among savages and
barbarians.

Thus the Australian blacks in the neighbourhood of Melbourne said that
Pund-jel, the creator, cut three large sheets of bark with his big knife. 
On one of these he placed some clay and worked it up with his knife into a
proper consistence.  He then laid a portion of the clay on one of the other
pieces of bark and shaped it into a human form; first he made the feet,
then the legs, then the trunk, the arms, and the head.  Thus he made a clay
man on each of the two pieces of bark; and being well pleased with them he
danced round them for joy.  Next he took stringy bark from the Eucalyptus
tree, made hair of it, and stuck it on the heads of his clay men.  Then he
looked at them again, was pleased with his work, and again danced round
them for joy.  He then lay down on them, blew his breath hard into their
mouths, their noses, and their navels; and presently they stirred, spoke,
and rose up as full-grown men.  (R. Brough Smyth, "The Aborigines of
Victoria" (Melbourne, 1878), I. 424.  This and many of the following
legends of creation have been already cited by me in a note on Pausanias X.
4. 4 ("Pausanias's Description of Greece, translated with a Commentary"
(London, 1898), Vol V. pages 220 sq.).)  The Maoris of New Zealand say that
Tiki made man after his own image.  He took red clay, kneaded it, like the
Babylonian Bel, with his own blood, fashioned it in human form, and gave
the image breath.  As he had made man in his own likeness he called him
Tiki-ahua or Tiki's likeness.  (R. Taylor "Te Ika A Maui, or New Zealand
and its Inhabitants", Second Edition (London, 1870), page 117.  Compare E.
Shortland, "Maori Religion and Mythology" (London, 1882), pages 21 sq.)  A
very generally received tradition in Tahiti was that the first human pair
was made by Taaroa, the chief god.  They say that after he had formed the
world he created man out of red earth, which was also the food of mankind
until bread-fruit was produced.  Further, some say that one day Taaroa
called for the man by name, and when he came he made him fall asleep.  As
he slept, the creator took out one of his bones (ivi) and made a woman of
it, whom he gave to the man to be his wife, and the pair became the
progenitors of mankind.  This narrative was taken down from the lips of the
natives in the early years of the mission to Tahiti.  The missionary who
records it observes:  "This always appeared to me a mere recital of the
Mosaic account of creation, which they had heard from some European, and I
never placed any reliance on it, although they have repeatedly told me it
was a tradition among them before any foreigner arrived.  Some have also
stated that the woman's name was Ivi, which would be by them pronounced as
if written "Eve".  "Ivi" is an aboriginal word, and not only signifies a
bone, but also a widow, and a victim slain in war.  Notwithstanding the
assertion of the natives, I am disposed to think that "Ivi", or Eve, is the
only aboriginal part of the story, as far as it respects the mother of the
human race.  (W. Ellis, "Polynesian Researches", Second Edition (London,
1832), I. 110 sq.  "Ivi" or "iwi" is the regular word for "bone" in the
various Polynesian languages.  See E. Tregear, "The Maori-Polynesian
Comparative Dictionary" (Wellington, New Zealand, 1891), page 109.) 
However, the same tradition has been recorded in other parts of Polynesia
besides Tahiti.  Thus the natives of Fakaofo or Bowditch Island say that
the first man was produced out of a stone.  After a time he bethought him
of making a woman.  So he gathered earth and moulded the figure of a woman
out of it, and having done so he took a rib out of his left side and thrust
it into the earthen figure, which thereupon started up a live woman.  He
called her Ivi (Eevee) or "rib" and took her to wife, and the whole human
race sprang from this pair.  (G. Turner, "Samoa" (London, 1884), pages 267
sq.)  The Maoris also are reported to believe that the first woman was made
out of the first man's ribs.  (J.L. Nicholas, "Narrative of a Voyage to New
Zealand" (London, 1817), I. 59, who writes "and to add still more to this
strange coincidence, the general term for bone is 'Hevee'.")  This wide
diffusion of the story in Polynesia raises a doubt whether it is merely, as
Ellis thought, a repetition of the Biblical narrative learned from
Europeans.  In Nui, or Netherland Island, it was the god Aulialia who made
earthen models of a man and woman, raised them up, and made them live.  He
called the man Tepapa and the woman Tetata.  (G. Turner, "Samoa", pages 300
sq.)

In the Pelew Islands they say that a brother and sister made men out of
clay kneaded with the blood of various animals, and that the characters of
these first men and of their descendants were determined by the characters
of the animals whose blood had been kneaded with the primordial clay; for
instance, men who have rat's blood in them are thieves, men who have
serpent's blood in them are sneaks, and men who have cock's blood in them
are brave.  (J. Kubary, "Die Religion der Pelauer", in A. Bastian's
"Allerlei aus Volks- und Menschenkunde" (Berlin, 1888), I. 3, 56.) 
According to a Melanesian legend, told in Mota, one of the Banks Islands,
the hero Qat moulded men of clay, the red clay from the marshy river-side
at Vanua Lava.  At first he made men and pigs just alike, but his brothers
remonstrated with him, so he beat down the pigs to go on all fours and made
men walk upright.  Qat fashioned the first woman out of supple twigs, and
when she smiled he knew she was a living woman.  (R.H. Codrington, "The
Melanesians" (Oxford, 1891), page 158.)  A somewhat different version of
the Melanesian story is told at Lakona, in Santa Maria.  There they say
that Qat and another spirit ("vui") called Marawa both made men.  Qat made
them out of the wood of dracaena-trees.  Six days he worked at them,
carving their limbs and fitting them together.  Then he allowed them six
days to come to life.  Three days he hid them away, and three days more he
worked to make them live.  He set them up and danced to them and beat his
drum, and little by little they stirred, till at last they could stand all
by themselves.  Then Qat divided them into pairs and called each pair
husband and wife.  Marawa also made men out of a tree, but it was a
different tree, the tavisoviso.  He likewise worked at them six days, beat
his drum, and made them live, just as Qat did.  But when he saw them move,
he dug a pit and buried them in it for six days, and then, when he scraped
away the earth to see what they were doing, he found them all rotten and
stinking.  That was the origin of death.  (R.H. Codrington op. cit., pages
157 sq.)

The inhabitants of Noo-Hoo-roa, in the Kei Islands say that their ancestors
were fashioned out of clay by the supreme god, Dooadlera, who breathed life
into the clay figures.  (C.M. Pleyte, "Ethnographische Beschrijving der
Kei-Eilanden", "Tijdschrift van het Nederlandsch Aardrijkskundig
Genootschap", Tweede Serie X. (1893), page 564.)  The aborigines of
Minahassa, in the north of Celebes, say that two beings called Wailan
Wangko and Wangi were alone on an island, on which grew a cocoa-nut tree. 
Said Wailan Wangko to Wangi, "Remain on earth while I climb up the tree." 
Said Wangi to Wailan Wangko, "Good."  But then a thought occurred to Wangi
and he climbed up the tree to ask Wailan Wangko why he, Wangi, should
remain down there all alone.  Said Wailan Wangko to Wangi, "Return and take
earth and make two images, a man and a woman."  Wangi did so, and both
images were men who could move but could not speak.  So Wangi climbed up
the tree to ask Wailan Wangko, "How now?  The two images are made, but they
cannot speak."  Said Wailan Wangko to Wangi, "Take this ginger and go and
blow it on the skulls and the ears of these two images, that they may be
able to speak; call the man Adam and the woman Ewa."  (N. Graafland "De
Minahassa" (Rotterdam, 1869), I. pages 96 sq.)  In this narrative the names
of the man and woman betray European influence, but the rest of the story
may be aboriginal.  The Dyaks of Sakarran in British Borneo say that the
first man was made by two large birds.  At first they tried to make men out
of trees, but in vain.  Then they hewed them out of rocks, but the figures
could not speak.  Then they moulded a man out of damp earth and infused
into his veins the red gum of the kumpang-tree.  After that they called to
him and he answered; they cut him and blood flowed from his wounds. 
(Horsburgh, quoted by H. Ling Roth, "The Natives of Sarawak and of British
North Borneo" (London, 1896), I. pages 299 sq.  Compare The Lord Bishop of
Labuan, "On the Wild Tribes of the North-West Coast of Borneo,"
"Transactions of the Ethnological Society of London", New Series, II.
(1863), page 27.)

The Kumis of South-Eastern India related to Captain Lewin, the Deputy
Commissioner of Hill Tracts, the following tradition of the creation of
man.  "God made the world and the trees and the creeping things first, and
after that he set to work to make one man and one woman, forming their
bodies of clay; but each night, on the completion of his work, there came a
great snake, which, while God was sleeping, devoured the two images.  This
happened twice or thrice, and God was at his wit's end, for he had to work
all day, and could not finish the pair in less than twelve hours; besides,
if he did not sleep, he would be no good," said Captain Lewin's informant. 
"If he were not obliged to sleep, there would be no death, nor would
mankind be afflicted with illness.  It is when he rests that the snake
carries us off to this day.  Well, he was at his wit's end, so at last he
got up early one morning and first made a dog and put life into it, and
that night, when he had finished the images, he set the dog to watch them,
and when the snake came, the dog barked and frightened it away.  This is
the reason at this day that when a man is dying the dogs begin to howl; but
I suppose God sleeps heavily now-a-days, or the snake is bolder, for men
die all the same."  (Capt. T.H. Lewin, "Wild Races of South-Eastern India"
(London, 1870), pages 224-26.)  The Khasis of Assam tell a similar tale. 
(A. Bastian, "Volkerstamme am Brahmaputra und verwandtschaftliche Nachbarn"
(Berlin, 1883), page 8; Major P.R.T. Gurdon, "The Khasis" (London, 1907),
page 106.)

The Ewe-speaking tribes of Togo-land, in West Africa, think that God still
makes men out of clay.  When a little of the water with which he moistens
the clay remains over, he pours it on the ground and out of that he makes
the bad and disobedient people.  When he wishes to make a good man he makes
him out of good clay; but when he wishes to make a bad man, he employs only
bad clay for the purpose.  In the beginning God fashioned a man and set him
on the earth; after that he fashioned a woman.  The two looked at each
other and began to laugh, whereupon God sent them into the world.  (J.
Spieth, "Die Ewe-Stamme, Material zur Kunde des Ewe-Volkes in Deutsch-Togo"
(Berlin, 1906), pages 828, 840.)  The Innuit or Esquimaux of Point Barrow,
in Alaska, tell of a time when there was no man in the land, till a spirit
named "a se lu", who resided at Point Barrow, made a clay man, set him up
on the shore to dry, breathed into him and gave him life.  ("Report of the
International Expedition to Point Barrow" (Washington, 1885), page 47.) 
Other Esquimaux of Alaska relate how the Raven made the first woman out of
clay to be a companion to the first man; he fastened water-grass to the
back of the head to be hair, flapped his wings over the clay figure, and it
arose, a beautiful young woman.  (E.W. Nelson, "The Eskimo about Bering
Strait", "Eighteenth Annual Report of the Bureau of American Ethnology",
Part I. (Washington, 1899), page 454.)  The Acagchemem Indians of
California said that a powerful being called Chinigchinich created man out
of clay which he found on the banks of a lake; male and female created he
them, and the Indians of the present day are their descendants.  (Friar
Geronimo Boscana, "Chinigchinich", appended to (A. Robinson's) "Life in
California" (New York, 1846), page 247.)  A priest of the Natchez Indians
in Louisiana told Du Pratz "that God had kneaded some clay, such as that
which potters use and had made it into a little man; and that after
examining it, and finding it well formed, he blew up his work, and
forthwith that little man had life, grew, acted, walked, and found himself
a man perfectly well shaped."  As to the mode in which the first woman was
created, the priest had no information, but thought she was probably made
in the same way as the first man; so Du Pratz corrected his imperfect
notions by reference to Scripture.  (M. Le Page Du Pratz, "The History of
Louisiana" (London, 1774), page 330.)  The Michoacans of Mexico said that
the great god Tucapacha first made man and woman out of clay, but that when
the couple went to bathe in a river they absorbed so much water that the
clay of which they were composed all fell to pieces.  Then the creator went
to work again and moulded them afresh out of ashes, and after that he
essayed a third time and made them of metal.  This last attempt succeeded. 
The metal man and woman bathed in the river without falling to pieces, and
by their union they became the progenitors of mankind.  (A. de Herrera,
"General History of the vast Continent and Islands of America", translated
into English by Capt. J. Stevens (London, 1725, 1726), III. 254; Brasseur
de Bourbourg, "Histoire des Nations Civilisees du Mexique et de l'Amerique-
Centrale" (Paris, 1857--1859), III. 80 sq; compare id. I. 54 sq.)

According to a legend of the Peruvian Indians, which was told to a Spanish
priest in Cuzco about half a century after the conquest, it was in
Tiahuanaco that man was first created, or at least was created afresh after
the deluge.  "There (in Tiahuanaco)," so runs the legend, "the Creator
began to raise up the people and nations that are in that region, making
one of each nation of clay, and painting the dresses that each one was to
wear; those that were to wear their hair, with hair, and those that were to
be shorn, with hair cut.  And to each nation was given the language, that
was to be spoken, and the songs to be sung, and the seeds and food that
they were to sow.  When the Creator had finished painting and making the
said nations and figures of clay, he gave life and soul to each one, as
well men as women, and ordered that they should pass under the earth. 
Thence each nation came up in the places to which he ordered them to go." 
(E.J. Payne, "History of the New World called America", I. (Oxford, 1892),
page 462.)

These examples suffice to prove that the theory of the creation of man out
of dust or clay has been current among savages in many parts of the world.
But it is by no means the only explanation which the savage philosopher has
given of the beginnings of human life on earth.  Struck by the resemblances
which may be traced between himself and the beasts, he has often supposed,
like Darwin himself, that mankind has been developed out of lower forms of
animal life.  For the simple savage has none of that high notion of the
transcendant dignity of man which makes so many superior persons shrink
with horror from the suggestion that they are distant cousins of the
brutes.  He on the contrary is not too proud to own his humble relations;
indeed his difficulty often is to perceive the distinction between him and
them.  Questioned by a missionary, a Bushman of more than average
intelligence "could not state any difference between a man and a brute--he
did not know but a buffalo might shoot with bows and arrows as well as man,
if it had them."  (Reverend John Campbell, "Travels in South Africa"
(London, 1822, II. page 34.)  When the Russians first landed on one of the
Alaskan islands, the natives took them for cuttle-fish "on account of the
buttons on their clothes."  (I. Petroff, "Report on the Population,
Industries, and Resources of Alaska", page 145.)  The Giliaks of the Amoor
think that the outward form and size of an animal are only apparent; in
substance every beast is a real man, just like a Giliak himself, only
endowed with an intelligence and strength, which often surpass those of
mere ordinary human beings.  (L. Sternberg, "Die Religion der Giljaken",
"Archiv fur Religionswissenschaft", VIII. (1905), page 248.)  The
Borororos, an Indian tribe of Brazil, will have it that they are parrots of
a gorgeous red plumage which live in their native forests.  Accordingly
they treat the birds as their fellow-tribesmen, keeping them in captivity,
refusing to eat their flesh, and mourning for them when they die.  (K. von
den Steinen, "Unter den Naturvolkern Zentral-Brasiliens" (Berlin, 1894),
pages 352 sq., 512.)

This sense of the close relationship of man to the lower creation is the
essence of totemism, that curious system of superstition which unites by a
mystic bond a group of human kinsfolk to a species of animals or plants. 
Where that system exists in full force, the members of a totem clan
identify themselves with their totem animals in a way and to an extent
which we find it hard even to imagine.  For example, men of the Cassowary
clan in Mabuiag think that cassowaries are men or nearly so.  "Cassowary,
he all same as relation, he belong same family," is the account they give
of their relationship with the long-legged bird.  Conversely they hold that
they themselves are cassowaries for all practical purposes.  They pride
themselves on having long thin legs like a cassowary.  This reflection
affords them peculiar satisfaction when they go out to fight, or to run
away, as the case may be; for at such times a Cassowary man will say to
himself, "My leg is long and thin, I can run and not feel tired; my legs
will go quickly and the grass will not entangle them."  Members of the
Cassowary clan are reputed to be pugnacious, because the cassowary is a
bird of very uncertain temper and can kick with extreme violence.  (A.C.
Haddon, "The Ethnography of the Western Tribe of Torres Straits", "Journal
of the Anthropological Institute", XIX. (1890), page 393; "Reports of the
Cambridge Anthropological Expedition to Torres Straits", V. (Cambridge,
1904), pages 166, 184.)  So among the Ojibways men of the Bear clan are
reputed to be surly and pugnacious like bears, and men of the Crane clan to
have clear ringing voices like cranes.  (W.W. Warren, "History of the
Ojibways", "Collections of the Minnesota Historical Society", V. (Saint
Paul, Minn. 1885), pages 47, 49.)  Hence the savage will often speak of his
totem animal as his father or his brother, and will neither kill it himself
nor allow others to do so, if he can help it.  For example, if somebody
were to kill a bird in the presence of a native Australian who had the bird
for his totem, the black might say, "What for you kill that fellow? that my
father!" or "That brother belonging to me you have killed; why did you do
it?"  (E. Palmer, "Notes on some Australian Tribes", "Journal of the
Anthropological Institute", XIII. (1884), page 300.)  Bechuanas of the
Porcupine clan are greatly afflicted if anybody hurts or kills a porcupine
in their presence.  They say, "They have killed our brother, our master,
one of ourselves, him whom we sing of"; and so saying they piously gather
the quills of their murdered brother, spit on them, and rub their eyebrows
with them.  They think they would die if they touched its flesh.  In like
manner Bechuanas of the Crocodile clan call the crocodile one of
themselves, their master, their brother; and they mark the ears of their
cattle with a long slit like a crocodile's mouth by way of a family crest. 
Similarly Bechuanas of the Lion clan would not, like the members of other
clans, partake of lion's flesh; for how, say they, could they eat their
grandfather?  If they are forced in self-defence to kill a lion, they do so
with great regret and rub their eyes carefully with its skin, fearing to
lose their sight if they neglected this precaution.  (T. Arbousset et F.
Daumas, "Relation d'un Voyage d'Exploration au Nord-Est de la Colonie du
Cap de Bonne-Esperance" (Paris, 1842), pages 349 sq., 422-24.)  A Mandingo
porter has been known to offer the whole of his month's pay to save the
life of a python, because the python was his totem and he therefore
regarded the reptile as his relation; he thought that if he allowed the
creature to be killed, the whole of his own family would perish, probably
through the vengeance to be taken by the reptile kinsfolk of the murdered
serpent.  (M. le Docteur Tautain, "Notes sur les Croyances et Pratiques
Religieuses des Banmanas", "Revue d'Ethnographie", III. (1885), pages 396
sq.; A. Rancon, "Dans la Haute-Gambie, Voyage d'Exploration Scientifique"
(Paris, 1894), page 445.)

Sometimes, indeed, the savage goes further and identifies the revered
animal not merely with a kinsman but with himself; he imagines that one of
his own more or less numerous souls, or at all events that a vital part of
himself, is in the beast, so that if it is killed he must die.  Thus, the
Balong tribe of the Cameroons, in West Africa, think that every man has
several souls, of which one is lodged in an elephant, a wild boar, a
leopard, or what not.  When any one comes home, feels ill, and says, "I
shall soon die," and is as good as his word, his friends are of opinion
that one of his souls has been shot by a hunter in a wild boar or a
leopard, for example, and that that is the real cause of his death.  (J.
Keller, "Ueber das Land und Volk der Balong", "Deutsches Kolonialblatt", 1
October, 1895, page 484.)  A Catholic missionary, sleeping in the hut of a
chief of the Fan negroes, awoke in the middle of the night to see a huge
black serpent of the most dangerous sort in the act of darting at him.  He
was about to shoot it when the chief stopped him, saying, "In killing that
serpent, it is me that you would have killed.  Fear nothing, the serpent is
my elangela."  (Father Trilles, "Chez les Fang, leurs Moeurs, leur Langue,
leur Religion", "Les Missions Catholiques", XXX. (1898), page 322.)  At
Calabar there used to be some years ago a huge old crocodile which was well
known to contain the spirit of a chief who resided in the flesh at Duke
Town.  Sporting Vice-Consuls, with a reckless disregard of human life, from
time to time made determined attempts to injure the animal, and once a
peculiarly active officer succeeded in hitting it.  The chief was
immediately laid up with a wound in his leg.  He SAID that a dog had bitten
him, but few people perhaps were deceived by so flimsy a pretext.  (Miss
Mary H. Kingsley, "Travels in West Africa" (London, 1897), pages 538 sq. 
As to the external or bush souls of human beings, which in this part of
Africa are supposed to be lodged in the bodies of animals, see Miss Mary H.
Kingsley op. cit. pages 459-461; R. Henshaw, "Notes on the Efik belief in
'bush soul'", "Man", VI.(1906), pages 121 sq.; J. Parkinson, "Notes on the
Asaba people (Ibos) of the Niger", "Journal of the Anthropological
Institute", XXXVI. (1906), pages 314 sq.)  Once when Mr Partridge's canoe-
men were about to catch fish near an Assiga town in Southern Nigeria, the
natives of the town objected, saying, "Our souls live in those fish, and if
you kill them we shall die."  (Charles Partridge, "Cross River Natives"
(London, 1905), pages 225 sq.)  On another occasion, in the same region, an
Englishman shot a hippopotamus near a native village.  The same night a
woman died in the village, and her friends demanded and obtained from the
marksman five pounds as compensation for the murder of the woman, whose
soul or second self had been in that hippopotamus.  (C.H. Robinson,
"Hausaland" (London, 1896), pages 36 sq.)  Similarly at Ndolo, in the Congo
region, we hear of a chief whose life was bound up with a hippopotamus, but
he prudently suffered no one to fire at the animal.  ("Notes Analytiques
sur les Collections Ethnographiques du Musee du Congo", I. (Brussels, 1902-
06), page 150.

Amongst people who thus fail to perceive any sharp line of distinction
between beasts and men it is not surprising to meet with the belief that
human beings are directly descended from animals.  Such a belief is often
found among totemic tribes who imagine that their ancestors sprang from
their totemic animals or plants; but it is by no means confined to them. 
Thus, to take instances, some of the Californian Indians, in whose
mythology the coyote or prairie-wolf is a leading personage, think that
they are descended from coyotes.  At first they walked on all fours; then
they began to have some members of the human body, one finger, one toe, one
eye, one ear, and so on; then they got two fingers, two toes, two eyes, two
ears, and so forth; till at last, progressing from period to period, they
became perfect human beings.  The loss of their tails, which they still
deplore, was produced by the habit of sitting upright.  (H.R. Schoolcraft,
"Indian Tribes of the United States", IV. (Philadelphia, 1856), pages 224
sq.; compare id. V. page 217.  The descent of some, not all, Indians from
coyotes is mentioned also by Friar Boscana, in (A. Robinson's) "Life in
California" (New York, 1846), page 299.)  Similarly Darwin thought that
"the tail has disappeared in man and the anthropomorphous apes, owing to
the terminal portion having been injured by friction during a long lapse of
time; the basal and embedded portion having been reduced and modified, so
as to become suitable to the erect or semi-erect position."  (Charles
Darwin, "The Descent of Man", Second Edition (London, 1879), page 60.)  The
Turtle clam of the Iroquois think that they are descended from real mud
turtles which used to live in a pool.  One hot summer the pool dried up,
and the mud turtles set out to find another.  A very fat turtle, waddling
after the rest in the heat, was much incommoded by the weight of his shell,
till by a great effort he heaved it off altogether.  After that he
gradually developed into a man and became the progenitor of the Turtle
clan.  (E.A. Smith, "Myths of the Iroquois", "Second Annual Report of the
Bureau of Ethnology" (Washington, 1883), page 77.)  The Crawfish band of
the Choctaws are in like manner descended from real crawfish, which used to
live under ground, only coming up occasionally through the mud to the
surface.  Once a party of Choctaws smoked them out, taught them the Choctaw
language, taught them to walk on two legs, made them cut off their toe
nails and pluck the hair from their bodies, after which they adopted them
into the tribe.  But the rest of their kindred, the crawfish, are crawfish
under ground to this day.  (Geo. Catlin, "North American Indians"4 (London,
1844), II. page 128.)  The Osage Indians universally believed that they
were descended from a male snail and a female beaver.  A flood swept the
snail down to the Missouri and left him high and dry on the bank, where the
sun ripened him into a man.  He met and married a beaver maid, and from the
pair the tribe of the Osages is descended.  For a long time these Indians
retained a pious reverence for their animal ancestors and refrained from
hunting beavers, because in killing a beaver they killed a brother of the
Osages.  But when white men came among them and offered high prices for
beaver skins, the Osages yielded to the temptation and took the lives of
their furry brethren.  (Lewis and Clarke, "Travels to the Source of the
Missouri River" (London, 1815), I. 12 (Vol. I. pages 44 sq. of the London
reprint, 1905).)  The Carp clan of the Ootawak Indians are descended from
the eggs of a carp which had been deposited by the fish on the banks of a
stream and warmed by the sun.  ("Lettres Edifiantes et Curieuses", Nouvelle
Edition, VI. (Paris, 1781), page 171.)  The Crane clan of the Ojibways are
sprung originally from a pair of cranes, which after long wanderings
settled on the rapids at the outlet of Lake Superior, where they were
changed by the Great Spirit into a man and woman.  (L.H. Morgan, "Ancient
Society" (London, 1877), page 180.)  The members of two Omaha clans were
originally buffaloes and lived, oddly enough, under water, which they
splashed about, making it muddy.  And at death all the members of these
clans went back to their ancestors the buffaloes.  So when one of them lay
adying, his friends used to wrap him up in a buffalo skin with the hair
outside and say to him, "You came hither from the animals and you are going
back thither.  Do not face this way again.  When you go, continue walking. 
(J. Owen Dorsey, "Omaha Sociology", "Third Annual Report of the Bureau of
Ethnology" (Washington, 1884), pages 229, 233.)  The Haida Indians of Queen
Charlotte Islands believe that long ago the raven, who is the chief figure
in the mythology of North-West America, took a cockle from the beach and
married it; the cockle gave birth to a female child, whom the raven took to
wife, and from their union the Indians were produced.  (G.M. Dawson,
"Report on the Queen Charlotte Islands" (Montreal, 1880), pages 149B sq. 
("Geological Survey of Canada"); F. Poole, "Queen Charlotte Islands", page
136.)  The Delaware Indians called the rattle-snake their grandfather and
would on no account destroy one of these reptiles, believing that were they
to do so the whole race of rattle-snakes would rise up and bite them. 
Under the influence of the white man, however, their respect for their
grandfather the rattle-snake gradually died away, till at last they killed
him without compunction or ceremony whenever they met him.  The writer who
records the old custom observes that he had often reflected on the curious
connection which appears to subsist in the mind of an Indian between man
and the brute creation; "all animated nature," says he, "in whatever
degree, is in their eyes a great whole, from which they have not yet
ventured to separate themselves."  (Rev. John Heckewelder, "An Account of
the History, Manners, and Customs, of the Indian Nations, who once
inhabited Pennsylvania and the Neighbouring States", "Transactions of the
Historical and Literary Committee of the American Philosophical Society",
I. (Philadelphia, 1819), pages 245, 247, 248.)

Some of the Indians of Peru boasted of being descended from the puma or
American lion; hence they adored the lion as a god and appeared at
festivals like Hercules dressed in the skins of lions with the heads of the
beasts fixed over their own.  Others claimed to be sprung from condors and
attired themselves in great black and white wings, like that enormous bird. 
(Garcilasso de la Vega, "First Part of the Royal Commentaries of the
Yncas", Vol. I. page 323, Vol. II. page 156 (Markham's translation).)  The
Wanika of East Africa look upon the hyaena as one of their ancestors or as
associated in some way with their origin and destiny.  The death of a
hyaena is mourned by the whole people, and the greatest funeral ceremonies
which they perform are performed for this brute.  The wake held over a
chief is as nothing compared to the wake held over a hyaena; one tribe only
mourns the death of its chief, but all the tribes unite to celebrate the
obsequies of a hyaena.  (Charles New, "Life, Wanderings, and Labours in
Eastern Africa" (London, 1873) page 122.)  Some Malagasy families claim to
be descended from the babacoote (Lichanotus brevicaudatus), a large lemur
of grave appearance and staid demeanour, which lives in the depth of the
forest.  When they find one of these creatures dead, his human descendants
bury it solemnly, digging a grave for it, wrapping it in a shroud, and
weeping and lamenting over its carcase.  A doctor who had shot a babacoote
was accused by the inhabitants of a Betsimisaraka village of having killed
"one of their grandfathers in the forest," and to appease their indignation
he had to promise not to skin the animal in the village but in a solitary
place where nobody could see him.  (Father Abinal, "Croyances fabuleuses
des Malgaches", "Les Missions Catholiques", XII. (1880), page 526; G.H.
Smith, "Some Betsimisaraka superstitions", "The Antananarivo Annual and
Madagascar Magazine", No. 10 (Antananarivo, 1886), page 239; H.W. Little,
"Madagascar, its History and People" (London, 1884), pages 321 sq; A. van
Gennep, "Tabou et Totemisme a Madagascar" (Paris, 1904), pages 214 sqq.) 
Many of the Betsimisaraka believe that the curious nocturnal animal called
the aye-aye (Cheiromys madagascariensis) "is the embodiment of their
forefathers, and hence will not touch it, much less do it an injury.  It is
said that when one is discovered dead in the forest, these people make a
tomb for it and bury it with all the forms of a funeral.  They think that
if they attempt to entrap it, they will surely die in consequence."  (G.A.
Shaw, "The Aye-aye", "Antananarivo Annual and Madagascar Magazine", Vol.
II. (Antananarivo, 1896), pages 201, 203 (Reprint of the Second four
Numbers).  Compare A. van Gennep, "Tabou et Totemisme a Madagascar", pages
223 sq.)  Some Malagasy tribes believe themselves descended from crocodiles
and accordingly they deem the formidable reptiles their brothers.  If one
of these scaly brothers so far forgets the ties of kinship as to devour a
man, the chief of the tribe, or in his absence an old man familiar with the
tribal customs, repairs at the head of the people to the edge of the water,
and summons the family of the culprit to deliver him up to the arm of
justice.  A hook is then baited and cast into the river or lake.  Next day
the guilty brother or one of his family is dragged ashore, formally tried,
sentenced to death, and executed.  The claims of justice being thus
satisfied, the dead animal is lamented and buried like a kinsman; a mound
is raised over his grave and a stone marks the place of his head.  (Father
Abinal, "Croyances fabuleuses des Malgaches", "Les Missions Catholiques",
XII. (1880), page 527; A. van Gennep, "Tabou et Totemisme a Madagascar",
pages 281 sq.)

Amongst the Tshi-speaking tribes of the Gold Coast in West Africa the
Horse-mackerel family traces its descent from a real horse-mackerel whom an
ancestor of theirs once took to wife.  She lived with him happily in human
shape on shore till one day a second wife, whom the man had married,
cruelly taunted her with being nothing but a fish.  That hurt her so much
that bidding her husband farewell she returned to her old home in the sea,
with her youngest child in her arms, and never came back again.  But ever
since the Horse-mackerel people have refrained from eating horse-mackerels,
because the lost wife and mother was a fish of that sort.  (A.B. Ellis,
"The Tshi-speaking Peoples of the Gold Coast of West Africa" (London,
1887), pages 208-11.  A similar tale is told by another fish family who
abstain from eating the fish (appei) from which they take their name (A.B.
Ellis op. cit. pages 211 sq.).)  Some of the Land Dyaks of Borneo tell a
similar tale to explain a similar custom.  "There is a fish which is taken
in their rivers called a puttin, which they would on no account touch,
under the idea that if they did they would be eating their relations.  The
tradition respecting it is, that a solitary old man went out fishing and
caught a puttin, which he dragged out of the water and laid down in his
boat.  On turning round, he found it had changed into a very pretty little
girl.  Conceiving the idea she would make, what he had long wished for, a
charming wife for his son, he took her home and educated her until she was
fit to be married.  She consented to be the son's wife cautioning her
husband to use her well.  Some time after their marriage, however, being
out of temper, he struck her, when she screamed, and rushed away into the
water; but not without leaving behind her a beautiful daughter, who became
afterwards the mother of the race."  (The Lord Bishop of Labuan, "On the
Wild Tribes of the North-West Coast of Borneo", "Transactions of the
Ethnological Society of London", New Series II. (London, 1863), pages 26
sq.  Such stories conform to a well-known type which may be called the
Swan-Maiden type of story, or Beauty and the Beast, or Cupid and Psyche. 
The occurrence of stories of this type among totemic peoples, such as the
Tshi-speaking negroes of the Gold Coast, who tell them to explain their
totemic taboos, suggests that all such tales may have originated in
totemism.  I shall deal with this question elsewhere.)

Members of a clan in Mandailing, on the west coast of Sumatra, assert that
they are descended from a tiger, and at the present day, when a tiger is
shot, the women of the clan are bound to offer betel to the dead beast. 
When members of this clan come upon the tracks of a tiger, they must, as a
mark of homage, enclose them with three little sticks.  Further, it is
believed that the tiger will not attack or lacerate his kinsmen, the
members of the clan.  (H. Ris, "De Onderafdeeling Klein Mandailing Oeloe en
Pahantan en hare Bevolking met uitzondering van de Oeloes", "Bijdragen tot
de Tall- Land- en Volkenkunde van Nederlansch-Indie, XLVI. (1896), page
473.)  The Battas of Central Sumatra are divided into a number of clans
which have for their totems white buffaloes, goats, wild turtle-doves,
dogs, cats, apes, tigers, and so forth; and one of the explanations which
they give of their totems is that these creatures were their ancestors, and
that their own souls after death can transmigrate into the animals.  (J.B.
Neumann, "Het Pane en Bila-stroomgebied op het eiland Sumatra",
"Tijdschrift van het Nederlandsch Aardrijkskundig Genootschap", Tweede
Serie, III. Afdeeling, Meer uitgebreide Artikelen, No. 2 (Amsterdam, 1886),
pages 311 sq.; id. ib. Tweede Serie, IV. Afdeeling, Meer uitgebreide
Artikelen, No. 1 (Amsterdam, 1887), pages 8 sq.)  In Amboyna and the
neighbouring islands the inhabitants of some villages aver that they are
descended from trees, such as the Capellenia moluccana, which had been
fertilised by the Pandion Haliaetus.  Others claim to be sprung from pigs,
octopuses, crocodiles, sharks, and eels.  People will not burn the wood of
the trees from which they trace their descent, nor eat the flesh of the
animals which they regard as their ancestors.  Sicknesses of all sorts are
believed to result from disregarding these taboos.  (J.G.F. Riedel, "De
sluik- en kroesharige rassen tusschen Selebes en Papua" (The Hague, 1886),
pages 32, 61; G.W.W.C. Baron van Hoevell, "Ambon en meer bepaaldelijk de
Oeliasers" (Dordrecht, 1875), page 152.)  Similarly in Ceram persons who
think they are descended from crocodiles, serpents, iguanas, and sharks
will not eat the flesh of these animals.  (J.G.F. Riedel op. cit. page
122.)  Many other peoples of the Molucca Islands entertain similar beliefs
and observe similar taboos.  (J.G.F. Riedel "De sluik- en kroesharige
rassen tusschen Selebes en Papua" (The Hague, 1886), pages 253, 334, 341,
348, 412, 414, 432.)  Again, in Ponape, one of the Caroline Islands, "The
different families suppose themselves to stand in a certain relation to
animals, and especially to fishes, and believe in their descent from them. 
They actually name these animals 'mothers'; the creatures are sacred to the
family and may not be injured.  Great dances, accompanied with the offering
of prayers, are performed in their honour.  Any person who killed such an
animal would expose himself to contempt and punishment, certainly also to
the vengeance of the insulted deity."  Blindness is commonly supposed to be
the consequence of such a sacrilege.  (Dr Hahl, "Mittheilungen uber Sitten
und rechtliche Verhaltnisse auf Ponape", "Ethnologisches Notizblatt", Vol.
II. Heft 2 (Berlin, 1901), page 10.)

Some of the aborigines of Western Australia believe that their ancestors
were swans, ducks, or various other species of water-fowl before they were
transformed into men.  (Captain G. Grey, "A Vocabulary of the Dialects of
South Western Australia", Second Edition (London, 1840), pages 29, 37, 61,
63, 66, 71.)  The Dieri tribe of Central Australia, who are divided into
totemic clans, explain their origin by the following legend.  They say that
in the beginning the earth opened in the midst of Perigundi Lake, and the
totems (murdus or madas) came trooping out one after the other.  Out came
the crow, and the shell parakeet, and the emu, and all the rest.  Being as
yet imperfectly formed and without members or organs of sense, they laid
themselves down on the sandhills which surrounded the lake then just as
they do now.  It was a bright day and the totems lay basking in the
sunshine, till at last, refreshed and invigorated by it, they stood up as
human beings and dispersed in all directions.  That is why people of the
same totem are now scattered all over the country.  You may still see the
island in the lake out of which the totems came trooping long ago.  (A.W.
Howitt, "Native Tribes of South-East Australia" (London, 1904), pages 476,
779 sq.)  Another Dieri legend relates how Paralina, one of the Mura-Muras
or mythical predecessors of the Dieri, perfected mankind.  He was out
hunting kangaroos, when he saw four incomplete beings cowering together. 
So he went up to them, smoothed their bodies, stretched out their limbs,
slit up their fingers and toes, formed their mouths, noses, and eyes, stuck
ears on them, and blew into their ears in order that they might hear. 
Having perfected their organs and so produced mankind out of these
rudimentary beings, he went about making men everywhere.  (A.W. Howitt op.
cit., pages 476, 780 sq.)  Yet another Dieri tradition sets forth how the
Mura-Mura produced the race of man out of a species of small black lizards,
which may still be met with under dry bark.  To do this he divided the feet
of the lizards into fingers and toes, and, applying his forefinger to the
middle of their faces, created a nose; likewise he gave them human eyes,
mouths and ears.  He next set one of them upright, but it fell down again
because of its tail; so he cut off its tail and the lizard then walked on
its hind legs.  That is the origin of mankind.  (S. Gason, "The Manners and
Customs of the Dieyerie tribe of Australian Aborigines", "Native Tribes of
South Australia" (Adelaide, 1879), page 260.  This writer fell into the
mistake of regarding the Mura-Mura (Mooramoora) as a Good-Spirit instead of
as one of the mythical but more or less human predecessors of the Dieri in
the country.  See A.W. Howitt, "Native Tribes of South-East Australia",
pages 475 sqq.)

The Arunta tribe of Central Australia similarly tell how in the beginning
mankind was developed out of various rudimentary forms of animal life. 
They say that in those days two beings called Ungambikula, that is, "out of
nothing," or "self-existing," dwelt in the western sky.  From their lofty
abode they could see, far away to the east, a number of inapertwa
creatures, that is, rudimentary human beings or incomplete men, whom it was
their mission to make into real men and women.  For at that time there were
no real men and women; the rudimentary creatures (inapertwa) were of
various shapes and dwelt in groups along the shore of the salt water which
covered the country.  These embryos, as we may call them, had no distinct
limbs or organs of sight, hearing, and smell; they did not eat food, and
they presented the appearance of human beings all doubled up into a rounded
mass, in which only the outline of the different parts of the body could be
vaguely perceived.  Coming down from their home in the western sky, armed
with great stone knives, the Ungambikula took hold of the embryos, one
after the other.  First of all they released the arms from the bodies, then
making four clefts at the end of each arm they fashioned hands and fingers;
afterwards legs, feet, and toes were added in the same way.  The figure
could now stand; a nose was then moulded and the nostrils bored with the
fingers.  A cut with the knife made the mouth, which was pulled open
several times to render it flexible.  A slit on each side of the face
separated the upper and lower eye-lids, disclosing the eyes, which already
existed behind them; and a few strokes more completed the body.  Thus out
of the rudimentary creatures were formed men and women.  These rudimentary
creatures or embryos, we are told, "were in reality stages in the
transformation of various animals and plants into human beings, and thus
they were naturally, when made into human beings, intimately associated
with the particular animal or plant, as the case may be, of which they were
the transformations--in other words, each individual of necessity belonged
to a totem, the name of which was of course that of the animal or plant of
which he or she was a transformation."  However, it is not said that all
the totemic clans of the Arunta were thus developed; no such tradition, for
example, is told to explain the origin of the important Witchetty Grub
clan.  The clans which are positively known, or at least said, to have
originated out of embryos in the way described are the Plum Tree, the Grass
Seed, the Large Lizard, the Small Lizard, the Alexandra Parakeet, and the
Small Rat clans.  When the Ungambikula had thus fashioned people of these
totems, they circumcised them all, except the Plum Tree men, by means of a
fire-stick.  After that, having done the work of creation or evolution, the
Ungambikula turned themselves into little lizards which bear a name meaning
"snappers-up of flies."  (Baldwin Spencer and F.J. Gillen, "Native Tribes
of Central Australia (London, 1899), pages 388 sq.; compare id., "Northern
Tribes of Central Australia" (London, 1904), page 150.)

This Arunta tradition of the origin of man, as Messrs Spencer and Gillen,
who have recorded it, justly observe, "is of considerable interest; it is
in the first place evidently a crude attempt to describe the origin of
human beings out of non-human creatures who were of various forms; some of
them were representatives of animals, others of plants, but in all cases
they are to be regarded as intermediate stages in the transition of an
animal or plant ancestor into a human individual who bore its name as that
of his or her totem."  (Baldwin Spencer and F.J. Gillen, "Native Tribes of
Central Australia", pages 391 sq.)  In a sense these speculations of the
Arunta on their own origin may be said to combine the theory of creation
with the theory of evolution; for while they represent men as developed out
of much simpler forms of life, they at the same time assume that this
development was effected by the agency of two powerful beings, whom so far
we may call creators.  It is well known that at a far higher stage of
culture a crude form of the evolutionary hypothesis was propounded by the
Greek philosopher Empedocles.  He imagined that shapeless lumps of earth
and water, thrown up by the subterranean fires, developed into monstrous
animals, bulls with the heads of men, men with the heads of bulls, and so
forth; till at last, these hybrid forms being gradually eliminated, the
various existing species of animals and men were evolved.  (E. Zeller, "Die
Philosophie der Griechen", I.4 (Leipsic, 1876), pages 718 sq.; H. Ritter et
L. Preller, "Historia Philosophiae Graecae et Romanae ex fontium locis
contexta"5, pages 102 sq.  H. Diels, "Die Fragmente der Vorsokratiker"2, I.
(Berlin, 1906), pages 190 sqq.  Compare Lucretius "De rerum natura", V. 837
sqq.)  The theory of the civilised Greek of Sicily may be set beside the
similar theory of the savage Arunta of Central Australia.  Both represent
gropings of the human mind in the dark abyss of the past; both were in a
measure grotesque anticipations of the modern theory of evolution.

In this essay I have made no attempt to illustrate all the many various and
divergent views which primitive man has taken of his own origin.  I have
confined myself to collecting examples of two radically different views,
which may be distinguished as the theory of creation and the theory of
evolution.  According to the one, man was fashioned in his existing shape
by a god or other powerful being; according to the other he was evolved by
a natural process out of lower forms of animal life.  Roughly speaking,
these two theories still divide the civilised world between them.  The
partisans of each can appeal in support of their view to a large consensus
of opinion; and if truth were to be decided by weighing the one consensus
against the other, with "Genesis" in the one scale and "The Origin of
Species" in the other, it might perhaps be found, when the scales were
finally trimmed, that the balance hung very even between creation and
evolution.


X.  THE INFLUENCE OF DARWIN ON THE STUDY OF ANIMAL EMBRYOLOGY.

By A. SEDGWICK, M.A., F.R.S.
Professor of Zoology and Comparative Anatomy in the University of
Cambridge.

The publication of "The Origin of Species" ushered in a new era in the
study of Embryology.  Whereas, before the year 1859 the facts of anatomy
and development were loosely held together by the theory of types, which
owed its origin to the great anatomists of the preceding generation, to
Cuvier, L. Agassiz, J. Muller, and R. Owen, they were now combined together
into one organic whole by the theory of descent and by the hypothesis of
recapitulation which was deduced from that theory.  The view (First clearly
enunciated by Fritz Muller in his well-known work, "Fur Darwin", Leipzig,
1864; (English Edition, "Facts for Darwin", 1869).) that a knowledge of
embryonic and larval histories would lay bare the secrets of race-history
and enable the course of evolution to be traced, and so lead to the
discovery of the natural system of classification, gave a powerful stimulus
to morphological study in general and to embryological investigation in
particular.  In Darwin's words:  "Embryology rises greatly in interest,
when we look at the embryo as a picture, more or less obscured, of the
progenitor, either in its adult or larval state, of all the members of the
same great class."  ("Origin" (6th edition), page 396.)  In the period
under consideration the output of embryological work has been enormous.  No
group of the animal kingdom has escaped exhaustive examination and no
effort has been spared to obtain the embryos of isolated and out of the way
forms, the development of which might have an important bearing upon
questions of phylogeny and classification.  Marine zoological stations have
been established, expeditions have been sent to distant countries, and the
methods of investigation have been greatly improved.  The result of this
activity has been that the main features of the developmental history of
all the most important animals are now known and the curiosity as to
developmental processes, so greatly excited by the promulgation of the
Darwinian theory, has to a considerable extent been satisfied.

To what extent have the results of this vast activity fulfilled the
expectations of the workers who have achieved them?  The Darwin centenary
is a fitting moment at which to take stock of our position.  In this
inquiry we shall leave out of consideration the immense and intensely
interesting additions to our knowledge of Natural History.  These may be
said to constitute a capital fund upon which philosophers, poets and men of
science will draw for many generations.  The interest of Natural History
existed long before Darwinian evolution was thought of and will endure
without any reference to philosophic speculations.  She is a mistress in
whose face are beauties and in whose arms are delights elsewhere
unattainable.  She is and always has been pursued for her own sake without
any reference to philosophy, science, or utility.

Darwin's own views of the bearing of the facts of embryology upon questions
of wide scientific interest are perfectly clear.  He writes ("Origin" (6th
edition), page 395.):

"On the other hand it is highly probable that with many animals the
embryonic or larval stages show us, more or less completely, the condition
of the progenitor of the whole group in its adult state.  In the great
class of the Crustacea, forms wonderfully distinct from each other, namely,
suctorial parasites, cirripedes, entomostraca, and even the malacostraca,
appear at first as larvae under the nauplius-form; and as these larvae live
and feed in the open sea, and are not adapted for any peculiar habits of
life, and from other reasons assigned by Fritz Muller, it is probable that
at some very remote period an independent adult animal, resembling the
Nauplius, existed, and subsequently produced, along several divergent lines
of descent, the above-named great Crustacean groups.  So again it is
probable, from what we know of the embryos of mammals, birds, fishes, and
reptiles, that these animals are the modified descendants of some ancient
progenitor, which was furnished in its adult state with branchiae, a swim-
bladder, four fin-like limbs, and a long tail, all fitted for an aquatic
life.

"As all the organic beings, extinct and recent, which have ever lived, can
be arranged within a few great classes; and as all within each class have,
according to our theory, been connected together by fine gradations, the
best, and, if our collections were nearly perfect, the only possible
arrangement, would be genealogical; descent being the hidden bond of
connexion which naturalists have been seeking under the term of the Natural
System.  On this view we can understand how it is that, in the eyes of most
naturalists, the structure of the embryo is even more important for
classification than that of the adult.  In two or more groups of animals,
however much they may differ from each other in structure and habits in
their adult condition, if they pass through closely similar embryonic
stages, we may feel assured that they all are descended from one parent-
form, and are therefore closely related.  Thus, community in embryonic
structure reveals community of descent; but dissimilarity in embryonic
development does not prove discommunity of descent, for in one of two
groups the developmental stages may have been suppressed, or may have been
so greatly modified through adaptation to new habits of life, as to be no
longer recognisable.  Even in groups, in which the adults have been
modified to an extreme degree, community of origin is often revealed by the
structure of the larvae; we have seen, for instance, that cirripedes,
though externally so like shell-fish, are at once known by their larvae to
belong to the great class of crustaceans.  As the embryo often shows us
more or less plainly the structure of the less modified and ancient
progenitor of the group, we can see why ancient and extinct forms so often
resemble in their adult state the embryos of existing species of the same
class.  Agassiz believes this to be a universal law of nature; and we may
hope hereafter to see the law proved true.  It can, however, be proved true
only in those cases in which the ancient state of the progenitor of the
group has not been wholly obliterated, either by successive variations
having supervened at a very early period of growth, or by such variations
having been inherited at an earlier stage than that at which they first
appeared.  It should also be borne in mind, that the law may be true, but
yet, owing to the geological record not extending far enough back in time,
may remain for a long period, or for ever, incapable of demonstration.  The
law will not strictly hold good in those cases in which an ancient form
became adapted in its larval state to some special line of life, and
transmitted the same larval state to a whole group of descendants; for such
larvae will not resemble any still more ancient form in its adult state."

As this passage shows, Darwin held that embryology was of interest because
of the light it seems to throw upon ancestral history (phylogeny) and
because of the help it would give in enabling us to arrive at a natural
system of classification.  With regard to the latter point, he quotes with
approval the opinion that "the structure of the embryo is even more
important for classification than that of the adult."  What justification
is there for this view?  The phase of life chosen for the ordinary
anatomical and physiological studies, namely, the adult phase, is merely
one of the large number of stages of structure through which the organism
passes.  By far the greater number of these are included in what is
specially called the developmental or (if we include larvae with embryos)
embryonic period, for the developmental changes are more numerous and take
place with greater rapidity at the beginning of life than in its later
periods.  As each of these stages is equal in value, for our present
purpose, to the adult phase, it clearly follows that if there is anything
in the view that the anatomical study of organisms is of importance in
determining their mutual relations, the study of the organism in its
various embryonic (and larval) stages must have a greater importance than
the study of the single and arbitrarily selected stage of life called the
adult.

But a deeper reason than this has been assigned for the importance of
embryology in classification.  It has been asserted, and is implied by
Darwin in the passage quoted, that the ancestral history is repeated in a
condensed form in the embryonic, and that a study of the latter enables us
to form a picture of the stages of structure through which the organism has
passed in its evolution.  It enables us on this view to reconstruct the
pedigrees of animals and so to form a genealogical tree which shall be the
true expression of their natural relations.

The real question which we have to consider is to what extent the
embryological studies of the last 50 years have confirmed or rendered
probable this "theory of recapitulation."  In the first place it must be
noted that the recapitulation theory is itself a deduction from the theory
of evolution.  The facts of embryology, particularly of vertebrate
embryology, and of larval history receive, it is argued, an explanation on
the view that the successive stages of development are, on the whole,
records of adult stages of structure which the species has passed through
in its evolution.  Whether this statement will bear a critical verbal
examination I will not now pause to inquire, for it is more important to
determine whether any independent facts can be alleged in favour of the
theory.  If it could be shown, as was stated to be the case by L. Agassiz,
that ancient and extinct forms of life present features of structure now
only found in embryos, we should have a body of facts of the greatest
importance in the present discussion.  But as Huxley (See Huxley's
"Scientific Memoirs", London, 1898, Vol. I. page 303:  "There is no real
parallel between the successive forms assumed in the development of the
life of the individual at present, and those which have appeared at
different epochs in the past."  See also his Address to the Geological
Society of London (1862) 'On the Palaeontological Evidence of Evolution',
ibid. Vol. II. page 512.) has shown and as the whole course of
palaeontological and embryological investigation has demonstrated, no such
statement can be made.  The extinct forms of life are very similar to those
now existing and there is nothing specially embryonic about them.  So that
the facts, as we know them, lend no support to theory.

But there is another class of facts which have been alleged in favour of
the theory, viz. the facts which have been included in the generalisation
known as the Law of v. Baer.  The law asserts that embryos of different
species of animals of the same group are more alike than the adults and
that, the younger the embryo, the greater are the resemblances.  If this
law could be established it would undoubtedly be a strong argument in
favour of the "recapitulation" explanation of the facts of embryology.  But
its truth has been seriously disputed.  If it were true we should expect to
find that the embryos of closely similar species would be indistinguishable
from one another, but this is notoriously not the case.  It is more
difficult to meet the assertion when it is made in the form given above,
for here we are dealing with matters of opinion.  For instance, no one
would deny that the embryo of a dogfish is different from the embryo of a
rabbit, but there is room for difference of opinion when it is asserted
that the difference is less than the difference between an adult dogfish
and an adult rabbit.  It would be perfectly true to say that the
differences between the embryos concern other organs more than do the
differences between the adults, but who is prepared to affirm that the
presence of a cephalic coelom and of cranial segments, of external gills,
of six gill slits, of the kidney tubes opening into the muscle-plate
coelom, of an enormous yolk-sac, of a neurenteric canal, and the absence of
any trace of an amnion, of an allantois and of a primitive streak are not
morphological facts of as high an import as those implied by the
differences between the adults?  The generalisation undoubtedly had its
origin in the fact that there is what may be called a family resemblance
between embryos and larvae, but this resemblance, which is by no means
exact, is largely superficial and does not extend to anatomical detail.

It is useless to say, as Weismann has stated ("The Evolution Theory", by A.
Weismann, English Translation, Vol. II. page 176, London, 1904.), that "it
cannot be disputed that the rudiments [vestiges his translator means] of
gill-arches and gill-clefts, which are peculiar to one stage of human
ontogeny, give us every ground for concluding that we possessed fish-like
ancestors."  The question at issue is:  did the pharyngeal arches and
clefts of mammalian embryos ever discharge a branchial function in an adult
ancestor of the mammalia?  We cannot therefore, without begging the
question at issue in the grossest manner, apply to them the terms "gill-
arches" and "gill-clefts".  That they are homologous with the "gill-arches"
and "gill-clefts" of fishes is true; but there is no evidence to show that
they ever discharged a branchial function.  Until such evidence is
forthcoming, it is beside the point to say that it "cannot be disputed"
that they are evidence of a piscine ancestry.

It must, therefore, be admitted that one outcome of the progress of
embryological and palaeontological research for the last 50 years is
negative.  The recapitulation theory originated as a deduction from the
evolution theory and as a deduction it still remains.

Let us before leaving the subject apply another test.  If the evolution
theory and the recapitulation theory are both true, how is it that living
birds are not only without teeth but have no rudiments of teeth at any
stage of their existence?  How is it that the missing digits in birds and
mammals, the missing or reduced limb of snakes and whales, the reduced
mandibulo-hyoid cleft of elasmobranch fishes are not present or relatively
more highly developed in the embryo than in the adult?  How is it that when
a marked variation, such as an extra digit, or a reduced limb, or an extra
segment, makes its appearance, it is not confined to the adult but can be
seen all through the development?  All the clear evidence we can get tends
to show that marked variations, whether of reduction or increase, of organs
are manifest during the whole of the development of the organ and do not
merely affect the adult.  And on reflection we see that it could hardly be
otherwise.  All such evidence is distinctly at variance with the theory of
recapitulation, at least as applied to embryos.  In the case of larvae of
course the case will be different, for in them the organs are functional,
and reduction in the adult will not be accompanied by reduction in the
larva unless a change in the conditions of life of the larva enables it to
occur.

If after 50 years of research and close examination of the facts of
embryology the recapitulation theory is still without satisfactory proof,
it seems desirable to take a wider sweep and to inquire whether the facts
of embryology cannot be included in a larger category.

As has been pointed out by Huxley, development and life are co-extensive,
and it is impossible to point to any period in the life of an organism when
the developmental changes cease.  It is true that these changes take place
more rapidly at the commencement of life, but they are never wholly absent,
and those which occur in the later or so-called adult stages of life do not
differ in their essence, however much they may differ in their degree, from
those which occur during the embryonic and larval periods.  This
consideration at once brings the changes of the embryonic period into the
same category as those of the adult and suggests that an explanation which
will account for the one will account for the other.  What then is the
problem we are dealing with?  Surely it is this:  Why does an organism as
soon as it is established at the fertilisation of the ovum enter upon a
cycle of transformations which never cease until death puts an end to them?
In other words what is the meaning of that cycle of changes which all
organisms present in a greater or less degree and which constitute the very
essence of life?  It is impossible to give an answer to this question so
long as we remain within the precincts of Biology--and it is not my present
purpose to penetrate beyond those precincts into the realms of philosophy.
We have to do with an ultimate biological fact, with a fundamental property
of living matter, which governs and includes all its other properties.  How
may this property be stated?  Thus:  it is a property of living matter to
react in a remarkable way to external forces without undergoing
destruction.  The life-cycle, of which the embryonic and larval periods are
a part, consists of the orderly interaction between the organism and its
environment.  The action of the environment produces certain morphological
changes in the organism.  These changes enable the organism to come into
relation with new external forces, to move into what is practically a new
environment, which in its turn produces further structural changes in the
organism.  These in their turn enable, indeed necessitate, the organism to
move again into a new environment, and so the process continues until the
structural changes are of such a nature that the organism is unable to
adapt itself to the environment in which it finds itself.  The essential
condition of success in this process is that the organism should always
shift into the environment to which its new structure is suited--any
failure in this leading to the impairment of the organism.  In most cases
the shifting of the environment is a very gradual process (whether
consisting in the very slight and gradual alteration in the relation of the
embryo as a whole to the egg-shell or uterine wall, or in the relations of
its parts to each other, or in the successive phases of adult life), and
the morphological changes in connection with each step of it are but
slight.  But in some cases jumps are made such as we find in the phenomena
known as hatching, birth, and metamorphosis.

This property of reacting to the environment without undergoing destruction
is, as has been stated, a fundamental property of organisms.  It is
impossible to conceive of any matter, to which the term living could be
applied, being without it.  And with this property of reacting to the
environment goes the further property of undergoing a change which alters
the relation of the organism to the old environment and places it in a new
environment.  If this reasoning is correct, it necessarily follows that
this property must have been possessed by living matter at its first
appearance on the earth.  In other words living matter must always have
presented a life-cycle, and the question arises what kind of modification
has that cycle undergone?  Has it increased or diminished in duration and
complexity since organisms first appeared on the earth?  The current view
is that the cycle was at first very short and that it has increased in
length by the evolutionary creation of new adult phases, that these new
phases are in addition to those already existing and that each of them as
it appears takes over from the preceding adult phase the functional
condition of the reproductive organs.  According to the same view the old
adult phases are not obliterated but persist in a more or less modified
form as larval stages.  It is further supposed that as the life-history
lengthens at one end by the addition of new adult phases, it is shortened
at the other by the abbreviation of embryonic development and by the
absorption of some of the early larval stages into the embryonic period;
but on the whole the lengthening process has exceeded that of shortening,
so that the whole life-history has, with the progress of evolution, become
longer and more complicated.

Now there can be no doubt that the life-history of organisms has been
shortened in the way above suggested, for cases are known in which this can
practically be seen to occur at the present day.  But the process of
lengthening by the creation of new stages at the other end of the life-
cycle is more difficult to conceive and moreover there is no evidence for
its having occurred.  This, indeed, may have occurred, as is suggested
below, but the evidence we have seems to indicate that evolutionary
modification has proceeded by ALTERING and not by SUPERSEDING:  that is to
say that each stage in the life-history, as we see it to-day, has proceeded
from a corresponding stage in a former era by the modification of that
stage and not by the creation of a new one.  Let me, at the risk of
repetition, explain my meaning more fully by taking a concrete
illustration.  The mandibulo-hyoid cleft (spiracle) of the elasmobranch
fishes, the lateral digits of the pig's foot, the hind-limbs of whales, the
enlarged digit of the ostrich's foot are supposed to be organs which have
been recently modified.  This modification is not confined to the final
adult stage of the life-history but characterises them throughout the whole
of their development.  A stage with a reduced spiracle does not proceed in
development from a preceding stage in which the spiracle shows no
reduction:  it is reduced at its first appearance.  The same statement may
be made of organs which have entirely disappeared in the adult, such as
bird's teeth and snake's fore-limbs:  the adult stage in which they have
disappeared is not preceded by embryonic stages in which the teeth and
limbs or rudiments of them are present.  In fact the evidence indicates
that adult variations of any part are accompanied by precedent variations
in the same direction in the embryo.  The evidence seems to show, not that
a stage is added on at the end of the life-history, but only that some of
the stages in the life-history are modified.  Indeed, on the wider view of
development taken in this essay, a view which makes it coincident with
life, one would not expect often to find, even if new stages are added in
the course of evolution, that they are added at the end of the series when
the organism has passed through its reproductive period.  It is possible of
course that new stages have been intercalated in the course of the life-
history, though it is difficult to see how this has occurred.  It is much
more likely, if we may judge from available evidence, that every stage has
had its counterpart in the ancestral form from which it has been derived by
descent with modification.  Just as the adult phase of the living form
differs, owing to evolutionary modification, from the adult phase of the
ancestor from which it has proceeded, so each larval phase will differ for
the same reason from the corresponding larval phase in the life-history of
the ancestor.  Inasmuch as the organism is variable at every stage of its
independent existence and is exposed to the action of natural selection
there is no reason why it should escape modification at any stage.

If there is any truth in these considerations it would seem to follow that
at the dawn of life the life-cycle must have been, either in posse or in
esse, at least as long as it is at the present time, and that the
peculiarity of passing through a series of stages in which new characters
are successively evolved is a primordial quality of living matter.

Before leaving this part of the subject, it is necessary to touch upon
another aspect of it.  What are these variations in structure which succeed
one another in the life-history of an organism?  I am conscious that I am
here on the threshold of a chamber which contains the clue to some of our
difficulties, and that I cannot enter it.  Looked at from one point of view
they belong to the class of genetic variations, which depend upon the
structure or constitution of the protoplasm; but instead of appearing in
different zygotes (A zygote is a fertilised ovum, i.e. a new organism
resulting from the fusion of an ovum and a spermatozoon.), they are present
in the same zygote though at different times in its life-history.  They are
of the same order as the mutational variations of the modern biologist upon
which the appearance of a new character depends.  What is a genetic or
mutational variation?  It is a genetic character which was not present in
either of the parents.  But these "growth variations" were present in the
parents, and in this they differ from mutational variations.  But what are
genetic characters?  They are characters which must appear if any
development occurs.  They are usually contrasted with "acquired
characters," using the expression "acquired character" in the Lamarckian
sense.  But strictly speaking they ARE acquired characters, for the zygote
at first has none of the characters which it subsequently acquires, but
only the power of acquiring them in response to the action of the
environment.  But the characters so acquired are not what we technically
understand and what Lamarck meant by "acquired characters."  They are
genetic characters, as defined above.  What then are Lamarck's "acquired
characters"?  They are variations in genetic characters caused in a
particular way.  There are, in fact, two kinds of variation in genetic
characters depending on the mode of causation.  Firstly, there are those
variations consequent upon a variation in the constitution of the
protoplasm of a particular zygote, and independent of the environment in
which the organism develops, save in so far as this simply calls them
forth:  these are the so-called genetic or mutational variations. 
Secondly, there are those variations which occur in zygotes of similar
germinal constitution and which are caused solely by differences in the
environment to which the individuals are respectively exposed:  these are
the "acquired characters" of Lamarck and of authors generally.  In
consequence of this double sense in which the term "acquired characters"
may be used, great confusion may and does occur.  If the protoplasm be
compared to a machine, and the external conditions to the hand that works
the machine, then it may be said that, as the machine can only work in one
way, it can only produce one kind of result (genetic character), but the
particular form or quality (Lamarckian "acquired character") of the result
will depend upon the hand that works the machine (environment), just as the
quality of the sound produced by a fiddle depends entirely upon the hand
which plays upon it.  It would be improper to apply the term "mutation" to
those genetic characters which are not new characters or new variants of
old characters, but such genetic characters are of the same nature as those
characters to which the term mutation has been applied.  It may be noticed
in passing that it is very questionable if the modern biologist has acted
in the real interests of science in applying the term mutation in the sense
in which he has applied it.  The genetic characters of organisms come from
one of two sources:  either they are old characters and are due to the
action of what we call inheritance or they are new and are due to what we
call variation.  If the term mutation is applied to the actual alteration
of the machinery of the protoplasm, no objection can be felt to its use;
but if it be applied, as it is, to the product of the action of the altered
machine, viz. to the new genetic character, it leads to confusion. 
Inheritance is the persistence of the structure of the machine; characters
are the products of the working of the machine; variation in genetic
characters is due to the alteration (mutation) in the arrangement of the
machinery, while variation in acquired characters (Lamarckian) is due to
differences in the mode of working the machinery.  The machinery when it
starts (in the new zygote) has the power of grinding out certain results,
which we call the characters of the organism.  These appear at successive
intervals of time, and the orderly manifestation of them is what we call
the life-history of the organism.  This brings us back to the question with
which we started this discussion, viz. what is the relation of these
variations in structure, which successively appear in an organism and
constitute its life-history, to the mutational variations which appear in
different organisms of the same brood or species.  The question is brought
home to us when we ask what is a bud-sport, such as a nectarine appearing
on a peach-tree?  From one point of view, it is simply a mutation appearing
in asexual reproduction; from another it is one of these successional
characters ("growth variations") which constitute the life-history of the
zygote, for it appears in the same zygote which first produces a peach. 
Here our analogy of a machine which only works in one way seems to fail us,
for these bud-sports do not appear in all parts of the organism, only in
certain buds or parts of it, so that one part of the zygotic machine would
appear to work differently to another.  To discuss this question further
would take us too far from our subject.  Suffice it to say that we cannot
answer it, any more than we can this further question of burning interest
at the present day, viz. to what extent and in what manner is the machine
itself altered by the particular way in which it is worked.  In connection
with this question we can only submit one consideration:  the zygotic
machine can, by its nature, only work once, so that any alteration in it
can only be ascertained by studying the replicas of it which are produced
in the reproductive organs.

It is a peculiarity that the result which we call the ripening of the
generative organs nearly always appears among the final products of the
action of the zygotic machine.  It is remarkable that this should be the
case.  What is the reason of it?  The late appearance of functional
reproductive organs is almost a universal law, and the explanation of it is
suggested by expressing the law in another way, viz. that the machine is
almost always so constituted that it ceases to work efficiently soon after
the reproductive organs have sufficiently discharged their function.  Why
this should occur we cannot explain:  it is an ultimate fact of nature, and
cannot be included in any wider category.  The period during which the
reproductive organs can act may be short as in ephemerids or long as in man
and trees, and there is no reason to suppose that their action damages the
vital machinery, though sometimes, as in the case of annual plants
(Metschnikoff), it may incidentally do so; but, long or short, the
cessation of their actions is always a prelude to the end.  When they and
their action are impaired, the organism ceases to react with precision to
the environment, and the organism as a whole undergoes retrogressive
changes.

It has been pointed out above that there is reason to believe that at the
dawn of life the life-cycle was, EITHER IN ESSE OR IN POSSE, at least as
long as it is at the present time.  The qualification implied by the words
in italics is necessary, for it is clearly possible that the external
conditions then existing were not suitable for the production of all the
stages of the potential life-history, and that what we call organic
evolution has consisted in a gradual evolution of new environments to which
the organism's innate capacity of change has enabled it to adapt itself. 
We have warrant for this possibility in the case of the Axolotl and in
other similar cases of neoteny.  And these cases further bring home to us
the fact, to which I have already referred, that the full development of
the functional reproductive organs is nearly always associated with the
final stages of the life-history.

On this view of the succession of characters in the life-history of
organisms, how shall we explain the undoubted fact that the development of
buds hardly ever presents any phenomena corresponding to the embryonic and
larval changes?  The reason is clearly this, that budding usually occurs
after the embryonic stage is past; when the characters of embryonic life
have been worked out by the machine.  When it takes place at an early stage
in embryonic life, as it does in cases of so-called embryonic fission, the
product shows, either partly or entirely, phenomena similar to those of
embryonic development.  The only case known to me in which budding by the
adult is accompanied by morphological features similar to those displayed
by embryos is furnished by the budding of the medusiform spore-sacs of
hydrozoon polyps.  But this case is exceptional, for here we have to do
with an attempt, which fails, to form a free-swimming organism, the medusa;
and the vestiges which appear in the buds are the umbrella-cavity, marginal
tentacles, circular canal, etc., of the medusa arrested in development.

But the question still remains, are there no cases in which, as implied by
the recapitulation theory, variations in any organ are confined to the
period in which the organ is functional and do not affect it in the
embryonic stages?  The teeth of the whalebone whales may be cited as a case
in which this is said to occur; but here the teeth are only imperfectly
developed in the embryo and are soon absorbed.  They have been affected by
the change which has produced their disappearance in the adult, but not to
complete extinction.  Nor are they now likely to be extinguished, for
having become exclusively embryonic they are largely protected from the
action of natural selection.  This consideration brings up a most important
aspect of the question, so far as disappearing organs are concerned.  Every
organ is laid down at a certain period in the embryo and undergoes a
certain course of growth until it obtains full functional development. 
When for any cause reduction begins, it is affected at all stages of its
growth, unless it has functional importance in the larva, and in some cases
its life is shortened at one or both ends.  In cases, as in that of the
whale's teeth, in which it entirely disappears in the adult, the latter
part of its life is cut off; in others, the beginning of its life may be
deferred.  This happens, for instance, with the spiracle of many
Elasmobranchs, which makes its appearance after the hyobranchial cleft, not
before it as it should do, being anterior to it in position, and as it does
in the Amniota in which it shows no reduction in size as compared with the
other pharyngeal clefts.  In those Elasmobranchs in which it is absent in
the adult but present in the embryo (e.g. Carcharias) its life is shortened
at both ends.  Many more instances of organs, of which the beginning and
end have been cut off, might be mentioned; e.g. the muscle-plate coelom of
Aves, the primitive streak and the neurenteric canal of amniote
blastoderms.  In yet other cases in which the reduced organ is almost on
the verge of disappearance, it may appear for a moment and disappear more
than once in the course of development.  As an instance of this striking
phenomenon I may mention the neurenteric canal of avine embryos, and the
anterior neuropore of Ascidians.  Lastly the reduced organ may disappear in
the developing stages before it does so in the adult.  As an instance of
this may be mentioned the mandibular palp of those Crustacea with zoaea
larvae.  This structure disappears in the larva only to reappear in a
reduced form in later stages.  In all these cases we are dealing with an
organ which, we imagine, attained a fuller functional development at some
previous stage in race-history, but in most of them we have no proof that
it did so.  It may be, and the possibility must not be lost sight of, that
these organs never were anything else than functionless and that though
they have been got rid of in the adult by elimination in the course of
time, they have been able to persist in embryonic stages which are
protected from the full action of natural selection.  There is no reason to
suppose that living matter at its first appearance differed from non-living
matter in possessing only properties conducive to its well-being and
prolonged existence.  No one thinks that the properties of the various
forms of inorganic matter are all strictly related to external conditions.
Of what use to the diamond is its high specific gravity and high
refrangibility, and to gold of its yellow colour and great weight?  These
substances continue to exist in virtue of other properties than these.  It
is impossible to suppose that the properties of living matter at its first
appearance were all useful to it, for even now after aeons of elimination
we find that it possesses many useless organs and that many of its
relations to the external world are capable of considerable improvement.

In writing this essay I have purposely refrained from taking a definite
position with regard to the problems touched.  My desire has been to write
a chapter showing the influence of Darwin's work so far as Embryology is
concerned, and the various points which come up for consideration in
discussing his views.  Darwin was the last man who would have claimed
finality for any of his doctrines, but he might fairly have claimed to have
set going a process of intellectual fermentation which is still very far
from completion.


XI.  THE PALAEONTOLOGICAL RECORD.

I.  ANIMALS.

By W.B. SCOTT.
Professor of Geology in the University of Princeton, U.S.A.

To no branch of science did the publication of "The Origin of Species"
prove to be a more vivifying and transforming influence than to
Palaeontology.  This science had suffered, and to some extent, still
suffers from its rather anomalous position between geology and biology,
each of which makes claim to its territory, and it was held in strict
bondage to the Linnean and Cuvierian dogma that species were immutable
entities.  There is, however, reason to maintain that this strict bondage
to a dogma now abandoned, was not without its good side, and served the
purpose of keeping the infant science in leading-strings until it was able
to walk alone, and preventing a flood of premature generalisations and
speculations.

As Zittel has said:  "Two directions were from the first apparent in
palaeontological research--a stratigraphical and a biological. 
Stratigraphers wished from palaeontology mainly confirmation regarding the
true order or relative age of zones of rock-deposits in the field. 
Biologists had, theoretically at least, the more genuine interest in fossil
organisms as individual forms of life."  (Zittel, "History of Geology and
Palaeontology", page 363, London, 1901.)  The geological or stratigraphical
direction of the science was given by the work of William Smith, "the
father of historical geology," in the closing decade of the eighteenth
century.  Smith was the first to make a systematic use of fossils in
determining the order of succession of the rocks which make up the
accessible crust of the earth, and this use has continued, without
essential change, to the present day.  It is true that the theory of
evolution has greatly modified our conceptions concerning the introduction
of new species and the manner in which palaeontological data are to be
interpreted in terms of stratigraphy, but, broadly speaking, the method
remains fundamentally the same as that introduced by Smith.

The biological direction of palaeontology was due to Cuvier and his
associates, who first showed that fossils were not merely varieties of
existing organisms, but belonged to extinct species and genera, an
altogether revolutionary conception, which startled the scientific world. 
Cuvier made careful studies, especially of fossil vertebrates, from the
standpoint of zoology and was thus the founder of palaeontology as a
biological science.  His great work on "Ossements Fossiles" (Paris, 1821)
has never been surpassed as a masterpiece of the comparative method of
anatomical investigation, and has furnished to the palaeontologist the
indispensable implements of research.

On the other hand, Cuvier's theoretical views regarding the history of the
earth and its successive faunas and floras are such as no one believes to-
day.  He held that the earth had been repeatedly devastated by great
cataclysms, which destroyed every living thing, necessitating an entirely
new creation, thus regarding the geological periods as sharply demarcated
and strictly contemporaneous for the whole earth, and each species of
animal and plant as confined to a single period.  Cuvier's immense
authority and his commanding personality dominated scientific thought for
more than a generation and marked out the line which the development of
palaeontology was to follow.  The work was enthusiastically taken up by
many very able men in the various European countries and in the United
States, but, controlled as it was by the belief in the fixity of species,
it remained almost entirely descriptive and consisted in the description
and classification of the different groups of fossil organisms.  As already
intimated, this narrowness of view had its compensations, for it deferred
generalisations until some adequate foundations for these had been laid.

Dominant as it was, Cuvier's authority was slowly undermined by the
progress of knowledge and the way was prepared for the introduction of more
rational conceptions.  The theory of "Catastrophism" was attacked by
several geologists, most effectively by Sir Charles Lyell, who greatly
amplified the principles enunciated by Hutton and Playfair in the preceding
century, and inaugurated a new era in geology.  Lyell's uniformitarian
views of the earth's history and of the agencies which had wrought its
changes, had undoubted effect in educating men's minds for the acceptance
of essentially similar views regarding the organic world.  In palaeontology
too the doctrine of the immutability of species, though vehemently
maintained and reasserted, was gradually weakening.  In reviewing long
series of fossils, relations were observed which pointed to genetic
connections and yet were interpreted as purely ideal.  Agassiz, for
example, who never accepted the evolutionary theory, drew attention to
facts which could be satisfactorily interpreted only in terms of that
theory.  Among the fossils he indicated "progressive," "synthetic,"
"prophetic," and "embryonic" types, and pointed out the parallelism which
obtains between the geological succession of ancient animals and the
ontogenetic development of recent forms.  In Darwin's words:  "This view
accords admirably well with our theory."  ("Origin of Species" (6th
edition), page 310.)  Of similar import were Owen's views on "generalised
types" and "archetypes."

The appearance of "The Origin of Species" in 1859 revolutionised all the
biological sciences.  From the very nature of the case, Darwin was
compelled to give careful consideration to the palaeontological evidence;
indeed, it was the palaeontology and modern distribution of animals in
South America which first led him to reflect upon the great problem.  In
his own words:  "I had been deeply impressed by discovering in the Pampean
formation great fossil animals covered with armour like that on the
existing armadillos; secondly, by the manner in which closely allied
animals replace one another in proceeding southward over the Continent; and
thirdly, by the South American character of most of the productions of the
Galapagos archipelago, and more especially by the manner in which they
differ slightly on each island of the group."  ("Life and Letters of
Charles Darwin", I. page 82.)  In the famous tenth and eleventh chapters of
the "Origin", the palaeontological evidence is examined at length and the
imperfection of the geological record is strongly emphasised.  The
conclusion is reached, that, in view of this extreme imperfection,
palaeontology could not reasonably be expected to yield complete and
convincing proof of the evolutionary theory.  "I look at the geological
record as a history of the world imperfectly kept, and written in a
changing dialect; of this history we possess the last volume alone,
relating only to two or three countries.  Of this volume, only here and
there a short chapter has been preserved; and of each page, only here and
there a few lines."  ("Origin of Species", page 289.)  Yet, aside from
these inevitable difficulties, he concludes, that "the other great leading
facts in palaeontology agree admirably with the theory of descent with
modification through variation and natural selection."  (Ibid. page 313.)

Darwin's theory gave an entirely new significance and importance to
palaeontology.  Cuvier's conception of the science had been a limited,
though a lofty one.  "How glorious it would be if we could arrange the
organised products of the universe in their chronological order!...The
chronological succession of organised forms, the exact determination of
those types which appeared first, the simultaneous origin of certain
species and their gradual decay, would perhaps teach us as much about the
mysteries of organisation as we can possibly learn through experiments with
living organisms."  (Zittel op. cit. page 140.)  This, however, was rather
the expression of a hope for the distant future than an account of what was
attainable, and in practice the science remained almost purely descriptive,
until Darwin gave it a new standpoint, new problems and an altogether fresh
interest and charm.  The revolution thus accomplished is comparable only to
that produced by the Copernican astronomy.

From the first it was obvious that one of the most searching tests of the
evolutionary theory would be given by the advance of palaeontological
discovery.  However imperfect the geological record might be, its
ascertained facts would necessarily be consistent, under any reasonable
interpretation, with the demands of a true theory; otherwise the theory
would eventually be overwhelmed by the mass of irreconcilable data.  A very
great stimulus was thus given to geological investigation and to the
exploration of new lands.  In the last forty years, the examination of
North and South America, of Africa and Asia has brought to light many
chapters in the history of life, which are astonishingly full and complete. 
The flood of new material continues to accumulate at such a rate that it is
impossible to keep abreast of it, and the very wealth of the collections is
a source of difficulty and embarrassment.  In modern palaeontology
phylogenetic questions and problems occupy a foremost place and, as a
result of the labours of many eminent investigators in many lands, it may
be said that this science has proved to be one of the most solid supports
of Darwin's theory.  True, there are very many unsolved problems, and the
discouraged worker is often tempted to believe that the fossils raise more
questions than they answer.  Yet, on the other hand, the whole trend of the
evidence is so strongly in favour of the evolutionary doctrine, that no
other interpretation seems at all rational.

To present any adequate account of the palaeontological record from the
evolutionary standpoint, would require a large volume and a singularly
unequal, broken and disjointed history it would be.  Here the record is
scanty, interrupted, even unintelligible, while there it is crowded with
embarrassing wealth of material, but too often these full chapters are
separated by such stretches of unrecorded time, that it is difficult to
connect them.  It will be more profitable to present a few illustrative
examples than to attempt an outline of the whole history.

At the outset, the reader should be cautioned not to expect too much, for
the task of determining phylogenies fairly bristles with difficulties and
encounters many unanswered questions.  Even when the evidence seems to be
as copious and as complete as could be wished, different observers will put
different interpretations upon it, as in the notorious case of the
Steinheim shells.  (In the Miocene beds of Steinheim, Wurtemberg, occur
countless fresh-water shells, which show numerous lines of modification,
but these have been very differently interpreted by different writers.) 
The ludicrous discrepances which often appear between the phylogenetic
"trees" of various writers have cast an undue discredit upon the science
and have led many zoologists to ignore palaeontology altogether as unworthy
of serious attention.  One principal cause of these discrepant and often
contradictory results is our ignorance concerning the exact modes of
developmental change.  What one writer postulates as almost axiomatic,
another will reject as impossible and absurd.  Few will be found to agree
as to how far a given resemblance is offset by a given unlikeness, and so
long as the question is one of weighing evidence and balancing
probabilities, complete harmony is not to be looked for.  These formidable
difficulties confront us even in attempting to work out from abundant
material a brief chapter in the phylogenetic history of some small and
clearly limited group, and they become disproportionately greater, when we
extend our view over vast periods of time and undertake to determine the
mutual relationships of classes and types.  If the evidence were complete
and available, we should hardly be able to unravel its infinite complexity,
or to find a clue through the mazes of the labyrinth.  "Our ideas of the
course of descent must of necessity be diagrammatic."  (D.H. Scott,
"Studies in Fossil Botany", page 524.  London, 1900.)

Some of the most complete and convincing examples of descent with
modification are to be found among the mammals, and nowhere more abundantly
than in North America, where the series of continental formations, running
through the whole Tertiary period, is remarkably full.  Most of these
formations contain a marvellous wealth of mammalian remains and in an
unusual state of preservation.  The oldest Eocene (Paleocene) has yielded a
mammalian fauna which is still of prevailingly Mesozoic character, and
contains but few forms which can be regarded as ancestral to those of later
times.  The succeeding fauna of the lower Eocene proper (Wasatch stage) is
radically different and, while a few forms continue over from the
Paleocene, the majority are evidently recent immigrants from some region
not yet identified.  From the Wasatch onward, the development of many phyla
may be traced in almost unbroken continuity, though from time to time the
record is somewhat obscured by migrations from the Old World and South
America.  As a rule, however, it is easy to distinguish between the
immigrant and the indigenous elements of the fauna.

From their gregarious habits and individual abundance, the history of many
hoofed animals is preserved with especial clearness.  So well known as to
have become a commonplace, is the phylogeny of the horses, which, contrary
to all that would have been expected, ran the greater part of its course in
North America.  So far as it has yet been traced, the line begins in the
lower Eocene with the genus Eohippus, a little creature not much larger
than a cat, which has a short neck, relatively short limbs, and in
particular, short feet, with four functional digits and a splint-like
rudiment in the fore-foot, three functional digits and a rudiment in the
hind-foot.  The forearm bones (ulna and radius) are complete and separate,
as are also the bones of the lower leg (fibula and tibia).  The skull has a
short face, with the orbit, or eye-socket, incompletely enclosed with bone,
and the brain-case is slender and of small capacity.  The teeth are short-
crowned, the incisors without "mark," or enamel pit, on the cutting edge;
the premolars are all smaller and simpler than the molars.  The pattern of
the upper molars is so entirely different from that seen in the modern
horses that, without the intermediate connecting steps, no one would have
ventured to derive the later from the earlier plan.  This pattern is
quadritubercular, with four principal, conical cusps arranged in two
transverse pairs, forming a square, and two minute cuspules between each
transverse pair, a tooth which is much more pig-like than horse-like.  In
the lower molars the cusps have already united to form two crescents, one
behind the other, forming a pattern which is extremely common in the early
representatives of many different families, both of the Perissodactyla and
the Artiodactyla.  In spite of the manifold differences in all parts of the
skeleton between Eohippus and the recent horses, the former has stamped
upon it an equine character which is unmistakable, though it can hardly be
expressed in words.

Each one of the different Eocene and Oligocene horizons has its
characteristic genus of horses, showing a slow, steady progress in a
definite direction, all parts of the structure participating in the
advance.  It is not necessary to follow each of these successive steps of
change, but it should be emphasised that the changes are gradual and
uninterrupted.  The genus Mesohippus, of the middle Oligocene, may be
selected as a kind of half-way stage in the long progression.  Comparing
Mesohippus with Eohippus, we observe that the former is much larger, some
species attaining the size of a sheep, and has a relatively longer neck,
longer limbs and much more elongate feet, which are tridactyl, and the
middle toe is so enlarged that it bears most of the weight, while the
lateral digits are very much more slender.  The fore-arm bones have begun
to co-ossify and the ulna is greatly reduced, while the fibula, though
still complete, is hardly more than a thread of bone.  The skull has a
longer face and a nearly enclosed orbit, and the brain-case is fuller and
more capacious, the internal cast of which shows that the brain was richly
convoluted.  The teeth are still very short-crowned, but the upper incisors
plainly show the beginning of the "mark"; the premolars have assumed the
molar form, and the upper molars, though plainly derived from those of
Eohippus, have made a long stride toward the horse pattern, in that the
separate cusps have united to form a continuous outer wall and two
transverse crests.

In the lower Miocene the interesting genus Desmatippus shows a further
advance in the development of the teeth, which are beginning to assume the
long-crowned shape, delaying the formation of roots; a thin layer of cement
covers the crowns, and the transverse crests of the upper grinding teeth
display an incipient degree of their modern complexity.  This tooth-pattern
is strictly intermediate between the recent type and the ancient type seen
in Mesohippus and its predecessors.  The upper Miocene genera, Protohippus
and Hipparion are, to all intents and purposes, modern in character, but
their smaller size, tridactyl feet and somewhat shorter-crowned teeth are
reminiscences of their ancestry.

From time to time, when a land-connection between North America and Eurasia
was established, some of the successive equine genera migrated to the Old
World, but they do not seem to have gained a permanent footing there until
the end of the Miocene or beginning of the Pliocene, eventually
diversifying into the horses, asses, and zebras of Africa, Asia and Europe. 
At about the same period, the family extended its range to South America
and there gave rise to a number of species and genera, some of them
extremely peculiar.  For some unknown reason, all the horse tribe had
become extinct in the western hemisphere before the European discovery, but
not until after the native race of man had peopled the continents.

In addition to the main stem of equine descent, briefly considered in the
foregoing paragraphs, several side-branches were given off at successive
levels of the stem.  Most of these branches were short-lived, but some of
them flourished for a considerable period and ramified into many species.

Apparently related to the horses and derived from the same root-stock is
the family of the Palaeotheres, confined to the Eocene and Oligocene of
Europe, dying out without descendants.  In the earlier attempts to work out
the history of the horses, as in the famous essay of Kowalevsky ("Sur
l'Anchitherium aurelianense Cuv. et sur l'histoire paleontologique des
Chevaux", "Mem. de l'Acad. Imp. des Sc. de St Petersbourg", XX. no. 5,
1873.), the Palaeotheres were placed in the direct line, because the number
of adequately known Eocene mammals was then so small, that Cuvier's types
were forced into various incongruous positions, to serve as ancestors for
unrelated series.

The American family of the Titanotheres may also be distantly related to
the horses, but passed through an entirely different course of development. 
From the lower Eocene to the lower sub-stage of the middle Oligocene the
series is complete, beginning with small and rather lightly built animals.
Gradually the stature and massiveness increase, a transverse pair of nasal
horns make their appearance and, as these increase in size, the canine
tusks and incisors diminish correspondingly.  Already in the oldest known
genus the number of digits had been reduced to four in the fore-foot and
three in the hind, but there the reduction stops, for the increasing body-
weight made necessary the development of broad and heavy feet.  The final
members of the series comprise only large, almost elephantine animals, with
immensely developed and very various nasal horns, huge and massive heads,
and altogether a grotesque appearance.  The growth of the brain did not at
all keep pace with the increase of the head and body, and the ludicrously
small brain may will have been one of the factors which determined the
startlingly sudden disappearance and extinction of the group.

Less completely known, but of unusual interest, is the genealogy of the
rhinoceros family, which probably, though not certainly, was likewise of
American origin.  The group in North America at least, comprised three
divisions, or sub-families, of very different proportions, appearance and
habits, representing three divergent lines from the same stem.  Though the
relationship between the three lines seems hardly open to question, yet the
form ancestral to all of them has not yet been identified.  This is because
of our still very incomplete knowledge of several perissodactyl genera of
the Eocene, any one of which may eventually prove to be the ancestor sought
for.

The first sub-family is the entirely extinct group of Hyracodonts, which
may be traced in successive modifications through the upper Eocene, lower
and middle Oligocene, then disappearing altogether.  As yet, the
hyracodonts have been found only in North America, and the last genus of
the series, Hyracodon, was a cursorial animal.  Very briefly stated, the
modifications consist in a gradual increase in size, with greater
slenderness of proportions, accompanied by elongation of the neck, limbs,
and feet, which become tridactyl and very narrow.  The grinding teeth have
assumed the rhinoceros-like pattern and the premolars resemble the molars
in form; on the other hand, the front teeth, incisors and canines, have
become very small and are useless as weapons.  As the animal had no horns,
it was quite defenceless and must have found its safety in its swift
running, for Hyracodon displays many superficial resemblances to the
contemporary Oligocene horses, and was evidently adapted for speed.  It may
well have been the competition of the horses which led to the extinction of
these cursorial rhinoceroses.

The second sub-family, that of the Amynodonts, followed a totally different
course of development, becoming short-legged and short-footed, massive
animals, the proportions of which suggest aquatic habits; they retained
four digits in the front foot.  The animal was well provided with weapons
in the large canine tusks, but was without horns.  Some members of this
group extended their range to the Old World, but they all died out in the
middle Oligocene, leaving no successors.

The sub-family of the true rhinoceroses cannot yet be certainly traced
farther back than to the base of the middle Oligocene, though some
fragmentary remains found in the lower Oligocene are probably also
referable to it.  The most ancient and most primitive member of this series
yet discovered, the genus Trigonias, is unmistakably a rhinoceros, yet much
less massive, having more the proportions of a tapir; it had four toes in
the front foot, three in the hind, and had a full complement of teeth,
except for the lower canines, though the upper canines are about to
disappear, and the peculiar modification of the incisors, characteristic of
the true rhinoceroses, is already apparent; the skull is hornless. 
Representatives of this sub-family continue through the Oligocene and
Miocene of North America, becoming rare and localised in the Pliocene and
then disappearing altogether.  In the Old World, on the other hand, where
the line appeared almost as early as it did in America, this group
underwent a great expansion and ramification, giving rise not only to the
Asiatic and African forms, but also to several extinct series.

Turning now to the Artiodactyla, we find still another group of mammals,
that of the camels and llamas, which has long vanished from North America,
yet took its rise and ran the greater part of its course in that continent.
From the lower Eocene onward the history of this series is substantially
complete, though much remains to be learned concerning the earlier members
of the family.  The story is very like that of the horses, to which in many
respects it runs curiously parallel.  Beginning with very small, five-toed
animals, we observe in the successive genera a gradual transformation in
all parts of the skeleton, an elongation of the neck, limbs and feet, a
reduction of the digits from five to two, and eventually the coalescence of
the remaining two digits into a "cannon-bone."  The grinding teeth, by
equally gradual steps, take on the ruminant pattern.  In the upper Miocene
the line divides into the two branches of the camels and llamas, the former
migrating to Eurasia and the latter to South America, though
representatives of both lines persisted in North America until a very late
period.  Interesting side-branches of this line have also been found, one
of which ended in the upper Miocene in animals which had almost the
proportions of the giraffes and must have resembled them in appearance.

The American Tertiary has yielded several other groups of ruminant-like
animals, some of which form beautifully complete evolutionary series, but
space forbids more than this passing mention of them.

It was in Europe that the Artiodactyla had their principal development, and
the upper Eocene, Oligocene and Miocene are crowded with such an
overwhelming number and variety of forms that it is hardly possible to
marshal them in orderly array and determine their mutual relationships. 
Yet in this chaotic exuberance of life, certain important facts stand out
clearly, among these none is of greater interest and importance than the
genealogy of the true Ruminants, or Pecora, which may be traced from the
upper Eocene onward.  The steps of modification and change are very similar
to those through which the camel phylum passed in North America, but it is
instructive to note that, despite their many resemblances, the two series
can be connected only in their far distant beginnings.  The pecoran stock
became vastly more expanded and diversified than did the camel line and was
evidently more plastic and adaptable, spreading eventually over all the
continents except Australia, and forming to-day one of the dominant types
of mammals, while the camels are on the decline and not far from
extinction.  The Pecora successively ramified into the deer, antelopes,
sheep, goats and oxen, and did not reach North America till the Miocene,
when they were already far advanced in specialisation.  To this invasion of
the Pecora, or true ruminants, it seems probable that the decline and
eventual disappearance of the camels is to be ascribed.

Recent discoveries in Egypt have thrown much light upon a problem which
long baffled the palaeontologist, namely, the origin of the elephants. 
(C.W. Andrews, "On the Evolution of the Proboscidea", "Phil. Trans. Roy.
Soc." London, Vol. 196, 1904, page 99.)  Early representatives of this
order, Mastodons, had appeared almost simultaneously (in the geological
sense of that word) in the upper Miocene of Europe and North America, but
in neither continent was any more ancient type known which could plausibly
be regarded as ancestral to them.  Evidently, these problematical animals
had reached the northern continents by migrating from some other region,
but no one could say where that region lay.  The Eocene and Oligocene beds
of the Fayoum show us that the region sought for is Africa, and that the
elephants form just such a series of gradual modifications as we have found
among other hoofed animals.  The later steps of the transformation, by
which the mastodons lost their lower tusks, and their relatively small and
simple grinding teeth acquired the great size and highly complex structure
of the true elephants, may be followed in the uppermost Miocene and
Pliocene fossils of India and southern Europe.

Egypt has also of late furnished some very welcome material which
contributes to the solution of another unsolved problem which had quite
eluded research, the origin of the whales.  The toothed-whales may be
traced back in several more or less parallel lines as far as the lower
Miocene, but their predecessors in the Oligocene are still so incompletely
known that safe conclusions can hardly be drawn from them.  In the middle
Eocene of Egypt, however, has been found a small, whale-like animal
(Protocetus), which shows what the ancestral toothed-whale was like, and at
the same time seems to connect these thoroughly marine mammals with land-
animals.  Though already entirely adapted to an aquatic mode of life, the
teeth, skull and backbone of Protocetus display so many differences from
those of the later whales and so many approximations to those of primitive,
carnivorous land-mammals, as, in a large degree, to bridge over the gap
between the two groups.  Thus one of the most puzzling of palaeontological
questions is in a fair way to receive a satisfactory answer.  The origin of
the whalebone-whales and their relations to the toothed-whales cannot yet
be determined, since the necessary fossils have not been discovered.

Among the carnivorous mammals, phylogenetic series are not so clear and
distinct as among the hoofed animals, chiefly because the carnivores are
individually much less abundant, and well-preserved skeletons are among the
prizes of the collector.  Nevertheless, much has already been learned
concerning the mutual relations of the carnivorous families, and several
phylogenetic series, notably that of the dogs, are quite complete.  It has
been made extremely probable that the primitive dogs of the Eocene
represent the central stock, from which nearly or quite all the other
families branched off, though the origin and descent of the cats have not
yet been determined.

It should be clearly understood that the foregoing account of mammalian
descent is merely a selection of a few representative cases and might be
almost indefinitely extended.  Nothing has been said, for example, of the
wonderful museum of ancient mammalian life which is entombed in the rocks
of South America, especially of Patagonia, and which opens a world so
entirely different from that of the northern continents, yet exemplifying
the same laws of "descent with modification."  Very beautiful phylogenetic
series have already been established among these most interesting and
marvellously preserved fossils, but lack of space forbids a consideration
of them.

The origin of the mammalia, as a class, offers a problem of which
palaeontology can as yet present no definitive solution.  Many
morphologists regard the early amphibia as the ancestral group from which
the mammals were derived, while most palaeontologists believe that the
mammals are descended from the reptiles.  The most ancient known mammals,
those from the upper Triassic of Europe and North America, are so extremely
rare and so very imperfectly known, that they give little help in
determining the descent of the class, but, on the other hand, certain
reptilian orders of the Permian period, especially well represented in
South Africa, display so many and such close approximations to mammalian
structure, as strongly to suggest a genetic relationship.  It is difficult
to believe that all those likenesses should have been independently
acquired and are without phylogenetic significance.

Birds are comparatively rare as fossils and we should therefore look in
vain among them for any such long and closely knit series as the mammals
display in abundance.  Nevertheless, a few extremely fortunate discoveries
have made it practically certain that birds are descended from reptiles, of
which they represent a highly specialised branch.  The most ancient
representative of this class is the extraordinary genus Archaeopteryx from
the upper Jurassic of Bavaria, which, though an unmistakable bird, retains
so many reptilian structures and characteristics as to make its derivation
plain.  Not to linger over anatomical minutiae, it may suffice to mention
the absence of a horny beak, which is replaced by numerous true teeth, and
the long lizard-like tail, which is made up of numerous distinct vertebrae,
each with a pair of quill-like feathers attached to it.  Birds with teeth
are also found in the Cretaceous, though in most other respects the birds
of that period had attained a substantially modern structure.  Concerning
the interrelations of the various orders and families of birds,
palaeontology has as yet little to tell us.

The life of the Mesozoic era was characterised by an astonishing number and
variety of reptiles, which were adapted to every mode of life, and
dominated the air, the sea and the land, and many of which were of colossal
proportions.  Owing to the conditions of preservation which obtained during
the Mesozoic period, the history of the reptiles is a broken and
interrupted one, so that we can make out many short series, rather than any
one of considerable length.  While the relations of several reptilian
orders can be satisfactorily determined, others still baffle us entirely,
making their first known appearance in a fully differentiated state.  We
can trace the descent of the sea-dragons, the Ichthyosaurs and Plesiosaurs,
from terrestrial ancestors, but the most ancient turtles yet discovered
show us no closer approximation to any other order than do the recent
turtles; and the oldest known Pterosaurs, the flying dragons of the
Jurassic, are already fully differentiated.  There is, however, no ground
for discouragement in this, for the progress of discovery has been so rapid
of late years, and our knowledge of Mesozoic life has increased with such
leaps and bounds, that there is every reason to expect a solution of many
of the outstanding problems in the near future.

Passing over the lower vertebrates, for lack of space to give them any
adequate consideration, we may briefly take up the record of invertebrate
life.  From the overwhelming mass of material it is difficult to make a
representative selection and even more difficult to state the facts
intelligibly without the use of unduly technical language and without the
aid of illustrations.

Several groups of the Mollusca, or shell-fish, yield very full and
convincing evidence of their descent from earlier and simpler forms, and of
these none is of greater interest than the Ammonites, an extinct order of
the cephalopoda.  The nearest living ally of the ammonites is the pearly
nautilus, the other existing cephalopods, such as the squids, cuttle-fish,
octopus, etc., are much more distantly related.  Like the nautilus, the
ammonites all possess a coiled and chambered shell, but their especial
characteristic is the complexity of the "sutures."  By sutures is meant the
edges of the transverse partitions, or septa, where these join the shell-
wall, and their complexity in the fully developed genera is extraordinary,
forming patterns like the most elaborate oak-leaf embroidery, while in the
nautiloids the sutures form simple curves.  In the rocks of the Mesozoic
era, wherever conditions of preservation are favourable, these beautiful
shells are stored in countless multitudes, of an incredible variety of
form, size and ornamentation, as is shown by the fact that nearly 5000
species have already been described.  The ammonites are particularly well
adapted for phylogenetic studies, because, by removing the successive
whorls of the coiled shell, the individual development may be followed back
in inverse order, to the microscopic "protoconch," or embryonic shell,
which lies concealed in the middle of the coil.  Thus the valuable aid of
embryology is obtained in determining relationships.

The descent of the ammonites, taken as a group, is simple and clear; they
arose as a branch of the nautiloids in the lower Devonian, the shells known
as goniatites having zigzag, angulated sutures.  Late in the succeeding
Carboniferous period appear shells with a truly ammonoid complexity of
sutures, and in the Permian their number and variety cause them to form a
striking element of the marine faunas.  It is in the Mesozoic era, however,
that these shells attain their full development; increasing enormously in
the Triassic, they culminate in the Jurassic in the number of families,
genera and species, in the complexity of the sutures, and in the variety of
shell-ornamentation.  A slow decline begins in the Cretaceous, ending in
the complete extinction of the whole group at the end of that period.  As a
final phase in the history of the ammonites, there appear many so-called
"abnormal" genera, in which the shell is irregularly coiled, or more or
less uncoiled, in some forms becoming actually straight.  It is interesting
to observe that some of these genera are not natural groups, but are
"polyphyletic," i.e. are each derived from several distinct ancestral
genera, which have undergone a similar kind of degeneration.

In the huge assembly of ammonites it is not yet possible to arrange all the
forms in a truly natural classification, which shall express the various
interrelations of the genera, yet several beautiful series have already
been determined.  In these series the individual development of the later
general shows transitory stages which are permanent in antecedent genera. 
To give a mere catalogue of names without figures would not make these
series more intelligible.

The Brachiopoda, or "lamp-shells," are a phylum of which comparatively few
survive to the present day; their shells have a superficial likeness to
those of the bivalved Mollusca, but are not homologous with the latter, and
the phylum is really very distinct from the molluscs.  While greatly
reduced now, these animals were incredibly abundant throughout the
Palaeozoic era, great masses of limestone being often composed almost
exclusively of their shells, and their variety is in keeping with their
individual abundance.  As in the case of the ammonites, the problem is to
arrange this great multitude of forms in an orderly array that shall
express the ramifications of the group according to a genetic system.  For
many brachiopods, both recent and fossil, the individual development, or
ontogeny, has been worked out and has proved to be of great assistance in
the problems of classification and phylogeny.  Already very encouraging
progress has been made in the solution of these problems.  All brachiopods
form first a tiny, embryonic shell, called the protegulum, which is
believed to represent the ancestral form of the whole group, and in the
more advanced genera the developmental stages clearly indicate the
ancestral genera of the series, the succession of adult forms in time
corresponding to the order of the ontogenetic stages.  The transformation
of the delicate calcareous supports of the arms, often exquisitely
preserved, are extremely interesting.  Many of the Palaeozoic genera had
these supports coiled like a pair of spiral springs, and it has been shown
that these genera were derived from types in which the supports were simply
shelly loops.

The long extinct class of crustacea known as the Trilobites are likewise
very favourable subjects for phylogenetic studies.  So far as the known
record can inform us, the trilobites are exclusively Palaeozoic in
distribution, but their course must have begun long before that era, as is
shown by the number of distinct types among the genera of the lower
Cambrian.  The group reached the acme of abundance and relative importance
in the Cambrian and Ordovician; then followed a long, slow decline, ending
in complete and final disappearance before the end of the Permian.  The
newly-hatched and tiny trilobite larva, known as the protaspis, is very
near to the primitive larval form of all the crustacea.  By the aid of the
correlated ontogenetic stages and the succession of the adult forms in the
rocks, many phylogenetic series have been established and a basis for the
natural arrangement of the whole class has been laid.

Very instructive series may also be observed among the Echinoderms and,
what is very rare, we are able in this sub-kingdom to demonstrate the
derivation of one class from another.  Indeed, there is much reason to
believe that the extinct class Cystidea of the Cambrian is the ancestral
group, from which all the other Echinoderms, star-fishes, brittle-stars,
sea-urchins, feather-stars, etc., are descended.

The foregoing sketch of the palaeontological record is, of necessity,
extremely meagre, and does not represent even an outline of the evidence,
but merely a few illustrative examples, selected almost at random from an
immense body of material.  However, it will perhaps suffice to show that
the geological record is not so hopelessly incomplete as Darwin believed it
to be.  Since "The Origin of Species" was written, our knowledge of that
record has been enormously extended and we now possess, no complete
volumes, it is true, but some remarkably full and illuminating chapters. 
The main significance of the whole lies in the fact, that JUST IN
PROPORTION TO THE COMPLETENESS OF THE RECORD IS THE UNEQUIVOCAL CHARACTER
OF ITS TESTIMONY TO THE TRUTH OF THE EVOLUTIONARY THEORY.

The test of a true, as distinguished from a false, theory is the manner in
which newly discovered and unanticipated facts arrange themselves under it. 
No more striking illustration of this can be found than in the contrasted
fates of Cuvier's theory and of that of Darwin.  Even before Cuvier's death
his views had been undermined and the progress of discovery soon laid them
in irreparable ruin, while the activity of half-a-century in many different
lines of inquiry has established the theory of evolution upon a foundation
of ever growing solidity.  It is Darwin's imperishable glory that he
prescribed the lines along which all the biological sciences were to
advance to conquests not dreamed of when he wrote.


XII.  THE PALAEONTOLOGICAL RECORD.

II.  PLANTS.

By D.H. SCOTT, F.R.S.
President of the Linnean Society.

There are several points of view from which the subject of the present
essay may be regarded.  We may consider the fossil record of plants in its
bearing:  I. on the truth of the doctrine of Evolution; II. on Phylogeny,
or the course of Evolution; III. on the theory of Natural Selection.  The
remarks which follow, illustrating certain aspects only of an extensive
subject, may conveniently be grouped under these three headings.

I.  THE TRUTH OF EVOLUTION.

When "The Origin of Species" was written, it was necessary to show that the
Geological Record was favourable to, or at least consistent with, the
Theory of Descent.  The point is argued, closely and fully, in Chapter X. 
"On the Imperfection of the Geological Record," and Chapter XI.  "On the
Geological Succession of Organic Beings"; there is, however, little about
plants in these chapters.  At the present time the truth of Evolution is no
longer seriously disputed, though there are writers, like Reinke, who
insist, and rightly so, that the doctrine is still only a belief, rather
than an established fact of science.  (J. Reinke, "Kritische
Abstammungslehre", "Wiesner-Festschrift", page 11, Vienna, 1908.) 
Evidently, then, however little the Theory of Descent may be questioned in
our own day, it is desirable to assure ourselves how the case stands, and
in particular how far the evidence from fossil plants has grown stronger
with time.

As regards direct evidence for the derivation of one species from another,
there has probably been little advance since Darwin wrote, at least so we
must infer from the emphasis laid on the discontinuity of successive fossil
species by great systematic authorities like Grand'Eury and Zeiller in
their most recent writings.  We must either adopt the mutationist views of
those authors (referred to in the last section of this essay) or must still
rely on Darwin's explanation of the absence of numerous intermediate
varieties.  The attempts which have been made to trace, in the Tertiary
rocks, the evolution of recent species, cannot, owing to the imperfect
character of the evidence, be regarded as wholly satisfactory.

When we come to groups of a somewhat higher order we have an interesting
history of the evolution of a recent family in the work, not yet completed,
of Kidston and Gwynne-Vaughan on the fossil Osmundaceae.  ("Trans. Royal
Soc. Edinburgh", Vol. 45, Part III. 1907, Vol. 46, Part II. 1908, Vol. 46,
Part III. 1909.)  The authors are able, mainly on anatomical evidence, to
trace back this now limited group of Ferns, through the Tertiary and
Mesozoic to the Permian, and to show, with great probability, how their
structure has been derived from that of early Palaeozoic types.

The history of the Ginkgoaceae, now represented only by the isolated
maidenhair tree, scarcely known in a wild state, offers another striking
example of a family which can be traced with certainty to the older
Mesozoic and perhaps further back still.  (See Seward and Gowan, "The
Maidenhair Tree (Gingko biloba)", "Annals of Botany", Vol. XIV. 1900, page
109; also A. Sprecher "Le Ginkgo biloba", L., Geneva, 1907.)

On the wider question of the derivation of the great groups of plants, a
very considerable advance has been made, and, so far as the higher plants
are concerned, we are now able to form a far better conception than before
of the probable course of evolution.  This is a matter of phylogeny, and
the facts will be considered under that head; our immediate point is that
the new knowledge of the relations between the classes of plants in
question materially strengthens the case for the theory of descent.  The
discoveries of the last few years throw light especially on the relation of
the Angiosperms to the Gymnosperms, on that of the Seed-plants generally to
the Ferns, and on the interrelations between the various classes of the
higher Cryptogams.

That the fossil record has not done still more for Evolution is due to the
fact that it begins too late--a point on which Darwin laid stress ("Origin
of Species" (6th edition), page 286.) and which has more recently been
elaborated by Poulton.  ("Essays on Evolution", pages 46 et seq., Oxford,
1908.)  An immense proportion of the whole evolutionary history lies behind
the lowest fossiliferous rocks, and the case is worse for plants than for
animals, as the record for the former begins, for all practical purposes,
much higher up in the rocks.

It may be well here to call attention to a question, often overlooked,
which has lately been revived by Reinke.  (Reinke, loc. cit. page 13.)  As
all admit, we know nothing of the origin of life; consequently, for all we
can tell, it is as probable that life began, on this planet, with many
living things, as with one.  If the first organic beings were many, they
may have been heterogeneous, or at least exposed to different conditions,
from their origin; in either case there would have been a number of
distinct series from the beginning, and if so we should not be justified in
assuming that all organisms are related to one another.  There may
conceivably be several of the original lines of descent still surviving, or
represented among extinct forms--to reverse the remark of a distinguished
botanist, there may be several Vegetable Kingdoms!  However improbable this
may sound, the possibility is one to be borne in mind.

That all VASCULAR plants really belong to one stock seems certain, and here
the palaeontological record has materially strengthened the case for a
monophyletic history.  The Bryophyta are not likely to be absolutely
distinct, for their sexual organs, and the stomata of the Mosses strongly
suggest community of descent with the higher plants; if this be so it no
doubt establishes a certain presumption in favour of a common origin for
plants generally, for the gap between "Mosses and Ferns" has been regarded
as the widest in the Vegetable Kingdom.  The direct evidence of
consanguinity is however much weaker when we come to the Algae, and it is
conceivable (even if improbable) that the higher plants may have had a
distinct ancestry (now wholly lost) from the beginning.  The question had
been raised in Darwin's time, and he referred to it in these words:  "No
doubt it is possible, as Mr G.H. Lewes has urged, that at the first
commencement of life many different forms were evolved; but if so, we may
conclude that only a very few have left modified descendants."  ("Origin of
Species", page 425.)  This question, though it deserves attention, does not
immediately affect the subject of the palaeontological record of plants,
for there can be no reasonable doubt as to the interrelationship of those
groups on which the record at present throws light.

The past history of plants by no means shows a regular progression from the
simple to the complex, but often the contrary.  This apparent anomaly is
due to two causes.

1.  The palaeobotanical record is essentially the story of the successive
ascendancy of a series of dominant families, each of which attained its
maximum, in organisation as well as in extent, and then sank into
comparative obscurity, giving place to other families, which under new
conditions were better able to take a leading place.  As each family ran
its downward course, either its members underwent an actual reduction in
structure as they became relegated to herbaceous or perhaps aquatic life
(this may have happened with the Horsetails and with Isoetes if derived
from Lepidodendreae), or the higher branches of the family were crowded out
altogether and only the "poor relations" were able to maintain their
position by evading the competition of the ascendant races; this is also
illustrated by the history of the Lycopod phylum.  In either case there
would result a lowering of the type of organisation within the group.

2.  The course of real progress is often from the complex to the simple. 
If, as we shall find some grounds for believing, the Angiosperms came from
a type with a flower resembling in its complexity that of Mesozoic
"Cycads," almost the whole evolution of the flower in the highest plants
has been a process of reduction.  The stamen, in particular, has
undoubtedly become extremely simplified during evolution; in the most
primitive known seed-plants it was a highly compound leaf or pinna; its
reduction has gone on in the Conifers and modern Cycads, as well as in the
Angiosperms, though in different ways and to a varying extent.

The seed offers another striking example; the Palaeozoic seeds (if we leave
the seed-like organs of certain Lycopods out of consideration) were always,
so far as we know, highly complex structures, with an elaborate vascular
system, a pollen-chamber, and often a much-differentiated testa.  In the
present day such seeds exist only in a few Gymnosperms which retain their
ancient characters--in all the higher Spermophytes the structure is very
much simplified, and this holds good even in the Coniferae, where there is
no countervailing complication of ovary and stigma.

Reduction, in fact, is not always, or even generally, the same thing as
degeneration.  Simplification of parts is one of the most usual means of
advance for the organism as a whole.  A large proportion of the higher
plants are microphyllous in comparison with the highly megaphyllous fern-
like forms from which they appear to have been derived.

Darwin treated the general question of advance in organisation with much
caution, saying:  "The geological record...does not extend far enough back,
to show with unmistakeable clearness that within the known history of the
world organisation has largely advanced."  ("Origin of Species", page 308.) 
Further on (Ibid. page 309.) he gives two standards by which advance may be
measured:  "We ought not solely to compare the highest members of a class
at any two periods...but we ought to compare all the members, high and low,
at the two periods."  Judged by either standard the Horsetails and Club
Mosses of the Carboniferous were higher than those of our own day, and the
same is true of the Mesozoic Cycads.  There is a general advance in the
succession of classes, but not within each class.

Darwin's argument that "the inhabitants of the world at each successive
period in its history have beaten their predecessors in the race for life,
and are, in so far, higher in the scale" ("Origin of Species", page 315.)
is unanswerable, but we must remember that "higher in the scale" only means
"better adapted to the existing conditions."  Darwin points out (Ibid. page
279.) that species have remained unchanged for long periods, probably
longer than the periods of modification, and only underwent change when the
conditions of their life were altered.  Higher organisation, judged by the
test of success, is thus purely relative to the changing conditions, a fact
of which we have a striking illustration in the sudden incoming of the
Angiosperms with all their wonderful floral adaptations to fertilisation by
the higher families of Insects.

II.  PHYLOGENY.

The question of phylogeny is really inseparable from that of the truth of
the doctrine of evolution, for we cannot have historical evidence that
evolution has actually taken place without at the same time having evidence
of the course it has followed.

As already pointed out, the progress hitherto made has been rather in the
way of joining up the great classes of plants than in tracing the descent
of particular species or genera of the recent flora.  There appears to be a
difference in this respect from the Animal record, which tells us so much
about the descent of living species, such as the elephant or the horse. 
The reason for this difference is no doubt to be found in the fact that the
later part of the palaeontological record is the most satisfactory in the
case of animals and the least so in the case of plants.  The Tertiary
plant-remains, in the great majority of instances, are impressions of
leaves, the conclusions to be drawn from which are highly precarious; until
the whole subject of Angiospermous palaeobotany has been reinvestigated, it
would be rash to venture on any statements as to the descent of the
families of Dicotyledons or Monocotyledons.

Our attention will be concentrated on the following questions, all relating
to the phylogeny of main groups of plants:  i. The Origin of the
Angiosperms.  ii. The Origin of the Seed-plants.  iii. The Origin of the
different classes of the Higher Cryptogamia.

i.  THE ORIGIN OF THE ANGIOSPERMS.

The first of these questions has long been the great crux of botanical
phylogeny, and until quite recently no light had been thrown upon the
difficulty.  The Angiosperms are the Flowering Plants, par excellence, and
form, beyond comparison, the dominant sub-kingdom in the flora of our own
age, including, apart from a few Conifers and Ferns, all the most familiar
plants of our fields and gardens, and practically all plants of service to
man.  All recent work has tended to separate the Angiosperms more widely
from the other seed-plants now living, the Gymnosperms.  Vast as is the
range of organisation presented by the great modern sub-kingdom, embracing
forms adapted to every environment, there is yet a marked uniformity in
certain points of structure, as in the development of the embryo-sac and
its contents, the pollination through the intervention of a stigma, the
strange phenomenon of double fertilisation (One sperm fertilising the egg,
while the other unites with the embryo-sac nucleus, itself the product of a
nuclear fusion, to give rise to a nutritive tissue, the endosperm.), the
structure of the stamens, and the arrangement of the parts of the flower. 
All these points are common to Monocotyledons and Dicotyledons, and
separate the Angiosperms collectively from all other plants.

In geological history the Angiosperms first appear in the Lower Cretaceous,
and by Upper Cretaceous times had already swamped all other vegetation and
seized the dominant position which they still hold.  Thus they are isolated
structurally from the rest of the Vegetable Kingdom, while historically
they suddenly appear, almost in full force, and apparently without
intermediaries with other groups.  To quote Darwin's vigorous words:  "The
rapid development, as far as we can judge, of all the higher plants within
recent geological times is an abominable mystery."  ("More Letters of
Charles Darwin", Vol. II. page 20, letter to J.D. Hooker, 1879.)  A couple
of years later he made a bold suggestion (which he only called an "idle
thought") to meet this difficulty.  He says: "I have been so astonished at
the apparently sudden coming in of the higher phanerogams, that I have
sometimes fancied that development might have slowly gone on for an immense
period in some isolated continent or large island, perhaps near the South
Pole."  (Ibid, page 26, letter to Hooker, 1881.)  This idea of an
Angiospermous invasion from some lost southern land has sometimes been
revived since, but has not, so far as the writer is aware, been supported
by evidence.  Light on the problem has come from a different direction.

The immense development of plants with the habit of Cycads, during the
Mesozoic Period up to the Lower Cretaceous, has long been known.  The
existing Order Cycadaceae is a small family, with 9 genera and perhaps 100
species, occurring in the tropical and sub-tropical zones of both the Old
and New World, but nowhere forming a dominant feature in the vegetation. 
Some few attain the stature of small trees, while in the majority the stem
is short, though often living to a great age.  The large pinnate or rarely
bipinnate leaves give the Cycads a superficial resemblance in habit to
Palms.  Recent Cycads are dioecious; throughout the family the male
fructification is in the form of a cone, each scale of the cone
representing a stamen, and bearing on its lower surface numerous pollen-
sacs, grouped in sori like the sporangia of Ferns.  In all the genera,
except Cycas itself, the female fructifications are likewise cones, each
carpel bearing two ovules on its margin.  In Cycas, however, no female cone
is produced, but the leaf-like carpels, bearing from two to six ovules
each, are borne directly on the main stem of the plant in rosettes
alternating with those of the ordinary leaves--the most primitive
arrangement known in any living seed-plant.  The whole Order is relatively
primitive, as shown most strikingly in its cryptogamic mode of
fertilisation, by means of spermatozoids, which it shares with the
maidenhair tree alone, among recent seed-plants.

In all the older Mesozoic rocks, from the Trias to the Lower Cretaceous,
plants of the Cycad class (Cycadophyta, to use Nathorst's comprehensive
name) are extraordinarily abundant in all parts of the world; in fact they
were almost as prominent in the flora of those ages as the Dicotyledons are
in that of our own day.  In habit and to a great extent in anatomy, the
Mesozoic Cycadophyta for the most part much resemble the recent Cycadaceae.
But, strange to say, it is only in the rarest cases that the fructification
has proved to be of the simple type characteristic of the recent family;
the vast majority of the abundant fertile specimens yielded by the Mesozoic
rocks possess a type of reproductive apparatus far more elaborate than
anything known in Cycadaceae or other Gymnosperms.  The predominant
Mesozoic family, characterised by this advanced reproductive organisation,
is known as the Bennettiteae; in habit these plants resembled the more
stunted Cycads of the recent flora, but differed from them in the presence
of numerous lateral fructifications, like large buds, borne on the stem
among the crowded bases of the leaves.  The organisation of these
fructifications was first worked out on European specimens by Carruthers,
Solms-Laubach, Lignier and others, but these observers had only more or
less ripe fruits to deal with; the complete structure of the flower has
only been elucidated within the last few years by the researches of Wieland
on the magnificent American material, derived from the Upper Jurassic and
Lower Cretaceous beds of Maryland, Dakota and Wyoming.  (G.R. Wieland,
"American Fossil Cycads", Carnegie Institution, Washington, 1906.)  The
word "flower" is used deliberately, for reasons which will be apparent from
the following brief description, based on Wieland's observations.

The fructification is attached to the stem by a thick stalk, which, in its
upper part, bears a large number of spirally arranged bracts, forming
collectively a kind of perianth and completely enclosing the essential
organs of reproduction.  The latter consist of a whorl of stamens, of
extremely elaborate structure, surrounding a central cone or receptacle
bearing numerous ovules.  The stamens resemble the fertile fronds of a
fern; they are of a compound, pinnate form, and bear very large numbers of
pollen-sacs, each of which is itself a compound structure consisting of a
number of compartments in which the pollen was formed.  In their lower part
the stamens are fused together by their stalks, like the "monadelphous"
stamens of a mallow.  The numerous ovules borne on the central receptacle
are stalked, and are intermixed with sterile scales; the latter are
expanded at their outer ends, which are united to form a kind of pericarp
or ovary-wall, only interrupted by the protruding micropyles of the ovules. 
There is thus an approach to the closed pistil of an Angiosperm, but it is
evident that the ovules received the pollen directly.  The whole
fructification is of large size; in the case of Cycadeoidea dacotensis, one
of the species investigated by Wieland, the total length, in the bud
condition, is about 12 cm., half of which belongs to the peduncle.

The general arrangement of the organs is manifestly the same as in a
typical Angiospermous flower, with a central pistil, a surrounding whorl of
stamens and an enveloping perianth; there is, as we have seen, some
approach to the closed ovary of an Angiosperm; another point, first
discovered nearly 20 years ago by Solms-Laubach in his investigation of a
British species, is that the seed was practically "exalbuminous," its
cavity being filled by the large, dicotyledonous embryo, whereas in all
known Gymnosperms a large part of the sac is occupied by a nutritive
tissue, the prothallus or endosperm; here also we have a condition only met
with elsewhere among the higher Flowering Plants.

Taking all the characters into account, the indications of affinity between
the Mesozoic Cycadophyta and the Angiosperms appear extremely significant,
as was recognised by Wieland when he first discovered the hermaphrodite
nature of the Bennettitean flower.  The Angiosperm with which he specially
compared the fossil type was the Tulip tree (Liriodendron) and certainly
there is a remarkable analogy with the Magnoliaceous flowers, and with
those of related orders such as Ranunculaceae and the Water-lilies.  It
cannot, of course, be maintained that the Bennettiteae, or any other
Mesozoic Cycadophyta at present known, were on the direct line of descent
of the Angiosperms, for there are some important points of difference, as,
for example, in the great complexity of the stamens, and in the fact that
the ovary-wall or pericarp was not formed by the carpels themselves, but by
the accompanying sterile scale-leaves.  Botanists, since the discovery of
the bisexual flowers of the Bennettiteae, have expressed different views as
to the nearness of their relation to the higher Flowering Plants, but the
points of agreement are so many that it is difficult to resist the
conviction that a real relation exists, and that the ancestry of the
Angiosperms, so long shrouded in complete obscurity, is to be sought among
the great plexus of Cycad-like plants which dominated the flora of the
world in Mesozoic times.  (On this subject see, in addition to Wieland's
great work above cited, F.W. Oliver, "Pteridosperms and Angiosperms", "New
Phytologist", Vol. V. 1906; D.H. Scott, "The Flowering Plants of the
Mesozoic Age in the Light of Recent Discoveries", "Journal R. Microscop.
Soc." 1907, and especially E.A.N. Arber and J. Parkin, "On the Origin of
Angiosperms", "Journal Linn. Soc." (Bot.) Vol. XXXVIII. page 29, 1907.)

The great complexity of the Bennettitean flower, the earliest known
fructification to which the word "flower" can be applied without forcing
the sense, renders it probable, as Wieland and others have pointed out,
that the evolution of the flower in Angiosperms has consisted essentially
in a process of reduction, and that the simplest forms of flower are not to
be regarded as the most primitive.  The older morphologists generally took
the view that such simple flowers were to be explained as reductions from a
more perfect type, and this opinion, though abandoned by many later
writers, appears likely to be true when we consider the elaboration of
floral structure attained among the Mesozoic Cycadophyta, which preceded
the Angiosperms in evolution.

If, as now seems probable, the Angiosperms were derived from ancestors
allied to the Cycads, it would naturally follow that the Dicotyledons were
first evolved, for their structure has most in common with that of the
Cycadophyta.  We should then have to regard the Monocotyledons as a side-
line, diverging probably at a very early stage from the main dicotyledonous
stock, a view which many botanists have maintained, of late, on other
grounds.  (See especially Ethel Sargant, "The Reconstruction of a Race of
Primitive Angiosperms", "Annals of Botany", Vol. XXII. page 121, 1908.)  So
far, however, as the palaeontological record shows, the Monocotyledons were
little if at all later in their appearance than the Dicotyledons, though
always subordinate in numbers.  The typical and beautifully preserved Palm-
wood from Cretaceous rocks is striking evidence of the early evolution of a
characteristic monocotyledonous family.  It must be admitted that the whole
question of the evolution of Monocotyledons remains to be solved.

Accepting, provisionally, the theory of the cycadophytic origin of
Angiosperms, it is interesting to see to what further conclusions we are
led.  The Bennettiteae, at any rate, were still at the gymnospermous level
as regards their pollination, for the exposed micropyles of the ovules were
in a position to receive the pollen directly, without the intervention of a
stigma.  It is thus indicated that the Angiosperms sprang from a
gymnospermous source, and that the two great phyla of Seed-plants have not
been distinct from the first, though no doubt the great majority of known
Gymnosperms, especially the Coniferae, represent branch-lines of their own.

The stamens of the Bennettiteae are arranged precisely as in an
angiospermous flower, but in form and structure they are like the fertile
fronds of a Fern, in fact the compound pollen-sacs, or synangia as they are
technically called, almost exactly agree with the spore-sacs of a
particular family of Ferns--the Marattiaceae, a limited group, now mainly
tropical, which was probably more prominent in the later Palaeozoic times
than at present.  The scaly hairs, or ramenta, which clothe every part of
the plant, are also like those of Ferns.

It is not likely that the characters in which the Bennettiteae resemble the
Ferns came to them directly from ancestors belonging to that class; an
extensive group of Seed-plants, the Pteridospermeae, existed in Palaeozoic
times and bear evident marks of affinity with the Fern phylum.  The fern-
like characters so remarkably persistent in the highly organised
Cycadophyta of the Mesozoic were in all likelihood derived through the
Pteridosperms, plants which show an unmistakable approach to the
cycadophytic type.

The family Bennettiteae thus presents an extraordinary association of
characters, exhibiting, side by side, features which belong to the
Angiosperms, the Gymnosperms and the Ferns.

ii.  ORIGIN OF SEED-PLANTS.

The general relation of the gymnospermous Seed-plants to the Higher
Cryptogamia was cleared up, independently of fossil evidence, by the
brilliant researches of Hofmeister, dating from the middle of the past
century.  (W. Hofmeister, "On the Germination, Development and
Fructification of the Higher Cryptogamia", Ray Society, London, 1862.  The
original German treatise appeared in 1851.)  He showed that "the embryo-sac
of the Coniferae may be looked upon as a spore remaining enclosed in its
sporangium; the prothallium which it forms does not come to the light." 
(Ibid. page 438.)  He thus determined the homologies on the female side. 
Recognising, as some previous observers had already done, that the
microspores of those Cryptogams in which two kinds of spore are developed,
are equivalent to the pollen-grains of the higher plants, he further
pointed out that fertilisation "in the Rhizocarpeae and Selaginellae takes
place by free spermatozoa, and in the Coniferae by a pollen-tube, in the
interior of which spermatozoa are probably formed"--a remarkable instance
of prescience, for though spermatozoids have not been found in the Conifers
proper, they were demonstrated in the allied groups Cycadaceae and Ginkgo,
in 1896, by the Japanese botanists Ikeno and Hirase.  A new link was thus
established between the Gymnosperms and the Cryptogams.

It remained uncertain, however, from which line of Cryptogams the
gymnospermous Seed-plants had sprung.  The great point of morphological
comparison was the presence of two kinds of spore, and this was known to
occur in the recent Lycopods and Water-ferns (Rhizocarpeae) and was also
found in fossil representatives of the third phylum, that of the
Horsetails.  As a matter of fact all the three great Cryptogamic classes
have found champions to maintain their claim to the ancestry of the Seed-
plants, and in every case fossil evidence was called in.  For a long time
the Lycopods were the favourites, while the Ferns found the least support. 
The writer remembers, however, in the year 1881, hearing the late Prof.
Sachs maintain, in a lecture to his class, that the descent of the Cycads
could be traced, not merely from Ferns, but from a definite family of
Ferns, the Marattiaceae, a view which, though in a somewhat crude form,
anticipated more modern ideas.

Williamson appears to have been the first to recognise the presence, in the
Carboniferous flora, of plants combining the characters of Ferns and
Cycads.  (See especially his "Organisation of the Fossil Plants of the
Coal-Measures", Part XIII. "Phil. Trans. Royal Soc." 1887 B. page 299.) 
This conclusion was first reached in the case of the genera Heterangium and
Lyginodendron, plants, which with a wholly fern-like habit, were found to
unite an anatomical structure holding the balance between that of Ferns and
Cycads, Heterangium inclining more to the former and Lyginodendron to the
latter.  Later researches placed Williamson's original suggestion on a
firmer basis, and clearly proved the intermediate nature of these genera,
and of a number of others, so far as their vegetative organs were
concerned.  This stage in our knowledge was marked by the institution of
the class Cycadofilices by Potonie in 1897.

Nothing, however, was known of the organs of reproduction of the
Cycadofilices, until F.W. Oliver, in 1903, identified a fossil seed,
Lagenostoma Lomaxi, as belonging to Lyginodendron, the identification
depending, in the first instance, on the recognition of an identical form
of gland, of very characteristic structure, on the vegetative organs of
Lyginodendron and on the cupule enveloping the seed.  This evidence was
supported by the discovery of a close anatomical agreement in other
respects, as well as by constant association between the seed and the
plant.  (F.W. Oliver and D.H. Scott, "On the Structure of the Palaeozoic
Seed, Lagenostoma Lomaxi, etc." "Phil. Trans. Royal Soc." Vol. 197 B.
1904.)  The structure of the seed of Lyginodendron, proved to be of the
same general type as that of the Cycads, as shown especially by the
presence of a pollen-chamber or special cavity for the reception of the
pollen-grains, an organ only known in the Cycads and Ginkgo among recent
plants.

Within a few months after the discovery of the seed of Lyginodendron,
Kidston found the large, nut-like seed of a Neuropteris, another fern-like
Carboniferous plant, in actual connection with the pinnules of the frond,
and since then seeds have been observed on the frond in species of
Aneimites and Pecopteris, and a vast body of evidence, direct or indirect,
has accumulated, showing that a large proportion of the Palaeozoic plants
formerly classed as Ferns were in reality reproduced by seeds of the same
type as those of recent Cycadaceae.  (A summary of the evidence will be
found in the writer's article "On the present position of Palaeozoic
Botany", "Progressus Rei Botanicae", 1907, page 139, and "Studies in Fossil
Botany", Vol. II. (2nd edition) London, 1909.)  At the same time, the
anatomical structure, where it is open to investigation, confirms the
suggestion given by the habit, and shows that these early seed-bearing
plants had a real affinity with Ferns.  This conclusion received strong
corroboration when Kidston, in 1905, discovered the male organs of
Lyginodendron, and showed that they were identical with a fructification of
the genus Crossotheca, hitherto regarded as belonging to Marattiaceous
Ferns.  (Kidston, "On the Microsporangia of the Pteridospermeae, etc." 
"Phil. Trans. Royal Soc." Vol. 198, B. 1906.)

The general conclusion which follows from the various observations alluded
to, is that in Palaeozoic times there was a great body of plants
(including, as it appears, a large majority of the fossils previously
regarded as Ferns) which had attained the rank of Spermophyta, bearing
seeds of a Cycadean type on fronds scarcely differing from the vegetative
foliage, and in other respects, namely anatomy, habit and the structure of
the pollen-bearing organs, retaining many of the characters of Ferns.  From
this extensive class of plants, to which the name Pteridospermeae has been
given, it can scarcely be doubted that the abundant Cycadophyta, of the
succeeding Mesozoic period, were derived.  This conclusion is of far-
reaching significance, for we have already found reason to think that the
Angiosperms themselves sprang, in later times, from the Cycadophytic stock;
it thus appears that the Fern-phylum, taken in a broad sense, ultimately
represents the source from which the main line of descent of the
Phanerogams took its rise.

It must further be borne in mind that in the Palaeozoic period there
existed another group of seed-bearing plants, the Cordaiteae, far more
advanced than the Pteridospermeae, and in many respects approaching the
Coniferae, which themselves begin to appear in the latest Palaeozoic rocks.
The Cordaiteae, while wholly different in habit from the contemporary fern-
like Seed-plants, show unmistakable signs of a common origin with them. 
Not only is there a whole series of forms connecting the anatomical
structure of the Cordaiteae with that of the Lyginodendreae among
Pteridosperms, but a still more important point is that the seeds of the
Cordaiteae, which have long been known, are of the same Cycadean type as
those of the Pteridosperms, so that it is not always possible, as yet, to
discriminate between the seeds of the two groups.  These facts indicate
that the same fern-like stock which gave rise to the Cycadophyta and
through them, as appears probable, to the Angiosperms, was also the source
of the Cordaiteae, which in their turn show manifest affinity with some at
least of the Coniferae.  Unless the latter are an artificial group, a view
which does not commend itself to the writer, it would appear probable that
the Gymnosperms generally, as well as the Angiosperms, were derived from an
ancient race of Cryptogams, most nearly related to the Ferns.  (Some
botanists, however, believe that the Coniferae, or some of them, are
probably more nearly related to the Lycopods.  See Seward and Ford, "The
Araucarieae, Recent and Extinct", "Phil. Trans. Royal Soc." Vol. 198 B.
1906.)

It may be mentioned here that the small gymnospermous group Gnetales
(including the extraordinary West African plant Welwitschia) which were
formerly regarded by some authorities as akin to the Equisetales, have
recently been referred, on better grounds, to a common origin with the
Angiosperms, from the Mesozoic Cycadophyta.

The tendency, therefore, of modern work on the palaeontological record of
the Seed-plants has been to exalt the importance of the Fern-phylum, which,
on present evidence, appears to be that from which the great majority,
possibly the whole, of the Spermophyta have been derived.

One word of caution, however, is necessary.  The Seed-plants are of
enormous antiquity; both the Pteridosperms and the more highly organised
family Cordaiteae, go back as far in geological history (namely to the
Devonian) as the Ferns themselves or any other Vascular Cryptogams.  It
must therefore be understood that in speaking of the derivation of the
Spermophyta from the Fern-phylum, we refer to that phylum at a very early
stage, probably earlier than the most ancient period to which our record of
land-plants extends.  The affinity between the oldest Seed-plants and the
Ferns, in the widest sense, seems established, but the common stock from
which they actually arose is still unknown; though no doubt nearer to the
Ferns than to any other group, it must have differed widely from the Ferns
as we now know them, or perhaps even from any which the fossil record has
yet revealed to us.

iii.  THE ORIGIN OF THE HIGHER CRYPTOGAMIA.

The Sub-kingdom of the higher Spore-plants, the Cryptogamia possessing a
vascular system, was more prominent in early geological periods than at
present.  It is true that the dominance of the Pteridophyta in Palaeozoic
times has been much exaggerated owing to the assumption that everything
which looked like a Fern really was a Fern.  But, allowing for the fact,
now established, that most of the Palaeozoic fern-like plants were already
Spermophyta, there remains a vast mass of Cryptogamic forms of that period,
and the familiar statement that they formed the main constituent of the
Coal-forests still holds good.  The three classes, Ferns (Filicales),
Horsetails (Equisetales) and Club-mosses (Lycopodiales), under which we now
group the Vascular Cryptogams, all extend back in geological history as far
as we have any record of the flora of the land; in the Palaeozoic, however,
a fourth class, the Sphenophyllales, was present.

As regards the early history of the Ferns, which are of special interest
from their relation to the Seed-plants, it is impossible to speak quite
positively, owing to the difficulty of discriminating between true fossil
Ferns and the Pteridosperms which so closely simulated them.  The
difficulty especially affects the question of the position of Marattiaceous
Ferns in the Palaeozoic Floras.  This family, now so restricted, was until
recently believed to have been one of the most important groups of
Palaeozoic plants, especially during later Carboniferous and Permian times.
Evidence both from anatomy and from sporangial characters appeared to
establish this conclusion.  Of late, however, doubts have arisen, owing to
the discovery that some supposed members of the Marattiaceae bore seeds,
and that a form of fructification previously referred to that family
(Crossotheca) was really the pollen-bearing apparatus of a Pteridosperm
(Lyginodendron).  The question presents much difficulty; though it seems
certain that our ideas of the extent of the family in Palaeozoic times will
have to be restricted, there is still a decided balance of evidence in
favour of the view that a considerable body of Marattiaceous Ferns actually
existed.  The plants in question were of large size (often arborescent) and
highly organised--they represent, in fact, one of the highest developments
of the Fern-stock, rather than a primitive type of the class.

There was, however, in the Palaeozoic period, a considerable group of
comparatively simple Ferns (for which Arber has proposed the collective
name Primofilices); the best known of these are referred to the family
Botryopterideae, consisting of plants of small or moderate dimensions,
with, on the whole, a simple anatomical structure, in certain cases
actually simpler than that of any recent Ferns.  On the other hand the
sporangia of these plants were usually borne on special fertile fronds, a
mark of rather high differentiation.  This group goes back to the Devonian
and includes some of the earliest types of Fern with which we are
acquainted.  It is probable that the Primofilices (though not the
particular family Botryopterideae) represent the stock from which the
various families of modern Ferns, already developed in the Mesozoic period,
may have sprung.

None of the early Ferns show any clear approach to other classes of
Vascular Cryptogams; so far as the fossil record affords any evidence,
Ferns have always been plants with relatively large and usually compound
leaves.  There is no indication of their derivation from a microphyllous
ancestry, though, as we shall see, there is some slight evidence for the
converse hypothesis.  Whatever the origin of the Ferns may have been it is
hidden in the older rocks.

It has, however, been held that certain other Cryptogamic phyla had a
common origin with the Ferns.  The Equisetales are at present a well-
defined group; even in the rich Palaeozoic floras the habit, anatomy and
reproductive characters usually render the members of this class
unmistakable, in spite of the great development and stature which they then
attained.  It is interesting, however, to find that in the oldest known
representatives of the Equisetales the leaves were highly developed and
dichotomously divided, thus differing greatly from the mere scale-leaves of
the recent Horsetails, or even from the simple linear leaves of the later
Calamites.  The early members of the class, in their forked leaves, and in
anatomical characters, show an approximation to the Sphenophyllales, which
are chiefly represented by the large genus Sphenophyllum, ranging through
the Palaeozoic from the Middle Devonian onwards.  These were plants with
rather slender, ribbed stems, bearing whorls of wedge-shaped or deeply
forked leaves, six being the typical number in each whorl.  From their weak
habit it has been conjectured, with much probability, that they may have
been climbing plants, like the scrambling Bedstraws of our hedgerows.  The
anatomy of the stem is simple and root-like; the cones are remarkable for
the fact that each scale or sporophyll is a double structure, consisting of
a lower, usually sterile lobe and one or more upper lobes bearing the
sporangia; in one species both parts of the sporophyll were fertile. 
Sphenophyllum was evidently much specialised; the only other known genus is
based on an isolated cone, Cheirostrobus, of Lower Carboniferous age, with
an extraordinarily complex structure.  In this genus especially, but also
in the entire group, there is an evident relation to the Equisetales; hence
it is of great interest that Nathorst has described, from the Devonian of
Bear Island in the Arctic regions, a new genus Pseudobornia, consisting of
large plants, remarkable for their highly compound leaves which, when found
detached, were taken for the fronds of a Fern.  The whorled arrangement of
the leaves, and the habit of the plant, suggest affinities either with the
Equisetales or the Sphenophyllales; Nathorst makes the genus the type of a
new class, the Pseudoborniales.  (A.G. Nathorst, "Zur Oberdevonischen Flora
der Baren-Insel", "Kongl. Svenska Vetenskaps-Akademiens Handlingar" Bd. 36,
No. 3, Stockholm, 1902.)

The available data, though still very fragmentary, certainly suggest that
both Equisetales and Sphenophyllales may have sprung from a common stock
having certain fern-like characters.  On the other hand the Sphenophylls,
and especially the peculiar genus Cheirostrobus, have in their anatomy a
good deal in common with the Lycopods, and of late years they have been
regarded as the derivatives of a stock common to that class and the
Equisetales.  At any rate the characters of the Sphenophyllales and of the
new group Pseudoborniales suggest the existence, at a very early period, of
a synthetic race of plants, combining the characters of various phyla of
the Vascular Cryptogams.  It may further be mentioned that the Psilotaceae,
an isolated epiphytic family hitherto referred to the Lycopods, have been
regarded by several recent authors as the last survivors of the
Sphenophyllales, which they resemble both in their anatomy and in the
position of their sporangia.

The Lycopods, so far as their early history is known, are remarkable rather
for their high development in Palaeozoic times than for any indications of
a more primitive ancestry.  In the recent Flora, two of the four living
genera (Excluding Psilotaceae.) (Selaginella and Isoetes) have spores of
two kinds, while the other two (Lycopodium and Phylloglossum) are
homosporous.  Curiously enough, no certain instance of a homosporous
Palaeozoic Lycopod has yet been discovered, though well-preserved
fructifications are numerous.  Wherever the facts have been definitely
ascertained, we find two kinds of spore, differentiated quite as sharply as
in any living members of the group.  Some of the Palaeozoic Lycopods, in
fact, went further, and produced bodies of the nature of seeds, some of
which were actually regarded, for many years, as the seeds of Gymnosperms. 
This specially advanced form of fructification goes back at least as far as
the Lower Carboniferous, while the oldest known genus of Lycopods,
Bothrodendron, which is found in the Devonian, though not seed-bearing, was
typically heterosporous, if we may judge from the Coal-measure species.  No
doubt homosporous Lycopods existed, but the great prevalence of the higher
mode of reproduction in days which to us appear ancient, shows how long a
course of evolution must have already been passed through before the oldest
known members of the group came into being.  The other characters of the
Palaeozoic Lycopods tell the same tale; most of them attained the stature
of trees, with a corresponding elaboration of anatomical structure, and
even the herbaceous forms show no special simplicity.  It appears from
recent work that herbaceous Lycopods, indistinguishable from our recent
Selaginellas, already existed in the time of the Coal-measures, while one
herbaceous form (Miadesmia) is known to have borne seeds.

The utmost that can be said for primitiveness of character in Palaeozoic
Lycopods is that the anatomy of the stem, in its primary ground-plan, as
distinguished from its secondary growth, was simpler than that of most
Lycopodiums and Selaginellas at the present day.  There are also some
peculiarities in the underground organs (Stigmaria) which suggest the
possibility of a somewhat imperfect differentiation between root and stem,
but precisely parallel difficulties are met with in the case of the living
Selaginellas, and in some degree in species of Lycopodium.

In spite of their high development in past ages the Lycopods, recent and
fossil, constitute, on the whole, a homogeneous group, and there is little
at present to connect them with other phyla.  Anatomically some relation to
the Sphenophylls is indicated, and perhaps the recent Psilotaceae give some
support to this connection, for while their nearest alliance appears to be
with the Sphenophylls, they approach the Lycopods in anatomy, habit, and
mode of branching.

The typically microphyllous character of the Lycopods, and the simple
relation between sporangium and sporophyll which obtains throughout the
class, have led various botanists to regard them as the most primitive
phylum of the Vascular Cryptogams.  There is nothing in the fossil record
to disprove this view, but neither is there anything to support it, for
this class so far as we know is no more ancient than the megaphyllous
Cryptogams, and its earliest representatives show no special simplicity. 
If the indications of affinity with Sphenophylls are of any value the
Lycopods are open to suspicion of reduction from a megaphyllous ancestry,
but there is no direct palaeontological evidence for such a history.

The general conclusions to which we are led by a consideration of the
fossil record of the Vascular Cryptogams are still very hypothetical, but
may be provisionally stated as follows:

The Ferns go back to the earliest known period.  In Mesozoic times
practically all the existing families had appeared; in the Palaeozoic the
class was less extensive than formerly believed, a majority of the supposed
Ferns of that age having proved to be seed-bearing plants.  The oldest
authentic representatives of the Ferns were megaphyllous plants, broadly
speaking, of the same type as those of later epochs, though differing much
in detail.  As far back as the record extends they show no sign of becoming
merged with other phyla in any synthetic group.

The Equisetales likewise have a long history, and manifestly attained their
greatest development in Palaeozoic times.  Their oldest forms show an
approach to the extinct class Sphenophyllales, which connects them to some
extent, by anatomical characters, with the Lycopods.  At the same time the
oldest Equisetales show a somewhat megaphyllous character, which was more
marked in the Devonian Pseudoborniales.  Some remote affinity with the
Ferns (which has also been upheld on other grounds) may thus be indicated.
It is possible that in the Sphenophyllales we may have the much-modified
representatives of a very ancient synthetic group.

The Lycopods likewise attained their maximum in the Palaeozoic, and show,
on the whole, a greater elaboration of structure in their early forms than
at any later period, while at the same time maintaining a considerable
degree of uniformity in morphological characters throughout their history.
The Sphenophyllales are the only other class with which they show any
relation; if such a connection existed, the common point of origin must lie
exceedingly far back.

The fossil record, as at present known, cannot, in the nature of things,
throw any direct light on what is perhaps the most disputed question in the
morphology of plants--the origin of the alternating generations of the
higher Cryptogams and the Spermophyta.  At the earliest period to which
terrestrial plants have been traced back all the groups of Vascular
Cryptogams were in a highly advanced stage of evolution, while innumerable
Seed-plants--presumably the descendants of Cryptogamic ancestors--were
already flourishing.  On the other hand we know practically nothing of
Palaeozoic Bryophyta, and the evidence even for their existence at that
period cannot be termed conclusive.  While there are thus no
palaeontological grounds for the hypothesis that the Vascular plants came
of a Bryophytic stock, the question of their actual origin remains
unsolved.

III.  NATURAL SELECTION.

Hitherto we have considered the palaeontological record of plants in
relation to Evolution.  The question remains, whether the record throws any
light on the theory of which Darwin and Wallace were the authors--that of
Natural Selection.  The subject is clearly one which must be investigated
by other methods than those of the palaeontologist; still there are certain
important points involved, on which the palaeontological record appears to
bear.

One of these points is the supposed distinction between morphological and
adaptive characters, on which Nageli, in particular, laid so much stress. 
The question is a difficult one; it was discussed by Darwin ("Origin of
Species" (6th edition), pages 170-176.), who, while showing that the
apparent distinction is in part to be explained by our imperfect knowledge
of function, recognised the existence of important morphological characters
which are not adaptations.  The following passage expresses his conclusion.
"Thus, as I am inclined to believe, morphological differences, which we
consider as important--such as the arrangement of the leaves, the divisions
of the flower or of the ovarium, the position of the ovules, etc.--first
appeared in many cases as fluctuating variations, which sooner or later
became constant through the nature of the organism and of the surrounding
conditions, as well as through the inter-crossing of distinct individuals,
but not through natural selection; for as these morphological characters do
not affect the welfare of the species, any slight deviations in them could
not have been governed or accumulated through this latter agency."  (Ibid.
page 176.)

This is a sufficiently liberal concession; Nageli, however, went much
further when he said:  "I do not know among plants a morphological
modification which can be explained on utilitarian principles."  (See "More
Letters", Vol. II. page 375 (footnote).)  If this were true the field of
Natural Selection would be so seriously restricted, as to leave the theory
only a very limited importance.

It can be shown, as the writer believes, that many typical "morphological
characters," on which the distinction between great classes of plants is
based, were adaptive in origin, and even that their constancy is due to
their functional importance.  Only one or two cases will be mentioned,
where the fossil evidence affects the question.

The pollen-tube is one of the most important morphological characters of
the Spermophyta as now existing--in fact the name Siphonogama is used by
Engler in his classification, as expressing a peculiarly constant character
of the Seed-plants.  Yet the pollen-tube is a manifest adaptation,
following on the adoption of the seed-habit, and serving first to bring the
spermatozoids with greater precision to their goal, and ultimately to
relieve them of the necessity for independent movement.  The pollen-tube is
constant because it has proved to be indispensable.

In the Palaeozoic Seed-plants there are a number of instances in which the
pollen-grains, contained in the pollen-chamber of a seed, are so
beautifully preserved that the presence of a group of cells within the
grain can be demonstrated; sometimes we can even see how the cell-walls
broke down to emit the sperms, and quite lately it is said that the sperms
themselves have been recognised.  (F.W. Oliver, "On Physostoma elegans, an
archaic type of seed from the Palaeozoic Rocks", "Annals of Botany",
January, 1909.  See also the earlier papers there cited.)  In no case,
however, is there as yet any satisfactory evidence for the formation of a
pollen-tube; it is probable that in these early Seed-plants the pollen-
grains remained at about the evolutionary level of the microspores in
Pilularia or Selaginella, and discharged their spermatozoids directly,
leaving them to find their own way to the female cells.  It thus appears
that there were once Spermophyta without pollen-tubes.  The pollen-tube
method ultimately prevailed, becoming a constant "morphological character,"
for no other reason than because, under the new conditions, it provided a
more perfect mechanism for the accomplishment of the act of fertilisation. 
We have still, in the Cycads and Ginkgo, the transitional case, where the
tube remains short, serves mainly as an anchor and water-reservoir, but yet
is able, by its slight growth, to give the spermatozoids a "lift" in the
right direction.  In other Seed-plants the sperms are mere passengers,
carried all the way by the pollen-tube; this fact has alone rendered the
Angiospermous method of fertilisation through a stigma possible.

We may next take the seed itself--the very type of a morphological
character.  Our fossil record does not go far enough back to tell us the
origin of the seed in the Cycadophyta and Pteridosperms (the main line of
its development) but some interesting sidelights may be obtained from the
Lycopod phylum.  In two Palaeozoic genera, as we have seen, seed-like
organs are known to have been developed, resembling true seeds in the
presence of an integument and of a single functional embryo-sac, as well as
in some other points.  We will call these organs "seeds" for the sake of
shortness.  In one genus (Lepidocarpon) the seeds were borne on a cone
indistinguishable from that of the ordinary cryptogamic Lepidodendreae, the
typical Lycopods of the period, while the seed itself retained much of the
detailed structure of the sporangium of that family.  In the second genus,
Miadesmia, the seed-bearing plant was herbaceous, and much like a recent
Selaginella.  (See Margaret Benson, "Miadesmia membranacea, a new
Palaeozoic Lycopod with a seed-like structure", "Phil. Trans. Royal Soc.
Vol. 199, B. 1908.)  The seeds of the two genera are differently
constructed, and evidently had an independent origin.  Here, then, we have
seeds arising casually, as it were, at different points among plants which
otherwise retain all the characters of their cryptogamic fellows; the seed
is not yet a morphological character of importance.  To suppose that in
these isolated cases the seed sprang into being in obedience to a Law of
Advance ("Vervollkommungsprincip"), from which other contemporary Lycopods
were exempt, involves us in unnecessary mysticism.  On the other hand it is
not difficult to see how these seeds may have arisen, as adaptive
structures, under the influence of Natural Selection.  The seed-like
structure afforded protection to the prothallus, and may have enabled the
embryo to be launched on the world in greater security.  There was further,
as we may suppose, a gain in certainty of fertilisation.  As the writer has
pointed out elsewhere, the chances against the necessary association of the
small male with the large female spores must have been enormously great
when the cones were borne high up on tall trees.  The same difficulty may
have existed in the case of the herbaceous Miadesmia, if, as Miss Benson
conjectures, it was an epiphyte.  One way of solving the problem was for
pollination to take place while the megaspore was still on the parent
plant, and this is just what the formation of an ovule or seed was likely
to secure.

The seeds of the Pteridosperms, unlike those of the Lycopod stock, have not
yet been found in statu nascendi--in all known cases they were already
highly developed organs and far removed from the cryptogamic sporangium. 
But in two respects we find that these seeds, or some of them, had not yet
realised their possibilities.  In the seed of Lyginodendron and other cases
the micropyle, or orifice of the integument, was not the passage through
which the pollen entered; the open neck of the pollen-chamber protruded
through the micropyle and itself received the pollen.  We have met with an
analogous case, at a more advanced stage of evolution, in the Bennettiteae,
where the wall of the gynaecium, though otherwise closed, did not provide a
stigma to catch the pollen, but allowed the micropyles of the ovules to
protrude and receive the pollen in the old gymnospermous fashion.  The
integument in the one case and the pistil in the other had not yet assumed
all the functions to which the organ ultimately became adapted.  Again, no
Palaeozoic seed has yet been found to contain an embryo, though the
preservation is often good enough for it to have been recognised if
present.  It is probable that the nursing of the embryo had not yet come to
be one of the functions of the seed, and that the whole embryonic
development was relegated to the germination stage.

In these two points, the reception of the pollen by the micropyle and the
nursing of the embryo, it appears that many Palaeozoic seeds were
imperfect, as compared with the typical seeds of later times.  As evolution
went on, one function was superadded on another, and it appears impossible
to resist the conclusion that the whole differentiation of the seed was a
process of adaptation, and consequently governed by Natural Selection, just
as much as the specialisation of the rostellum in an Orchid, or of the
pappus in a Composite.

Did space allow, other examples might be added.  We may venture to maintain
that the glimpses which the fossil record allows us into early stages in
the evolution of organs now of high systematic importance, by no means
justify the belief in any essential distinction between morphological and
adaptive characters.

Another point, closely connected with Darwin's theory, on which the fossil
history of plants has been supposed to have some bearing, is the question
of Mutation, as opposed to indefinite variation.  Arber and Parkin, in
their interesting memoir on the Origin of Angiosperms, have suggested
calling in Mutation to explain the apparently sudden transition from the
cycadean to the angiospermous type of foliage, in late Mesozoic times,
though they express themselves with much caution, and point out "a distinct
danger that Mutation may become the last resort of the phylogenetically
destitute"!

The distinguished French palaeobotanists, Grand'Eury (C. Grand'Eury, "Sur
les mutations de quelques Plantes fossiles du Terrain houiller".  "Comptes
Rendus", CXLII. page 25, 1906.) and Zeiller (R. Zeiller "Les Vegetaux
fossiles et leurs Enchainements", "Revue du Mois", III. February, 1907.),
are of opinion, to quote the words of the latter writer, that the facts of
fossil Botany are in agreement with the sudden appearance of new forms,
differing by marked characters from those that have given them birth; he
adds that these results give more amplitude to this idea of Mutation,
extending it to groups of a higher order, and even revealing the existence
of discontinuous series between the successive terms of which we yet
recognise bonds of filiation.  (Loc. cit. page 23.)

If Zeiller's opinion should be confirmed, it would no doubt be a serious
blow to the Darwinian theory.  As Darwin said:  "Under a scientific point
of view, and as leading to further investigation, but little advantage is
gained by believing that new forms are suddenly developed in an
inexplicable manner from old and widely different forms, over the old
belief in the creation of species from the dust of the earth."  ("Origin of
Species", page 424.)

It most however be pointed out, that such mutations as Zeiller, and to some
extent Arber and Parkin, appear to have in view, bridging the gulf between
different Orders and Classes, bear no relation to any mutations which have
been actually observed, such as the comparatively small changes, of sub-
specific value, described by De Vries in the type-case of Oenothera
Lamarckiana.  The results of palaeobotanical research have undoubtedly
tended to fill up gaps in the Natural System of plants--that many such gaps
still persist is not surprising; their presence may well serve as an
incentive to further research but does not, as it seems to the writer,
justify the assumption of changes in the past, wholly without analogy among
living organisms.

As regards the succession of species, there are no greater authorities than
Grand'Eury and Zeiller, and great weight must be attached to their opinion
that the evidence from continuous deposits favours a somewhat sudden change
from one specific form to another.  At the same time it will be well to
bear in mind that the subject of the "absence of numerous intermediate
varieties in any single formation" was fully discussed by Darwin.  ("Origin
of Species", pages 275-282, and page 312.); the explanation which he gave
may go a long way to account for the facts which recent writers have
regarded as favouring the theory of saltatory mutation.

The rapid sketch given in the present essay can do no more than call
attention to a few salient points, in which the palaeontological records of
plants has an evident bearing on the Darwinian theory.  At the present day
the whole subject of palaeobotany is a study in evolution, and derives its
chief inspiration from the ideas of Darwin and Wallace.  In return it
contributes something to the verification of their teaching; the recent
progress of the subject, in spite of the immense difficulties which still
remain, has added fresh force to Darwin's statement that "the great leading
facts in palaeontology agree admirably with the theory of descent with
modification through variation and natural selection."  (Ibid. page 313.)


XIII.  THE INFLUENCE OF ENVIRONMENT ON THE FORMS OF PLANTS.

By GEORG KLEBS, PH.D.
Professor of Botany in the University of Heidelberg.

The dependence of plants on their environment became the object of
scientific research when the phenomena of life were first investigated and
physiology took its place as a special branch of science.  This occurred in
the course of the eighteenth century as the result of the pioneer work of
Hales, Duhamel, Ingenhousz, Senebier and others.  In the nineteenth
century, particularly in the second half, physiology experienced an
unprecedented development in that it began to concern itself with the
experimental study of nutrition and growth, and with the phenomena
associated with stimulus and movement; on the other hand, physiology
neglected phenomena connected with the production of form, a department of
knowledge which was the province of morphology, a purely descriptive
science.  It was in the middle of the last century that the growth of
comparative morphology and the study of phases of development reached their
highest point.

The forms of plants appeared to be the expression of their inscrutable
inner nature; the stages passed through in the development of the
individual were regarded as the outcome of purely internal and hidden laws.
The feasibility of experimental inquiry seemed therefore remote. 
Meanwhile, the recognition of the great importance of such a causal
morphology emerged from the researches of the physiologists of that time,
more especially from those of Hofmeister (Hofmeister, "Allgemeine
Morphologie", Leipzig, 1868, page 579.), and afterwards from the work of
Sachs.  (Sachs, "Stoff und Form der Pflanzenorgane", Vol. I. 1880; Vol. II.
1882.  "Gesammelte Abhandlungen uber Pflanzen-Physiologie", II. Leipzig,
1893.)  Hofmeister, in speaking of this line of inquiry, described it as
"the most pressing and immediate aim of the investigator to discover to
what extent external forces acting on the organism are of importance in
determining its form."  This advance was the outcome of the influence of
that potent force in biology which was created by Darwin's "Origin of
Species" (1859).

The significance of the splendid conception of the transformation of
species was first recognised and discussed by Lamarck (1809); as an
explanation of transformation he at once seized upon the idea--an
intelligible view--that the external world is the determining factor. 
Lamarck (Lamarck, "Philosophie zoologique", pages 223-227.  Paris, 1809.)
endeavoured, more especially, to demonstrate from the behaviour of plants
that changes in environment induce change in form which eventually leads to
the production of new species.  In the case of animals, Lamarck adopted the
teleological view that alterations in the environment first lead to
alterations in the needs of the organisms, which, as the result of a kind
of conscious effort of will, induce useful modifications and even the
development of new organs.  His work has not exercised any influence on the
progress of science:  Darwin himself confessed in regard to Lamarck's work
--"I got not a fact or idea from it."  ("Life and Letters", Vol. II. page
215.)

On a mass of incomparably richer and more essential data Darwin based his
view of the descent of organisms and gained for it general acceptance; as
an explanation of modification he elaborated the ingeniously conceived
selection theory.  The question of special interest in this connection,
namely what is the importance of the influence of the environment, Darwin
always answered with some hesitation and caution, indeed with a certain
amount of indecision.

The fundamental principle underlying his theory is that of general
variability as a whole, the nature and extent of which, especially in
cultivated organisms, are fully dealt with in his well-known book. 
(Darwin, "The variation of Animals and Plants under domestication", 2
vols., edition 1, 1868; edition 2, 1875; popular edition 1905.)  In regard
to the question as to the cause of variability Darwin adopts a consistently
mechanical view.  He says:  "These several considerations alone render it
probable that variability of every kind is directly or indirectly caused by
changed conditions of life.  Or, to put the case under another point of
view, if it were possible to expose all the individuals of a species during
many generations to absolutely uniform conditions of life, there would be
no variability."  ("The variation of Animals and Plants" (2nd edition),
Vol. II. page 242.)  Darwin did not draw further conclusions from this
general principle.

Variations produced in organisms by the environment are distinguished by
Darwin as "the definite" and "the indefinite."  (Ibid. II. page 260.  See
also "Origin of Species" (6th edition), page 6.)  The first occur "when all
or nearly all the offspring of an individual exposed to certain conditions
during several generations are modified in the same manner."  Indefinite
variation is much more general and a more important factor in the
production of new species; as a result of this, single individuals are
distinguished from one another by "slight" differences, first in one then
in another character.  There may also occur, though this is very rare, more
marked modifications, "variations which seem to us in our ignorance to
arise spontaneously."  ("Origin of Species" (6th edition), page 421.)  The
selection theory demands the further postulate that such changes, "whether
extremely slight or strongly marked," are inherited.  Darwin was no nearer
to an experimental proof of this assumption than to the discovery of the
actual cause of variability.  It was not until the later years of his life
that Darwin was occupied with the "perplexing problem...what causes almost
every cultivated plant to vary" ("Life and Letters", Vol. III. page 342.): 
he began to make experiments on the influence of the soil, but these were
soon given up.

In the course of the violent controversy which was the outcome of Darwin's
work the fundamental principles of his teaching were not advanced by any
decisive observations.  Among the supporters and opponents, Nageli (Nageli,
"Theorie der Abstammungslehre", Munich, 1884; cf. Chapter III.) was one of
the few who sought to obtain proofs by experimental methods.  His extensive
cultural experiments with alpine Hieracia led him to form the opinion that
the changes which are induced by an alteration in the food-supply, in
climate or in habitat, are not inherited and are therefore of no importance
from the point of view of the production of species.  And yet Nageli did
attribute an important influence to the external world; he believed that
adaptations of plants arise as reactions to continuous stimuli, which
supply a need and are therefore useful.  These opinions, which recall the
teleological aspect of Lamarckism, are entirely unsupported by proof. 
While other far-reaching attempts at an explanation of the theory of
descent were formulated both in Nageli's time and afterwards, some in
support of, others in opposition to Darwin, the necessity of investigating,
from different standpoints, the underlying causes, variability and
heredity, was more and more realised.  To this category belong the
statistical investigations undertaken by Quetelet and Galton, the
researches into hybridisation, to which an impetus was given by the re-
discovery of the Mendelian law of segregation, as also by the culture
experiments on mutating species following the work of de Vries, and lastly
the consideration of the question how far variation and heredity are
governed by external influences.  These latter problems, which are
concerned in general with the causes of form-production and form-
modification, may be treated in a short summary which falls under two
heads, one having reference to the conditions of form-production in single
species, the other being concerned with the conditions governing the
transformation of species.

I. THE INFLUENCE OF EXTERNAL CONDITIONS ON FORM-PRODUCTION IN SINGLE
SPECIES.

The members of plants, which we express by the terms stem, leaf, flower,
etc. are capable of modification within certain limits; since Lamarck's
time this power of modification has been brought more or less into relation
with the environment.  We are concerned not only with the question of
experimental demonstration of this relationship, but, more generally, with
an examination of the origin of forms, the sequences of stages in
development that are governed by recognisable causes.  We have to consider
the general problem; to study the conditions of all typical as well as of
atypic forms, in other words, to found a physiology of form.

If we survey the endless variety of plant-forms and consider the highly
complex and still little known processes in the interior of cells, and if
we remember that the whole of this branch of investigation came into
existence only a few decades ago, we are able to grasp the fact that a
satisfactory explanation of the factors determining form cannot be
discovered all at once.  The goal is still far away.  We are not concerned
now with the controversial question, whether, on the whole, the fundamental
processes in the development of form can be recognised by physiological
means.  A belief in the possibility of this can in any case do no harm. 
What we may and must attempt is this--to discover points of attack on one
side or another, which may enable us by means of experimental methods to
come into closer touch with these elusive and difficult problems.  While we
are forced to admit that there is at present much that is insoluble there
remains an inexhaustible supply of problems capable of solution.

The object of our investigations is the species; but as regards the
question, what is a species, science of to-day takes up a position
different from that of Darwin.  For him it was the Linnean species which
illustrates variation:  we now know, thanks to the work of Jordan, de Bary,
and particularly to that of de Vries (de Vries, "Die Mutationstheorie",
Leipzig, 1901, Vol. I. page 33.), that the Linnean species consists of a
large or small number of entities, elementary species.  In experimental
investigation it is essential that observations be made on a pure species,
or, as Johannsen (Johannsen, "Ueber Erblichkeit in Populationen und reinen
Linien", Jena, 1903.) says, on a pure "line."  What has long been
recognised as necessary in the investigation of fungi, bacteria and algae
must also be insisted on in the case of flowering plants; we must start
with a single individual which is reproduced vegetatively or by strict
self-fertilisation.  In dioecious plants we must aim at the reproduction of
brothers and sisters.

We may at the outset take it for granted that a pure species remains the
same under similar external conditions; it varies as these vary.  IT IS
CHARACTERISTIC OF A SPECIES THAT IT ALWAYS EXHIBITS A CONSTANT RELATION TO
A PARTICULAR ENVIRONMENT.  In the case of two different species, e.g. the
hay and anthrax bacilli or two varieties of Campanula with blue and white
flowers respectively, a similar environment produces a constant difference. 
The cause of this is a mystery.

According to the modern standpoint, the living cell is a complex chemico-
physical system which is regarded as a dynamical system of equilibrium, a
conception suggested by Herbert Spencer and which has acquired a constantly
increasing importance in the light of modern developments in physical
chemistry.  The various chemical compounds, proteids, carbohydrates, fats,
the whole series of different ferments, etc. occur in the cell in a
definite physical arrangement.  The two systems of two species must as a
matter of fact possess a constant difference, which it is necessary to
define by a special term.  We say, therefore, that the SPECIFIC STRUCTURE
is different.

By way of illustrating this provisionally, we may assume that the proteids
of the two species possess a constant chemical difference.  This conception
of specific structure is specially important in its bearing on a further
treatment of the subject.  In the original cell, eventually also in every
cell of a plant, the characters which afterwards become apparent must exist
somewhere; they are integral parts of the capabilities or potentialities of
specific structure.  Thus not only the characters which are exhibited under
ordinary conditions in nature, but also many others which become apparent
only under special conditions (In this connection I leave out of account,
as before, the idea of material carriers of heredity which since the
publication of Darwin's Pangenesis hypothesis has been frequently
suggested.  See my remarks in "Variationen der Bluten", "Pringsheim's
Jahrb. Wiss. Bot." 1905, page 298; also Detto, "Biol. Centralbl." 1907,
page 81, "Die Erklarbarkeit der Ontogenese durch materielle Anlagen".), are
to be included as such potentialities in cells; the conception of specific
structure includes the WHOLE OF THE POTENTIALITIES OF A SPECIES; specific
structure comprises that which we must always assume without being able to
explain it.

A relatively simple substance, such as oxalate of lime, is known under a
great number of different crystalline forms belonging to different systems
(Compare Kohl's work on "Anatomisch-phys. Untersuchungen uber Kalksalze",
etc. Marburg, 1889.); these may occur as single crystals, concretions or as
concentric sphaerites.  The power to assume this variety of form is in some
way inherent in the molecular structure, though we cannot, even in this
case, explain the necessary connection between structure and crystalline
form.  These potentialities can only become operative under the influence
of external conditions; their stimulation into activity depends on the
degree of concentration of the various solutions, on the nature of the
particular calcium salt, on the acid or alkaline reactions.  Broadly
speaking, the plant cell behaves in a similar way.  The manifestation of
each form, which is inherent as a potentiality in the specific structure,
is ultimately to be referred to external conditions.

An insight into this connection is, however, rendered exceedingly
difficult, often quite impossible, because the environment never directly
calls into action the potentialities.  Its influence is exerted on what we
may call the inner world of the organism, the importance of which increases
with the degree of differentiation.  The production of form in every plant
depends upon processes in the interior of the cells, and the nature of
these determines which among the possible characters is to be brought to
light.  In no single case are we acquainted with the internal process
responsible for the production of a particular form.  All possible factors
may play a part, such as osmotic pressure, permeability of the protoplasm,
the degree of concentration of the various chemical substances, etc.; all
these factors should be included in the category of INTERNAL CONDITIONS. 
This inner world appears the more hidden from our ken because it is always
represented by a certain definite state, whether we are dealing with a
single cell or with a small group of cells.  These have been produced from
pre-existing cells and they in turn from others; the problem is constantly
pushed back through a succession of generations until it becomes identified
with that of the origin of species.

A way, however, is opened for investigation; experience teaches us that
this inner world is not a constant factor:  on the contrary, it appears to
be very variable.  The dependence of VARIABLE INTERNAL on VARIABLE EXTERNAL
conditions gives us the key with which research may open the door.  In the
lower plants this dependence is at once apparent, each cell is directly
subject to external influences.  In the higher plants with their different
organs, these influences were transmitted to cells in course of development
along exceedingly complex lines.  In the case of the growing-point of a
bud, which is capable of producing a complete plant, direct influences play
a much less important part than those exerted through other organs,
particularly through the roots and leaves, which are essential in
nutrition.  These correlations, as we may call them, are of the greatest
importance as aids to an understanding of form-production.  When a bud is
produced on a particular part of a plant, it undergoes definite internal
modifications induced by the influence of other organs, the activity of
which is governed by the environment, and as the result of this it develops
along a certain direction; it may, for example, become a flower.  The
particular direction of development is determined before the rudiment is
differentiated and is exerted so strongly that further development ensues
without interruption, even though the external conditions vary considerably
and exert a positively inimical influence:  this produces the impression
that development proceeds entirely independently of the outer world.  The
widespread belief that such independence exists is very premature and at
all events unproven.

The state of the young rudiment is the outcome of previous influences of
the external world communicated through other organs.  Experiments show
that in certain cases, if the efficiency of roots and leaves as organs
concerned with nutrition is interfered with, the production of flowers is
affected, and their characters, which are normally very constant, undergo
far-reaching modifications.  To find the right moment at which to make the
necessary alteration in the environment is indeed difficult and in many
cases not yet possible.  This is especially the case with fertilised eggs,
which in a higher degree than buds have acquired, through parental
influences, an apparently fixed internal organisation, and this seems to
have pre-determined their development.  It is, however, highly probable
that it will be possible, by influencing the parents, to alter the internal
organisation and to switch off development on to other lines.

Having made these general observations I will now cite a few of the many
facts at our disposal, in order to illustrate the methods and aim of the
experimental methods of research.  As a matter of convenience I will deal
separately with modification of development and with modification of single
organs.

I.  EFFECT OF ENVIRONMENT UPON THE COURSE OF DEVELOPMENT.

Every plant, whether an alga or a flowering plant passes, under natural
conditions, through a series of developmental stages characteristic of each
species, and these consist in a regular sequence of definite forms.  It is
impossible to form an opinion from mere observation and description as to
what inner changes are essential for the production of the several forms. 
We must endeavour to influence the inner factors by known external
conditions in such a way that the individual stages in development are
separately controlled and the order of their sequence determined at will by
experimental treatment.  Such control over the course of development may be
gained with special certainty in the case of the lower organisms.

With these it is practicable to control the principal conditions of
cultivation and to vary them in various ways.  By this means it has been
demonstrated that each developmental stage depends upon special external
conditions, and in cases where our knowledge is sufficient, a particular
stage may be obtained at will.  In the Green Algae (See Klebs, "Die
Bedingung der Fortpflanzung...", Jena, 1896; also "Jahrb. fur Wiss. Bot."
1898 and 1900; "Probleme der Entwickelung, III."  "Biol. Centralbl." 1904,
page 452.), as in the case of Fungi, we may classify the stages of
development into purely vegetative growth (growth, cell-division,
branching), asexual reproduction (formation of zoospores, conidia) and
sexual processes (formation of male and female sexual organs).  By
modifying the external conditions it is possible to induce algae or fungi
(Vaucheria, Saprolegnia) to grow continuously for several years or, in the
course of a few days, to die after an enormous production of asexual or
sexual cells.  In some instances even an almost complete stoppage of growth
may be caused, reproductive cells being scarcely formed before the organism
is again compelled to resort to reproduction.  Thus the sequence of the
different stages in development can be modified as we may desire.

The result of a more thorough investigation of the determining conditions
appears to produce at first sight a confused impression of all sorts of
possibilities.  Even closely allied species exhibit differences in regard
to the connection between their development and external conditions.  It is
especially noteworthy that the same form in development may be produced as
the result of very different alterations in the environment.  At the same
time we can undoubtedly detect a certain unity in the multiplicity of the
individual phenomena.

If we compare the factors essential for the different stages in
development, we see that the question always resolves itself into one of
modification of similar conditions common to all life-processes.  We should
rather have inferred that there exist specific external stimuli for each
developmental stage, for instance, certain chemical agencies.  Experiments
hitherto made support the conclusion that QUANTITATIVE alterations in the
general conditions of life produce different types of development.  An alga
or a fungus grows so long as all the conditions of nutrition remain at a
certain optimum for growth.  In order to bring about asexual reproduction,
e.g. the formation of zoospores, it is sometimes necessary to increase the
degree of intensity of external factors; sometimes, on the other hand,
these must be reduced in intensity.  In the case of many algae a decrease
in light-intensity or in the amount of salts in the culture solution, or in
the temperature, induces asexual reproduction, while in others, on the
contrary, an increase in regard to each of these factors is required to
produce the same result.  This holds good for the quantitative variations
which induce sexual reproduction in algae.  The controlling factor is found
to be a reduction in the supply of nutritive salts and the exposure of the
plants to prolonged illumination or, better still, an increase in the
intensity of the light, the efficiency of illumination depending on the
consequent formation of organic substances such as carbohydrates.

The quantitative alterations of external conditions may be spoken of as
releasing stimuli.  They produce, in the complex equilibrium of the cell,
quantitative modifications in the arrangement and distribution of mass, by
means of which other chemical processes are at once set in motion, and
finally a new condition of equilibrium is attained.  But the commonly
expressed view that the environment can as a rule act only as a releasing
agent is incorrect, because it overlooks an essential point.  The power of
a cell to receive stimuli is only acquired as the result of previous
nutrition, which has produced a definite condition of concentration of
different substances.  Quantities are in this case the determining factors. 
The distribution of quantities is especially important in the sexual
reproduction of algae, for which a vigorous production of the materials
formed during carbon-assimilation appears to be essential.

In the Flowering plants, on the other hand, for reasons already mentioned,
the whole problem is more complicated.  Investigations on changes in the
course of development of fertilised eggs have hitherto been unsuccessful;
the difficulty of influencing egg-cells deeply immersed in tissue
constitutes a serious obstacle.  Other parts of plants are, however,
convenient objects of experiment; e.g. the growing apices of buds which
serve as cuttings for reproductive purposes, or buds on tubers, runners,
rhizomes, etc.  A growing apex consists of cells capable of division in
which, as in egg-cells, a complete series of latent possibilities of
development is embodied.  Which of these possibilities becomes effective
depends upon the action of the outer world transmitted by organs concerned
with nutrition.

Of the different stages which a flowering plant passes through in the
course of its development we will deal only with one in order to show that,
in spite of its great complexity, the problem is, in essentials, equally
open to attack in the higher plants and in the simplest organisms.  The
most important stage in the life of a flowering plant is the transition
from purely vegetative growth to sexual reproduction--that is, the
production of flowers.  In certain cases it can be demonstrated that there
is no internal cause, dependent simply on the specific structure, which
compels a plant to produce its flowers after a definite period of
vegetative growth.  (Klebs, "Willkurliche Entwickelungsanderungen", Jena
1903; see also "Probleme der Entwickelung", I. II.  "Centralbl." 1904.)

One extreme case, that of exceptionally early flowering, has been observed
in nature and more often in cultivation.  A number of plants under certain
conditions are able to flower soon after germination.  (Cf. numerous
records of this kind by Diels, "Jugendformen und Bluten", Berlin, 1906.) 
This shortening of the period of development is exhibited in the most
striking form in trees, as in the oak (Mobius, "Beitrage zur Lehre von der
Fortpflanzung", Jena, 1897, page 89.), flowering seedlings of which have
been observed from one to three years old, whereas normally the tree does
not flower until it is sixty or eighty years old.

Another extreme case is represented by prolonged vegetative growth leading
to the complete suppression of flower-production.  This result may be
obtained with several plants, such as Glechoma, the sugar beet, Digitalis,
and others, if they are kept during the winter in a warm, damp atmosphere,
and in rich soil; in the following spring or summer they fail to flower. 
(Klebs, "Willkurliche Aenderungen", etc. Jena, 1903, page 130.) 
Theoretically, however, experiments are of greater importance in which the
production of flowers is inhibited by very favourable conditions of
nutrition (Klebs, "Ueber kunstliche Metamorphosen", Stuttgart, 1906, page
115 ("Abh. Naturf. Ges. Halle", XXV.) occurring at the normal flowering
period.  Even in the case of plants of Sempervivum several years old,
which, as is shown by control experiments on precisely similar plants, are
on the point of flowering, flowering is rendered impossible if they are
forced to very vigorous growth by an abundant supply of water and salts in
the spring.  Flowering, however, occurs, if such plants are cultivated in
relatively dry sandy soil and in the presence of strong light.  Careful
researches into the conditions of growth have led, in the cases
Sempervivum, to the following results:  (1)  With a strong light and
vigorous carbon-assimilation a considerably increased supply of water and
nutritive salts produces active vegetative growth.  (2)  With a vigorous
carbon-assimilation in strong light, and a decrease in the supply of water
and salts active flower-production is induced.  (3)  If an average supply
of water and salts is given both processes are possible; the intensity of
carbon-assimilation determines which of the two is manifested.  A
diminution in the production of organic substances, particularly of
carbohydrates, induces vegetative growth.  This can be effected by culture
in feeble light or in light deprived of the yellow-red rays:  on the other
hand, flower-production follows an increase in light-intensity.  These
results are essentially in agreement with well-known observations on
cultivated plants, according to which, the application of much moisture,
after a plentiful supply of manure composed of inorganic salts, hinders the
flower-production of many vegetables, while a decrease in the supply of
water and salts favours flowering.

ii.  INFLUENCE OF THE ENVIRONMENT ON THE FORM OF SINGLE ORGANS.  (A
considerable number of observations bearing on this question are given by
Goebel in his "Experimentelle Morphologie der Pflanzen", Leipzig, 1908.  It
is not possible to deal here with the alteration in anatomical structure;
cf. Kuster, "Pathologische Pflanzenanatomie", Jena, 1903.)

If we look closely into the development of a flowering plant, we notice
that in a given species differently formed organs occur in definite
positions.  In a potato plant colourless runners are formed from the base
of the main stem which grow underground and produce tubers at their tips: 
from a higher level foliage shoots arise nearer the apex.  External
appearances suggest that both the place of origin and the form of these
organs were predetermined in the egg-cell or in the tuber.  But it was
shown experimentally by the well-known investigator Knight (Knight,
"Selection from the Physiological and Horticultural Papers", London, 1841.)
that tubers may be developed on the aerial stem in place of foliage shoots. 
These observations were considerably extended by Vochting.  (Vochting,
"Ueber die Bildung der Knollen", Cassel, 1887; see also "Bot. Zeit." 1902,
87.)  In one kind of potato, germinating tubers were induced to form
foliage shoots under the influence of a higher temperature; at a lower
temperature they formed tuber-bearing shoots.  Many other examples of the
conversion of foliage-shoots into runners and rhizomes, or vice versa, have
been described by Goebel and others.  As in the asexual reproduction of
algae quantitative alteration in the amount of moisture, light,
temperature, etc. determines whether this or that form of shoot is
produced.  If the primordia of these organs are exposed to altered
conditions of nutrition at a sufficiently early stage a complete
substitution of one organ for another is effected.  If the rudiment has
reached a certain stage in development before it is exposed to these
influences, extraordinary intermediate forms are obtained, bearing the
characters of both organs.

The study of regeneration following injury is of greater importance as
regards the problem of the development and place of origin of organs. 
(Reference may be made to the full summary of results given by Goebel in
his "Experimentelle Morphologie", Leipzig and Berlin, 1908, Section IV.) 
Only in relatively very rare cases is there a complete re-formation of the
injured organ itself, as e.g. in the growing-apex.  Much more commonly
injury leads to the development of complementary formations, it may be the
rejuvenescence of a hitherto dormant rudiment, or it may be the formation
of such ab initio.  In all organs, stems, roots, leaves, as well as
inflorescences, this kind of regeneration, which occurs in a great variety
of ways according to the species, may be observed on detached pieces of the
plant.  Cases are also known, such, for example, as the leaves of many
plants which readily form roots but not shoots, where a complete
regeneration does not occur.

The widely spread power of reacting to wounding affords a very valuable
means of inducing a fresh development of buds and roots on places where
they do not occur in normal circumstances.  Injury creates special
conditions, but little is known as yet in regard to alterations directly
produced in this way.  Where the injury consists in the separation of an
organ from its normal connections, the factors concerned are more
comprehensible.  A detached leaf, e.g., is at once cut off from a supply of
water and salts, and is deprived of the means of getting rid of organic
substances which it produces; the result is a considerable alteration in
the degree of concentration.  No experimental investigation on these lines
has yet been made.  Our ignorance has often led to the view that we are
dealing with a force whose specific quality is the restitution of the parts
lost by operation; the proof, therefore, that in certain cases a similar
production of new roots or buds may be induced without previous injury and
simply by a change in external conditions assumes an importance.  (Klebs,
"Willkurliche Entwickelung", page 100; also, "Probleme der Entwickelung",
"Biol. Centralbl." 1904, page 610.)

A specially striking phenomenon of regeneration, exhibited also by
uninjured plants, is afforded by polarity, which was discovered by
Vochting.  (See the classic work of Vochting, "Ueber Organbildung im
Pflanzenreich", I. Bonn, 1888; also "Bot. Zeit. 1906, page 101; cf. Goebel,
"Experimentelle Morphologie", Leipzig and Berlin, 1908, Section V,
Polaritat.)  It is found, for example, that roots are formed from the base
of a detached piece of stem and shoots from the apex.  Within the limits of
this essay it is impossible to go into this difficult question; it is,
however, important from the point of view of our general survey to
emphasise the fact that the physiological distinctions between base and
apex of pieces of stem are only of a quantitative kind, that is, they
consist in the inhibition of certain phenomena or in favouring them.  As a
matter of fact roots may be produced from the apices of willows and
cuttings of other plants; the distinction is thus obliterated under the
influence of environment.  The fixed polarity of cuttings from full grown
stems cannot be destroyed; it is the expression of previous development. 
Vochting speaks of polarity as a fixed inherited character.  This is an
unconvincing conclusion, as nothing can be deduced from our present
knowledge as to the causes which led up to polarity.  We know that the
fertilised egg, like the embryo, is fixed at one end by which it hangs
freely in the embryo-sac and afterwards in the endosperm.  From the first,
therefore, the two ends have different natures, and these are revealed in
the differentiation into root-apex and stem-apex.  A definite direction in
the flow of food-substances is correlated with this arrangement, and this
eventually leads to a polarity in the tissues.  This view requires
experimental proof, which in the case of the egg-cells of flowering plants
hardly appears possible; but it derives considerable support from the fact
that in herbaceous plants, e.g. Sempervivum (Klebs, "Variationen der
Bluten", "Jahrb. Wiss. Bot." 1905, page 260.), rosettes or flower-shoots
are formed in response to external conditions at the base, in the middle,
or at the apex of the stem, so that polarity as it occurs under normal
conditions cannot be the result of unalterable hereditary factors.  On the
other hand, the lower plants should furnish decisive evidence on this
question, and the experiments of Stahl, Winkler, Kniep, and others indicate
the right method of attacking the problem.

The relation of leaf-form to environment has often been investigated and is
well known.  The leaves of bog and water plants (Cf.Goebel, loc. cit.
chapter II.; also Gluck, "Untersuchungen uber Wasser- und Sumpfgewachse",
Jena, Vols. I.-II. 1905-06.) afford the most striking examples of
modifications:  according as they are grown in water, moist or dry air, the
form of the species characteristic of the particular habitat is produced,
since the stems are also modified.  To the same group of phenomena belongs
the modification of the forms of leaves and stems in plants on
transplantation from the plains to the mountains (Bonnier, "Recherches sur
l'Anatomie experimentale des Vegetaux", Corbeil, 1895.) or vice versa. 
Such variations are by no means isolated examples.  All plants exhibit a
definite alteration in form as the result of prolonged cultivation in moist
or dry air, in strong or feeble light, or in darkness, or in salt solutions
of different composition and strength.

Every individual which is exposed to definite combinations of external
factors exhibits eventually the same type of modification.  This is the
type of variation which Darwin termed "definite."  It is easy to realise
that indefinite or fluctuating variations belong essentially to the same
class of phenomena; both are reactions to changes in environment.  In the
production of individual variations two different influences undoubtedly
cooperate.  One set of variations is caused by different external
conditions, during the production, either of sexual cells or of vegetative
primordia; another set is the result of varying external conditions during
the development of the embryo into an adult plant.  The two sets of
influences cannot as yet be sharply differentiated.  If, for purposes of
vegetative reproduction, we select pieces of the same parent-plant of a
pure species, the second type of variation predominates.  Individual
fluctuations depend essentially in such cases on small variations in
environment during development.

These relations must be borne in mind if we wish to understand the results
of statistical methods.  Since the work of Quetelet, Galton, and others the
statistical examination of individual differences in animals and plants has
become a special science, which is primarily based on the consideration
that the application of the theory of probability renders possible
mathematical statement and control of the results.  The facts show that any
character, size of leaf, length of stem, the number of members in a flower,
etc. do not vary haphazard but in a very regular manner.  In most cases it
is found that there is a value which occurs most commonly, the average or
medium value, from which the larger and smaller deviations, the so-called
plus and minus variations fall away in a continuous series and end in a
limiting value.  In the simpler cases a falling off occurs equally on both
sides of the curve; the curve constructed from such data agrees very
closely with the Gaussian curve of error.  In more complicated cases
irregular curves of different kinds are obtained which may be calculated on
certain suppositions.

The regular fluctuations about a mean according to the rule of probability
is often attributed to some law underlying variability.  (de Vries,
"Mutationstheorie", Vol. I. page 35, Leipzig, 1901.)  But there is no such
law which compels a plant to vary in a particular manner.  Every
experimental investigation shows, as we have already remarked, that the
fluctuation of characters depends on fluctuation in the external factors. 
The applicability of the method of probability follows from the fact that
the numerous individuals of a species are influenced by a limited number of
variable conditions.  (Klebs, "Willkurl. Ent." Jena, 1903, page 141.)  As
each of these conditions includes within certain limits all possible values
and exhibits all possible combinations, it follows that, according to the
rules of probability, there must be a mean value, about which the larger
and smaller deviations are distributed.  Any character will be found to
have the mean value which corresponds with that combination of determining
factors which occurs most frequently.  Deviations towards plus and minus
values will be correspondingly produced by rarer conditions.

A conclusion of fundamental importance may be drawn from this conception,
which is, to a certain extent, supported by experimental investigation. 
(Klebs, "Studien uber Variation", "Arch. fur Entw." 1907.)  There is no
normal curve for a particular CHARACTER, there is only a curve for the
varying combinations of conditions occurring in nature or under
cultivation.  Under other conditions entirely different curves may be
obtained with other variants as a mean value.  If, for example, under
ordinary conditions the number 10 is the most frequent variant for the
stamens of Sedum spectabile, in special circumstances (red light) this is
replaced by the number 5.  The more accurately we know the conditions for a
particular form or number, and are able to reproduce it by experiment, the
nearer we are to achieving our aim of rendering a particular variation
impossible or of making it dominant.

In addition to the individual variations of a species, more pronounced
fluctuations occur relatively rarely and sporadically which are spoken of
as "single variations," or if specially striking as abnormalities or
monstrosities.  These forms have long attracted the attention of
morphologists; a large number of observations of this kind are given in the
handbooks of Masters (Masters, "Vegetable Teratology", London, 1869.) and
Penzig (Penzig, "Pflanzen-Teratologie, Vols I. and II. Genua, 1890-94.) 
These variations, which used to be regarded as curiosities, have now
assumed considerable importance in connection with the causes of form-
development.  They also possess special interest in relation to the
question of heredity, a subject which does not at present concern us, as
such deviations from normal development undoubtedly arise as individual
variations induced by the influence of environment.

Abnormal developments of all kinds in stems, leaves, and flowers, may be
produced by parasites, insects, or fungi.  They may also be induced by
injury, as Blaringhem (Blaringhem, "Mutation et traumatismes", Paris,
1907.) has more particularly demonstrated, which, by cutting away the
leading shoots of branches in an early stage of development, caused
fasciation, torsion, anomalous flowers, etc.  The experiments of Blaringhem
point to the probability that disturbances in the conditions of food-supply
consequent on injury are the cause of the production of monstrosities. 
This is certainly the case in my experiments with species of Sempervivum
(Klebs, "Kunstliche Metamorphosen", Stuttgart, 1906.); individuals, which
at first formed normal flowers, produced a great variety of abnormalities
as the result of changes in nutrition, we may call to mind the fact that
the formation of inflorescences occurs normally when a vigorous production
of organic compounds, such as starch, sugar, etc. follows a diminution in
the supply of mineral salts.  On the other hand, the development of
inflorescences is entirely suppressed if, at a suitable moment before the
actual foundations have been laid, water and mineral salts are supplied to
the roots.  If, during the week when the inflorescence has just been laid
down and is growing very slowly, the supply of water and salts is
increased, the internal conditions of the cells are essentially changed. 
At a later stage, after the elongation of the inflorescence, rosettes of
leaves are produced instead of flowers, and structures intermediate between
the two kinds of organs; a number of peculiar plant-forms are thus obtained
(Cf. Lotsy, "Vorlesungen uber Deszendenztheorien", Vol. II. pl. 3, Jena,
1908.)  Abnormalities in the greatest variety are produced in flowers by
varying the time at which the stimulus is applied, and by the cooperation
of other factors such as temperature, darkness, etc.  In number and
arrangement the several floral members vary within wide limits; sepals,
petals, stamens, and carpels are altered in form and colour, a
transformation of stamens to carpels and from carpels to stamens occurs in
varying degrees.  The majority of the deviations observed had not
previously been seen either under natural conditions or in cultivation;
they were first brought to light through the influence of external factors.

Such transformations of flowers become apparent at a time, which is
separated by about two months from the period at which the particular cause
began to act.  There is, therefore, no close connection between the
appearance of the modifications and the external conditions which prevail
at the moment.  When we are ignorant of the causes which are operative so
long before the results are seen, we gain the impression that such
variations as occur are spontaneous or autonomous expressions of the inner
nature of the plant.  It is much more likely that, as in Sempervivum, they
were originally produced by an external stimulus which had previously
reached the sexual cells or the young embryo.  In any case abnormalities of
this kind appear to be of a special type as compared with ordinary
fluctuating variations.  Darwin pointed out this difference; Bateson
(Bateson, "Materials for the study of Variation", London, 1894, page 5.)
has attempted to make the distinction sharper, at the same time emphasising
its importance in heredity.

Bateson applies the term CONTINUOUS to small variations connected with one
another by transitional stages, while those which are more striking and
characterised from the first by a certain completeness, he names
DISCONTINUOUS.  He drew attention to a great difficulty which stands in the
way of Lamarck's hypothesis, as also of Darwin's view.  "According to both
theories, specific diversity of form is consequent upon diversity of
environment, and diversity of environment is thus the ultimate measure of
diversity of specific form.  Here then we meet the difficulty that diverse
environments often shade into each other insensibly and form a continuous
series, whereas the Specific Forms of life which are subject to them on the
whole form a Discontinuous Series."  This difficulty is, however, not of
fundamental importance as well authenticated facts have been adduced
showing that by alteration of the environment discontinuous variations,
such as alterations in the number and form of members of a flower, may be
produced.  We can as yet no more explain how this happens than we can
explain the existence of continuous variations.  We can only assert that
both kinds of variation arise in response to quantitative alterations in
external conditions.  The question as to which kind of variation is
produced depends on the greater or less degree of alteration; it is
correlated with the state of the particular cells at the moment.

In this short sketch it is only possible to deal superficially with a small
part of the subject.  It has been clearly shown that in view of the general
dependence of development on the factors of the environment a number of
problems are ready for experimental treatment.  One must, however, not
forget that the science of the physiology of form has not progressed beyond
its initial stages.  Just now our first duty is to demonstrate the
dependence on external factors in as many forms of plants as possible, in
order to obtain a more thorough control of all the different plant-forms.
The problem is not only to produce at will (and independently of their
normal mode of life) forms which occur in nature, but also to stimulate
into operation potentialities which necessarily lie dormant under the
conditions which prevail in nature.  The constitution of a species is much
richer in possibilities of development than would appear to be the case
under normal conditions.  It remains for man to stimulate into activity all
the potentialities.

But the control of plant-form is only a preliminary step--the foundation
stones on which to erect a coherent scientific structure.  We must discover
what are the internal processes in the cell produced by external factors,
which as a necessary consequence result in the appearance of a definite
form.  We are here brought into contact with the most obscure problem of
life.  Progress can only be made pari passu with progress in physics and
chemistry, and with the growth of our knowledge of nutrition, growth, etc.

Let us take one of the simplest cases--an alteration in form.  A
cylindrical cell of the alga Stigeoclonium assumes, as Livingstone
(Livingstone, "On the nature of the stimulus which causes the change of
form, etc."  "Botanical Gazette", XXX. 1900; also XXXII. 1901.) has shown,
a spherical form when the osmotic pressure of the culture fluid is
increased; or a spore of Mucor, which, in a sugar solution grows into a
branched filament, in the presence of a small quantity of acid (hydrogen
ions) becomes a comparatively large sphere.  (Ritter, "Ueber Kugelhefe,
etc."  "Ber. bot. Gesell." Berlin, XXV. page 255, 1907.)  In both cases
there has undoubtedly been an alteration in the osmotic pressure of the
cell-sap, but this does not suffice to explain the alteration in form,
since the unknown alterations, which are induced in the protoplasm, must in
their turn influence the cell-membrane.  In the case of the very much more
complex alterations in form, such as we encounter in the course of
development of plants, there do not appear to be any clues which lead us to
a deeper insight into the phenomena.  Nevertheless we continue the attempt,
seeking with the help of any available hypothesis for points of attack,
which may enable us to acquire a more complete mastery of physiological
methods.  To quote a single example; I may put the question, what internal
changes produce a transition from vegetative growth to sexual reproduction?

The facts, which are as clearly established from the lower as for the
higher plants, teach us that quantitative alteration in the environment
produces such a transition.  This suggests the conclusion that quantitative
internal changes in the cells, and with them disturbances in the degree of
concentration, are induced, through which the chemical reactions are led in
the direction of sexual reproduction.  An increase in the production of
organic substances in the presence of light, chiefly of the carbohydrates,
with a simultaneous decrease in the amount of inorganic salts and water,
are the cause of the disturbance and at the same time of the alteration in
the direction of development.  Possibly indeed mineral salts as such are
not in question, but only in the form of other organic combinations,
particularly proteid material, so that we are concerned with an alteration
in the relation of the carbohydrates and proteids.  The difficulties of
such researches are very great because the methods are not yet sufficiently
exact to demonstrate the frequently small quantitative differences in
chemical composition.  Questions relating to the enzymes, which are of the
greatest importance in all these life-processes, are especially
complicated.  In any case it is the necessary result of such an hypothesis
that we must employ chemical methods of investigation in dealing with
problems connected with the physiology of form.

II.  INFLUENCE OF ENVIRONMENT ON THE TRANSFORMATION OF SPECIES.

The study of the physiology of form-development in a pure species has
already yielded results and makes slow but sure progress.  The physiology
of the possibility of the transformation of one species into another is
based, as yet, rather on pious hope than on accomplished fact.  From the
first it appeared to be hopeless to investigate physiologically the origin
of Linnean species and at the same time that of the natural system, an aim
which Darwin had before him in his enduring work.  The historical sequence
of events, of which an organism is the expression, can only be treated
hypothetically with the help of facts supplied by comparative morphology,
the history of development, geographical distribution, and palaeontology. 
(See Lotsy, "Vorlesungen" (Jena, I. 1906, II. 1908), for summary of the
facts.)  A glance at the controversy which is going on today in regard to
different hypotheses shows that the same material may lead different
investigators to form entirely different opinions.  Our ultimate aim is to
find a solution of the problem as to the cause of the origin of species. 
Indeed such attempts are now being made:  they are justified by the fact
that under cultivation new and permanent strains are produced; the
fundamental importance of this was first grasped by Darwin.  New points of
view in regard to these lines of inquiry have been adopted by H. de Vries
who has succeeded in obtaining from Oenothera Lamarckiana a number of
constant "elementary" species.  Even if it is demonstrated that he was
simply dealing with the complex splitting up of a hybrid (Bateson, "Reports
to the Evolution Committee of the Royal Society", London, 1902; cf. also
Lotsy, "Vorlesungen", Vol. I. page 234.), the facts adduced in no sense
lose their very great value.

We must look at the problem in its simplest form; we find it in every case
where a new race differs essentially from the original type in a single
character only; for example, in the colour of the flowers or in the
petalody of the stamens (doubling of flowers).  In this connection we must
keep in view the fact that every visible character in a plant is the
resultant of the cooperation of specific structure, with its various
potentialities, and the influence of the environment.  We know, that in a
pure species all characters vary, that a blue-flowering Campanula or a red
Sempervivum can be converted by experiment into white-flowering forms, that
a transformation of stamens into petals may be caused by fungi or by the
influence of changed conditions of nutrition, or that plants in dry and
poor soil become dwarfed.  But so far as the experiments justify a
conclusion, it would appear that such alterations are not inherited by the
offspring.  Like all other variations they appear only so long as special
conditions prevail in the surroundings.

It has been shown that the case is quite different as regards the white-
flowering, double or dwarf races, because these retain their characters
when cultivated under practically identical conditions, and side by side
with the blue, single-flowering or tall races.  The problem may therefore
be stated thus:  how can a character, which appears in the one case only
under the strictly limited conditions of the experiment, in other cases
become apparent under the very much wider conditions of ordinary
cultivation?  If a character appears, in these circumstances, in the case
of all individuals, we then speak of constant races.  In such simple cases
the essential point is not the creation of a new character but rather an
ALTERATION OF THIS CHARACTER IN ACCORDANCE WITH THE ENVIRONMENT.  In the
examples mentioned the modified character in the simple varieties (or a
number of characters in elementary species) appears more or less suddenly
and is constant in the above sense.  The result is what de Vries has termed
a Mutation.  In this connection we must bear in mind the fact that no
difference, recognisable externally, need exist between individual
variation and mutation.  Even the most minute quantitative difference
between two plants may be of specific value if it is preserved under
similar external conditions during many successive generations.  We do not
know how this happens.  We may state the problem in other terms; by saying
that the specific structure must be altered.  It is possible, to some
extent, to explain this sudden alteration, if we regard it as a chemical
alteration of structure either in the specific qualities of the proteids or
of the unknown carriers of life.  In the case of many organic compounds
their morphological characters (the physical condition, crystalline form,
etc.) are at once changed by alteration of atomic relations or by
incorporation of new radicals.  (For instance ethylchloride (C2H5Cl) is a
gas at 21 deg C., ethylenechloride (C2H4Cl2) a fluid boiling at 84 deg C.,
beta trichlorethane (C2H3Cl3) a fluid boiling at 113 deg C., perchlorethane
(C2Cl6) a crystalline substance.  Klebs, ("Willkurliche
Entwickelungsanderungen" page 158.)  Much more important, however, would be
an answer to the question, whether an individual variation can be converted
experimentally into an inherited character--a mutation in de Vries's sense.

In all circumstances we may recognise as a guiding principle the assumption
adopted by Lamarck, Darwin, and many others, that the inheritance of any
one character, or in more general terms, the transformation of one species
into another, is, in the last instance, to be referred to a change in the
environment.  From a causal-mechanical point of view it is not a priori
conceivable that one species can ever become changed into another so long
as external conditions remain constant.  The inner structure of a species
must be essentially altered by external influences.  Two methods of
experimental research may be adopted, the effect of crossing distinct
species and, secondly, the effect of definite factors of the environment.

The subject of hybridisation is dealt with in another part of this essay. 
It is enough to refer here to the most important fact, that as the result
of combinations of characters of different species new and constant forms
are produced.  Further, Tschermack, Bateson and others have demonstrated
the possibility that hitherto unknown inheritable characters may be
produced by hybridisation.

The other method of producing constant races by the influence of special
external conditions has often been employed.  The sporeless races of
Bacteria and Yeasts (Cf. Detto, "Die Theorie der direkten Anpassung...",
pages 98 et seq., Jena, 1904; see also Lotsy, "Vorlesungen", II. pages 636
et seq., where other similar cases are described.) are well known, in which
an internal alteration of the cells is induced by the influence of poison
or higher temperature, so that the power of producing spores even under
normal conditions appears to be lost.  A similar state of things is found
in some races which under certain definite conditions lose their colour or
their virulence.  Among the phanerogams the investigations of Schubler on
cereals afford parallel cases, in which the influence of a northern climate
produces individuals which ripen their seeds early; these seeds produce
plants which seed early in southern countries.  Analogous results were
obtained by Cieslar in his experiments; seeds of conifers from the Alps
when planted in the plains produced plants of slow growth and small
diameter.

All these observations are of considerable interest theoretically; they
show that the action of environment certainly induces such internal
changes, and that these are transmitted to the next generation.  But as
regards the main question, whether constant races may be obtained by this
means, the experiments cannot as yet supply a definite answer.  In
phanerogams, the influence very soon dies out in succeeding generations; in
the case of bacteria, in which it is only a question of the loss of a
character it is relatively easy for this to reappear.  It is not
impossible, that in all such cases there is a material hanging-on of
certain internal conditions, in consequence of which the modification of
the character persists for a time in the descendants, although the original
external conditions are no longer present.

Thus a slow dying-out of the effect of a stimulus was seen in my
experiments on Veronica chamaedrys.  (Klebs, "Kunstliche Metamorphosen",
Stuttgart, 1906, page 132.)  During the cultivation of an artificially
modified inflorescence I obtained a race showing modifications in different
directions, among which twisting was especially conspicuous.  This plant,
however, does not behave as the twisted race of Dipsacus isolated by de
Vries (de Vries, "Mutationstheorie", Vol. II. Leipzig, 1903, page 573.),
which produced each year a definite percentage of twisted individuals.  In
the vegetative reproduction of this Veronica the torsion appeared in the
first, also in the second and third year, but with diminishing intensity. 
In spite of good cultivation this character has apparently now disappeared;
it disappeared still more quickly in seedlings.  In another character of
the same Veronica chamaedrys the influence of the environment was stronger. 
The transformation of the inflorescences to foliage-shoots formed the
starting-point; it occurred only under narrowly defined conditions, namely
on cultivation as a cutting in moist air and on removal of all other leaf-
buds.  In the majority (7/10) of the plants obtained from the transformed
shoots, the modification appeared in the following year without any
interference.  Of the three plants which were under observation several
years the first lost the character in a short time, while the two others
still retain it, after vegetative propagation, in varying degrees.  The
same character occurs also in some of the seedlings; but anything
approaching a constant race has not been produced.

Another means of producing new races has been attempted by Blaringhem. 
(Blaringhem, "Mutation et Traumatisme", Paris, 1907.)  On removing at an
early stage the main shoots of different plants he observed various
abnormalities in the newly formed basal shoots.  From the seeds of such
plants he obtained races, a large percentage of which exhibited these
abnormalities.  Starting from a male Maize plant with a fasciated
inflorescence, on which a proportion of the flowers had become male, a new
race was bred in which hermaphrodite flowers were frequently produced.  In
the same way Blaringhem obtained, among other similar results, a race of
barley with branched ears.  These races, however, behaved in essentials
like those which have been demonstrated by de Vries to be inconstant, e.g.
Trifolium pratense quinquefolium and others.  The abnormality appears in a
proportion of the individuals and only under very special conditions.  It
must be remembered too that Blaringhem worked with old cultivated plants,
which from the first had been disposed to split into a great variety of
races.  It is possible, but difficult to prove, that injury contributed to
this result.

A third method has been adopted by MacDougal (MacDougal, "Heredity and
Origin of species", "Monist", 1906; "Report of department of botanical
research", "Fifth Year-book of the Carnegie Institution of Washington",
page 119, 1907.) who injected strong (10 percent) sugar solution or weak
solutions of calcium nitrate and zinc sulphate into young carpels of
different plants.  From the seeds of a plant of Raimannia odorata the
carpels of which had been thus treated he obtained several plants
distinguished from the parent-forms by the absence of hairs and by distinct
forms of leaves.  Further examination showed that he had here to do with a
new elementary species.  MacDougal also obtained a more or less distinct
mutant of Oenothera biennis.  We cannot as yet form an opinion as to how
far the effect is due to the wound or to the injection of fluid as such, or
to its chemical properties.  This, however, is not so essential as to
decide whether the mutant stands in any relation to the influence of
external factors.  It is at any rate very important that this kind of
investigation should be carried further.

If it could be shown that new and inherited races were obtained by
MacDougal's method, it would be safe to conclude that the same end might be
gained by altering the conditions of the food-stuff conducted to the sexual
cells.  New races or elementary species, however, arise without wounding or
injection.  This at once raises the much discussed question, how far
garden-cultivation has led to the creation of new races?  Contrary to the
opinion expressed by Darwin and others, de Vries ("Mutationstheorie", Vol.
I. pages 412 et seq.) tried to show that garden-races have been produced
only from spontaneous types which occur in a wild state or from sub-races,
which the breeder has accidentally discovered but not originated.  In a
small number of cases only has de Vries adduced definite proof.  On the
other side we have the work of Korschinsky (Korschinsky, "Heterogenesis und
Evolution", "Flora", 1901.) which shows that whole series of garden-races
have made their appearance only after years of cultivation.  In the
majority of races we are entirely ignorant of their origin.

It is, however, a fact that if a plant is removed from natural conditions
into cultivation, a well-marked variation occurs.  The well-known plant-
breeder L. de Vilmorin (L. de Vilmorin, "Notices sur l'amelioration des
plantes", Paris, 1886, page 36.), speaking from his own experience, states
that a plant is induced to "affoler," that is to exhibit all possible
variations from which the breeder may make a further selection only after
cultivation for several generations.  The effect of cultivation was
particularly striking in Veronica chamaedrys (Klebs, "Kunstliche
Metamorphosen", Stuttgart, 1906, page 152.) which, in spite of its wide
distribution in nature, varies very little.  After a few years of
cultivation this "good" and constant species becomes highly variable.  The
specimens on which the experiments were made were three modified
inflorescence cuttings, the parent-plants of which certainly exhibited no
striking abnormalities.  In a short time many hitherto latent
potentialities became apparent, so that characters, never previously
observed, or at least very rarely, were exhibited, such as scattered leaf-
arrangement, torsion, terminal or branched inflorescences, the conversion
of the inflorescence into foliage-shoots, every conceivable alteration in
the colour of flowers, the assumption of a green colour by parts of the
flowers, the proliferation of flowers.

All this points to some disturbance in the species resulting from methods
of cultivation.  It has, however, not yet been possible to produce constant
races with any one of these modified characters.  But variations appeared
among the seedlings, some of which, e.g. yellow variegation, were not
inheritable, while others have proved constant.  This holds good, so far as
we know at present, for a small rose-coloured form which is to be reckoned
as a mutation.  Thus the prospect of producing new races by cultivation
appears to be full of promise.

So long as the view is held that good nourishment, i.e. a plentiful supply
of water and salts, constitutes the essential characteristic of garden-
cultivation, we can hardly conceive that new mutations can be thus
produced.  But perhaps the view here put forward in regard to the
production of form throws new light on this puzzling problem.

Good manuring is in the highest degree favourable to vegetative growth, but
is in no way equally favourable to the formation of flowers.  The
constantly repeated expression, good or favourable nourishment, is not only
vague but misleading, because circumstances favourable to growth differ
from those which promote reproduction; for the production of every form
there are certain favourable conditions of nourishment, which may be
defined for each species.  Experience shows that, within definite and often
very wide limits, it does not depend upon the ABSOLUTE AMOUNT of the
various food substances, but upon their respective degrees of
concentration.  As we have already stated, the production of flowers
follows a relative increase in the amount of carbohydrates formed in the
presence of light, as compared with the inorganic salts on which the
formation of albuminous substances depends.  (Klebs, "Kunstliche
Metamorphosen", page 117.)  The various modifications of flowers are due to
the fact that a relatively too strong solution of salts is supplied to the
rudiments of these organs.  As a general rule every plant form depends upon
a certain relation between the different chemical substances in the cells
and is modified by an alteration of that relation.

During long cultivation under conditions which vary in very different
degrees, such as moisture, the amount of salts, light intensity,
temperature, oxygen, it is possible that sudden and special disturbances in
the relations of the cell substances have a directive influence on the
inner organisation of the sexual cells, so that not only inconstant but
also constant varieties will be formed.

Definite proof in support of this view has not yet been furnished, and we
must admit that the question as to the cause of heredity remains,
fundamentally, as far from solution as it was in Darwin's time.  As the
result of the work of many investigators, particularly de Vries, the
problem is constantly becoming clearer and more definite.  The penetration
into this most difficult and therefore most interesting problem of life and
the creation by experiment of new races or elementary species are no longer
beyond the region of possibility.


XIV.  EXPERIMENTAL STUDY OF THE INFLUENCE OF ENVIRONMENT ON ANIMALS.

By JACQUES LOEB, M.D.
Professor of Physiology in the University of California.

I. INTRODUCTORY REMARKS.

What the biologist calls the natural environment of an animal is from a
physical point of view a rather rigid combination of definite forces.  It
is obvious that by a purposeful and systematic variation of these and by
the application of other forces in the laboratory, results must be
obtainable which do not appear in the natural environment.  This is the
reasoning underlying the modern development of the study of the effects of
environment upon animal life.  It was perhaps not the least important of
Darwin's services to science that the boldness of his conceptions gave to
the experimental biologist courage to enter upon the attempt of controlling
at will the life-phenomena of animals, and of bringing about effects which
cannot be expected in Nature.

The systematic physico-chemical analysis of the effect of outside forces
upon the form and reactions of animals is also our only means of
unravelling the mechanism of heredity beyond the scope of the Mendelian
law.  The manner in which a germ-cell can force upon the adult certain
characters will not be understood until we succeed in varying and
controlling hereditary characteristics; and this can only be accomplished
on the basis of a systematic study of the effects of chemical and physical
forces upon living matter.

Owing to limitation of space this sketch is necessarily very incomplete,
and it must not be inferred that studies which are not mentioned here were
considered to be of minor importance.  All the writer could hope to do was
to bring together a few instances of the experimental analysis of the
effect of environment, which indicate the nature and extent of our control
over life-phenomena and which also have some relation to the work of
Darwin.  In the selection of these instances preference is given to those
problems which are not too technical for the general reader.

The forces, the influence of which we shall discuss, are in succession
chemical agencies, temperature, light, and gravitation.  We shall also
treat separately the effect of these forces upon form and instinctive
reactions.

II.  THE EFFECTS OF CHEMICAL AGENCIES.

(a)  HETEROGENEOUS HYBRIDISATION.

It was held until recently that hybridisation is not possible except
between closely related species and that even among these a successful
hybridisation cannot always be counted upon.  This view was well supported
by experience.  It is, for instance, well known that the majority of marine
animals lay their unfertilised eggs in the ocean and that the males shed
their sperm also into the sea-water.  The numerical excess of the
spermatozoa over the ova in the sea-water is the only guarantee that the
eggs are fertilised, for the spermatozoa are carried to the eggs by chance
and are not attracted by the latter.  This statement is the result of
numerous experiments by various authors, and is contrary to common belief.
As a rule all or the majority of individuals of a species in a given region
spawn on the same day, and when this occurs the sea-water constitutes a
veritable suspension of sperm.  It has been shown by experiment that in
fresh sea-water the sperm may live and retain its fertilising power for
several days.  It is thus unavoidable that at certain periods more than one
kind of spermatozoon is suspended in the sea-water and it is a matter of
surprise that the most heterogeneous hybridisations do not constantly
occur.  The reason for this becomes obvious if we bring together mature
eggs and equally mature and active sperm of a different family.  When this
is done no egg is, as a rule, fertilised.  The eggs of a sea-urchin can be
fertilised by sperm of their own species, or, though in smaller numbers, by
the sperm of other species of sea-urchins, but not by the sperm of other
groups of echinoderms, e.g. starfish, brittle-stars, holothurians or
crinoids, and still less by the sperm of more distant groups of animals. 
The consensus of opinion seemed to be that the spermatozoon must enter the
egg through a narrow opening or canal, the so-called micropyle, and that
the micropyle allowed only the spermatozoa of the same or of a closely
related species to enter the egg.

It seemed to the writer that the cause of this limitation of hybridisation
might be of another kind and that by a change in the constitution of the
sea-water it might be possible to bring about heterogenous hybridisations,
which in normal sea-water are impossible.  This assumption proved correct.
Sea-water has a faintly alkaline reaction (in terms of the physical chemist
its concentration of hydroxyl ions is about (10 to the power minus six)N at
Pacific Grove, California, and about (10 to the power minus 5)N at Woods
Hole, Massachusetts).  If we slightly raise the alkalinity of the sea-water
by adding to it a small but definite quantity of sodium hydroxide or some
other alkali, the eggs of the sea-urchin can be fertilised with the sperm
of widely different groups of animals, possibly with the sperm of any
marine animal which sheds it into the ocean.  In 1903 it was shown that if
we add from about 0.5 to 0.8 cubic centimetre N/10 sodium hydroxide to 50
cubic centimetres of sea-water, the eggs of Strongylocentrotus purpuratus
(a sea-urchin which is found on the coast of California) can be fertilised
in large quantities by the sperm of various kinds of starfish, brittle-
stars and holothurians; while in normal sea-water or with less sodium
hydroxide not a single egg of the same female could be fertilised with the
starfish sperm which proved effective in the hyper-alkaline sea-water.  The
sperm of the various forms of starfish was not equally effective for these
hybridisations; the sperm of Asterias ochracea and A. capitata gave the
best results, since it was possible to fertilise 50 per cent or more of the
sea-urchin eggs, while the sperm of Pycnopodia and Asterina fertilised only
2 per cent of the same eggs.

Godlewski used the same method for the hybridisation of the sea-urchin eggs
with the sperm of a crinoid (Antedon rosacea).  Kupelwieser afterwards
obtained results which seemed to indicate the possibility of fertilising
the eggs of Strongylocentrotus with the sperm of a mollusc (Mytilus.) 
Recently, the writer succeeded in fertilising the eggs of
Strongylocentrotus franciscanus with the sperm of a mollusc--Chlorostoma. 
This result could only be obtained in sea-water the alkalinity of which had
been increased (through the addition of 0.8 cubic centimetre N/10 sodium
hydroxide to 50 cubic centimetres of sea-water).  We thus see that by
increasing the alkalinity of the sea-water it is possible to effect
heterogeneous hybridisations which are at present impossible in the natural
environment of these animals.

It is, however, conceivable that in former periods of the earth's history
such heterogeneous hybridisations were possible.  It is known that in
solutions like sea-water the degree of alkalinity must increase when the
amount of carbon-dioxide in the atmosphere is diminished.  If it be true,
as Arrhenius assumes, that the Ice age was caused or preceded by a
diminution in the amount of carbon-dioxide in the air, such a diminution
must also have resulted in an increase of the alkalinity of the sea-water,
and one result of such an increase must have been to render possible
heterogeneous hybridisations in the ocean which in the present state of
alkalinity are practically excluded.

But granted that such hybridisations were possible, would they have
influenced the character of the fauna?  In other words, are the hybrids
between sea-urchin and starfish, or better still, between sea-urchin and
mollusc, capable of development, and if so, what is their character?  The
first experiment made it appear doubtful whether these heterogeneous
hybrids could live.  The sea-urchin eggs which were fertilised in the
laboratory by the spermatozoa of the starfish, as a rule, died earlier than
those of the pure breeds.  But more recent results indicate that this was
due merely to deficiencies in the technique of the earlier experiments. 
The writer has recently obtained hybrid larvae between the sea-urchin egg
and the sperm of a mollusc (Chlorostoma) which, in the laboratory,
developed as well and lived as long as the pure breeds of the sea-urchin,
and there was nothing to indicate any difference in the vitality of the two
breeds.

So far as the question of heredity is concerned, all the experiments on
heterogeneous hybridisation of the egg of the sea-urchin with the sperm of
starfish, brittle-stars, crinoids and molluscs, have led to the same
result, namely, that the larvae have purely maternal characteristics and
differ in no way from the pure breed of the form from which the egg is
taken.  By way of illustration it may be said that the larvae of the sea-
urchin reach on the third day or earlier (according to species and
temperature) the so-called pluteus stage, in which they possess a typical
skeleton; while neither the larvae of the starfish nor those of the mollusc
form a skeleton at the corresponding stage.  It was, therefore, a matter of
some interest to find out whether or not the larvae produced by the
fertilisation of the sea-urchin egg with the sperm of starfish or mollusc
would form the normal and typical pluteus skeleton.  This was invariably
the case in the experiments of Godlewski, Kupelwieser, Hagedoorn, and the
writer.  These hybrid larvae were exclusively maternal in character.

It might be argued that in the case of heterogeneous hybridisation the
sperm-nucleus does not fuse with the egg-nucleus, and that, therefore, the
spermatozoon cannot transmit its hereditary substances to the larvae.  But
these objections are refuted by Godlewski's experiments, in which he showed
definitely that if the egg of the sea-urchin is fertilised with the sperm
of a crinoid the fusion of the egg-nucleus and sperm-nucleus takes place in
the normal way.  It remains for further experiments to decide what the
character of the adult hybrids would be.

(b).  ARTIFICIAL PARTHENOGENESIS.

Possibly in no other field of Biology has our ability to control life-
phenomena by outside conditions been proved to such an extent as in the
domain of fertilisation.  The reader knows that the eggs of the
overwhelming majority of animals cannot develop unless a spermatozoon
enters them.  In this case a living agency is the cause of development and
the problem arises whether it is possible to accomplish the same result
through the application of well-known physico-chemical agencies.  This is,
indeed, true, and during the last ten years living larvae have been
produced by chemical agencies from the unfertilised eggs of sea-urchins,
starfish, holothurians and a number of annelids and molluscs; in fact this
holds true in regard to the eggs of practically all forms of animals with
which such experiments have been tried long enough.  In each form the
method of procedure is somewhat different and a long series of experiments
is often required before the successful method is found.

The facts of Artificial Parthenogenesis, as the chemical fertilisation of
the egg is called, have, perhaps, some bearing on the problem of evolution.
If we wish to form a mental image of the process of evolution we have to
reckon with the possibility that parthenogenetic propagation may have
preceded sexual reproduction.  This suggests also the possibility that at
that period outside forces may have supplied the conditions for the
development of the egg which at present the spermatozoon has to supply. 
For this, if for no other reason, a brief consideration of the means of
artificial parthenogenesis may be of interest to the student of evolution.

It seemed necessary in these experiments to imitate as completely as
possible by chemical agencies the effects of the spermatozoon upon the egg.
When a spermatozoon enters the egg of a sea-urchin or certain starfish or
annelids, the immediate effect is a characteristic change of the surface of
the egg, namely the formation of the so-called membrane of fertilisation. 
The writer found that we can produce this membrane in the unfertilised egg
by certain acids, especially the monobasic acids of the fatty series, e.g.
formic, acetic, propionic, butyric, etc.  Carbon-dioxide is also very
efficient in this direction.  It was also found that the higher acids are
more efficient than the lower ones, and it is possible that the
spermatozoon induces membrane-formation by carrying into the egg a higher
fatty acid, namely oleic acid or one of its salts or esters.

The physico-chemical process which underlies the formation of the membrane
seems to be the cause of the development of the egg.  In all cases in which
the unfertilised egg has been treated in such a way as to cause it to form
a membrane it begins to develop.  For the eggs of certain animals membrane-
formation is all that is required to induce a complete development of the
unfertilised egg, e.g. in the starfish and certain annelids.  For the eggs
of other animals a second treatment is necessary, presumably to overcome
some of the injurious effects of acid treatment.  Thus the unfertilised
eggs of the sea-urchin Strongylocentrotus purpuratus of the Californian
coast begin to develop when membrane-formation has been induced by
treatment with a fatty acid, e.g. butyric acid; but the development soon
ceases and the eggs perish in the early stages of segmentation, or after
the first nuclear division.  But if we treat the same eggs, after membrane-
formation, for from 35 to 55 minutes (at 15 deg C.) with sea-water the
concentration (osmotic pressure) of which has been raised through the
addition of a definite amount of some salt or sugar, the eggs will segment
and develop normally, when transferred back to normal sea-water.  If care
is taken, practically all the eggs can be caused to develop into plutei,
the majority of which may be perfectly normal and may live as long as
larvae produced from eggs fertilised with sperm.

It is obvious that the sea-urchin egg is injured in the process of
membrane-formation and that the subsequent treatment with a hypertonic
solution only acts as a remedy.  The nature of this injury became clear
when it was discovered that all the agencies which cause haemolysis, i.e.
the destruction of the red blood corpuscles, also cause membrane-formation
in unfertilised eggs, e.g. fatty acids or ether, alcohols or chloroform,
etc., or saponin, solanin, digitalin, bile salts and alkali.  It thus
happens that the phenomena of artificial parthenogenesis are linked
together with the phenomena of haemolysis which at present play so
important a role in the study of immunity.  The difference between
cytolysis (or haemolysis) and fertilisation seems to be this, that the
latter is caused by a superficial or slight cytolysis of the egg, while if
the cytolytic agencies have time to act on the whole egg the latter is
completely destroyed.  If we put unfertilised eggs of a sea-urchin into
sea-water which contains a trace of saponin we notice that, after a few
minutes, all the eggs form the typical membrane of fertilisation.  If the
eggs are then taken out of the saponin solution, freed from all traces of
saponin by repeated washing in normal sea-water, and transferred to the
hypertonic sea-water for from 35 to 55 minutes, they develop into larvae. 
If, however, they are left in the sea-water containing the saponin they
undergo, a few minutes after membrane-formation, the disintegration known
in pathology as CYTOLYSIS.  Membrane-formation is, therefore, caused by a
superficial or incomplete cytolysis.  The writer believes that the
subsequent treatment of the egg with hypertonic sea-water is needed only to
overcome the destructive effects of this partial cytolysis.  The full
reasons for this belief cannot be given in a short essay.

Many pathologists assume that haemolysis or cytolysis is due to a
liquefaction of certain fatty or fat-like compounds, the so-called lipoids,
in the cell.  If this view is correct, it would be necessary to ascribe the
fertilisation of the egg to the same process.

The analogy between haemolysis and fertilisation throws, possibly, some
light on a curious observation.  It is well known that the blood
corpuscles, as a rule, undergo cytolysis if injected into the blood of an
animal which belongs to a different family.  The writer found last year
that the blood of mammals, e.g. the rabbit, pig, and cattle, causes the egg
of Strongylocentrotus to form a typical fertilisation-membrane.  If such
eggs are afterwards treated for a short period with hypertonic sea-water
they develop into normal larvae (plutei).  Some substance contained in the
blood causes, presumably, a superficial cytolysis of the egg and thus
starts its development.

We can also cause the development of the sea-urchin egg without membrane-
formation.  The early experiments of the writer were done in this way and
many experimenters still use such methods.  It is probable that in this
case the mechanism of fertilisation is essentially the same as in the case
where the membrane-formation is brought about, with this difference only,
that the cytolytic effect is less when no fertilisation-membrane is formed.
This inference is corroborated by observations on the fertilisation of the
sea-urchin egg with ox blood.  It very frequently happens that not all of
the eggs form membranes in this process.  Those eggs which form membranes
begin to develop, but perish if they are not treated with hypertonic sea-
water.  Some of the other eggs, however, which do not form membranes,
develop directly into normal larvae without any treatment with hypertonic
sea-water, provided they are exposed to the blood for only a few minutes. 
Presumably some blood enters the eggs and causes the cytolytic effects in a
less degree than is necessary for membrane-formation, but in a sufficient
degree to cause their development.  The slightness of the cytolytic effect
allows the egg to develop without treatment with hypertonic sea-water.

Since the entrance of the spermatozoon causes that degree of cytolysis
which leads to membrane-formation, it is probable that, in addition to the
cytolytic or membrane-forming substance (presumably a higher fatty acid),
it carries another substance into the egg which counteracts the deleterious
cytolytic effects underlying membrane-formation.

The question may be raised whether the larvae produced by artificial
parthenogenesis can reach the mature stage.  This question may be answered
in the affirmative, since Delage has succeeded in raising several
parthenogenetic sea-urchin larvae beyond the metamorphosis into the adult
stage and since in all the experiments made by the writer the
parthenogenetic plutei lived as long as the plutei produced from fertilised
eggs.

(c).  ON THE PRODUCTION OF TWINS FROM ONE EGG THROUGH A CHANGE IN THE
CHEMICAL CONSTITUTION OF THE SEA-WATER.

The reader is probably familiar with the fact that there exist two
different types of human twins.  In the one type the twins differ as much
as two children of the same parents born at different periods; they may or
may not have the same sex.  In the second type the twins have invariably
the same sex and resemble each other most closely.  Twins of the latter
type are produced from the same egg, while twins of the former type are
produced from two different eggs.

The experiments of Driesch and others have taught us that twins originate
from one egg in this manner, namely, that the first two cells into which
the egg divides after fertilisation become separated from each other.  This
separation can be brought about by a change in the chemical constitution of
the sea-water.  Herbst observed that if the fertilised eggs of the sea-
urchin are put into sea-water which is freed from calcium, the cells into
which the egg divides have a tendency to fall apart.  Driesch afterwards
noticed that eggs of the sea-urchin treated with sea-water which is free
from lime have a tendency to give rise to twins.  The writer has recently
found that twins can be produced not only by the absence of lime, but also
through the absence of sodium or of potassium; in other words, through the
absence of one or two of the three important metals in the sea-water. 
There is, however, a second condition, namely, that the solution used for
the production of twins must have a neutral or at least not an alkaline
reaction.

The procedure for the production of twins in the sea-urchin egg consists
simply in this:--the eggs are fertilised as usual in normal sea-water and
then, after repeated washing in a neutral solution of sodium chloride (of
the concentration of the sea-water), are placed in a neutral mixture of
potassium chloride and calcium chloride, or of sodium chloride and
potassium chloride, or of sodium chloride and calcium chloride, or of
sodium chloride and magnesium chloride.  The eggs must remain in this
solution until half an hour or an hour after they have reached the two-cell
stage.  They are then transferred into normal sea-water and allowed to
develop.  From 50 to 90 per cent of the eggs of Strongylocentrotus
purpuratus treated in this manner may develop into twins.  These twins may
remain separate or grow partially together and form double monsters, or
heal together so completely that only slight or even no imperfections
indicate that the individual started its career as a pair of twins.  It is
also possible to control the tendency of such twins to grow together by a
change in the constitution of the sea-water.  If we use as a twin-producing
solution a mixture of sodium, magnesium and potassium chlorides (in the
proportion in which these salts exist in the sea-water) the tendency of the
twins to grow together is much more pronounced than if we use simply a
mixture of sodium chloride and magnesium chloride.

The mechanism of the origin of twins, as the result of altering the
composition of the sea-water, is revealed by observation of the first
segmentation of the egg in these solutions.  This cell-division is modified
in a way which leads to a separation of the first two cells.  If the egg is
afterwards transferred back into normal sea-water, each of these two cells
develops into an independent embryo.  Since normal sea-water contains all
three metals, sodium, calcium, and potassium, and since it has besides an
alkaline reaction, we perceive the reason why twins are not normally
produced from one egg.  These experiments suggest the possibility of a
chemical cause for the origin of twins from one egg or of double
monstrosities in mammals.  If, for some reason, the liquids which surround
the human egg a short time before and after the first cell-division are
slightly acid, and at the same time lacking in one of the three important
metals, the conditions for the separation of the first two cells and the
formation of identical twins are provided.

In conclusion it may be pointed out that the reverse result, namely, the
fusion of normally double organs, can also be brought about experimentally
through a change in the chemical constitution of the sea-water.  Stockard
succeeded in causing the eyes of fish embryos (Fundulus heteroclitus) to
fuse into a single cyclopean eye through the addition of magnesium chloride
to the sea-water.  When he added about 6 grams of magnesium chloride to 100
cubic centimetres of sea-water and placed the fertilised eggs in the
mixture, about 50 per cent of the eggs gave rise to one-eyed embryos. 
"When the embryos were studied the one-eyed condition was found to result
from the union or fusion of the 'anlagen' of the two eyes.  Cases were
observed which showed various degrees in this fusion; it appeared as though
the optic vessels were formed too far forward and ventral, so that their
antero-ventro-median surfaces fused.  This produces one large optic cup,
which in all cases gives more or less evidence of its double nature." 
(Stockard, "Archiv f. Entwickelungsmechanik", Vol. 23, page 249, 1907.)

We have confined ourselves to a discussion of rather simple effects of the
change in the constitution of the sea-water upon development.  It is a
priori obvious, however, that an unlimited number of pathological
variations might be produced by a variation in the concentration and
constitution of the sea-water, and experience confirms this statement.  As
an example we may mention the abnormalities observed by Herbst in the
development of sea-urchins through the addition of lithium to sea-water. 
It is, however, as yet impossible to connect in a rational way the effects
produced in this and similar cases with the cause which produced them; and
it is also impossible to define in a simple way the character of the change
produced.

III.  THE INFLUENCE OF TEMPERATURE.

(a)  THE INFLUENCE OF TEMPERATURE UPON THE DENSITY OF PELAGIC ORGANISMS AND
THE DURATION OF LIFE.

It has often been noticed by explorers who have had a chance to compare the
faunas in different climates that in polar seas such species as thrive at
all in those regions occur, as a rule, in much greater density than they do
in the moderate or warmer regions of the ocean.  This refers to those
members of the fauna which live at or near the surface, since they alone
lend themselves to a statistical comparison.  In his account of the
Valdivia expedition, Chun (Chun, "Aus den Tiefen des Weltmeeres", page 225,
Jena, 1903.) calls especial attention to this quantitative difference in
the surface fauna and flora of different regions.  "In the icy water of the
Antarctic, the temperature of which is below 0 deg C., we find an
astonishingly rich animal and plant life.  The same condition with which we
are familiar in the Arctic seas is repeated here, namely, that the quantity
of plankton material exceeds that of the temperate and warm seas."  And
again, in regard to the pelagic fauna in the region of the Kerguelen
Islands, he states:  "The ocean is alive with transparent jelly fish,
Ctenophores (Bolina and Callianira) and of Siphonophore colonies of the
genus Agalma."

The paradoxical character of this general observation lies in the fact that
a low temperature retards development, and hence should be expected to have
the opposite effect from that mentioned by Chun.  Recent investigations
have led to the result that life-phenomena are affected by temperature in
the same sense as the velocity of chemical reactions.  In the case of the
latter van't Hoff had shown that a decrease in temperature by 10 degrees
reduces their velocity to one half or less, and the same has been found for
the influence of temperature on the velocity of physiological processes. 
Thus Snyder and T.B. Robertson found that the rate of heartbeat in the
tortoise and in Daphnia is reduced to about one-half if the temperature is
lowered 10 deg C., and Maxwell, Keith Lucas, and Snyder found the same
influence of temperature for the rate with which an impulse travels in the
nerve.  Peter observed that the rate of development in a sea-urchin's egg
is reduced to less than one-half if the temperature (within certain limits)
is reduced by 10 degrees.  The same effect of temperature upon the rate of
development holds for the egg of the frog, as Cohen and Peter calculated
from the experiments of O. Hertwig.  The writer found the same temperature-
coefficient for the rate of maturation of the egg of a mollusc (Lottia).

All these facts prove that the velocity of development of animal life in
Arctic regions, where the temperature is near the freezing point of water,
must be from two to three times smaller than in regions where the
temperature of the ocean is about 10 deg C. and from four to nine times
smaller than in seas the temperature of which is about 20 deg C.  It is,
therefore, exactly the reverse of what we should expect when authors state
that the density of organisms at or near the surface of the ocean in polar
regions is greater than in more temperate regions.

The writer believes that this paradox finds its explanation in experiments
which he has recently made on the influence of temperature on the duration
of life of cold-blooded marine animals.  The experiments were made on the
fertilised and unfertilised eggs of the sea-urchin, and yielded the result
that for the lowering of temperature by 1 deg C. the duration of life was
about doubled.  Lowering the temperature by 10 degrees therefore prolongs
the life of the organism 2 to the power 10, i.e. over a thousand times, and
a lowering by 20 degrees prolongs it about one million times.  Since this
prolongation of life is far in excess of the retardation of development
through a lowering of temperature, it is obvious that, in spite of the
retardation of development in Arctic seas, animal life must be denser there
than in temperate or tropical seas.  The excessive increase of the duration
of life at the poles will necessitate the simultaneous existence of more
successive generations of the same species in these regions than in the
temperate or tropical regions.

The writer is inclined to believe that these results have some bearing upon
a problem which plays an important role in theories of evolution, namely,
the cause of natural death.  It has been stated that the processes of
differentiation and development lead also to the natural death of the
individual.  If we express this in chemical terms it means that the
chemical processes which underlie development also determine natural death. 
Physical chemistry has taught us to identify two chemical processes even if
only certain of their features are known.  One of these means of
identification is the temperature coefficient.  When two chemical processes
are identical, their velocity must be reduced by the same amount if the
temperature is lowered to the same extent.  The temperature coefficient for
the duration of life of cold-blooded organisms seems, however, to differ
enormously from the temperature coefficient for their rate of development. 
For a difference in temperature of 10 deg C. the duration of life is
altered five hundred times as much as the rate of development; and, for a
change of 20 deg C., it is altered more than a hundred thousand times as
much.  From this we may conclude that, at least for the sea-urchin eggs and
embryo, the chemical processes which determine natural death are certainly
not identical with the processes which underlie their development.  T.B.
Robertson has also arrived at the conclusion, for quite different reasons,
that the process of senile decay is essentially different from that of
growth and development.

(b)  CHANGES IN THE COLOUR OF BUTTERFLIES PRODUCED THROUGH THE INFLUENCE OF
TEMPERATURE.

The experiments of Dorfmeister, Weismann, Merrifield, Standfuss, and
Fischer, on seasonal dimorphism and the aberration of colour in butterflies
have so often been discussed in biological literature that a short
reference to them will suffice.  By seasonal dimorphism is meant the fact
that species may appear at different seasons of the year in a somewhat
different form or colour.  Vanessa prorsa is the summer form, Vanessa
levana the winter form of the same species.  By keeping the pupae of
Vanessa prorsa several weeks at a temperature of from 0 deg to 1 deg
Weismann succeeded in obtaining from the summer chrysalids specimens which
resembled the winter variety, Vanessa levana.

If we wish to get a clear understanding of the causes of variation in the
colour and pattern of butterflies, we must direct our attention to the
experiments of Fischer, who worked with more extreme temperatures than his
predecessors, and found that almost identical aberrations of colour could
be produced by both extremely high and extremely low temperatures.  This
can be clearly seen from the following tabulated results of his
observations.  At the head of each column the reader finds the temperature
to which Fischer submitted the pupae, and in the vertical column below are
found the varieties that were produced.  In the vertical column A are given
the normal forms:

(Temperatures in deg C.)
0 to -20     0 to +10    A.           +35 to +37    +36 to +41  +42 to +46
                        (Normal forms)

ichnusoides  polaris     urticae      ichnusa       polaris     ichnusoides
  (nigrita)                                                       (nigrita)

antigone     fischeri    io             -           fischeri    antigone
  (iokaste)                                                       (iokaste)

testudo      dixeyi      polychloros  erythromelas  dixeyi      testudo

hygiaea      artemis     antiopa      epione        artemis     hygiaea

elymi        wiskotti    cardui         -           wiskotti    elymi

klymene      merrifieldi atalanta       -           merrifieldi klymene

weismanni    porima      prorsa         -           porima      weismanni

The reader will notice that the aberrations produced at a very low
temperature (from 0 to -20 deg C.) are absolutely identical with the
aberrations produced by exposing the pupae to extremely high temperatures
(42 to 46 deg C.).  Moreover the aberrations produced by a moderately low
temperature (from 0 to 10 deg C.) are identical with the aberrations
produced by a moderately high temperature (36 to 41 deg C.)

From these observations Fischer concludes that it is erroneous to speak of
a specific effect of high and of low temperatures, but that there must be a
common cause for the aberration found at the high as well as at the low
temperature limits.  This cause he seems to find in the inhibiting effects
of extreme temperatures upon development.

If we try to analyse such results as Fischer's from a physico-chemical
point of view, we must realise that what we call life consists of a series
of chemical reactions, which are connected in a catenary way; inasmuch as
one reaction or group of reactions (a) (e.g. hydrolyses) causes or
furnishes the material for a second reaction or group of reactions (b)
(e.g. oxydations).  We know that the temperature coefficient for
physiological processes varies slightly at various parts of the scale; as a
rule it is higher near 0 and lower near 30 deg.  But we know also that the
temperature coefficients do not vary equally from the various physiological
processes.  It is, therefore, to be expected that the temperature
coefficients for the group of reactions of the type (a) will not be
identical through the whole scale with the temperature coefficients for the
reactions of the type (b).  If therefore a certain substance is formed at
the normal temperature of the animal in such quantities as are needed for
the catenary reaction (b), it is not to be expected that this same perfect
balance will be maintained for extremely high or extremely low
temperatures; it is more probable that one group of reactions will exceed
the other and thus produce aberrant chemical effects, which may underlie
the colour aberrations observed by Fischer and other experimenters.

It is important to notice that Fischer was also able to produce aberrations
through the application of narcotics.  Wolfgang Ostwald has produced
experimentally, through variation of temperature, dimorphism of form in
Daphnia.  Lack of space precludes an account of these important
experiments, as of so many others.

IV.  THE EFFECTS OF LIGHT.

At the present day nobody seriously questions the statement that the action
of light upon organisms is primarily one of a chemical character.  While
this chemical action is of the utmost importance for organisms, the
nutrition of which depends upon the action of chlorophyll, it becomes of
less importance for organisms devoid of chlorophyll.  Nevertheless, we find
animals in which the formation of organs by regeneration is not possible
unless they are exposed to light.  An observation made by the writer on the
regeneration of polyps in a hydroid, Eudendrium racemosum, at Woods Hole,
may be mentioned as an instance of this.  If the stem of this hydroid,
which is usually covered with polyps, is put into an aquarium the polyps
soon fall off.  If the stems are kept in an aquarium where light strikes
them during the day, a regeneration of numerous polyps takes place in a few
days.  If, however, the stems of Eudendrium are kept permanently in the
dark, no polyps are formed even after an interval of some weeks; but they
are formed in a few days after the same stems have been transferred from
the dark to the light.  Diffused daylight suffices for this effect. 
Goldfarb, who repeated these experiments, states that an exposure of
comparatively short duration is sufficient for this effect, it is possible
that the light favours the formation of substances which are a prerequisite
for the origin of polyps and their growth.

Of much greater significance than this observation are the facts which show
that a large number of animals assume, to some extent, the colour of the
ground on which they are placed.  Pouchet found through experiments upon
crustaceans and fish that this influence of the ground on the colour of
animals is produced through the medium of the eyes.  If the eyes are
removed or the animals made blind in another way these phenomena cease. 
The second general fact found by Pouchet was that the variation in the
colour of the animal is brought about through an action of the nerves on
the pigment-cells of the skin; the nerve-action being induced through the
agency of the eye.

The mechanism and the conditions for the change in colouration were made
clear through the beautiful investigations of Keeble and Gamble, on the
colour-change in crustaceans.  According to these authors the pigment-cells
can, as a rule, be considered as consisting of a central body from which a
system of more or less complicated ramifications or processes spreads out
in all directions.  As a rule, the centre of the cell contains one or more
different pigments which under the influence of nerves can spread out
separately or together into the ramifications.  These phenomena of
spreading and retraction of the pigments into or from the ramifications of
the pigment-cells form on the whole the basis for the colour changes under
the influence of environment.  Thus Keeble and Gamble observed that
Macromysis flexuosa appears transparent and colourless or grey on sandy
ground.  On a dark ground their colour becomes darker.  These animals have
two pigments in their chromatophores, a brown pigment and a whitish or
yellow pigment; the former is much more plentiful than the latter.  When
the animal appears transparent all the pigment is contained in the centre
of the cells, while the ramifications are free from pigment.  When the
animal appears brown both pigments are spread out into the ramifications. 
In the condition of maximal spreading the animals appear black.

This is a comparatively simple case.  Much more complicated conditions were
found by Keeble and Gamble in other crustaceans, e.g. in Hippolyte
cranchii, but the influence of the surroundings upon the colouration of
this form was also satisfactorily analysed by these authors.

While many animals show transitory changes in colour under the influence of
their surroundings, in a few cases permanent changes can be produced.  The
best examples of this are those which were observed by Poulton in the
chrysalids of various butterflies, especially the small tortoise-shell. 
These experiments are so well known that a short reference to them will
suffice.  Poulton (Poulton, E.B., "Colours of Animals" (The International
Scientific Series), London, 1890, page 121.) found that in gilt or white
surroundings the pupae became light coloured and there was often an immense
development of the golden spots, "so that in many cases the whole surface
of the pupae glittered with an apparent metallic lustre.  So remarkable was
the appearance that a physicist to whom I showed the chrysalids, suggested
that I had played a trick and had covered them with goldleaf."  When black
surroundings were used "the pupae were as a rule extremely dark, with only
the smallest trace, and often no trace at all, of the golden spots which
are so conspicuous in the lighter form."  The susceptibility of the animal
to this influence of its surroundings was found to be greatest during a
definite period when the caterpillar undergoes the metamorphosis into the
chrysalis stage.  As far as the writer is aware, no physico-chemical
explanation, except possibly Wiener's suggestion of colour-photography by
mechanical colour adaptation, has ever been offered for the results of the
type of those observed by Poulton.

V.  EFFECTS OF GRAVITATION.

(a)  EXPERIMENTS ON THE EGG OF THE FROG.

Gravitation can only indirectly affect life-phenomena; namely, when we have
in a cell two different non-miscible liquids (or a liquid and a solid) of
different specific gravity, so that a change in the position of the cell or
the organ may give results which can be traced to a change in the position
of the two substances.  This is very nicely illustrated by the frog's egg,
which has two layers of very viscous protoplasm one of which is black and
one white.  The dark one occupies normally the upper position in the egg
and may therefore be assumed to possess a smaller specific gravity than the
white substance.  When the egg is turned with the white pole upwards a
tendency of the white protoplasm to flow down again manifests itself.  It
is, however, possible to prevent or retard this rotation of the highly
viscous protoplasm, by compressing the eggs between horizontal glass
plates.  Such compression experiments may lead to rather interesting
results, as O. Schultze first pointed out.  Pflueger had already shown that
the first plane of division in a fertilised frog's egg is vertical and Roux
established the fact that the first plane of division is identical with the
plane of symmetry of the later embryo.  Schultze found that if the frog's
egg is turned upside down at the time of its first division and kept in
this abnormal position, through compression between two glass plates for
about 20 hours, a small number of eggs may give rise to twins.  It is
possible, in this case, that the tendency of the black part of the egg to
rotate upwards along the surface of the egg leads to a separation of its
first cells, such a separation leading to the formation of twins.

T.H. Morgan made an interesting additional observation.  He destroyed one
half of the egg after the first segmentation and found that the half which
remained alive gave rise to only one half of an embryo, thus confirming an
older observation of Roux.  When, however, Morgan put the egg upside down
after the destruction of one of the first two cells, and compressed the
eggs between two glass plates, the surviving half of the egg gave rise to a
perfect embryo of half size (and not to a half embryo of normal size as
before.)  Obviously in this case the tendency of the protoplasm to flow
back to its normal position was partially successful and led to a partial
or complete separation of the living from the dead half; whereby the former
was enabled to form a whole embryo, which, of course, possessed only half
the size of an embryo originating from a whole egg.

(b)  EXPERIMENTS ON HYDROIDS.

A striking influence of gravitation can be observed in a hydroid,
Antennularia antennina, from the bay of Naples.  This hydroid consists of a
long straight main stem which grows vertically upwards and which has at
regular intervals very fine and short bristle-like lateral branches, on the
upper side of which the polyps grow.  The main stem is negatively
geotropic, i.e. its apex continues to grow vertically upwards when we put
it obliquely into the aquarium, while the roots grow vertically downwards.
The writer observed that when the stem is put horizontally into the water
the short lateral branches on the lower side give rise to an altogether
different kind of organ, namely, to roots, and these roots grow
indefinitely in length and attach themselves to solid bodies; while if the
stem had remained in its normal position no further growth would have
occurred in the lateral branches.  From the upper side of the horizontal
stem new stems grow out, mostly directly from the original stem,
occasionally also from the short lateral branches.  It is thus possible to
force upon this hydroid an arrangement of organs which is altogether
different from the hereditary arrangement.  The writer had called the
change in the hereditary arrangement of organs or the transformation of
organs by external forces HETEROMORPHOSIS.  We cannot now go any further
into this subject, which should, however, prove of interest in relation to
the problem of heredity.

If it is correct to apply inferences drawn from the observation on the
frog's egg to the behaviour of Antennularia, one might conclude that the
cells of Antennularia also contain non-miscible substances of different
specific gravity, and that wherever the specifically lighter substance
comes in contact with the sea-water (or gets near the surface of the cell)
the growth of a stem is favoured; while contact with the sea-water of the
specifically heavier of the substances, will favour the formation of roots.

VI.  THE EXPERIMENTAL CONTROL OF ANIMAL INSTINCTS.

(a)  EXPERIMENTS ON THE MECHANISM OF HELIOTROPIC REACTIONS IN ANIMALS.

Since the instinctive reactions of animals are as hereditary as their
morphological character, a discussion of experiments on the physico-
chemical character of the instinctive reactions of animals should not be
entirely omitted from this sketch.  It is obvious that such experiments
must begin with the simplest type of instincts, if they are expected to
lead to any results; and it is also obvious that only such animals must be
selected for this purpose, the reactions of which are not complicated by
associative memory, or, as it may preferably be termed, associative
hysteresis.

The simplest type of instincts is represented by the purposeful motions of
animals to or from a source of energy, e.g. light; and it is with some of
these that we intend to deal here.  When we expose winged aphides (after
they have flown away from the plant), or young caterpillars of Porthesia
chrysorrhoea (when they are aroused from their winter sleep) or marine or
freshwater copepods and many other animals, to diffused daylight falling in
from a window, we notice a tendency among these animals to move towards the
source of light.  If the animals are naturally sensitive, or if they are
rendered sensitive through the agencies which we shall mention later, and
if the light is strong enough, they move towards the source of light in as
straight a line as the imperfections and peculiarities of their locomotor
apparatus will permit.  It is also obvious that we are here dealing with a
forced reaction in which the animals have no more choice in the direction
of their motion than have the iron filings in their arrangement in a
magnetic field.  This can be proved very nicely in the case of starving
caterpillars of Porthesia.  The writer put such caterpillars into a glass
tube the axis of which was at right angles to the plane of the window:  the
caterpillars went to the window side of the tube and remained there, even
if leaves of their food-plant were put into the tube directly behind them. 
Under such conditions the animals actually died from starvation, the light
preventing them from turning to the food, which they eagerly ate when the
light allowed them to do so.  One cannot say that these animals, which we
call positively helioptropic, are attracted by the light, since it can be
shown that they go towards the source of the light even if in so doing they
move from places of a higher to places of a lower degree of illumination.

The writer has advanced the following theory of these instinctive
reactions.  Animals of the type of those mentioned are automatically
orientated by the light in such a way that symmetrical elements of their
retina (or skin) are struck by the rays of light at the same angle.  In
this case the intensity of light is the same for both retinae or
symmetrical parts of the skin.

This automatic orientation is determined by two factors, first a peculiar
photo-sensitiveness of the retina (or skin), and second a peculiar nervous
connection between the retina and the muscular apparatus.  In symmetrically
built heliotropic animals in which the symmetrical muscles participate
equally in locomotion, the symmetrical muscles work with equal energy as
long as the photo-chemical processes in both eyes are identical.  If,
however, one eye is struck by stronger light than the other, the
symmetrical muscles will work unequally and in positively heliotropic
animals those muscles will work with greater energy which bring the plane
of symmetry back into the direction of the rays of light and the head
towards the source of light.  As soon as both eyes are struck by the rays
of light at the same angle, there is no more reason for the animal to
deviate from this direction and it will move in a straight line.  All this
holds good on the supposition that the animals are exposed to only one
source of light and are very sensitive to light.

Additional proof for the correctness of this theory was furnished through
the experiments of G.H. Parker and S.J. Holmes.  The former worked on a
butterfly, Vanessa antiope, the latter on other arthropods.  All the
animals were in a marked degree positively heliotropic.  These authors
found that if one cornea is blackened in such an animal, it moves
continually in a circle when it is exposed to a source of light, and in
these motions the eye which is not covered with paint is directed towards
the centre of the circle.  The animal behaves, therefore, as if the
darkened eye were in the shade.

(b)  THE PRODUCTION OF POSITIVE HELIOTROPISM BY ACIDS AND OTHER MEANS AND
THE PERIODIC DEPTH-MIGRATIONS OF PELAGIC ANIMALS.

When we observe a dense mass of copepods collected from a freshwater pond,
we notice that some have a tendency to go to the light while others go in
the opposite direction and many, if not the majority, are indifferent to
light.  It is an easy matter to make the negatively heliotropic or the
indifferent copepods almost instantly positively heliotropic by adding a
small but definite amount of carbon-dioxide in the form of carbonated water
to the water in which the animals are contained.  If the animals are
contained in 50 cubic centimetres of water it suffices to add from three to
six cubic centimetres of carbonated water to make all the copepods
energetically positively heliotropic.  This heliotropism lasts about half
an hour (probably until all the carbon-dioxide has again diffused into the
air.)  Similar results may be obtained with any other acid.

The same experiments may be made with another freshwater crustacean, namely
Daphnia, with this difference, however, that it is as a rule necessary to
lower the temperature of the water also.  If the water containing the
Daphniae is cooled and at the same time carbon-dioxide added, the animals
which were before indifferent to light now become most strikingly
positively heliotropic.  Marine copepods can be made positively heliotropic
by the lowering of the temperature alone, or by a sudden increase in the
concentration of the sea-water.

These data have a bearing upon the depth-migrations of pelagic animals, as
was pointed out years ago by Theo. T. Groom and the writer.  It is well
known that many animals living near the surface of the ocean or freshwater
lakes, have a tendency to migrate upwards towards evening and downwards in
the morning and during the day.  These periodic motions are determined to a
large extent, if not exclusively, by the heliotropism of these animals. 
Since the consumption of carbon-dioxide by the green plants ceases towards
evening, the tension of this gas in the water must rise and this must have
the effect of inducing positive heliotropism or increasing its intensity. 
At the same time the temperature of the water near the surface is lowered
and this also increases the positive heliotropism in the organisms.

The faint light from the sky is sufficient to cause animals which are in a
high degree positively heliotropic to move vertically upwards towards the
light, as experiments with such pelagic animals, e.g. copepods, have shown. 
When, in the morning, the absorption of carbon-dioxide by the green algae
begins again and the temperature of the water rises, the animals lose their
positive heliotropism, and slowly sink down or become negatively
heliotropic and migrate actively downwards.

These experiments have also a bearing upon the problem of the inheritance
of instincts.  The character which is transmitted in this case is not the
tendency to migrate periodically upwards and downwards, but the positive
heliotropism.  The tendency to migrate is the outcome of the fact that
periodically varying external conditions induce a periodic change in the
sense and intensity of the heliotropism of these animals.  It is of course
immaterial for the result, whether the carbon-dioxide or any other acid
diffuse into the animal from the outside or whether they are produced
inside in the tissue cells of the animals.  Davenport and Cannon found that
Daphniae, which at the beginning of the experiment, react sluggishly to
light react much more quickly after they have been made to go to the light
a few times.  The writer is inclined to attribute this result to the effect
of acids, e.g. carbon-dioxide, produced in the animals themselves in
consequence of their motion.  A similar effect of the acids was shown by
A.D. Waller in the case of the response of nerve to stimuli.

The writer observed many years ago that winged male and female ants are
positively helioptropic and that their heliotropic sensitiveness increases
and reaches its maximum towards the period of nuptial flight.  Since the
workers show no heliotropism it looks as if an internal secretion from the
sexual glands were the cause of their heliotropic sensitiveness.  V.
Kellogg has observed that bees also become intensely positively heliotropic
at the period of their wedding flight, in fact so much so that by letting
light fall into the observation hive from above, the bees are prevented
from leaving the hive through the exit at the lower end.

We notice also the reverse phenomenon, namely, that chemical changes
produced in the animal destroy its heliotropism.  The caterpillars of
Porthesia chrysorrhoea are very strongly positively heliotropic when they
are first aroused from their winter sleep.  This heliotropic sensitiveness
lasts only as long as they are not fed.  If they are kept permanently
without food they remain permanently positively heliotropic until they die
from starvation.  It is to be inferred that as soon as these animals take
up food, a substance or substances are formed in their bodies which
diminish or annihilate their heliotropic sensitiveness.

The heliotropism of animals is identical with the heliotropism of plants. 
The writer has shown that the experiments on the effect of acids on the
heliotropism of copepods can be repeated with the same result in Volvox. 
It is therefore erroneous to try to explain these heliotropic reactions of
animals on the basis of peculiarities (e.g. vision) which are not found in
plants.

We may briefly discuss the question of the transmission through the sex
cells of such instincts as are based upon heliotropism.  This problem
reduces itself simply to that of the method whereby the gametes transmit
heliotropism to the larvae or to the adult.  The writer has expressed the
idea that all that is necessary for this transmission is the presence in
the eyes (or in the skin) of the animal of a photo-sensitive substance. 
For the transmission of this the gametes need not contain anything more
than a catalyser or ferment for the synthesis of the photo-sensitive
substance in the body of the animal.  What has been said in regard to
animal heliotropism might, if space permitted, be extended, mutatis
mutandis, to geotropism and stereotropism.

(c)  THE TROPIC REACTIONS OF CERTAIN TISSUE-CELLS AND THE MORPHOGENETIC
EFFECTS OF THESE REACTIONS.

Since plant-cells show heliotropic reactions identical with those of
animals, it is not surprising that certain tissue-cells also show reactions
which belong to the class of tropisms.  These reactions of tissue-cells are
of special interest by reason of their bearing upon the inheritance of
morphological characters.  An example of this is found in the tiger-like
marking of the yolk-sac of the embryo of Fundulus and in the marking of the
young fish itself.  The writer found that the former is entirely, and the
latter at least in part, due to the creeping of the chromatophores upon the
blood-vessels.  The chromatophores are at first scattered irregularly over
the yolk-sac and show their characteristic ramifications.  There is at that
time no definite relation between blood-vessels and chromatophores.  As
soon as a ramification of a chromatophore comes in contact with a blood-
vessel the whole mass of the chromatophore creeps gradually on the blood-
vessel and forms a complete sheath around the vessel, until finally all the
chromatophores form a sheath around the vessels and no more pigment cells
are found in the meshes between the vessels.  Nobody who has not actually
watched the process of the creeping of the chromatophores upon the blood-
vessels would anticipate that the tiger-like colouration of the yolk-sac in
the later stages of the development was brought about in this way.  Similar
facts can be observed in regard to the first marking of the embryo itself. 
The writer is inclined to believe that we are here dealing with a case of
chemotropism, and that the oxygen of the blood may be the cause of the
spreading of the chromatophores around the blood-vessels.  Certain
observations seem to indicate the possibility that in the adult the
chromatophores have, in some forms at least, a more rigid structure and are
prevented from acting in the way indicated.  It seems to the writer that
such observations as those made on Fundulus might simplify the problem of
the hereditary transmission of certain markings.

Driesch has found that a tropism underlies the arrangement of the skeleton
in the pluteus larvae of the sea-urchin.  The position of this skeleton is
predetermined by the arrangement of the mesenchyme cells, and Driesch has
shown that these cells migrate actively to the place of their destination,
possibly led there under the influence of certain chemical substances. 
When Driesch scattered these cells mechanically before their migration,
they nevertheless reached their destination.

In the developing eggs of insects the nuclei, together with some cytoplasm,
migrate to the periphery of the egg.  Herbst pointed out that this might be
a case of chemotropism, caused by the oxygen surrounding the egg.  The
writer has expressed the opinion that the formation of the blastula may be
caused generally by a tropic reaction of the blastomeres, the latter being
forced by an outside influence to creep to the surface of the egg.

These examples may suffice to indicate that the arrangement of definite
groups of cells and the morphological effects resulting therefrom may be
determined by forces lying outside the cells.  Since these forces are
ubiquitous and constant it appears as if we were dealing exclusively with
the influence of a gamete; while in reality all that it is necessary for
the gamete to transmit is a certain form of irritability.

(d)  FACTORS WHICH DETERMINE PLACE AND TIME FOR THE DEPOSITION OF EGGS.

For the preservation of species the instinct of animals to lay their eggs
in places in which the young larvae find their food and can develop is of
paramount importance.  A simple example of this instinct is the fact that
the common fly lays its eggs on putrid material which serves as food for
the young larvae.  When a piece of meat and of fat of the same animal are
placed side by side, the fly will deposit its eggs upon the meat on which
the larvae can grow, and not upon the fat, on which they would starve. 
Here we are dealing with the effect of a volatile nitrogenous substance
which reflexly causes the peristaltic motions for the laying of the egg in
the female fly.

Kammerer has investigated the conditions for the laying of eggs in two
forms of salamanders, e.g. Salamandra atra and S. maculosa.  In both forms
the eggs are fertilised in the body and begin to develop in the uterus. 
Since there is room only for a few larvae in the uterus, a large number of
eggs perish and this number is the greater the longer the period of
gestation.  It thus happens that when the animals retain their eggs a long
time, very few young ones are born; and these are in a rather advanced
stage of development, owing to the long time which elapsed since they were
fertilised.  When the animal lays its eggs comparatively soon after
copulation, many eggs (from 12 to 72) are produced and the larvae are of
course in an early stage of development.  In the early stage the larvae
possess gills and can therefore live in water, while in later stages they
have no gills and breathe through their lungs.  Kammerer showed that both
forms of Salamandra can be induced to lay their eggs early or late,
according to the physical conditions surrounding them.  If they are kept in
water or in proximity to water and in a moist atmosphere they have a
tendency to lay their eggs earlier and a comparatively high temperature
enhances the tendency to shorten the period of gestation.  If the
salamanders are kept in comparative dryness they show a tendency to lay
their eggs rather late and a low temperature enhances this tendency.

Since Salamandra atra is found in rather dry alpine regions with a
relatively low temperature and Salamandra maculosa in lower regions with
plenty of water and a higher temperature, the fact that S. atra bears young
which are already developed and beyond the stage of aquatic life, while S.
maculosa bears young ones in an earlier stage, has been termed adaptation. 
Kammerer's experiments, however, show that we are dealing with the direct
effects of definite outside forces.  While we may speak of adaptation when
all or some of the variables which determine a reaction are unknown, it is
obviously in the interest of further scientific progress to connect cause
and effect directly whenever our knowledge allows us to do so.

VII.  CONCLUDING REMARKS.

The discovery of De Vries, that new species may arise by mutation and the
wide if not universal applicability of Mendel's Law to phenomena of
heredity, as shown especially by Bateson and his pupils, must, for the time
being, if not permanently, serve as a basis for theories of evolution. 
These discoveries place before the experimental biologist the definite task
of producing mutations by physico-chemical means.  It is true that certain
authors claim to have succeeded in this, but the writer wishes to apologise
to these authors for his inability to convince himself of the validity of
their claims at the present moment.  He thinks that only continued breeding
of these apparent mutants through several generations can afford convincing
evidence that we are here dealing with mutants rather than with merely
pathological variations.

What was said in regard to the production of new species by physico-
chemical means may be repeated with still more justification in regard to
the second problem of transformation, namely the making of living from
inanimate matter.  The purely morphological imitations of bacteria or cells
which physicists have now and then proclaimed as artificially produced
living beings; or the plays on words by which, e.g. the regeneration of
broken crystals and the regeneration of lost limbs by a crustacean were
declared identical, will not appeal to the biologist.  We know that growth
and development in animals and plants are determined by definite although
complicated series of catenary chemical reactions, which result in the
synthesis of a DEFINITE compound or group of compounds, namely, NUCLEINS.

The nucleins have the peculiarity of acting as ferments or enzymes for
their own synthesis.  Thus a given type of nucleus will continue to
synthesise other nuclein of its own kind.  This determines the continuity
of a species; since each species has, probably, its own specific nuclein or
nuclear material.  But it also shows us that whoever claims to have
succeeded in making living matter from inanimate will have to prove that he
has succeeded in producing nuclein material which acts as a ferment for its
own synthesis and thus reproduces itself.  Nobody has thus far succeeded in
this, although nothing warrants us in taking it for granted that this task
is beyond the power of science.

XV.  THE VALUE OF COLOUR IN THE STRUGGLE FOR LIFE.

By E.B. POULTON.
Hope Professor of Zoology in the University of Oxford.

INTRODUCTION.

The following pages have been written almost entirely from the historical
stand-point.  Their principal object has been to give some account of the
impressions produced on the mind of Darwin and his great compeer Wallace by
various difficult problems suggested by the colours of living nature.  In
order to render the brief summary of Darwin's thoughts and opinions on the
subject in any way complete, it was found necessary to say again much that
has often been said before.  No attempt has been made to display as a whole
the vast contribution of Wallace; but certain of its features are
incidentally revealed in passages quoted from Darwin's letters.  It is
assumed that the reader is familiar with the well-known theories of
Protective Resemblance, Warning Colours, and Mimicry both Batesian and
Mullerian.  It would have been superfluous to explain these on the present
occasion; for a far more detailed account than could have been attempted in
these pages has recently appeared.  (Poulton, "Essays on Evolution" Oxford,
1908, pages 293-382.)  Among the older records I have made a point of
bringing together the principal observations scattered through the note-
books and collections of W.J. Burchell.  These have never hitherto found a
place in any memoir dealing with the significance of the colours of
animals.

INCIDENTAL COLOURS.

Darwin fully recognised that the colours of living beings are not
necessarily of value as colours, but that they may be an incidental result
of chemical or physical structure.  Thus he wrote to T. Meehan, Oct. 9,
1874:  "I am glad that you are attending to the colours of dioecious
flowers; but it is well to remember that their colours may be as
unimportant to them as those of a gall, or, indeed, as the colour of an
amethyst or ruby is to these gems."  ("More Letters of Charles Darwin",
Vol. I. pages 354, 355.  See also the admirable account of incidental
colours in "Descent of Man" (2nd edition), 1874, pages 261, 262.)

Incidental colours remain as available assets of the organism ready to be
turned to account by natural selection.  It is a probable speculation that
all pigmentary colours were originally incidental; but now and for immense
periods of time the visible tints of animals have been modified and
arranged so as to assist in the struggle with other organisms or in
courtship.  The dominant colouring of plants, on the other hand, is an
essential element in the paramount physiological activity of chlorophyll. 
In exceptional instances, however, the shapes and visible colours of plants
may be modified in order to promote concealment.

TELEOLOGY AND ADAPTATION.

In the department of Biology which forms the subject of this essay, the
adaptation of means to an end is probably more evident than in any other;
and it is therefore of interest to compare, in a brief introductory
section, the older with the newer teleological views.

The distinctive feature of Natural Selection as contrasted with other
attempts to explain the process of Evolution is the part played by the
struggle for existence.  All naturalists in all ages must have known
something of the operations of "Nature red in tooth and claw"; but it was
left for this great theory to suggest that vast extermination is a
necessary condition of progress, and even of maintaining the ground already
gained.

Realising that fitness is the outcome of this fierce struggle, thus turned
to account for the first time, we are sometimes led to associate the
recognition of adaptation itself too exclusively with Natural Selection. 
Adaptation had been studied with the warmest enthusiasm nearly forty years
before this great theory was given to the scientific world, and it is
difficult now to realise the impetus which the works of Paley gave to the
study of Natural History.  That they did inspire the naturalists of the
early part of the last century is clearly shown in the following passages.

In the year 1824 the Ashmolean Museum at Oxford was intrusted to the care
of J.S. Duncan of New College.  He was succeeded in this office by his
brother, P.B. Duncan, of the same College, author of a History of the
Museum, which shows very clearly the influence of Paley upon the study of
nature, and the dominant position given to his teachings:  "Happily at this
time (1824) a taste for the study of natural history had been excited in
the University by Dr Paley's very interesting work on Natural Theology, and
the very popular lectures of Dr Kidd on Comparative Anatomy, and Dr
Buckland on Geology."  In the arrangement of the contents of the Museum the
illustration of Paley's work was given the foremost place by J.S. Duncan: 
"The first division proposes to familiarize the eye to those relations of
all natural objects which form the basis of argument in Dr Paley's Natural
Theology; to induce a mental habit of associating the view of natural
phenomena with the conviction that they are the media of Divine
manifestation; and by such association to give proper dignity to every
branch of natural science."  ((From "History and Arrangement of the
Ashmolean Museum" by P.B. Duncan:  see pages vi, vii of "A Catalogue of the
Ashmolean Museum", Oxford, 1836.)

The great naturalist, W.J. Burchell, in his classical work shows the same
recognition of adaptation in nature at a still earlier date.  Upon the
subject of collections he wrote ("Travels in the Interior of Southern
Africa", London, Vol. I. 1822, page 505.  The references to Burchell's
observations in the present essay are adapted from the author's article in
"Report of the British and South African Associations", 1905, Vol. III.
pages 57-110.):  "It must not be supposed that these charms (the pleasures
of Nature) are produced by the mere discovery of new objects:  it is the
harmony with which they have been adapted by the Creator to each other, and
to the situations in which they are found, which delights the observer in
countries where Art has not yet introduced her discords."  The remainder of
the passage is so admirable that I venture to quote it:  "To him who is
satisfied with amassing collections of curious objects, simply for the
pleasure of possessing them, such objects can afford, at best, but a
childish gratification, faint and fleeting; while he who extends his view
beyond the narrow field of nomenclature, beholds a boundless expanse, the
exploring of which is worthy of the philosopher, and of the best talents of
a reasonable being."

On September 14, 1811, Burchell was at Zand Valley (Vlei), or Sand Pool, a
few miles south-west of the site of Prieska, on the Orange River.  Here he
found a Mesembryanthemum (M. turbiniforme, now M. truncatum) and also a
"Gryllus" (Acridian), closely resembling the pebbles with which their
locality was strewn.  He says of both of these, "The intention of Nature,
in these instances, seems to have been the same as when she gave to the
Chameleon the power of accommodating its color, in a certain degree, to
that of the object nearest to it, in order to compensate for the deficiency
of its locomotive powers.  By their form and colour, this insect may pass
unobserved by those birds, which otherwise would soon extirpate a species
so little able to elude its pursuers, and this juicy little
Mesembryanthemum may generally escape the notice of cattle and wild
animals."  (Loc. cit. pages 310, 311.  See Sir William Thiselton-Dyer
"Morphological Notes", XI.; "Protective Adaptations", I.; "Annals of
Botany", Vol. XX. page 124.  In plates VII., VIII. and IX. accompanying
this article the author represents the species observed by Burchell,
together with others in which analogous adaptations exist.  He writes: 
"Burchell was clearly on the track on which Darwin reached the goal.  But
the time had not come for emancipation from the old teleology.  This,
however, in no respect detracts from the merit or value of his work.  For,
as Huxley has pointed out ("Life and Letters of Thomas Henry Huxley",
London, 1900, I. page 457), the facts of the old teleology are immediately
transferable to Darwinism, which simply supplies them with a natural in
place of a supernatural explanation.")  Burchell here seems to miss, at
least in part, the meaning of the relationship between the quiescence of
the Acridian and its cryptic colouring.  Quiescence is an essential element
in the protective resemblance to a stone--probably even more indispensable
than the details of the form and colouring.  Although Burchell appears to
overlook this point he fully recognised the community between protection by
concealment and more aggressive modes of defence; for, in the passage of
which a part is quoted above, he specially refers to some earlier remarks
on page 226 of his Vol. I.  We here find that even when the oxen were
resting by the Juk rivier (Yoke river), on July 19, 1811, Burchell observed
"Geranium spinosum, with a fleshy stem and large white flowers...; and a
succulent species of Pelargonium...so defended by the old panicles, grown
to hard woody thorns, that no cattle could browze upon it."  He goes on to
say, "In this arid country, where every juicy vegetable would soon be eaten
up by the wild animals, the Great Creating Power, with all-provident
wisdom, has given to such plants either an acrid or poisonous juice, or
sharp thorns, to preserve the species from annihilation..."  All these
modes of defence, especially adapted to a desert environment, have since
been generally recognised, and it is very interesting to place beside
Burchell's statement the following passage from a letter written by Darwin,
Aug. 7, 1868, to G.H. Lewes;  "That Natural Selection would tend to produce
the most formidable thorns will be admitted by every one who has observed
the distribution in South America and Africa (vide Livingstone) of thorn-
bearing plants, for they always appear where the bushes grow isolated and
are exposed to the attacks of mammals.  Even in England it has been noticed
that all spine-bearing and sting-bearing plants are palatable to
quadrupeds, when the thorns are crushed."  ("More Letters", I. page 308.)

ADAPTATION AND NATURAL SELECTION.

I have preferred to show the influence of the older teleology upon Natural
History by quotations from a single great and insufficiently appreciated
naturalist.  It might have been seen equally well in the pages of Kirby and
Spence and those of many other writers.  If the older naturalists who
thought and spoke with Burchell of "the intention of Nature" and the
adaptation of beings "to each other, and to the situations in which they
are found," could have conceived the possibility of evolution, they must
have been led, as Darwin was, by the same considerations to Natural
Selection.  This was impossible for them, because the philosophy which they
followed contemplated the phenomena of adaptation as part of a static
immutable system.  Darwin, convinced that the system is dynamic and
mutable, was prevented by these very phenomena from accepting anything
short of the crowning interpretation offered by Natural Selection.  ("I had
always been much struck by such adaptations (e.g. woodpecker and tree-frog
for climbing, seeds for dispersal), and until these could be explained it
seemed to me almost useless to endeavour to prove by indirect evidence that
species have been modified."  "Autobiography" in "Life and Letters of
Charles Darwin", Vol. I. page 82.  The same thought is repeated again and
again in Darwin's letters to his friends.  It is forcibly urged in the
Introduction to the "Origin" (1859), page 3.)  And the birth of Darwin's
unalterable conviction that adaptation is of dominant importance in the
organic world,--a conviction confirmed and ever again confirmed by his
experience as a naturalist--may probably be traced to the influence of the
great theologian.  Thus Darwin, speaking of his Undergraduate days, tells
us in his "Autobiography" that the logic of Paley's "Evidences of
Christianity" and "Moral Philosophy" gave him as much delight as did
Euclid.

"The careful study of these works, without attempting to learn any part by
rote, was the only part of the academical course which, as I then felt and
as I still believe, was of the least use to me in the education of my mind.
I did not at that time trouble myself about Paley's premises; and taking
these on trust, I was charmed and convinced by the long line of
argumentation."  ("Life and Letters", I. page 47.)

When Darwin came to write the "Origin" he quoted in relation to Natural
Selection one of Paley's conclusions.  "No organ will be formed, as Paley
has remarked, for the purpose of causing pain or for doing an injury to its
possessor."  ("Origin of Species" (1st edition) 1859, page 201.)

The study of adaptation always had for Darwin, as it has for many, a
peculiar charm.  His words, written Nov. 28, 1880, to Sir W. Thiselton-
Dyer, are by no means inapplicable to-day:  "Many of the Germans are very
contemptuous about making out use of organs; but they may sneer the souls
out of their bodies, and I for one shall think it the most interesting part
of natural history."  ("More Letters" II. page 428.)

PROTECTIVE AND AGGRESSIVE RESEMBLANCE:  PROCRYPTIC AND ANTICRYPTIC
COLOURING.

Colouring for the purpose of concealment is sometimes included under the
head Mimicry, a classification adopted by H.W. Bates in his classical
paper.  Such an arrangement is inconvenient, and I have followed Wallace in
keeping the two categories distinct.

The visible colours of animals are far more commonly adapted for Protective
Resemblance than for any other purpose.  The concealment of animals by
their colours, shapes and attitudes, must have been well known from the
period at which human beings first began to take an intelligent interest in
Nature.  An interesting early record is that of Samuel Felton, who (Dec. 2,
1763) figured and gave some account of an Acridian (Phyllotettix) from
Jamaica.  Of this insect he says "THE THORAX is like a leaf that is raised
perpendicularly from the body."  ("Phil. Trans. Roy. Soc." Vol. LIV. Tab.
VI. page 55.)

Both Protective and Aggressive Resemblances were appreciated and clearly
explained by Erasmus Darwin in 1794:  "The colours of many animals seem
adapted to their purposes of concealing themselves either to avoid danger,
or to spring upon their prey."  ("Zoonomia", Vol. I. page 509, London,
1794.)

Protective Resemblance of a very marked and beautiful kind is found in
certain plants, inhabitants of desert areas.  Examples observed by Burchell
almost exactly a hundred years ago have already been mentioned.  In
addition to the resemblance to stones Burchell observed, although he did
not publish the fact, a South African plant concealed by its likeness to
the dung of birds.  (Sir William Thiselton-Dyer has suggested the same
method of concealment ("Annals of Botany", Vol. XX. page 123).  Referring
to Anacampseros papyracea, figured on plate IX., the author says of its
adaptive resemblance:  "At the risk of suggesting one perhaps somewhat far-
fetched, I must confess that the aspect of the plant always calls to my
mind the dejecta of some bird, and the more so owing to the whitening of
the branches towards the tips" (loc. cit. page 126).  The student of
insects, who is so familiar with this very form of protective resemblance
in larvae, and even perfect insects, will not be inclined to consider the
suggestion far-fetched.)  The observation is recorded in one of the
manuscript journals kept by the great explorer during his journey.  I owe
the opportunity of studying it to the kindness of Mr Francis A. Burchell of
the Rhodes University College, Grahamstown.  The following account is given
under the date July 5, 1812, when Burchell was at the Makkwarin River,
about half-way between the Kuruman River and Litakun the old capital of the
Bachapins (Bechuanas):  "I found a curious little Crassula (not in flower)
so snow white, that I should never has (have) distinguished it from the
white limestones...It was an inch high and a little branchy,...and was at
first mistaken for the dung of birds of the passerine order.  I have often
had occasion to remark that in stony place(s) there grow many small
succulent plants and abound insects (chiefly Grylli) which have exactly the
same colour as the ground and must for ever escape observation unless a
person sit on the ground and observe very attentively."

The cryptic resemblances of animals impressed Darwin and Wallace in very
different degrees, probably in part due to the fact that Wallace's tropical
experiences were so largely derived from the insect world, in part to the
importance assigned by Darwin to Sexual Selection "a subject which had
always greatly interested me," as he says in his "Autobiography", ("Life
and Letters", Vol. I. page 94.)  There is no reference to Cryptic
Resemblance in Darwin's section of the Joint Essay, although he gives an
excellent short account of Sexual Selection (see page 295).  Wallace's
section on the other hand contains the following statement:  "Even the
peculiar colours of many animals, especially insects, so closely resembling
the soil or the leaves or the trunks on which they habitually reside, are
explained on the same principle; for though in the course of ages varieties
of many tints may have occurred, YET THOSE RACES HAVING COLOURS BEST
ADAPTED TO CONCEALMENT FROM THEIR ENEMIES WOULD INEVITABLY SURVIVE THE
LONGEST."  ("Journ. Proc. Linn. Soc." Vol. III. 1859, page 61.  The italics
are Wallace's.)

It would occupy too much space to attempt any discussion of the difference
between the views of these two naturalists, but it is clear that Darwin,
although fully believing in the efficiency of protective resemblance and
replying to St George Mivart's contention that Natural Selection was
incompetent to produce it ("Origin" (6th edition) London, 1872, pages 181,
182; see also page 66.), never entirely agreed with Wallace's estimate of
its importance.  Thus the following extract from a letter to Sir Joseph
Hooker, May 21, 1868, refers to Wallace:  "I find I must (and I always
distrust myself when I differ from him) separate rather widely from him all
about birds' nests and protection; he is riding that hobby to death." 
("More Letters", I. page 304.)  It is clear from the account given in "The
Descent of Man", (London, 1874, pages 452-458.  See also "Life and
Letters", III. pages 123-125, and "More Letters", II. pages 59-63, 72-74,
76-78, 84-90, 92, 93.), that the divergence was due to the fact that Darwin
ascribed more importance to Sexual Selection than did Wallace, and Wallace
more importance to Protective Resemblance than Darwin.  Thus Darwin wrote
to Wallace, Oct. 12 and 13, 1867:  "By the way, I cannot but think that you
push protection too far in some cases, as with the stripes on the tiger." 
("More Letters", I. page 283.)  Here too Darwin was preferring the
explanation offered by Sexual Selection ("Descent of Man" (2nd edition)
1874, pages 545, 546.), a preference which, considering the relation of the
colouring of the lion and tiger to their respective environments, few
naturalists will be found to share.  It is also shown that Darwin
contemplated the possibility of cryptic colours such as those of Patagonian
animals being due to sexual selection influenced by the aspect of
surrounding nature.

Nearly a year later Darwin in his letter of May 5, 1868?, expressed his
agreement with Wallace's views:  "Expect that I should put sexual selection
as an equal, or perhaps as even a more important agent in giving colour
than Natural Selection for protection."  ("More Letters", II. pages 77,
78.)  The conclusion expressed in the above quoted passage is opposed by
the extraordinary development of Protective Resemblance in the immature
stages of animals, especially insects.

It must not be supposed, however, that Darwin ascribed an unimportant role
to Cryptic Resemblances, and as observations accumulated he came to
recognise their efficiency in fresh groups of the animal kingdom.  Thus he
wrote to Wallace, May 5, 1867:  "Haeckel has recently well shown that the
transparency and absence of colour in the lower oceanic animals, belonging
to the most different classes, may be well accounted for on the principle
of protection."  ("More Letters", II. page 62.  See also "Descent of Man",
page 261.)  Darwin also admitted the justice of Professor E.S. Morse's
contention that the shells of molluscs are often adaptively coloured. 
("More Letters", II. page 95.)  But he looked upon cryptic colouring and
also mimicry as more especially Wallace's departments, and sent to him and
to Professor Meldola observations and notes bearing upon these subjects. 
Thus the following letter given to me by Dr A.R. Wallace and now, by kind
permission, published for the first time, accompanied a photograph of the
chrysalis of Papilio sarpedon choredon, Feld., suspended from a leaf of its
food-plant:

July 9th,
Down, Beckenham, Kent.

My Dear Wallace,

Dr G. Krefft has sent me the enclosed from Sydney.  A nurseryman saw a
caterpillar feeding on a plant and covered the whole up, but when he
searched for the cocoon (pupa), was long before he could find it, so good
was its imitation in colour and form to the leaf to which it was attached.
I hope that the world goes well with you.  Do not trouble yourself by
acknowledging this.

Ever yours

Ch. Darwin.

Another deeply interesting letter of Darwin's bearing upon protective
resemblance, has only recently been shown to me by my friend Professor E.B.
Wilson, the great American Cytologist.  With his kind consent and that of
Mr Francis Darwin, this letter, written four months before Darwin's death
on April 19, 1882, is reproduced here (The letter is addressed:  "Edmund B.
Wilson, Esq., Assistant in Biology, John Hopkins University, Baltimore Md,
U. States.":

December 21, 1881.

Dear Sir,

I thank you much for having taken so much trouble in describing fully your
interesting and curious case of mimickry.

I am in the habit of looking through many scientific Journals, and though
my memory is now not nearly so good as it was, I feel pretty sure that no
such case as yours has been described (amongst the nudibranch) molluscs. 
You perhaps know the case of a fish allied to Hippocampus, (described some
years ago by Dr Gunther in "Proc. Zoolog. Socy.") which clings by its tail
to sea-weeds, and is covered with waving filaments so as itself to look
like a piece of the same sea-weed.  The parallelism between your and Dr
Gunther's case makes both of them the more interesting; considering how far
a fish and a mollusc stand apart.  It would be difficult for anyone to
explain such cases by the direct action of the environment.--I am glad that
you intend to make further observations on this mollusc, and I hope that
you will give a figure and if possible a coloured figure.

With all good wishes from an old brother naturalist,

I remain, Dear Sir,

Yours faithfully,

Charles Darwin.

Professor E.B. Wilson has kindly given the following account of the
circumstances under which he had written to Darwin:  "The case to which
Darwin's letter refers is that of the nudibranch mollusc Scyllaea, which
lives on the floating Sargassum and shows a really astonishing resemblance
to the plant, having leaf-shaped processes very closely similar to the
fronds of the sea-weed both in shape and in colour.  The concealment of the
animal may be judged from the fact that we found the animal quite by
accident on a piece of Sargassum that had been in a glass jar in the
laboratory for some time and had been closely examined in the search for
hydroids and the like without disclosing the presence upon it of two large
specimens of the Scyllaea (the animal, as I recall it, is about two inches
long).  It was first detected by its movements alone, by someone (I think a
casual visitor to the laboratory) who was looking closely at the Sargassum
and exclaimed 'Why, the sea-weed is moving its leaves'!  We found the
example in the summer of 1880 or 1881 at Beaufort, N.C., where the Johns
Hopkins laboratory was located for the time being.  It must have been seen
by many others, before or since.

"I wrote and sent to Darwin a short description of the case at the
suggestion of Brooks, with whom I was at the time a student.  I was, of
course, entirely unknown to Darwin (or to anyone else) and to me the
principal interest of Darwin's letter is the evidence that it gives of his
extraordinary kindness and friendliness towards an obscure youngster who
had of course absolutely no claim upon his time or attention.  The little
incident made an indelible impression upon my memory and taught me a lesson
that was worth learning."

VARIABLE PROTECTIVE RESEMBLANCE.

The wonderful power of rapid colour adjustment possessed by the cuttle-fish
was observed by Darwin in 1832 at St Jago, Cape de Verd Islands, the first
place visited during the voyage of the "Beagle".  From Rio he wrote to
Henslow, giving the following account of his observations, May 18, 1832: 
"I took several specimens of an Octopus which possessed a most marvellous
power of changing its colours, equalling any chameleon, and evidently
accommodating the changes to the colour of the ground which it passed over.
Yellowish green, dark brown, and red, were the prevailing colours; this
fact appears to be new, as far as I can find out."  ("Life and Letters", I.
pages 235, 236.  See also Darwin's "Journal of Researches", 1876, pages 6-
8, where a far more detailed account is given together with a reference to
"Encycl. of Anat. and Physiol.")

Darwin was well aware of the power of individual colour adjustment, now
known to be possessed by large numbers of lepidopterous pupae and larvae. 
An excellent example was brought to his notice by C.V. Riley ("More
Letters" II, pages 385, 386.), while the most striking of the early results
obtained with the pupae of butterflies--those of Mrs M.E. Barber upon
Papilio nireus--was communicated by him to the Entomological Society of
London.  ("Trans. Ent. Soc. Lond." 1874, page 519.  See also "More
Letters", II. page 403.)

It is also necessary to direct attention to C.W. Beebe's ("Zoologica:  N.Y.
Zool. Soc." Vol. I. No. 1, Sept. 25, 1907: "Geographic variation in birds
with especial reference to the effects of humidity".) recent discovery that
the pigmentation of the plumage of certain birds is increased by
confinement in a superhumid atmosphere.  In Scardafella inca, on which the
most complete series of experiments was made, the changes took place only
at the moults, whether normal and annual or artificially induced at shorter
periods.  There was a corresponding increase in the choroidal pigment of
the eye.  At a certain advanced stage of feather pigmentation a brilliant
iridescent bronze or green tint made its appearance on those areas where
iridescence most often occurs in allied genera.  Thus in birds no less than
in insects, characters previously regarded as of taxonomic value, can be
evoked or withheld by the forces of the environment.

WARNING OR APOSEMATIC COLOURS.

From Darwin's description of the colours and habits it is evident that he
observed, in 1833, an excellent example of warning colouring in a little
South American toad (Phryniscus nigricans).  He described it in a letter to
Henslow, written from Monte Video, Nov. 24, 1832:  "As for one little toad,
I hope it may be new, that it may be christened 'diabolicus.'  Milton must
allude to this very individual when he talks of 'squat like a toad'; its
colours are by Werner ("Nomenclature of Colours", 1821) ink black,
vermilion red and buff orange."  ("More Letters", I. page 12.)  In the
"Journal of Researches" (1876, page 97.) its colours are described as
follows:  "If we imagine, first, that it had been steeped in the blackest
ink, and then, when dry, allowed to crawl over a board, freshly painted
with the brightest vermilion, so as to colour the soles of its feet and
parts of its stomach, a good idea of its appearance will be gained." 
"Instead of being nocturnal in its habits, as other toads are, and living
in damp obscure recesses, it crawls during the heat of the day about the
dry sand-hillocks and arid plains,..."  The appearance and habits recall T.
Belt's well-known description of the conspicuous little Nicaraguan frog
which he found to be distasteful to a duck.  ("The Naturalist in Nicaragua"
(2nd edition) London, 1888, page 321.)

The recognition of the Warning Colours of caterpillars is due in the first
instance to Darwin, who, reflecting on Sexual Selection, was puzzled by the
splendid colours of sexually immature organisms.  He applied to Wallace
"who has an innate genius for solving difficulties."  ("Descent of Man",
page 325.  On this and the following page an excellent account of the
discovery will be found, as well as in Wallace's "Natural Selection",
London, 1875, pages 117-122.)  Darwin's original letter exists ("Life and
Letters", III. pages 93, 94.), and in it we are told that he had taken the
advice given by Bates:  "You had better ask Wallace."  After some
consideration Wallace replied that he believed the colours of conspicuous
caterpillars and perfect insects were a warning of distastefulness and that
such forms would be refused by birds.  Darwin's reply ("Life and Letters",
III. pages 94, 95.) is extremely interesting both for its enthusiasm at the
brilliancy of the hypothesis and its caution in acceptance without full
confirmation:

"Bates was quite right; you are the man to apply to in a difficulty.  I
never heard anything more ingenious than your suggestion, and I hope you
may be able to prove it true.  That is a splendid fact about the white
moths (A single white moth which was rejected by young turkeys, while other
moths were greedily devoured:  "Natural Selection", 1875, page 78.); it
warms one's very blood to see a theory thus almost proved to be true."

Two years later the hypothesis was proved to hold for caterpillars of many
kinds by J. Jenner Weir and A.G. Butler, whose observations have since been
abundantly confirmed by many naturalists.  Darwin wrote to Weir, May 13,
1869:  "Your verification of Wallace's suggestion seems to me to amount to
quite a discovery."  ("More Letters", II. page 71 (footnote).)

RECOGNITION OR EPISEMATIC CHARACTERS.

This principle does not appear to have been in any way foreseen by Darwin,
although he draws special attention to several elements of pattern which
would now be interpreted by many naturalists as epismes.  He believed that
the markings in question interfered with the cryptic effect, and came to
the conclusion that, even when common to both sexes, they "are the result
of sexual selection primarily applied to the male."  ("Descent of Man",
page 544.)  The most familiar of all recognition characters was carefully
explained by him, although here too explained as an ornamental feature now
equally transmitted to both sexes:  "The hare on her form is a familiar
instance of concealment through colour; yet this principle partly fails in
a closely-allied species, the rabbit, for when running to its burrow, it is
made conspicuous to the sportsman, and no doubt to all beasts of prey, by
its upturned white tail."  ("Descent of Man", page 542.)

The analogous episematic use of the bright colours of flowers to attract
insects for effecting cross-fertilisation and of fruits to attract
vertebrates for effecting dispersal is very clearly explained in the
"Origin".  (Edition 1872, page 161.  For a good example of Darwin's caution
in dealing with exceptions see the allusion to brightly coloured fruit in
"More Letters", II. page 348.)

It is not, at this point, necessary to treat sematic characters at any
greater length.  They will form the subject of a large part of the
following section, where the models of Batesian (Pseudaposematic) mimicry
are considered as well as the Mullerian (Synaposematic) combinations of
Warning Colours.

MIMICRY,--BATESIAN OR PSEUDAPOSEMATIC, MULLERIAN OR SYNAPOSEMATIC.

The existence of superficial resemblances between animals of various
degrees of affinity must have been observed for hundreds of years.  Among
the early examples, the best known to me have been found in the manuscript
note-books and collections of W.J. Burchell, the great traveller in Africa
(1810-15) and Brazil (1825-30).  The most interesting of his records on
this subject are brought together in the following paragraphs.

Conspicuous among well-defended insects are the dark steely or iridescent
greenish blue fossorial wasps or sand-wasps, Sphex and the allied genera. 
Many Longicorn beetles mimic these in colour, slender shape of body and
limbs, rapid movements, and the readiness with which they take to flight. 
On Dec. 21, 1812, Burchell captured one such beetle (Promeces viridis) at
Kosi Fountain on the journey from the source of the Kuruman River to
Klaarwater.  It is correctly placed among the Longicorns in his catalogue,
but opposite to its number is the comment "Sphex! totus purpureus."

In our own country the black-and-yellow colouring of many stinging insects,
especially the ordinary wasps, affords perhaps the commonest model for
mimicry.  It is reproduced with more or less accuracy on moths, flies and
beetles.  Among the latter it is again a Longicorn which offers one of the
best-known, although by no means one of the most perfect, examples.  The
appearance of the well-known "wasp-beetle" (Clytus arietis) in the living
state is sufficiently suggestive to prevent the great majority of people
from touching it.  In Burchell's Brazilian collection there is a nearly
allied species (Neoclytus curvatus) which appears to be somewhat less wasp-
like than the British beetle.  The specimen bears the number "1188," and
the date March 27, 1827, when Burchell was collecting in the neighbourhood
of San Paulo.  Turning to the corresponding number in the Brazilian note-
book we find this record:  "It runs rapidly like an ichneumon or wasp, of
which it has the appearance."

The formidable, well-defended ants are as freely mimicked by other insects
as the sand-wasps, ordinary wasps and bees.  Thus on February 17, 1901, Guy
A.K. Marshall captured, near Salisbury, Mashonaland, three similar species
of ants (Hymenoptera) with a bug (Hemiptera) and a Locustid (Orthoptera),
the two latter mimicking the former.  All the insects, seven in number,
were caught on a single plant, a small bushy vetch.  ("Trans. Ent. Soc.
Lond." 1902, page 535, plate XIX. figs. 53-59.)

This is an interesting recent example from South Africa, and large numbers
of others might be added--the observations of many naturalists in many
lands; but nearly all of them known since that general awakening of
interest in the subject which was inspired by the great hypotheses of H.W.
Bates and Fritz Muller.  We find, however, that Burchell had more than once
recorded the mimetic resemblance to ants.  An extremely ant-like bug (the
larva of a species of Alydus) in his Brazilian collection is labelled
"1141," with the date December 8, 1826, when Burchell was at the Rio das
Pedras, Cubatao, near Santos.  In the note-book the record is as follows: 
"1141 Cimex.  I collected this for a Formica."

Some of the chief mimics of ants are the active little hunting spiders
belonging to the family Attidae.  Examples have been brought forward during
many recent years, especially by my friends Dr and Mrs Peckham, of
Milwaukee, the great authorities on this group of Araneae.  Here too we
find an observation of the mimetic resemblance recorded by Burchell, and
one which adds in the most interesting manner to our knowledge of the
subject.  A fragment, all that is now left, of an Attid spider, captured on
June 30, 1828, at Goyaz, Brazil, bears the following note, in this case on
the specimen and not in the note-book:  "Black...runs and seems like an ant
with large extended jaws."  My friend Mr R.I. Pocock, to whom I have
submitted the specimen, tells me that it is not one of the group of species
hitherto regarded as ant-like, and he adds, "It is most interesting that
Burchell should have noticed the resemblance to an ant in its movements. 
This suggests that the perfect imitation in shape, as well as in movement,
seen in many species was started in forms of an appropriate size and colour
by the mimicry of movement alone."  Up to the present time Burchell is the
only naturalist who has observed an example which still exhibits this
ancestral stage in the evolution of mimetic likeness.

Following the teachings of his day, Burchell was driven to believe that it
was part of the fixed and inexorable scheme of things that these strange
superficial resemblances existed.  Thus, when he found other examples of
Hemipterous mimics, including one (Luteva macrophthalma) with "exactly the
manners of a Mantis," he added the sentence, "In the genus Cimex (Linn.)
are to be found the outward resemblances of insects of many other genera
and orders" (February 15, 1829).  Of another Brazilian bug, which is not to
be found in his collection, and cannot therefore be precisely identified,
he wrote:  "Cimex...Nature seems to have intended it to imitate a Sphex,
both in colour and the rapid palpitating and movement of the antennae"
(November 15, 1826).  At the same time it is impossible not to feel the
conviction that Burchell felt the advantage of a likeness to stinging
insects and to aggressive ants, just as he recognised the benefits
conferred on desert plants by spines and by concealment.  Such an
interpretation of mimicry was perfectly consistent with the theological
doctrines of his day.  (See Kirby and Spence, "An Introduction to
Entomology" (1st edition), London, Vol. II. 1817, page 223.)

The last note I have selected from Burchell's manuscript refers to one of
the chief mimics of the highly protected Lycid beetles.  The whole
assemblage of African insects with a Lycoid colouring forms a most
important combination and one which has an interesting bearing upon the
theories of Bates and Fritz Muller.  This most wonderful set of mimetic
forms, described in 1902 by Guy A.K. Marshall, is composed of flower-
haunting beetles belonging to the family Lycidae, and the heterogeneous
group of varied insects which mimic their conspicuous and simple scheme of
colouring.  The Lycid beetles, forming the centre or "models" of the whole
company, are orange-brown in front for about two-thirds of the exposed
surface, black behind for the remaining third.  They are undoubtedly
protected by qualities which make them excessively unpalatable to the bulk
of insect-eating animals.  Some experimental proof of this has been
obtained by Mr Guy Marshall.  What are the forms which surround them? 
According to the hypothesis of Bates they would be, at any rate mainly,
palatable hard-pressed insects which only hold their own in the struggle
for life by a fraudulent imitation of the trade-mark of the successful and
powerful Lycidae.  According to Fritz Muller's hypothesis we should expect
that the mimickers would be highly protected, successful and abundant
species, which (metaphorically speaking) have found it to their advantage
to possess an advertisement, a danger-signal, in common with each other,
and in common with the beetles in the centre of the group.

How far does the constitution of this wonderful combination--the largest
and most complicated as yet known in all the world--convey to us the idea
of mimicry working along the lines supposed by Bates or those suggested by
Muller?  Figures 1 to 52 of Mr Marshall's coloured plate ("Trans. Ent. Soc.
Lond." 1902, plate XVIII.  See also page 517, where the group is analysed.)
represent a set of forty-two or forty-three species or forms of insects
captured in Mashonaland, and all except two in the neighbourhood of
Salisbury.  The combination includes six species of Lycidae; nine beetles
of five groups all specially protected by nauseous qualities, Telephoridae,
Melyridae, Phytophaga, Lagriidae, Cantharidae; six Longicorn beetles; one
Coprid beetle; eight stinging Hymenoptera; three or four parasitic
Hymenoptera (Braconidae, a group much mimicked and shown by some
experiments to be distasteful); five bugs (Hemiptera, a largely unpalatable
group); three moths (Arctiidae and Zygaenidae, distasteful families); one
fly.  In fact the whole combination, except perhaps one Phytophagous, one
Coprid and the Longicorn beetles, and the fly, fall under the hypothesis of
Muller and not under that of Bates.  And it is very doubtful whether these
exceptions will be sustained:  indeed the suspicion of unpalatability
already besets the Longicorns and is always on the heels,--I should say the
hind tarsi--of a Phytophagous beetle.

This most remarkable group which illustrates so well the problem of mimicry
and the alternative hypotheses proposed for its solution, was, as I have
said, first described in 1902.  Among the most perfect of the mimetic
resemblances in it is that between the Longicorn beetle, Amphidesmus
analis, and the Lycidae.  It was with the utmost astonishment and pleasure
that I found this very resemblance had almost certainly been observed by
Burchell.  A specimen of the Amphidesmus exists in his collection and it
bears "651."  Turning to the same number in the African Catalogue we find
that the beetle is correctly placed among the Longicorns, that it was
captured at Uitenhage on Nov. 18, 1813, and that it was found associated
with Lycid beetles in flowers ("consocians cum Lycis 78-87 in floribus"). 
Looking up Nos. 78-87 in the collection and catalogue, three species of
Lycidae are found, all captured on Nov. 18, 1813, at Uitenhage.  Burchell
recognised the wide difference in affinity, shown by the distance between
the respective numbers; for his catalogue is arranged to represent
relationships.  He observed, what students of mimicry are only just
beginning to note and record, the coincidence between model and mimic in
time and space and in habits.  We are justified in concluding that he
observed the close superficial likeness although he does not in this case
expressly allude to it.

One of the most interesting among the early observations of superficial
resemblance between forms remote in the scale of classification was made by
Darwin himself, as described in the following passage from his letter to
Henslow, written from Monte Video, Aug. 15, 1832:  "Amongst the lower
animals nothing has so much interested me as finding two species of
elegantly coloured true Planaria inhabiting the dewy forest!  The false
relation they bear to snails is the most extraordinary thing of the kind I
have ever seen."  ("More Letters", I. page 9.)

Many years later, in 1867, he wrote to Fritz Muller suggesting that the
resemblance of a soberly coloured British Planarian to a slug might be due
to mimicry.  ("Life and Letters", III. page 71.)

The most interesting copy of Bates's classical memoir on Mimicry
("Contributions to an Insect Fauna of the Amazon Valley".  "Trans. Linn.
Soc."  Vol. XXIII. 1862, page 495.), read before the Linnean Society in
1861, is that given by him to the man who has done most to support and
extend the theory.  My kind friend has given that copy to me; it bears the
inscription:

"Mr A.R. Wallace from his old travelling companion the Author."

Only a year and a half after the publication of the "Origin", we find that
Darwin wrote to Bates on the subject which was to provide such striking
evidence of the truth of Natural Selection:  "I am glad to hear that you
have specially attended to 'mimetic' analogies--a most curious subject; I
hope you publish on it.  I have for a long time wished to know whether what
Dr Collingwood asserts is true--that the most striking cases generally
occur between insects inhabiting the same country."  (The letter is dated
April 4, 1861.  "More Letters", I. page 183.)

The next letter, written about six months later, reveals the remarkable
fact that the illustrious naturalist who had anticipated Edward Forbes in
the explanation of arctic forms on alpine heights ("I was forestalled in
only one important point, which my vanity has always made me regret,
namely, the explanation by means of the Glacial period of the presence of
the same species of plants and of some few animals on distant mountain
summits and in the arctic regions.  This view pleased me so much that I
wrote it out in extenso, and I believe that it was read by Hooker some
years before E. Forbes published his celebrated memoir on the subject.  In
the very few points in which we differed, I still think that I was in the
right.  I have never, of course, alluded in print to my having
independently worked out this view."  "Autobiography, Life and Letters", I.
page 88.), had also anticipated H.W. Bates in the theory of Mimicry:  "What
a capital paper yours will be on mimetic resemblances!  You will make quite
a new subject of it.  I had thought of such cases as a difficulty; and
once, when corresponding with Dr Collingwood, I thought of your
explanation; but I drove it from my mind, for I felt that I had not
knowledge to judge one way or the other."  (The letter is dated Sept. 25,
1861:  "More Letters", I. page 197.)

Bates read his paper before the Linnean Society, Nov. 21, 1861, and
Darwin's impressions on hearing it were conveyed in a letter to the author
dated Dec. 3:  "Under a general point of view, I am quite convinced (Hooker
and Huxley took the same view some months ago) that a philosophic view of
nature can solely be driven into naturalists by treating special subjects
as you have done.  Under a special point of view, I think you have solved
one of the most perplexing problems which could be given to solve."  ("Life
and Letters", II. page 378.)  The memoir appeared in the following year,
and after reading it Darwin wrote as follows, Nov. 20, 1862:  "...In my
opinion it is one of the most remarkable and admirable papers I ever read
in my life...I am rejoiced that I passed over the whole subject in the
"Origin", for I should have made a precious mess of it.  You have most
clearly stated and solved a wonderful problem...Your paper is too good to
be largely appreciated by the mob of naturalists without souls; but, rely
on it, that it will have LASTING value, and I cordially congratulate you on
your first great work.  You will find, I should think, that Wallace will
fully appreciate it."  ("Life and Letters", II. pages 391-393.)  Four days
later, Nov. 24, Darwin wrote to Hooker on the same subject:  "I have now
finished his paper...' it seems to me admirable.  To my mind the act of
segregation of varieties into species was never so plainly brought forward,
and there are heaps of capital miscellaneous observations."  ("More
Letters", I. page 214.)

Darwin was here referring to the tendency of similar varieties of the same
species to pair together, and on Nov. 25 he wrote to Bates asking for
fuller information on this subject.  ("More Letters", I. page 215.  See
also parts of Darwin's letter to Bates in "Life and Letters", II. page
392.)  If Bates's opinion were well founded, sexual selection would bear a
most important part in the establishment of such species.  (See Poulton,
"Essays on Evolution", 1908, pages 65, 85-88.)  It must be admitted,
however, that the evidence is as yet quite insufficient to establish this
conclusion.  It is interesting to observe how Darwin at once fixed on the
part of Bates's memoir which seemed to bear upon sexual selection.  A
review of Bates's theory of Mimicry was contributed by Darwin to the
"Natural History Review" (New Ser. Vol. III. 1863, page 219.) and an
account of it is to be found in the "Origin" (Edition 1872, pages 375-378.)
and in "The Descent of Man".  (Edition 1874, pages 323-325.)

Darwin continually writes of the value of hypothesis as the inspiration of
inquiry.  We find an example in his letter to Bates, Nov. 22, 1860:  "I
have an old belief that a good observer really means a good theorist, and I
fully expect to find your observations most valuable."  ("More Letters", I.
page 176.)  Darwin's letter refers to many problems upon which Bates had
theorised and observed, but as regards Mimicry itself the hypothesis was
thought out after the return of the letter from the Amazons, when he no
longer had the opportunity of testing it by the observation of living
Nature.  It is by no means improbable that, had he been able to apply this
test, Bates would have recognised that his division of butterfly
resemblances into two classes,--one due to the theory of mimicry, the other
to the influence of local conditions,--could not be sustained.

Fritz Muller's contributions to the problem of Mimicry were all made in
S.E. Brazil, and numbers of them were communicated, with other observations
on natural history, to Darwin, and by him sent to Professor R. Meldola who
published many of the facts.  Darwin's letters to Meldola (Poulton,
"Charles Darwin and the theory of Natural Selection", London, 1896, pages
199-218.) contain abundant proofs of his interest in Muller's work upon
Mimicry.  One deeply interesting letter (Loc. cit. pages 201, 202.) dated
Jan. 23, 1872, proves that Fritz Muller before he originated the theory of
Common Warning Colours (Synaposematic Resemblance or Mullerian Mimicry),
which will ever be associated with his name, had conceived the idea of the
production of mimetic likeness by sexual selection.

Darwin's letter to Meldola shows that he was by no means inclined to
dismiss the suggestion as worthless, although he considered it daring. 
"You will also see in this letter a strange speculation, which I should not
dare to publish, about the appreciation of certain colours being developed
in those species which frequently behold other forms similarly ornamented. 
I do not feel at all sure that this view is as incredible as it may at
first appear.  Similar ideas have passed through my mind when considering
the dull colours of all the organisms which inhabit dull-coloured regions,
such as Patagonia and the Galapagos Is."  A little later, on April 5, he
wrote to Professor August Weismann on the same subject:  "It may be
suspected that even the habit of viewing differently coloured surrounding
objects would influence their taste, and Fritz Muller even goes so far as
to believe that the sight of gaudy butterflies might influence the taste of
distinct species."  ("Life and Letters", III. page 157.)

This remarkable suggestion affords interesting evidence that F. Muller was
not satisfied with the sufficiency of Bates's theory.  Nor is this
surprising when we think of the numbers of abundant conspicuous butterflies
which he saw exhibiting mimetic likenesses.  The common instances in his
locality, and indeed everywhere in tropical America, were anything but the
hard-pressed struggling forms assumed by the theory of Bates.  They
belonged to the groups which were themselves mimicked by other butterflies.
Fritz Muller's suggestion also shows that he did not accept Bates's
alternative explanation of a superficial likeness between models
themselves, based on some unknown influence of local physico-chemical
forces.  At the same time Muller's own suggestion was subject to this
apparently fatal objection, that the sexual selection he invoked would tend
to produce resemblances in the males rather than the females, while it is
well known that when the sexes differ the females are almost invariably
more perfectly mimetic than the males and in a high proportion of cases are
mimetic while the males are non-mimetic.

The difficulty was met several years later by Fritz Muller's well-known
theory, published in 1879 ("Kosmos", May 1879, page 100.), and immediately
translated by Meldola and brought before the Entomological Society. 
("Proc. Ent. Soc. Lond." 1879, page xx.)  Darwin's letter to Meldola dated
June 6, 1879, shows "that the first introduction of this new and most
suggestive hypothesis into this country was due to the direct influence of
Darwin himself, who brought it before the notice of the one man who was
likely to appreciate it at its true value and to find the means for its
presentation to English naturalists."  ("Charles Darwin and the Theory of
Natural Selection", page 214.)  Of the hypothesis itself Darwin wrote "F.
Muller's view of the mutual protection was quite new to me."  (Ibid. page
213.)  The hypothesis of Mullerian mimicry was at first strongly opposed. 
Bates himself could never make up his mind to accept it.  As the Fellows
were walking out of the meeting at which Professor Meldola explained the
hypothesis, an eminent entomologist, now deceased, was heard to say to
Bates:  "It's a case of save me from my friends!"  The new ideas
encountered and still encounter to a great extent the difficulty that the
theory of Bates had so completely penetrated the literature of natural
history.  The present writer has observed that naturalists who have not
thoroughly absorbed the older hypothesis are usually far more impressed by
the newer one than are those whose allegiance has already been rendered. 
The acceptance of Natural Selection itself was at first hindered by similar
causes, as Darwin clearly recognised:  "If you argue about the non-
acceptance of Natural Selection, it seems to me a very striking fact that
the Newtonian theory of gravitation, which seems to every one now so
certain and plain, was rejected by a man so extraordinarily able as
Leibnitz.  The truth will not penetrate a preoccupied mind."  (To Sir J.
Hooker, July 28, 1868, "More Letters", I. page 305.  See also the letter to
A.R. Wallace, April 30, 1868, in "More Letters" II. page 77, lines 6-8 from
top.)

There are many naturalists, especially students of insects, who appear to
entertain an inveterate hostility to any theory of mimicry.  Some of them
are eager investigators in the fascinating field of geographical
distribution, so essential for the study of Mimicry itself.  The changes of
pattern undergone by a species of Erebia as we follow it over different
parts of the mountain ranges of Europe is indeed a most interesting
inquiry, but not more so than the differences between e.g. the Acraea
johnstoni of S.E. Rhodesia and of Kilimanjaro.  A naturalist who is
interested by the Erebia should be equally interested by the Acraea; and so
he would be if the student of mimicry did not also record that the
characteristics which distinguish the northern from the southern
individuals of the African species correspond with the presence, in the
north but not in the south, of certain entirely different butterflies. 
That this additional information should so greatly weaken, in certain
minds, the appeal of a favourite study, is a psychological problem of no
little interest.  This curious antagonism is I believe confined to a few
students of insects.  Those naturalists who, standing rather farther off,
are able to see the bearings of the subject more clearly, will usually
admit the general support yielded by an ever-growing mass of observations
to the theories of Mimicry propounded by H.W. Bates and Fritz Muller.  In
like manner natural selection itself was in the early days often best
understood and most readily accepted by those who were not naturalists. 
Thus Darwin wrote to D.T. Ansted, Oct. 27, 1860:  "I am often in despair in
making the generality of NATURALISTS even comprehend me.  Intelligent men
who are not naturalists and have not a bigoted idea of the term species,
show more clearness of mind."  ("More Letters", I. page 175.)

Even before the "Origin" appeared Darwin anticipated the first results upon
the mind of naturalists.  He wrote to Asa Gray, Dec. 21, 1859:  "I have
made up my mind to be well abused; but I think it of importance that my
notions should be read by intelligent men, accustomed to scientific
argument, though NOT naturalists.  It may seem absurd, but I think such men
will drag after them those naturalists who have too firmly fixed in their
heads that a species is an entity."  ("Life and Letters" II. page 245.)

Mimicry was not only one of the first great departments of zoological
knowledge to be studied under the inspiration of natural Selection, it is
still and will always remain one of the most interesting and important of
subjects in relation to this theory as well as to evolution.  In mimicry we
investigate the effect of environment in its simplest form:  we trace the
effects of the pattern of a single species upon that of another far removed
from it in the scale of classification.  When there is reason to believe
that the model is an invader from another region and has only recently
become an element in the environment of the species native to its second
home, the problem gains a special interest and fascination.  Although we
are chiefly dealing with the fleeting and changeable element of colour we
expect to find and we do find evidence of a comparatively rapid evolution. 
The invasion of a fresh model is for certain species an unusually sudden
change in the forces of the environment and in some instances we have
grounds for the belief that the mimetic response has not been long delayed.

MIMICRY AND SEX.

Ever since Wallace's classical memoir on mimicry in the Malayan Swallowtail
butterflies, those naturalists who have written on the subject have
followed his interpretation of the marked prevalence of mimetic resemblance
in the female sex as compared with the male.  They have believed with
Wallace that the greater dangers of the female, with slower flight and
often alighting for oviposition, have been in part met by the high
development of this special mode of protection.  The fact cannot be
doubted.  It is extremely common for a non-mimetic male to be accompanied
by a beautifully mimetic female and often by two or three different forms
of female, each mimicking a different model.  The male of a polymorphic
mimetic female is, in fact, usually non-mimetic (e.g. Papilio dardanus =
merope), or if a mimic (e.g. the Nymphaline genus Euripus), resembles a
very different model.  On the other hand a non-mimetic female accompanied
by a mimetic male is excessively rare.  An example is afforded by the
Oriental Nymphaline, Cethosia, in which the males of some species are rough
mimics of the brown Danaines.  In some of the orb-weaving spiders the males
mimic ants, while the much larger females are non-mimetic.  When both sexes
mimic, it is very common in butterflies and is also known in moths, for the
females to be better and often far better mimics than the males.

Although still believing that Wallace's hypothesis in large part accounts
for the facts briefly summarised above, the present writer has recently
been led to doubt whether it offers a complete explanation.  Mimicry in the
male, even though less beneficial to the species than mimicry in the
female, would still surely be advantageous.  Why then is it so often
entirely restricted to the female?  While the attempt to find an answer to
this question was haunting me, I re-read a letter written by Darwin to
Wallace, April 15, 1868, containing the following sentences:  "When female
butterflies are more brilliant than their males you believe that they have
in most cases, or in all cases, been rendered brilliant so as to mimic some
other species, and thus escape danger.  But can you account for the males
not having been rendered equally brilliant and equally protected?  Although
it may be most for the welfare of the species that the female should be
protected, yet it would be some advantage, certainly no disadvantage, for
the unfortunate male to enjoy an equal immunity from danger.  For my part,
I should say that the female alone had happened to vary in the right
manner, and that the beneficial variations had been transmitted to the same
sex alone.  Believing in this, I can see no improbability (but from analogy
of domestic animals a strong probability) that variations leading to beauty
must often have occurred in the males alone, and been transmitted to that
sex alone.  Thus I should account in many cases for the greater beauty of
the male over the female, without the need of the protective principle." 
("More Letters", II. pages 73, 74.  On the same subject--"the gay-coloured
females of Pieris" (Perrhybris (Mylothris) pyrrha of Brazil), Darwin wrote
to Wallace, May 5, 1868, as follows:  "I believe I quite follow you in
believing that the colours are wholly due to mimicry; and I further believe
that the male is not brilliant from not having received through inheritance
colour from the female, and from not himself having varied; in short, that
he has not been influenced by selection."  It should be noted that the male
of this species does exhibit a mimetic pattern on the under surface.  "More
Letters" II. page 78.)

The consideration of the facts of mimicry thus led Darwin to the conclusion
that the female happens to vary in the right manner more commonly than the
male, while the secondary sexual characters of males supported the
conviction "that from some unknown cause such characters (viz. new
characters arising in one sex and transmitted to it alone) apparently
appear oftener in the male than in the female."  (Letter from Darwin to
Wallace, May 5, 1867, "More Letters", II. Page 61.)

Comparing these conflicting arguments we are led to believe that the first
is the stronger.  Mimicry in the male would be no disadvantage but an
advantage, and when it appears would be and is taken advantage of by
selection.  The secondary sexual characters of males would be no advantage
but a disadvantage to females, and, as Wallace thinks, are withheld from
this sex by selection.  It is indeed possible that mimicry has been
hindered and often prevented from passing to the males by sexual selection.
We know that Darwin was much impressed ("Descent of Man", page 325.) by
Thomas Belt's daring and brilliant suggestion that the white patches which
exist, although ordinarily concealed, on the wings of mimetic males of
certain Pierinae (Dismorphia), have been preserved by preferential mating.
He supposed this result to have been brought about by the females
exhibiting a deep-seated preference for males that displayed the chief
ancestral colour, inherited from periods before any mimetic pattern had
been evolved in the species.  But it has always appeared to me that Belt's
deeply interesting suggestion requires much solid evidence and repeated
confirmation before it can be accepted as a valid interpretation of the
facts.  In the present state of our knowledge, at any rate of insects and
especially of Lepidoptera, it is probable that the female is more apt to
vary than the male and that an important element in the interpretation of
prevalent female mimicry is provided by this fact.

In order adequately to discuss the question of mimicry and sex it would be
necessary to analyse the whole of the facts, so far as they are known in
butterflies.  On the present occasion it is only possible to state the
inferences which have been drawn from general impressions,--inferences
which it is believed will be sustained by future inquiry.

(1)  Mimicry may occasionally arise in one sex because the differences
which distinguish it from the other sex happen to be such as to afford a
starting-point for the resemblance.  Here the male is at no disadvantage as
compared with the female, and the rarity of mimicry in the male alone (e.g.
Cethosia) is evidence that the great predominance of female mimicry is not
to be thus explained.

(2)  The tendency of the female to dimorphism and polymorphism has been of
great importance in determining this predominance.  Thus if the female
appear in two different forms and the male in only one it will be twice as
probable that she will happen to possess a sufficient foundation for the
evolution of mimicry.

(3)  The appearance of melanic or partially melanic forms in the female has
been of very great service, providing as it does a change of ground-colour.
Thus the mimicry of the black generally red-marked American "Aristolochia
swallowtails" (Pharmacophagus) by the females of Papilio swallowtails was
probably begun in this way.

(4)  It is probably incorrect to assume with Haase that mimicry always
arose in the female and was later acquired by the male.  Both sexes of the
third section of swallowtails (Cosmodesmus) mimic Pharmacophagus in
America, far more perfectly than do the females of Papilio.  But this is
not due to Cosmodesmus presenting us with a later stage of history begun in
Papilio; for in Africa Cosmodesmus is still mimetic (of Danainae) in both
sexes although the resemblances attained are imperfect, while many African
species of Papilio have non-mimetic males with beautifully mimetic females.
The explanation is probably to be sought in the fact that the females of
Papilio are more variable and more often tend to become dimorphic than
those of Cosmodesmus, while the latter group has more often happened to
possess a sufficient foundation for the origin of the resemblance in
patterns which, from the start, were common to male and female.

(5)  In very variable species with sexes alike, mimicry can be rapidly
evolved in both sexes out of very small beginnings.  Thus the reddish marks
which are common in many individuals of Limenitis arthemis were almost
certainly the starting-point for the evolution of the beautifully mimetic
L. archippus.  Nevertheless in such cases, although there is no reason to
suspect any greater variability, the female is commonly a somewhat better
mimic than the male and often a very much better mimic.  Wallace's
principle seems here to supply the obvious interpretation.

(6)  When the difference between the patterns of the model and presumed
ancestor of the mimic is very great, the female is often alone mimetic;
when the difference is comparatively small, both sexes are commonly
mimetic.  The Nymphaline genus Hypolimnas is a good example.  In Hypolimnas
itself the females mimic Danainae with patterns very different from those
preserved by the non-mimetic males:  in the sub-genus Euralia, both sexes
resemble the black and white Ethiopian Danaines with patterns not very
dissimilar from that which we infer to have existed in the non-mimetic
ancestor.

(7)  Although a melanic form or other large variation may be of the utmost
importance in facilitating the start of a mimetic likeness, it is
impossible to explain the evolution of any detailed resemblance in this
manner.  And even the large colour variation itself may well be the
expression of a minute and "continuous" change in the chemical and physical
constitution of pigments.

SEXUAL SELECTION (EPIGAMIC CHARACTERS).

We do not know the date at which the idea of Sexual Selection arose in
Darwin's mind, but it was probably not many years after the sudden flash of
insight which, in October 1838, gave to him the theory of Natural
Selection.  An excellent account of Sexual Selection occupies the
concluding paragraph of Part I. of Darwin's Section of the Joint Essay on
Natural Selection, read July 1st, 1858, before the Linnean Society. 
("Journ. Proc. Linn. Soc." Vol. III. 1859, page 50.)  The principles are so
clearly and sufficiently stated in these brief sentences that it is
appropriate to quote the whole:  "Besides this natural means of selection,
by which those individuals are preserved, whether in their egg, or larval,
or mature state, which are best adapted to the place they fill in nature,
there is a second agency at work in most unisexual animals, tending to
produce the same effect, namely, the struggle of the males for the females. 
These struggles are generally decided by the law of battle, but in the case
of birds, apparently, by the charms of their song, by their beauty or their
power of courtship, as in the dancing rock-thrush of Guiana.  The most
vigorous and healthy males, implying perfect adaptation, must generally
gain the victory in their contests.  This kind of selection, however, is
less rigorous than the other; it does not require the death of the less
successful, but gives to them fewer descendants.  The struggle falls,
moreover, at a time of year when food is generally abundant, and perhaps
the effect chiefly produced would be the modification of the secondary
sexual characters, which are not related to the power of obtaining food, or
to defence from enemies, but to fighting with or rivalling other males. 
The result of this struggle amongst the males may be compared in some
respects to that produced by those agriculturists who pay less attention to
the careful selection of all their young animals, and more to the
occasional use of a choice mate."

A full exposition of Sexual Selection appeared in the "The Descent of Man"
in 1871, and in the greatly augmented second edition, in 1874.  It has been
remarked that the two subjects, "The Descent of Man and Selection in
Relation to Sex", seem to fuse somewhat imperfectly into the single work of
which they form the title.  The reason for their association is clearly
shown in a letter to Wallace, dated May 28, 1864:  "...I suspect that a
sort of sexual selection has been the most powerful means of changing the
races of man."  ("More Letters", II. page 33.)

Darwin, as we know from his Autobiography ("Life and Letters", I. page
94.), was always greatly interested in this hypothesis, and it has been
shown in the preceding pages that he was inclined to look favourably upon
it as an interpretation of many appearances usually explained by Natural
Selection.  Hence Sexual Selection, incidentally discussed in other
sections of the present essay, need not be considered at any length, in the
section specially allotted to it.

Although so interested in the subject and notwithstanding his conviction
that the hypothesis was sound, Darwin was quite aware that it was probably
the most vulnerable part of the "Origin".  Thus he wrote to H.W. Bates,
April 4, 1861:  "If I had to cut up myself in a review I would have
(worried?) and quizzed sexual selection; therefore, though I am fully
convinced that it is largely true, you may imagine how pleased I am at what
you say on your belief."  ("More Letters", I. page 183.)

The existence of sound-producing organs in the males of insects was, Darwin
considered, the strongest evidence in favour of the operation of sexual
selection in this group.  ("Life and Letters", III. pages 94, 138.)  Such a
conclusion has received strong support in recent years by the numerous
careful observations of Dr F.A. Dixey ("Proc. Ent. Soc. Lond." 1904, page
lvi; 1905, pages xxxvii, liv; 1906, page ii.) and Dr G.B. Longstaff ("Proc.
Ent. Soc. Lond." 1905, page xxxv; "Trans. Ent. Soc. Lond." 1905, page 136;
1908, page 607.) on the scents of male butterflies.  The experience of
these naturalists abundantly confirms and extends the account given by
Fritz Muller ("Jen. Zeit." Vol. XI. 1877, page 99; "Trans. Ent. Soc. Lond."
1878, page 211.) of the scents of certain Brazilian butterflies.  It is a
remarkable fact that the apparently epigamic scents of male butterflies
should be pleasing to man while the apparently aposematic scents in both
sexes of species with warning colours should be displeasing to him.  But
the former is far more surprising than the latter.  It is not perhaps
astonishing that a scent which is ex hypothesi unpleasant to an insect-
eating Vertebrate should be displeasing to the human sense; but it is
certainly wonderful that an odour which is ex hypothesi agreeable to a
female butterfly should also be agreeable to man.

Entirely new light upon the seasonal appearance of epigamic characters is
shed by the recent researches of C.W. Beebe ("The American Naturalist",
Vol. XLII. No. 493, Jan. 1908, page 34.), who caused the scarlet tanager
(Piranga erythromelas) and the bobolink (Dolichonyx oryzivorus) to retain
their breeding plumage through the whole year by means of fattening food,
dim illumination, and reduced activity.  Gradual restoration to the light
and the addition of meal-worms to the diet invariably brought back the
spring song, even in the middle of winter.  A sudden alteration of
temperature, either higher or lower, caused the birds nearly to stop
feeding, and one tanager lost weight rapidly and in two weeks moulted into
the olive-green winter plumage.  After a year, and at the beginning of the
normal breeding season, "individual tanagers and bobolinks were gradually
brought under normal conditions and activities," and in every case moulted
from nuptial plumage to nuptial plumage.  "The dull colours of the winter
season had been skipped."  The author justly claims to have established
"that the sequence of plumage in these birds is not in any way predestined
through inheritance..., but that it may be interrupted by certain factors
in the environmental complex."


XVI.  GEOGRAPHICAL DISTRIBUTION OF PLANTS.

By SIR WILLIAM THISELTON-DYER, K.C.M.G., C.I.E. Sc.D., F.R.S.

The publication of "The Origin of Species" placed the study of Botanical
Geography on an entirely new basis.  It is only necessary to study the
monumental "Geographie Botanique raisonnee" of Alphonse De Candolle,
published four years earlier (1855), to realise how profound and far-
reaching was the change.  After a masterly and exhaustive discussion of all
available data De Candolle in his final conclusions could only arrive at a
deadlock.  It is sufficient to quote a few sentences:--

"L'opinion de Lamarck est aujourd'hui abandonee par tous les naturalistes
qui ont etudie sagement les modifications possibles des etres organises...

"Et si l'on s'ecarte des exagerations de Lamarck, si l'on suppose un
premier type de chaque genre, de chaque famille tout au moins, on se trouve
encore a l'egard de l'origine de ces types en presence de la grande
question de la creation.

"Le seul parti a prendre est donc d'envisager les etres organises comme
existant depuis certaines epoques, avec leurs qualites particulieres." 
(Vol. II. page 1107.)

Reviewing the position fourteen years afterwards, Bentham remarked:--"These
views, generally received by the great majority of naturalists at the time
De Candolle wrote, and still maintained by a few, must, if adhered to,
check all further enquiry into any connection of facts with causes," and he
added, "there is little doubt but that if De Candolle were to revise his
work, he would follow the example of so many other eminent naturalists,
and...insist that the present geographical distribution of plants was in
most instances a derivative one, altered from a very different former
distribution."  ("Pres. Addr." (1869) "Proc. Linn. Soc." 1868-69, page
lxviii.)

Writing to Asa Gray in 1856, Darwin gave a brief preliminary account of his
ideas as to the origin of species, and said that geographical distribution
must be one of the tests of their validity.  ("Life and Letters", II. page
78.)  What is of supreme interest is that it was also their starting-point. 
He tells us:--"When I visited, during the voyage of H.M.S. "Beagle", the
Galapagos Archipelago,...I fancied myself brought near to the very act of
creation.  I often asked myself how these many peculiar animals and plants
had been produced:  the simplest answer seemed to be that the inhabitants
of the several islands had descended from each other, undergoing
modification in the course of their descent."  ("The Variation of Animals
and Plants" (2nd edition), 1890, I. pages 9, 10.)  We need not be surprised
then, that in writing in 1845 to Sir Joseph Hooker, he speaks of "that
grand subject, that almost keystone of the laws of creation, Geographical
Distribution."  ("Life and Letters", I. page 336.)

Yet De Candolle was, as Bentham saw, unconsciously feeling his way, like
Lyell, towards evolution, without being able to grasp it.  They both strove
to explain phenomena by means of agencies which they saw actually at work. 
If De Candolle gave up the ultimate problem as insoluble:--"La creation ou
premiere formation des etres organises echappe, par sa nature et par son
anciennete, a nos moyens d'observation" (Loc. cit. page 1106.), he steadily
endeavoured to minimise its scope.  At least half of his great work is
devoted to the researches by which he extricated himself from a belief in
species having had a multiple origin, the view which had been held by
successive naturalists from Gmelin to Agassiz.  To account for the obvious
fact that species constantly occupy dissevered areas, De Candolle made a
minute study of their means of transport.  This was found to dispose of the
vast majority of cases, and the remainder he accounted for by geographical
change.  (Loc. cit. page 1116.)

But Darwin strenuously objected to invoking geographical change as a
solution of every difficulty.  He had apparently long satisfied himself as
to the "permanence of continents and great oceans."  Dana, he tells us
"was, I believe, the first man who maintained" this ("Life and Letters",
III. page 247.  Dana says:--"The continents and oceans had their general
outline or form defined in earliest time," "Manual of Geology", revised
edition.  Philadelphia, 1869, page 732.  I have no access to an earlier
edition.), but he had himself probably arrived at it independently.  Modern
physical research tends to confirm it.  The earth's centre of gravity, as
pointed out by Pratt from the existence of the Pacific Ocean, does not
coincide with its centre of figure, and it has been conjectured that the
Pacific Ocean dates its origin from the separation of the moon from the
earth.

The conjecture appears to be unnecessary.  Love shows that "the force that
keeps the Pacific Ocean on one side of the earth is gravity, directed more
towards the centre of gravity than the centre of the figure."  ("Report of
the 77th Meeting of the British Association" (Leicester, 1907), London,
1908, page 431.)  I can only summarise the conclusions of a technical but
masterly discussion.  "The broad general features of the distribution of
continent and ocean can be regarded as the consequences of simple causes of
a dynamical character," and finally, "As regards the contour of the great
ocean basins, we seem to be justified in saying that the earth is
approximately an oblate spheroid, but more nearly an ellipsoid with three
unequal axes, having its surface furrowed according to the formula for a
certain spherical harmonic of the third degree" (Ibid. page 436.), and he
shows that this furrowed surface must be produced "if the density is
greater in one hemispheroid than in the other, so that the position of the
centre of gravity is eccentric."  (Ibid. page 431.)  Such a modelling of
the earth's surface can only be referred to a primitive period of
plasticity.  If the furrows account for the great ocean basins, the
disposition of the continents seems equally to follow.  Sir George Darwin
has pointed out that they necessarily "arise from a supposed primitive
viscosity or plasticity of the earth's mass.  For during this course of
evolution the earth's mass must have suffered a screwing motion, so that
the polar regions have travelled a little from west to east relatively to
the equator.  This affords a possible explanation of the north and south
trend of our great continents."  ("Encycl. Brit." (9th edition), Vol.
XXIII. "Tides", page 379.)

It would be trespassing on the province of the geologist to pursue the
subject at any length.  But as Wallace ("Island Life" (2nd edition), 1895,
page 103.), who has admirably vindicated Darwin's position, points out, the
"question of the permanence of our continents...lies at the root of all our
inquiries into the great changes of the earth and its inhabitants."  But he
proceeds:  "The very same evidence which has been adduced to prove the
GENERAL stability and permanence of our continental areas also goes to
prove that they have been subjected to wonderful and repeated changes in
DETAIL."  (Loc. cit. page 101.)  Darwin of course would have admitted this,
for with a happy expression he insisted to Lyell (1856) that "the
skeletons, at least, of our continents are ancient."  ("More Letters", II.
page 135.)  It is impossible not to admire the courage and tenacity with
which he carried on the conflict single-handed.  But he failed to convince
Lyell.  For we still find him maintaining in the last edition of the
"Principles":  "Continents therefore, although permanent for whole
geological epochs, shift their positions entirely in the course of ages." 
(Lyell's "Principles of Geology" (11th edition), London, 1872, I. page
258.)

Evidence, however, steadily accumulates in Darwin's support.  His position
still remains inexpugnable that it is not permissible to invoke
geographical change to explain difficulties in distribution without valid
geological and physical support.  Writing to Mellard Reade, who in 1878 had
said, "While believing that the ocean-depths are of enormous age, it is
impossible to reject other evidences that they have once been land," he
pointed out "the statement from the 'Challenger' that all sediment is
deposited within one or two hundred miles from the shores."  ("More
Letters", II. page 146.)  The following year Sir Archibald Geikie
("Geographical Evolution", "Proc. R. Geogr. Soc." 1879, page 427.) informed
the Royal Geographical Society that "No part of the results obtained by the
'Challenger' expedition has a profounder interest for geologists and
geographers than the proof which they furnish that the floor of the ocean
basins has no real analogy among the sedimentary formations which form most
of the framework of the land."

Nor has Darwin's earlier argument ever been upset.  "The fact which I
pointed out many years ago, that all oceanic islands are volcanic (except
St Paul's, and now that is viewed by some as the nucleus of an ancient
volcano), seem to me a strong argument that no continent ever occupied the
great oceans."  ("More Letters", II. page 146.)

Dr Guppy, who devoted several years to geological and botanical
investigations in the Pacific, found himself forced to similar conclusions.
"It may be at once observed," he says, "that my belief in the general
principle that islands have always been islands has not been shaken," and
he entirely rejects "the hypothesis of a Pacific continent."  He comes
back, in full view of the problems on the spot, to the position from which,
as has been seen, Darwin started:  "If the distribution of a particular
group of plants or animals does not seem to accord with the present
arrangement of the land, it is by far the safest plan, even after
exhausting all likely modes of explanation, not to invoke the intervention
of geographical changes; and I scarcely think that our knowledge of any one
group of organisms is ever sufficiently precise to justify a recourse to
hypothetical alterations in the present relations of land and sea." 
("Observations of a Naturalist in the Pacific between 1896 and 1899",
London, 1903, I. page 380.)  Wallace clinches the matter when he finds
"almost the whole of the vast areas of the Atlantic, Pacific, Indian, and
Southern Oceans, without a solitary relic of the great islands or
continents supposed to have sunk beneath their waves."  ("Island Life",
page 105.)

Writing to Wallace (1876), Darwin warmly approves the former's "protest
against sinking imaginary continents in a quite reckless manner, as was
stated by Forbes, followed, alas, by Hooker, and caricatured by Wollaston
and (Andrew) Murray."  ("Life and Letters", III. page 230.)  The transport
question thus became of enormously enhanced importance.  We need not be
surprised then at his writing to Lyell in 1856:--"I cannot avoid thinking
that Forbes's 'Atlantis' was an ill-service to science, as checking a close
study of means of dissemination" (Ibid. II. page 78.), and Darwin spared no
pains to extend our knowledge of them.  He implores Hooker, ten years
later, to "admit how little is known on the subject," and summarises with
some satisfaction what he had himself achieved:--"Remember how recently you
and others thought that salt water would soon kill seeds...Remember that no
one knew that seeds would remain for many hours in the crops of birds and
retain their vitality; that fish eat seeds, and that when the fish are
devoured by birds the seeds can germinate, etc.  Remember that every year
many birds are blown to Madeira and to the Bermudas.  Remember that dust is
blown 1000 miles across the Atlantic."  ("More Letters", I. page 483.)

It has always been the fashion to minimise Darwin's conclusions, and these
have not escaped objection.  The advocatus diaboli has a useful function in
science.  But in attacking Darwin his brief is generally found to be
founded on a slender basis of facts.  Thus Winge and Knud Andersen have
examined many thousands of migratory birds and found "that their crops and
stomachs were always empty.  They never observed any seeds adhering to the
feathers, beaks or feet of the birds."  (R.F. Scharff, "European Animals",
page 64, London, 1907.)  The most considerable investigation of the problem
of Plant Dispersal since Darwin is that of Guppy.  He gives a striking
illustration of how easily an observer may be led into error by relying on
negative evidence.

"When Ekstam published, in 1895, the results of his observations on the
plants of Nova Zembla, he observed that he possessed no data to show
whether swimming and wading birds fed on berries; and he attached all
importance to dispersal by winds.  On subsequently visiting Spitzbergen he
must have been at first inclined, therefore, to the opinion of Nathorst,
who, having found only a solitary species of bird (a snow-sparrow) in that
region, naturally concluded that birds had been of no importance as agents
in the plant-stocking.  However, Ekstam's opportunities were greater, and
he tells us that in the craws of six specimens of Lagopus hyperboreus shot
in Spitzbergen in August he found represented almost 25 per cent. of the
usual phanerogamic flora of that region in the form of fruits, seeds,
bulbils, flower-buds, leaf-buds, etc..."

"The result of Ekstam's observations in Spitzbergen was to lead him to
attach a very considerable importance in plant dispersal to the agency of
birds; and when in explanation of the Scandinavian elements in the
Spitzbergen flora he had to choose between a former land connection and the
agency of birds, he preferred the bird."  (Guppy, op. cit. II. pages 511,
512.)

Darwin objected to "continental extensions" on geological grounds, but he
also objected to Lyell that they do not "account for all the phenomena of
distribution on islands" ("Life and Letters", II. page 77.), such for
example as the absence of Acacias and Banksias in New Zealand.  He agreed
with De Candolle that "it is poor work putting together the merely POSSIBLE
means of distribution."  But he also agreed with him that they were the
only practicable door of escape from multiple origins.  If they would not
work then "every one who believes in single centres will have to admit
continental extensions" (Ibid. II. page 82.), and that he regarded as a
mere counsel of despair:--"to make continents, as easily as a cook does
pancakes."  (Ibid. II. page 74.)

The question of multiple origins however presented itself in another shape
where the solution was much more difficult.  The problem, as stated by
Darwin, is this:--"The identity of many plants and animals, on mountain-
summits, separated from each other by hundreds of miles of
lowlands...without the apparent possibility of their having migrated from
one point to the other."  He continues, "even as long ago as 1747, such
facts led Gmelin to conclude that the same species must have been
independently created at several distinct points; and we might have
remained in this same belief, had not Agassiz and others called vivid
attention to the Glacial period, which affords...a simple explanation of
the facts."  ("Origin of Species" (6th edition) page 330.)

The "simple explanation" was substantially given by E. Forbes in 1846.  It
is scarcely too much to say that it belongs to the same class of fertile
and far-reaching ideas as "natural selection" itself.  It is an
extraordinary instance, if one were wanted at all, of Darwin's magnanimity
and intense modesty that though he had arrived at the theory himself, he
acquiesced in Forbes receiving the well-merited credit.  "I have never," he
says, "of course alluded in print to my having independently worked out
this view."  But he would have been more than human if he had not added:--
"I was forestalled in...one important point, which my vanity has always
made me regret."  ("Life and Letters", I. page 88.)

Darwin, however, by applying the theory to trans-tropical migration, went
far beyond Forbes.  The first enunciation to this is apparently contained
in a letter to Asa Gray in 1858.  The whole is too long to quote, but the
pith is contained in one paragraph.  "There is a considerable body of
geological evidence that during the Glacial epoch the whole world was
colder; I inferred that,...from erratic boulder phenomena carefully
observed by me on both the east and west coast of South America.  Now I am
so bold as to believe that at the height of the Glacial epoch, AND WHEN ALL
TROPICAL PRODUCTIONS MUST HAVE BEEN CONSIDERABLY DISTRESSED, several
temperate forms slowly travelled into the heart of the Tropics, and even
reached the southern hemisphere; and some few southern forms penetrated in
a reverse direction northward."  ("Life and Letters", II. page 136.)  Here
again it is clear that though he credits Agassiz with having called vivid
attention to the Glacial period, he had himself much earlier grasped the
idea of periods of refrigeration.

Putting aside the fact, which has only been made known to us since Darwin's
death, that he had anticipated Forbes, it is clear that he gave the theory
a generality of which the latter had no conception.  This is pointed out by
Hooker in his classical paper "On the Distribution of Arctic Plants"
(1860).  "The theory of a southern migration of northern types being due to
the cold epochs preceding and during the glacial, originated, I believe,
with the late Edward Forbes; the extended one, of the trans-tropical
migration, is Mr Darwin's."  ("Linn. Trans." XXIII. page 253.  The attempt
appears to have been made to claim for Heer priority in what I may term for
short the arctic-alpine theory (Scharff, "European Animals", page 128).  I
find no suggestion of his having hit upon it in his correspondence with
Darwin or Hooker.  Nor am I aware of any reference to his having done so in
his later publications.  I am indebted to his biographer, Professor
Schroter, of Zurich, for an examination of his earlier papers with an
equally negative result.)  Assuming that local races have derived from a
common ancestor, Hooker's great paper placed the fact of the migration on
an impregnable basis.  And, as he pointed out, Darwin has shown that "such
an explanation meets the difficulty of accounting for the restriction of so
many American and Asiatic arctic types to their own peculiar longitudinal
zones, and for what is a far greater difficulty, the representation of the
same arctic genera by most closely allied species in different longitudes."

The facts of botanical geography were vital to Darwin's argument.  He had
to show that they admitted of explanation without assuming multiple origins
for species, which would be fatal to the theory of Descent.  He had
therefore to strengthen and extend De Candolle's work as to means of
transport.  He refused to supplement them by hypothetical geographical
changes for which there was no independent evidence:  this was simply to
attempt to explain ignotum per ignotius.  He found a real and, as it has
turned out, a far-reaching solution in climatic change due to cosmical
causes which compelled the migration of species as a condition of their
existence.  The logical force of the argument consists in dispensing with
any violent assumption, and in showing that the principle of descent is
adequate to explain the ascertained facts.

It does not, I think, detract from the merit of Darwin's conclusions that
the tendency of modern research has been to show that the effects of the
Glacial period were less simple, more localised and less general than he
perhaps supposed.  He admitted that "equatorial refrigeration...must have
been small."  ("More Letters", I. page 177.)  It may prove possible to
dispense with it altogether.  One cannot but regret that as he wrote to
Bates:--"the sketch in the 'Origin' gives a very meagre account of my
fuller MS. essay on this subject."  (Loc. cit.)  Wallace fully accepted
"the effect of the Glacial epoch in bringing about the present distribution
of Alpine and Arctic plants in the NORTHERN HEMISPHERE," but rejected "the
lowering of the temperature of the tropical regions during the Glacial
period" in order to account for their presence in the SOUTHERN hemisphere. 
("More Letters", II. page 25 (footnote 1).)  The divergence however does
not lie very deep.  Wallace attaches more importance to ordinary means of
transport.  "If plants can pass in considerable numbers and variety over
wide seas and oceans, it must be yet more easy for them to traverse
continuous areas of land, wherever mountain-chains offer suitable
stations."  ("Island Life" (2nd edition), London, 1895, page 512.)  And he
argues that such periodical changes of climate, of which the Glacial period
may be taken as a type, would facilitate if not stimulate the process. 
(Loc. cit. page 518.)

It is interesting to remark that Darwin drew from the facts of plant
distribution one of his most ingenious arguments in support of this theory. 
(See "More Letters", I. page 424.)  He tells us, "I was led to anticipate
that the species of the larger genera in each country would oftener present
varieties, than the species of the smaller genera."  ("Origin", page 44.) 
He argues "where, if we may use the expression, the manufactory of species
has been active, we ought generally to find the manufactory still in
action."  (Ibid. page 45.)  This proved to be the case.  But the labour
imposed upon him in the study was immense.  He tabulated local floras
"belting the whole northern hemisphere" ("More Letters", I. page 107.),
besides voluminous works such as De Candolle's "Prodromus".  The results
scarcely fill a couple of pages.  This is a good illustration of the
enormous pains which he took to base any statement on a secure foundation
of evidence, and for this the world, till the publication of his letters,
could not do him justice.  He was a great admirer of Herbert Spencer, whose
"prodigality of original thought" astonished him.  "But," he says, "the
reflection constantly recurred to me that each suggestion, to be of real
value to service, would require years of work."  (Ibid. II. page 235.)

At last the ground was cleared and we are led to the final conclusion.  "If
the difficulties be not insuperable in admitting that in the long course of
time all the individuals of the same species belonging to the same genus,
have proceeded from some one source; then all the grand leading facts of
geographical distribution are explicable on the theory of migration,
together with subsequent modification and the multiplication of new forms."
("Origin", page 360.)  In this single sentence Darwin has stated a theory
which, as his son F. Darwin has said with justice, has "revolutionized
botanical geography."  ("The Botanical Work of Darwin", "Ann. Bot." 1899, 
page xi.)  It explains how physical barriers separate and form botanical
regions; how allied species become concentrated in the same areas; how,
under similar physical conditions, plants may be essentially dissimilar,
showing that descent and not the surroundings is the controlling factor;
how insular floras have acquired their peculiarities; in short how the most
various and apparently uncorrelated problems fall easily and inevitably
into line.

The argument from plant distribution was in fact irresistible.  A proof, if
one were wanted, was the immediate conversion of what Hooker called "the
stern keen intellect" ("More Letters", I. page 134.) of Bentham, by general
consent the leading botanical systematist at the time.  It is a striking
historical fact that a paper of his own had been set down for reading at
the Linnean Society on the same day as Darwin's, but had to give way.  In
this he advocated the fixity of species.  He withdrew it after hearing
Darwin's.  We can hardly realise now the momentous effect on the scientific
thought of the day of the announcement of the new theory.  Years afterwards
(1882) Bentham, notwithstanding his habitual restraint, could not write of
it without emotion.  "I was forced, however reluctantly, to give up my
long-cherished convictions, the results of much labour and study."  The
revelation came without preparation.  Darwin, he wrote, "never made any
communications to me in relation to his views and labours."  But, he adds,
I...fully adopted his theories and conclusions, notwithstanding the severe
pain and disappointment they at first occasioned me."  ("Life and Letters",
II. page 294.)  Scientific history can have few incidents more worthy.  I
do not know what is most striking in the story, the pathos or the moral
dignity of Bentham's attitude.

Darwin necessarily restricted himself in the "Origin" to establishing the
general principles which would account for the facts of distribution, as a
part of his larger argument, without attempting to illustrate them in
particular cases.  This he appears to have contemplated doing in a separate
work.  But writing to Hooker in 1868 he said:--"I shall to the day of my
death keep up my full interest in Geographical Distribution, but I doubt
whether I shall ever have strength to come in any fuller detail than in the
"Origin" to this grand subject."  ("More Letters", II. page 7.)  This must
be always a matter for regret.  But we may gather some indication of his
later speculations from the letters, the careful publication of which by F.
Darwin has rendered a service to science, the value of which it is
difficult to exaggerate.  They admit us to the workshop, where we see a
great theory, as it were, in the making.  The later ideas that they contain
were not it is true public property at the time.  But they were
communicated to the leading biologists of the day and indirectly have had a
large influence.

If Darwin laid the foundation, the present fabric of Botanical Geography
must be credited to Hooker.  It was a happy partnership.  The far-seeing,
generalising power of the one was supplied with data and checked in
conclusions by the vast detailed knowledge of the other.  It may be
permitted to quote Darwin's generous acknowledgment when writing the
"Origin":--"I never did pick any one's pocket, but whilst writing my
present chapter I keep on feeling (even when differing most from you) just
as if I were stealing from you, so much do I owe to your writings and
conversation, so much more than mere acknowledgements show."  ("Life and
Letters", II. page 148 (footnote).)  Fourteen years before he had written
to Hooker:  "I know I shall live to see you the first authority in Europe
on...Geographical Distribution."  (Ibid. I. page 336.)  We owe it to Hooker
that no one now undertakes the flora of a country without indicating the
range of the species it contains.  Bentham tells us:  "After De Candolle,
independently of the great works of Darwin...the first important addition
to the science of geographical botany was that made by Hooker in his
"Introductory Essay to the Flora of Tasmania", which, though
contemporaneous only with the "Origin of Species", was drawn up with a
general knowledge of his friend's observations and views."  (Pres. Addr.
(1869), "Proc. Linn. Soc." 1868-69, page lxxiv.)  It cannot be doubted that
this and the great memoir on the "Distribution of Arctic Plants" were only
less epoch-making than the "Origin" itself, and must have supplied a
powerful support to the general theory of organic evolution.

Darwin always asserted his "entire ignorance of Botany."  ("More Letters",
I. page 400.)  But this was only part of his constant half-humorous self-
depreciation.  He had been a pupil of Henslow, and it is evident that he
had a good working knowledge of systematic botany.  He could find his way
about in the literature and always cites the names of plants with
scrupulous accuracy.  It was because he felt the want of such a work for
his own researches that he urged the preparation of the "Index Kewensis",
and undertook to defray the expense.  It has been thought singular that he
should have been elected a "correspondant" of the Academie des Sciences in
the section of Botany, but it is not surprising that his work in
Geographical Botany made the botanists anxious to claim him.  His heart
went with them.  "It has always pleased me," he tells us, "to exalt plants
in the scale of organised beings."  ("Life and Letters", I. page 98.)  And
he declares that he finds "any proposition more easily tested in botanical
works (Ibid. II. page 99.) than in zoological."

In the "Introductory Essay" Hooker dwelt on the "continuous current of
vegetation from Scandinavia to Tasmania" ("Introductory Essay to the Flora
of Tasmania", London, 1859.  Reprinted from the "Botany of the Antarctic
Expedition", Part III., "Flora of Tasmania", Vol I. page ciii.), but finds
little evidence of one in the reverse direction.  "In the New World,
Arctic, Scandinavian, and North American genera and species are
continuously extended from the north to the south temperate and even
Antarctic zones; but scarcely one Antarctic species, or even genus advances
north beyond the Gulf of Mexico" (page civ.).  Hooker considered that this
negatived "the idea that the Southern and Northern Floras have had common
origin within comparatively modern geological epochs."  (Loc. cit.)  This
is no doubt a correct conclusion.  But it is difficult to explain on
Darwin's view alone, of alternating cold in the two hemispheres, the
preponderant migration from the north to the south.  He suggests,
therefore, that it "is due to the greater extent of land in the north and
to the northern forms...having...been advanced through natural selection
and competition to a higher stage of perfection or dominating power." 
("Origin of Species" (6th edition), page 340; cf. also "Life and Letters",
II. page 142.)  The present state of the Flora of New Zealand affords a
striking illustration of the correctness of this view.  It is poor in
species, numbering only some 1400, of which three-fourths are endemic. 
They seem however quite unable to resist the invasion of new comers and
already 600 species of foreign origin have succeeded in establishing
themselves.

If we accept the general configuration of the earth's surface as permanent
a continuous and progressive dispersal of species from the centre to the
circumference, i.e. southwards, seems inevitable.  If an observer were
placed above a point in St George's Channel from which one half of the
globe was visible he would see the greatest possible quantity of land
spread out in a sort of stellate figure.  The maritime supremacy of the
English race has perhaps flowed from the central position of its home. 
That such a disposition would facilitate a centrifugal migration of land
organisms is at any rate obvious, and fluctuating conditions of climate
operating from the pole would supply an effective means of propulsion.  As
these became more rigorous animals at any rate would move southwards to
escape them.  It would be equally the case with plants if no insuperable
obstacle interposed.  This implies a mobility in plants, notwithstanding
what we know of means of transport which is at first sight paradoxical. 
Bentham has stated this in a striking way:  "Fixed and immovable as is the
individual plant, there is no class in which the race is endowed with
greater facilities for the widest dispersion...Plants cast away their
offspring in a dormant state, ready to be carried to any distance by those
external agencies which we may deem fortuitous, but without which many a
race might perish from the exhaustion of the limited spot of soil in which
it is rooted."  (Pres. Addr.(1869), "Proc. Linn. Soc." 1868-69, pages lxvi,
lxvii.)

I have quoted this passage from Bentham because it emphasises a point which
Darwin for his purpose did not find it necessary to dwell upon, though he
no doubt assumed it.  Dispersal to a distance is, so to speak, an
accidental incident in the life of a species.  Lepidium Draba, a native of
South-eastern Europe, owes its prevalence in the Isle of Thanet to the
disastrous Walcheren expedition; the straw-stuffing of the mattresses of
the fever-stricken soldiers who were landed there was used by a farmer for
manure.  Sir Joseph Hooker ("Royal Institution Lecture", April 12, 1878.)
tells us that landing on Lord Auckland's Island, which was uninhabited,
"the first evidence I met with of its having been previously visited by man
was the English chickweed; and this I traced to a mound that marked the
grave of a British sailor, and that was covered with the plant, doubtless
the offspring of seed that had adhered to the spade or mattock with which
the grave had been dug."

Some migration from the spot where the individuals of a species have
germinated is an essential provision against extinction.  Their descendants
otherwise would be liable to suppression by more vigorous competitors.  But
they would eventually be extinguished inevitably, as pointed out by
Bentham, by the exhaustion of at any rate some one necessary constituent of
the soil.  Gilbert showed by actual analysis that the production of a
"fairy ring" is simply due to the using up by the fungi of the available
nitrogen in the enclosed area which continually enlarges as they seek a
fresh supply on the outside margin.  Anyone who cultivates a garden can
easily verify the fact that every plant has some adaptation for varying
degrees of seed-dispersal.  It cannot be doubted that slow but persistent
terrestrial migration has played an enormous part in bringing about
existing plant-distribution, or that climatic changes would intensify the
effect because they would force the abandonment of a former area and the
occupation of a new one.  We are compelled to admit that as an incident of
the Glacial period a whole flora may have moved down and up a mountain
side, while only some of its constituent species would be able to take
advantage of means of long-distance transport.

I have dwelt on the importance of what I may call short-distance dispersal
as a necessary condition of plant life, because I think it suggests the
solution of a difficulty which leads Guppy to a conclusion with which I am
unable to agree.  But the work which he has done taken as a whole appears
to me so admirable that I do so with the utmost respect.  He points out, as
Bentham had already done, that long-distance dispersal is fortuitous.  And
being so it cannot have been provided for by previous adaptation.  He says
(Guppy, op. cit. II. page 99.):  "It is not conceivable that an organism
can be adapted to conditions outside its environment."  To this we must
agree; but, it may be asked, do the general means of plant dispersal
violate so obvious a principle?  He proceeds:  "The great variety of the
modes of dispersal of seeds is in itself an indication that the dispersing
agencies avail themselves in a hap-hazard fashion of characters and
capacities that have been developed in other connections."  (Loc. cit. page
102.)  "Their utility in these respects is an accident in the plant's
life."  (Loc. cit. page 100.)  He attributes this utility to a "determining
agency," an influence which constantly reappears in various shapes in the
literature of Evolution and is ultra-scientific in the sense that it bars
the way to the search for material causes.  He goes so far as to doubt
whether fleshy fruits are an adaptation for the dispersal of their
contained seeds.  (Loc. cit. page 102.)  Writing as I am from a hillside
which is covered by hawthorn bushes sown by birds, I confess I can feel
little doubt on the subject myself.  The essential fact which Guppy brings
out is that long-distance unlike short-distance dispersal is not universal
and purposeful, but selective and in that sense accidental.  But it is not
difficult to see how under favouring conditions one must merge into the
other.

Guppy has raised one novel point which can only be briefly referred to but
which is of extreme interest.  There are grounds for thinking that flowers
and insects have mutually reacted upon one another in their evolution. 
Guppy suggests that something of the same kind may be true of birds.  I
must content myself with the quotation of a single sentence.  "With the
secular drying of the globe and the consequent differentiation of climate
is to be connected the suspension to a great extent of the agency of birds
as plant dispersers in later ages, not only in the Pacific Islands but all
over the tropics.  The changes of climate, birds and plants have gone on
together, the range of the bird being controlled by the climate, and the
distribution of the plant being largely dependent on the bird."  (Loc.cit.
II. page 221.)

Darwin was clearly prepared to go further than Hooker in accounting for the
southern flora by dispersion from the north.  Thus he says:  "We must, I
suppose, admit that every yard of land has been successively covered with a
beech-forest between the Caucasus and Japan."  ("More Letters", II. page
9.)  Hooker accounted for the dissevered condition of the southern flora by
geographical change, but this Darwin could not admit.  He suggested to
Hooker that the Australian and Cape floras might have had a point of
connection through Abyssinia (Ibid. I. page 447.), an idea which was
promptly snuffed out.  Similarly he remarked to Bentham (1869):  "I suppose
you think that the Restiaceae, Proteaceae, etc., etc. once extended over
the whole world, leaving fragments in the south."  (Ibid. I. page 380.) 
Eventually he conjectured "that there must have been a Tertiary Antarctic
continent, from which various forms radiated to the southern extremities of
our present continents."  ("Life and Letters", III. page 231.)  But
characteristically he could not admit any land connections and trusted to
"floating ice for transporting seed."  ("More Letters", I. page 116.)  I am
far from saying that this theory is not deserving of serious attention,
though there seems to be no positive evidence to support it, and it
immediately raises the difficulty how did such a continent come to be
stocked?

We must, however, agree with Hooker that the common origin of the northern
and southern floras must be referred to a remote past.  That Darwin had
this in his mind at the time of the publication of the "Origin" is clear
from a letter to Hooker.  "The view which I should have looked at as
perhaps most probable (though it hardly differs from yours) is that the
whole world during the Secondary ages was inhabited by marsupials,
araucarias (Mem.--Fossil wood of this nature in South America), Banksia,
etc.; and that these were supplanted and exterminated in the greater area
of the north, but were left alive in the south."  (Ibid. I. page 453.) 
Remembering that Araucaria, unlike Banksia, belongs to the earlier Jurassic
not to the angiospermous flora, this view is a germinal idea of the widest
generality.

The extraordinary congestion in species of the peninsulas of the Old World
points to the long-continued action of a migration southwards.  Each is in
fact a cul-de-sac into which they have poured and from which there is no
escape.  On the other hand the high degree of specialisation in the
southern floras and the little power the species possess of holding their
own in competition or in adaptation to new conditions point to long-
continued isolation.  "An island...will prevent free immigration and
competition, hence a greater number of ancient forms will survive."  (Ibid.
I. page 481.)  But variability is itself subject to variation.  The nemesis
of a high degree of protected specialisation is the loss of adaptability. 
(See Lyell, "The Geological Evidences of the Antiquity of Man", London,
1863, page 446.)  It is probable that many elements of the southern flora
are doomed:  there is, for example, reason to think that the singular
Stapelieae of S. Africa are a disappearing group.  The tree Lobelias which
linger in the mountains of Central Africa, in Tropical America and in the
Sandwich Islands have the aspect of extreme antiquity.  I may add a further
striking illustration from Professor Seward:  "The tall, graceful fronds of
Matonia pectinata, forming miniature forests on the slopes of Mount Ophir
and other districts in the Malay Peninsula in association with Dipteris
conjugata and Dipteris lobbiana, represent a phase of Mesozoic life which
survives 

'Like a dim picture of the drowned past.'" ("Report of the 73rd Meeting of
the British Assoc."  (Southport, 1903), London, 1904, page 844.)

The Matonineae are ferns with an unusually complex vascular system and were
abundant "in the northern hemisphere during the earlier part of the
Mesozoic era."

It was fortunate for science that Wallace took up the task which his
colleague had abandoned.  Writing to him on the publication of his
"Geographical Distribution of Animals" Darwin said:  "I feel sure that you
have laid a broad and safe foundation for all future work on Distribution.
How interesting it will be to see hereafter plants treated in strict
relation to your views."  ("More Letters", II. page 12.)  This hope was
fulfilled in "Island Life".  I may quote a passage from it which admirably
summarises the contrast between the northern and the southern floras.

"Instead of the enormous northern area, in which highly organised and
dominant groups of plants have been developed gifted with great colonising
and aggressive powers, we have in the south three comparatively small and
detached areas, in which rich floras have been developed with SPECIAL
adaptations to soil, climate, and organic environment, but comparatively
impotent and inferior beyond their own domain."  (Wallace, "Island Life",
pages 527, 528.)

It will be noticed that in the summary I have attempted to give of the
history of the subject, efforts have been concentrated on bringing into
relation the temperate floras of the northern and southern hemispheres, but
no account has been taken of the rich tropical vegetation which belts the
world and little to account for the original starting-point of existing
vegetation generally.  It must be remembered on the one hand that our
detailed knowledge of the floras of the tropics is still very incomplete
and far inferior to that of temperate regions; on the other hand
palaeontological discoveries have put the problem in an entirely new light. 
Well might Darwin, writing to Heer in 1875, say:  "Many as have been the
wonderful discoveries in Geology during the last half-century, I think none
have exceeded in interest your results with respect to the plants which
formerly existed in the arctic regions."  ("More Letters", II. page 240.)

As early as 1848 Debey had described from the Upper Cretaceous rocks of
Aix-la-Chapelle Flowering plants of as high a degree of development as
those now existing.  The fact was commented upon by Hooker ("Introd. Essay
to the Flora of Tasmania", page xx.), but its full significance seems to
have been scarcely appreciated.  For it implied not merely that their
evolution must have taken place but the foundations of existing
distribution must have been laid in a preceding age.  We now know from the
discoveries of the last fifty years that the remains of the Neocomian flora
occur over an area extending through 30 deg of latitude.  The conclusion is
irresistible that within this was its centre of distribution and probably
of origin.

Darwin was immensely impressed with the outburst on the world of a fully
fledged angiospermous vegetation.  He warmly approved the brilliant theory
of Saporta that this happened "as soon (as) flower-frequenting insects were
developed and favoured intercrossing."  ("More Letters", II. page 21.) 
Writing to him in 1877 he says:  "Your idea that dicotyledonous plants were
not developed in force until sucking insects had been evolved seems to me a
splendid one.  I am surprised that the idea never occurred to me, but this
is always the case when one first hears a new and simple explanation of
some mysterious phenomenon."  ("Life and Letters", III. page 285. 
Substantially the same idea had occurred earlier to F.W.A. Miquel. 
Remarking that "sucking insects (Haustellata)...perform in nature the
important duty of maintaining the existence of the vegetable kingdom, at
least as far as the higher orders are concerned," he points our that "the
appearance in great numbers of haustellate insects occurs at and after the
Cretaceous epoch, when the plants with pollen and closed carpels
(Angiosperms) are found, and acquire little by little the preponderance in
the vegetable kingdom."  "Archives Neerlandaises", III. (1868).  English
translation in "Journ. of Bot." 1869, page 101.)

Even with this help the abruptness still remains an almost insoluble
problem, though a forecast of floral structure is now recognised in some
Jurassic and Lower Cretaceous plants.  But the gap between this and the
structural complexity and diversity of angiosperms is enormous.  Darwin
thought that the evolution might have been accomplished during a period of
prolonged isolation.  Writing to Hooker (1881) he says:  "Nothing is more
extraordinary in the history of the Vegetable Kingdom, as it seems to me,
than the APPARENTLY very sudden or abrupt development of the higher plants.
I have sometimes speculated whether there did not exist somewhere during
long ages an extremely isolated continent, perhaps near the South Pole." 
("Life and Letters", III. page 248.)

The present trend of evidence is, however, all in favour of a northern
origin for flowering plants, and we can only appeal to the imperfection of
the geological record as a last resource to extricate us from the
difficulty of tracing the process.  But Darwin's instinct that at some time
or other the southern hemisphere had played an important part in the
evolution of the vegetable kingdom did not mislead him.  Nothing probably
would have given him greater satisfaction than the masterly summary in
which Seward has brought together the evidence for the origin of the
Glossopteris flora in Gondwana land.

"A vast continental area, of which remnants are preserved in Australia,
South Africa and South America...A tract of enormous extent occupying an
area, part of which has since given place to a southern ocean, while
detached masses persist as portions of more modern continents, which have
enabled us to read in their fossil plants and ice-scratched boulders the
records of a lost continent, in which the Mesozoic vegetation of the
northern continent had its birth."  ("Encycl. Brit." (10th edition 1902),
Vol. XXXI. ("Palaeobotany; Mesozoic"), page 422.)  Darwin would probably
have demurred on physical grounds to the extent of the continent, and
preferred to account for the transoceanic distribution of its flora by the
same means which must have accomplished it on land.

It must in fairness be added that Guppy's later views give some support to
the conjectural existence of the "lost continent."  "The distribution of
the genus Dammara" (Agathis) led him to modify his earlier conclusions.  He
tells us:--"In my volume on the geology of Vanua Levu it was shown that the
Tertiary period was an age of submergence in the Western Pacific, and a
disbelief in any previous continental condition was expressed.  My later
view is more in accordance with that of Wichmann, who, on geological
grounds, contended that the islands of the Western Pacific were in a
continental condition during the Palaeozoic and Mesozoic periods, and that
their submergence and subsequent emergence took place in Tertiary times." 
(Guppy, op. cit. II. page 304.)

The weight of the geological evidence I am unable to scrutinise.  But
though I must admit the possibility of some unconscious bias in my own mind
on the subject, I am impressed with the fact that the known distribution of
the Glossopteris flora in the southern hemisphere is precisely paralleled
by that of Proteaceae and Restiaceae in it at the present time.  It is not
unreasonable to suppose that both phenomena, so similar, may admit of the
same explanation.  I confess it would not surprise me if fresh discoveries
in the distribution of the Glossopteris flora were to point to the
possibility of its also having migrated southwards from a centre of origin
in the northern hemisphere.

Darwin, however, remained sceptical "about the travelling of plants from
the north EXCEPT DURING THE TERTIARY PERIOD."  But he added, "such
speculations seem to me hardly scientific, seeing how little we know of the
old floras."  ("Life and Letters", III. page 247.)  That in later
geological times the south has been the grave of the weakened offspring of
the aggressive north can hardly be doubted.  But if we look to the
Glossopteris flora for the ancestry of Angiosperms during the Secondary
period, Darwin's prevision might be justified, though he has given us no
clue as to how he arrived at it.

It may be true that technically Darwin was not a botanist.  But in two
pages of the "Origin" he has given us a masterly explanation of "the
relationship, with very little identity, between the productions of North
America and Europe."  (Pages 333, 334.)  He showed that this could be
accounted for by their migration southwards from a common area, and he told
Wallace that he "doubted much whether the now called Palaearctic and
Neartic regions ought to be separated."  ("Life and Letters", III. page
230.)  Catkin-bearing deciduous trees had long been seen to justify
Darwin's doubt:  oaks, chestnuts, beeches, hazels, hornbeams, birches,
alders, willows and poplars are common both to the Old and New World. 
Newton found that the separate regions could not be sustained for birds,
and he is now usually followed in uniting them as the Holartic.  One feels
inclined to say in reading the two pages, as Lord Kelvin did to a
correspondent who asked for some further development of one of his papers,
It is all there.  We have only to apply the principle to previous
geological ages to understand why the flora of the Southern United States
preserves a Cretaceous facies.  Applying it still further we can understand
why, when the northern hemisphere gradually cooled through the Tertiary
period, the plants of the Eocene "suggest a comparison of the climate and
forests with those of the Malay Archipelago and Tropical America." 
(Clement Reid, "Encycl. Brit." (10th edition), Vol. XXXI.  ("Palaeobotany;
Tertiary"), page 435.)  Writing to Asa Gray in 1856 with respect to the
United States flora, Darwin said that "nothing has surprised me more than
the greater generic and specific affinity with East Asia than with West
America."  ("More Letters", I. page 434.)  The recent discoveries of a
Tulip tree and a Sassafras in China afford fresh illustrations.  A few
years later Asa Gray found the explanation in both areas being centres of
preservation of the Cretaceous flora from a common origin.  It is
interesting to note that the paper in which this was enunciated at once
established his reputation.

In Europe the latitudinal range of the great mountain chains gave the
Miocene flora no chance of escape during the Glacial period, and the
Mediterranean appears to have equally intercepted the flow of alpine plants
to the Atlas.  (John Ball in Appendix G, page 438, in "Journal of a Tour in
Morocco and the Great Atlas", J.D. Hooker and J. Ball, London, 1878.)  In
Southern Europe the myrtle, the laurel, the fig and the dwarf-palm are the
sole representatives of as many great tropical families.  Another great
tropical family, the Gesneraceae has left single representatives from the
Pyrenees to the Balkans; and in the former a diminutive yam still lingers.
These are only illustrations of the evidence which constantly accumulates
and which finds no rational explanation except that which Darwin has given
to it.

The theory of southward migration is the key to the interpretation of the
geographical distribution of plants.  It derived enormous support from the
researches of Heer and has now become an accepted commonplace.  Saporta in
1888 described the vegetable kingdom as "emigrant pour suivre une direction
determinee et marcher du nord au sud, a la recherche de regions et de
stations plus favorables, mieux appropriees aux adaptations acquises, a
meme que la temperature terrestre perd ses conditions premieres." 
("Origine Paleontologique des arbres", Paris, 1888, page 28.)  If, as is so
often the case, the theory now seems to be a priori inevitable, the
historian of science will not omit to record that the first germ sprang
from the brain of Darwin.

In attempting this sketch of Darwin's influence on Geographical
Distribution, I have found it impossible to treat it from an external point
of view.  His interest in it was unflagging; all I could say became
necessarily a record of that interest and could not be detached from it. 
He was in more or less intimate touch with everyone who was working at it.
In reading the letters we move amongst great names.  With an extraordinary
charm of persuasive correspondence he was constantly suggesting,
criticising and stimulating.  It is hardly an exaggeration to say that from
the quiet of his study at Down he was founding and directing a wide-world
school.

POSTSCRIPTUM.

Since this essay was put in type Dr Ernst's striking account of the "New
Flora of the Volcanic Island of Krakatau" (Cambridge, 1909.) has reached
me.  All botanists must feel a debt of gratitude to Prof. Seward for his
admirable translation of a memoir which in its original form is practically
unprocurable and to the liberality of the Cambridge University Press for
its publication.  In the preceding pages I have traced the laborious
research by which the methods of Plant Dispersal were established by
Darwin.  In the island of Krakatau nature has supplied a crucial experiment
which, if it had occurred earlier, would have at once secured conviction of
their efficiency.  A quarter of a century ago every trace of organic life
in the island was "destroyed and buried under a thick covering of glowing
stones."  Now, it is "again covered with a mantle of green, the growth
being in places so luxuriant that it is necessary to cut one's way
laboriously through the vegetation."  (Op. cit. page 4.)  Ernst traces
minutely how this has been brought about by the combined action of wind,
birds and sea currents, as means of transport.  The process will continue,
and he concludes:--"At last after a long interval the vegetation on the
desolated island will again acquire that wealth of variety and luxuriance
which we see in the fullest development which Nature has reached in the
primaeval forest in the tropics."  (Op. cit. page 72.)  The possibility of
such a result revealed itself to the insight of Darwin with little
encouragement or support from contemporary opinion.

One of the most remarkable facts established by Ernst is that this has not
been accomplished by the transport of seeds alone.  "Tree stems and
branches played an important part in the colonisation of Krakatau by plants
and animals.  Large piles of floating trees, stems, branches and bamboos
are met with everywhere on the beach above high-water mark and often
carried a considerable distance inland.  Some of the animals on the island,
such as the fat Iguana (Varanus salvator) which suns itself in the beds of
streams, may have travelled on floating wood, possibly also the ancestors
of the numerous ants, but certainly plants."  (Op. cit. page 56.)  Darwin
actually had a prevision of this.  Writing to Hooker he says:--"Would it
not be a prodigy if an unstocked island did not in the course of ages
receive colonists from coasts whence the currents flow, trees are drifted
and birds are driven by gales?"  ("More Letters", I. page 483.)  And ten
years earlier:--"I must believe in the...whole plant or branch being washed
into the sea; with floods and slips and earthquakes; this must continually
be happening."  ("Life and Letters", II. pages 56, 57.)  If we give to
"continually" a cosmic measure, can the fact be doubted?  All this, in the
light of our present knowledge, is too obvious to us to admit of
discussion.  But it seems to me nothing less than pathetic to see how in
the teeth of the obsession as to continental extension, Darwin fought
single-handed for what we now know to be the truth.

Guppy's heart failed him when he had to deal with the isolated case of
Agathis which alone seemed inexplicable by known means of transport.  But
when we remember that it is a relic of the pre-Angiospermous flora, and is
of Araucarian ancestry, it cannot be said that the impossibility, in so
prolonged a history, of the bodily transference of cone-bearing branches or
even of trees, compels us as a last resort to fall back on continental
extension to account for its existing distribution.

When Darwin was in the Galapagos Archipelago, he tells us that he fancied
himself "brought near to the very act of creation."  He saw how new species
might arise from a common stock.  Krakatau shows us an earlier stage and
how by simple agencies, continually at work, that stock might be supplied.
It also shows us how the mixed and casual elements of a new colony enter
into competition for the ground and become mutually adjusted.  The study of
Plant Distribution from a Darwinian standpoint has opened up a new field of
research in Ecology.  The means of transport supply the materials for a
flora, but their ultimate fate depends on their equipment for the "struggle
for existence."  The whole subject can no longer be regarded as a mere
statistical inquiry which has seemed doubtless to many of somewhat arid
interest.  The fate of every element of the earth's vegetation has sooner
or later depended on its ability to travel and to hold its own under new
conditions.  And the means by which it has secured success is an each case
a biological problem which demands and will reward the most attentive
study.  This is the lesson which Darwin has bequeathed to us.  It is summed
up in the concluding paragraph of the "Origin" ("Origin of Species" (6th
edition), page 429.):--"It is interesting to contemplate a tangled bank,
clothed with many plants of many kinds, with birds singing on the bushes,
with various insects flitting about, and with worms crawling through the
damp earth, and to reflect that these elaborately constructed forms, so
different from each other, and dependent upon each other in so complex a
manner, have all been produced by laws acting around us."


XVII.  GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

By HANS GADOW, M.A., Ph.D., F.R.S.
Strickland Curator and Lecturer on Zoology in the University of Cambridge.

The first general ideas about geographical distribution may be found in
some of the brilliant speculations contained in Buffon's "Histoire
Naturelle".  The first special treatise on the subject was however written
in 1777 by E.A.W. Zimmermann, Professor of Natural Science at Brunswick,
whose large volume, "Specimen Zoologiae Geographicae Quadrupedum"..., deals
in a statistical way with the mammals; important features of the large
accompanying map of the world are the ranges of mountains and the names of
hundreds of genera indicating their geographical range.  In a second work
he laid special stress on domesticated animals with reference to the
spreading of the various races of Mankind.

In the following year appeared the "Philosophia Entomologica" by J.C.
Fabricius, who was the first to divide the world into eight regions.  In
1803 G.R. Treviranus ("Biologie oder Philosophie der lebenden Natur", Vol.
II. Gottingen, 1803.) devoted a long chapter of his great work on
"Biologie" to a philosophical and coherent treatment of the distribution of
the whole animal kingdom.  Remarkable progress was made in 1810 by F.
Tiedemann ("Anatomie und Naturgeschichte der Vogel".  Heidelberg, 1810.) of
Heidelberg.  Few, if any, of the many subsequent Ornithologists seem to
have appreciated, or known of, the ingenious way in which Tiedemann
marshalled his statistics in order to arrive at general conclusions.  There
are, for instance, long lists of birds arranged in accordance with their
occurrence in one or more continents:  by correlating the distribution of
the birds with their food he concludes "that the countries of the East
Indian flora have no vegetable feeders in common with America," and "that
it is probably due to the great peculiarity of the African flora that
Africa has few phytophagous kinds in common with other countries, whilst
zoophagous birds have a far more independent, often cosmopolitan,
distribution."  There are also remarkable chapters on the influence of
environment, distribution, and migration, upon the structure of the Birds! 
In short, this anatomist dealt with some of the fundamental causes of
distribution.

Whilst Tiedemann restricted himself to Birds, A. Desmoulins in 1822 wrote a
short but most suggestive paper on the Vertebrata, omitting the birds; he
combated the view recently proposed by the entomologist Latreille that
temperature was the main factor in distribution.  Some of his ten main
conclusions show a peculiar mixture of evolutionary ideas coupled with the
conception of the stability of species:  whilst each species must have
started from but one creative centre, there may be several "analogous
centres of creation" so far as genera and families are concerned. 
Countries with different faunas, but lying within the same climatic zones,
are proof of the effective and permanent existence of barriers preventing
an exchange between the original creative centres.

The first book dealing with the "geography and classification" of the whole
animal kingdom was written by W. Swainson ("A Treatise on the Geography and
Classification of Animals", Lardner's "Cabinet Cyclopaedia" London, 1835.)
in 1835.  He saw in the five races of Man the clue to the mapping of the
world into as many "true zoological divisions," and he reconciled the five
continents with his mystical quinary circles.

Lyell's "Principles of Geology" should have marked a new epoch, since in
his "Elements" he treats of the past history of the globe and the
distribution of animals in time, and in his "Principles" of their
distribution in space in connection with the actual changes undergone by
the surface of the world.  But as the sub-title of his great work "Modern
changes of the Earth and its inhabitants" indicates, he restricted himself
to comparatively minor changes, and, emphatically believing in the
permanency of the great oceans, his numerous and careful interpretations of
the effect of the geological changes upon the dispersal of animals did
after all advance the problem but little.

Hitherto the marine faunas had been neglected.  This was remedied by E.
Forbes, who established nine homozoic zones, based mainly on the study of
the mollusca, the determining factors being to a great extent the isotherms
of the sea, whilst the 25 provinces were given by the configuration of the
land.  He was followed by J.D. Dana, who, taking principally the Crustacea
as a basis, and as leading factors the mean temperatures of the coldest and
of the warmest months, established five latitudinal zones.  By using these
as divisors into an American, Afro-European, Oriental, Arctic and Antarctic
realm, most of which were limited by an eastern and western land-boundary,
he arrived at about threescore provinces.

In 1853 appeared L.K. Schmarda's ("Die geographische Verbreitung der
Thiere", Wien, 1853.) two volumes, embracing the whole subject.  Various
centres of creation being, according to him, still traceable, he formed the
hypothesis that these centres were originally islands, which later became
enlarged and joined together to form the great continents, so that the
original faunas could overlap and mix whilst still remaining pure at their
respective centres.  After devoting many chapters to the possible physical
causes and modes of dispersal, he divided the land into 21 realms which he
shortly characterises, e.g. Australia as the only country inhabited by
marsupials, monotremes and meliphagous birds.  Ten main marine divisions
were diagnosed in a similar way.  Although some of these realms were not
badly selected from the point of view of being applicable to more than one
class of animals, they were obviously too numerous for general purposes,
and this drawback was overcome, in 1857, by P.L. Sclater.  ("On the general
Geographical Distribution of the members of the class Aves", "Proc. Linn.
Soc." (Zoology II. 1858, pages 130-145.)  Starting with the idea, that
"each species must have been created within and over the geographical area,
which it now occupies," he concluded "that the most natural primary
ontological divisions of the Earth's surface" were those six regions, which
since their adoption by Wallace in his epoch-making work, have become
classical.  Broadly speaking, these six regions are equivalent to the great
masses of land; they are convenient terms for geographical facts,
especially since the Palaearctic region expresses the unity of Europe with
the bulk of Asia.  Sclater further brigaded the regions of the Old World as
Palaeogaea and the two Americas as Neogaea, a fundamental mistake,
justifiable to a certain extent only since he based his regions mainly upon
the present distribution of the Passerine birds.

Unfortunately these six regions are not of equal value.  The Indian
countries and the Ethiopian region (Africa south of the Sahara) are
obviously nothing but the tropical, southern continuations or appendages of
one greater complex.  Further, the great eastern mass of land is so
intimately connected with North America that this continent has much more
in common with Europe and Asia than with South America.  Therefore, instead
of dividing the world longitudinally as Sclater had done, Huxley, in 1868
("On the classification and distribution of the Alectoromorphae and
Heteromorphae", "Proc. Zool. Soc." 1868, page 294.), gave weighty reasons
for dividing it transversely.  Accordingly he established two primary
divisions, Arctogaea or the North world in a wider sense, comprising
Sclater's Indian, African, Palaearctic and Neartic regions; and Notogaea,
the Southern world, which he divided into (1) Austro-Columbia (an
unfortunate substitute for the neotropical region), (2) Australasia, and
(3) New Zealand, the number of big regions thus being reduced to three but
for the separation of New Zealand upon rather negative characters.  Sclater
was the first to accept these four great regions and showed, in 1874 ("The
geographical distribution of Mammals", "Manchester Science Lectures",
1874.), that they were well borne out by the present distribution of the
Mammals.

Although applicable to various other groups of animals, for instance to the
tailless Amphibia and to Birds (Huxley himself had been led to found his
two fundamental divisions on the distribution of the Gallinaceous birds),
the combination of South America with Australia was gradually found to be
too sweeping a measure.  The obvious and satisfactory solution was provided
by W.T. Blanford (Anniversary address (Geological Society, 1889), "Proc.
Geol. Soc." 1889-90, page 67; "Quart. Journ." XLVI 1890.), who in 1890
recognised three main divisions, namely Australian, South American, and the
rest, for which the already existing terms (although used partly in a new
sense, as proposed by an anonymous writer in "Natural Science", III. page
289) "Notogaea," "Neogaea" and "Arctogaea" have been gladly accepted by a
number of English writers.

After this historical survey of the search for larger and largest or
fundamental centres of animal creation, which resulted in the mapping of
the world into zoological regions and realms of after all doubtful value,
we have to return to the year 1858.  The eleventh and twelfth chapters of
"The Origin of Species" (1859), dealing with "Geographical Distribution,"
are based upon a great amount of observation, experiment and reading.  As
Darwin's main problem was the origin of species, nature's way of making
species by gradual changes from others previously existing, he had to
dispose of the view, held universally, of the independent creation of each
species and at the same time to insist upon a single centre of creation for
each species; and in order to emphasise his main point, the theory of
descent, he had to disallow convergent, or as they were then called,
analogous forms.  To appreciate the difficulty of his position we have to
take the standpoint of fifty years ago, when the immutability of the
species was an axiom and each was supposed to have been created within or
over the geographical area which it now occupies.  If he once admitted that
a species could arise from many individuals instead of from one pair, there
was no way of shutting the door against the possibility that these
individuals may have been so numerous that they occupied a very large
district, even so large that it had become as discontinuous as the
distribution of many a species actually is.  Such a concession would at
once be taken as an admission of multiple, independent, origin instead of
descent in Darwin's sense.

For the so-called multiple, independently repeated creation of species as
an explanation of their very wide and often quite discontinuous
distribution, he substituted colonisation from the nearest and readiest
source together with subsequent modification and better adaptation to their
new home.

He was the first seriously to call attention to the many accidental means,
"which more properly should be called occasional means of distribution,"
especially to oceanic islands.  His specific, even individual, centres of
creation made migrations all the more necessary, but their extent was sadly
baulked by the prevailing dogma of the permanency of the oceans.  Any
number of small changes ("many islands having existed as halting places, of
which not a wreck now remains" ("The Origin of Species" (1st edition), page
396.).) were conceded freely, but few, if any, great enough to permit
migration of truly terrestrial creatures.  The only means of getting across
the gaps was by the principle of the "flotsam and jetsam," a theory which
Darwin took over from Lyell and further elaborated so as to make it
applicable to many kinds of plants and animals, but sadly deficient, often
grotesque, in the case of most terrestrial creatures.

Another very fertile source was Darwin's strong insistence upon the great
influence which the last glacial epoch must have had upon the distribution
of animals and plants.  Why was the migration of northern creatures
southwards of far-reaching and most significant importance?  More
northerners have established themselves in southern lands than vice versa,
because there is such a great mass of land in the north and greater
continents imply greater intensity of selection.  "The productions of real
islands have everywhere largely yielded to continental forms."  (Ibid. page
380.)..."The Alpine forms have almost everywhere largely yielded to the
more dominant forms generated in the larger areas and more efficient
workshops of the North."

Let us now pass in rapid survey the influence of the publication of "The
Origin of Species" upon the study of Geographical Distribution in its wider
sense.

Hitherto the following thought ran through the minds of most writers: 
Wherever we examine two or more widely separated countries their respective
faunas are very different, but where two faunas can come into contact with
each other, they intermingle.  Consequently these faunas represent centres
of creation, whence the component creatures have spread peripherally so far
as existing boundaries allowed them to do so.  This is of course the
fundamental idea of "regions."  There is not one of the numerous writers
who considered the possibility that these intermediate belts might
represent not a mixture of species but transitional forms, the result of
changes undergone by the most peripheral migrants in adaptation to their
new surroundings.  The usual standpoint was also that of Pucheran ("Note
sur l'equateur zoologique", "Rev. et Mag. de Zoologie", 1855; also several
other papers, ibid. 1865, 1866, and 1867.) in 1855.  But what a change
within the next ten years!  Pucheran explains the agreement in coloration
between the desert and its fauna as "une harmonie post-etablie"; the
Sahara, formerly a marine basin, was peopled by immigrants from the
neighbouring countries, and these new animals adapted themselves to the new
environment.  He also discusses, among other similar questions, the Isthmus
of Panama with regard to its having once been a strait.  From the same
author may be quoted the following passage as a strong proof of the new
influence:  "By the radiation of the contemporaneous faunas, each from one
centre, whence as the various parts of the world successively were formed
and became habitable, they spread and became modified according to the
local physical conditions."

The "multiple" origin of each species as advocated by Sclater and Murray,
although giving the species a broader basis, suffered from the same
difficulties.  There was only one alternative to the old orthodox view of
independent creation, namely the bold acceptance of land-connections to an
extent for which geological and palaeontological science was not yet ripe.
Those who shrank from either view, gave up the problem as mysterious and
beyond the human intellect.  This was the expressed opinion of men like
Swainson, Lyell and Humboldt.  Only Darwin had the courage to say that the
problem was not insoluble.  If we admit "that in the long course of time
the individuals of the same species, and likewise of allied species, have
proceeded from some one source; then I think all the grand leading facts of
geographical distribution are explicable on the theory of
migration...together with subsequent modification and the multiplication of
new forms."  We can thus understand how it is that in some countries the
inhabitants "are linked to the extinct beings which formerly inhabited the
same continent."  We can see why two areas, having nearly the same physical
conditions, should often be inhabited by very different forms of
life,...and "we can see why in two areas, however distant from each other,
there should be a correlation, in the presence of identical species...and
of distinct but representative species."  ("The Origin of Species" (1st
edition), pages 408, 409.)

Darwin's reluctance to assume great geological changes, such as a land-
connection of Europe with North America, is easily explained by the fact
that he restricted himself to the distribution of the present and
comparatively recent species.  "I do not believe that it will ever be
proved that within the recent period continents which are now quite
separate, have been continuously, or almost continuously, united with each
other, and with the many existing oceanic islands."  (Ibid. page 357.) 
Again, "believing...that our continents have long remained in nearly the
same relative position, though subjected to large, but partial oscillations
of level," that means to say within the period of existing species, or
"within the recent period."  (Ibid. page. 370.)  The difficulty was to a
great extent one of his own making.  Whilst almost everybody else believed
in the immutability of the species, which implies an enormous age,
logically since the dawn of creation, to him the actually existing species
as the latest results of evolution, were necessarily something very new, so
young that only the very latest of the geological epochs could have
affected them.  It has since come to our knowledge that a great number of
terrestrial "recent" species, even those of the higher classes of
Vertebrates, date much farther back than had been thought possible.  Many
of them reach well into the Miocene, a time since which the world seems to
have assumed the main outlines of the present continents.

In the year 1866 appeared A. Murray's work on the "Geographical
Distribution of Mammals", a book which has perhaps received less
recognition than it deserves.  His treatment of the general introductory
questions marks a considerable advance of our problem, although, and partly
because, he did not entirely agree with Darwin's views as laid down in the
first edition of "The Origin of Species", which after all was the great
impulse given to Murray's work.  Like Forbes he did not shrink from
assuming enormous changes in the configuration of the continents and oceans
because the theory of descent, with its necessary postulate of great
migrations, required them.  He stated, for instance, "that a Miocene
Atlantis sufficiently explains the common distribution of animals and
plants in Europe and America up to the glacial epoch."  And next he
considers how, and by what changes, the rehabilitation and distribution of
these lands themselves were effected subsequent to that period.  Further,
he deserves credit for having cleared up a misunderstanding of the idea of
specific centres of creation.  Whilst for instance Schmarda assumed without
hesitation that the same species, if occurring at places separated by great
distances, or apparently insurmountable barriers, had been there created
independently (multiple centres), Lyell and Darwin held that each species
had only one single centre, and with this view most of us agree, but their
starting point was to them represented by one individual, or rather one
single pair.  According to Murray, on the other hand, this centre of a
species is formed by all the individuals of a species, all of which equally
undergo those changes which new conditions may impose upon them.  In this
respect a new species has a multiple origin, but this in a sense very
different from that which was upheld by L. Agassiz.  As Murray himself puts
it:  "To my multiple origin, communication and direct derivation is
essential.  The species is compounded of many influences brought together
through many individuals, and distilled by Nature into one species; and,
being once established it may roam and spread wherever it finds the
conditions of life not materially different from those of its original
centre."  (Murray, "The Geographical Distribution of Mammals", page 14. 
London, 1866.)  This declaration fairly agrees with more modern views, and
it must be borne in mind that the application of the single-centre
principle to the genera, families and larger groups in the search for
descent inevitably leads to one creative centre for the whole animal
kingdom, a condition as unwarrantable as the myth of Adam and Eve being the
first representatives of Mankind.

It looks as if it had required almost ten years for "The Origin of Species"
to show its full effect, since the year 1868 marks the publication of
Haeckel's "Naturliche Schoepfungsgeschichte" in addition to other great
works.  The terms "Oecology" (the relation of organisms to their
environment) and "Chorology" (their distribution in space) had been given
us in his "Generelle Morphologie" in 1866.  The fourteenth chapter of the
"History of Creation" is devoted to the distribution of organisms, their
chorology, with the emphatic assertion that "not until Darwin can chorology
be spoken of as a separate science, since he supplied the acting causes for
the elucidation of the hitherto accumulated mass of facts."  A map (a
"hypothetical sketch") shows the monophyletic origin and the routes of
distribution of Man.

Natural Selection may be all-mighty, all-sufficient, but it requires time,
so much that the countless aeons required for the evolution of the present
fauna were soon felt to be one of the most serious drawbacks of the theory. 
Therefore every help to ease and shorten this process should have been
welcomed.  In 1868 M. Wagner (The first to formulate clearly the
fundamental idea of a theory of migration and its importance in the origin
of new species was L. von Buch, who in his "Physikalische Beschreibung der
Canarischen Inseln", written in 1825, wrote as follows:  "Upon the
continents the individuals of the genera by spreading far, form, through
differences of the locality, food and soil, varieties which finally become
constant as new species, since owing to the distances they could never be
crossed with other varieties and thus be brought back to the main type. 
Next they may again, perhaps upon different roads, return to the old home
where they find the old type likewise changed, both having become so
different that they can interbreed no longer.  Not so upon islands, where
the individuals shut up in narrow valleys or within narrow districts, can
always meet one another and thereby destroy every new attempt towards the
fixing of a new variety."  Clearly von Buch explains here why island types
remain fixed, and why these types themselves have become so different from
their continental congeners.--Actually von Buch is aware of a most
important point, the difference in the process of development which exists
between a new species b, which is the result of an ancestral species a
having itself changed into b and thereby vanished itself, and a new species
c which arose through separation out of the same ancestral a, which itself
persists as such unaltered.  Von Buch's prophetic view seems to have
escaped Lyell's and even Wagner's notice.) came to the rescue with his
"Darwin'sche Theorie und das Migrations-Gesetz der Organismen".  (Leipzig,
1868.)  He shows that migration, i.e. change of locality, implies new
environmental conditions (never mind whether these be new stimuli to
variation, or only acting as their selectors or censors), and moreover
secures separation from the original stock and thus eliminates or lessens
the reactionary dangers of panmixia.  Darwin accepted Wagner's theory as
"advantageous."  Through the heated polemics of the more ardent
selectionists Wagner's theory came to grow into an alternative instead of a
help to the theory of selectional evolution.  Separation is now rightly
considered a most important factor by modern students of geographical
distribution.

For the same year, 1868, we have to mention Huxley, whose Arctogaea and
Notogaea are nothing less than the reconstructed main masses of land of the
Mesozoic period.  Beyond doubt the configuration of land at that remote
period has left recognisable traces in the present continents, but whether
they can account for the distribution of such a much later group as the
Gallinaceous birds is more than questionable.  In any case he took for his
text a large natural group of birds, cosmopolitan as a whole, but with a
striking distribution.  The Peristeropodes, or pigeon-footed division, are
restricted to the Australian and Neotropical regions, in distinction to the
Alectoropodes (with the hallux inserted at a level above the front toes)
which inhabit the whole of the Arctogaea, only a few members having spread
into the South World.  Further, as Asia alone has its Pheasants and allies,
so is Africa characterised by its Guinea-fowls and relations, America has
the Turkey as an endemic genus, and the Grouse tribe in a wider sense has
its centre in the holarctic region:  a splendid object lesson of descent,
world-wide spreading and subsequent differentiation.  Huxley, by the way,
was the first--at least in private talk--to state that it will be for the
morphologist, the well-trained anatomist, to give the casting vote in
questions of geographical distribution, since he alone can determine
whether we have to deal with homologous, or analogous, convergent,
representative forms.

It seems late to introduce Wallace's name in 1876, the year of the
publication of his standard work.  ("The Geographical Distribution of
Animals", 2 vols.  London, 1876.)  We cannot do better than quote the
author's own words, expressing the hope that his "book should bear a
similar relation to the eleventh and twelfth chapters of the "Origin of
Species" as Darwin's "Animals and Plants under Domestication" does to the
first chapter of that work," and to add that he has amply succeeded. 
Pleading for a few primary centres he accepts Sclater's six regions and
does not follow Huxley's courageous changes which Sclater himself had
accepted in 1874.  Holding the view of the permanence of the oceans he
accounts for the colonisation of outlying islands by further elaborating
the views of Lyell and Darwin, especially in his fascinating "Island Life",
with remarkable chapters on the Ice Age, Climate and Time and other
fundamental factors.  His method of arriving at the degree of relationship
of the faunas of the various regions is eminently statistical.  Long lists
of genera determine by their numbers the affinity and hence the source of
colonisation.  In order to make sure of his material he performed the
laborious task of evolving a new classification of the host of Passerine
birds.  This statistical method has been followed by many authors, who,
relying more upon quantity than quality, have obscured the fact that the
key to the present distribution lies in the past changes of the earth's
surface.  However, with Wallace begins the modern study of the geographical
distribution of animals and the sudden interest taken in this subject by an
ever widening circle of enthusiasts far beyond the professional
brotherhood.

A considerable literature has since grown up, almost bewildering in its
range, diversity of aims and style of procedure.  It is a chaos, with many
paths leading into the maze, but as yet very few take us to a position
commanding a view of the whole intricate terrain with its impenetrable
tangle and pitfalls.

One line of research, not initiated but greatly influenced by Wallace's
works, became so prominent as to almost constitute a period which may be
characterised as that of the search by specialists for either the
justification or the amending of his regions.  As class after class of
animals was brought up to reveal the secret of the true regions, some
authors saw in their different results nothing but the faultiness of
previously established regions; others looked upon eventual agreements as
their final corroboration, especially when for instance such diverse groups
as mammals and scorpions could, with some ingenuity, be made to harmonise. 
But the obvious result of all these efforts was the growing knowledge that
almost every class seemed to follow principles of its own.  The regions
tallied neither in extent nor in numbers, although most of them gravitated
more and more towards three centres, namely Australia, South America and
the rest of the world.  Still zoologists persisted in the search, and the
various modes and capabilities of dispersal of the respective groups were
thought sufficient explanation of the divergent results in trying to bring
the mapping of the world under one scheme.

Contemporary literature is full of devices for the mechanical dispersal of
animals.  Marine currents, warm and cold, were favoured all the more since
they showed the probable original homes of the creatures in question.  If
these could not stand sea-water, they floated upon logs or icebergs, or
they were blown across by storms; fishes were lifted over barriers by
waterspouts, and there is on record even an hypothetical land tortoise,
full of eggs, which colonised an oceanic island after a perilous sea voyage
upon a tree trunk.  Accidents will happen, and beyond doubt many freaks of
discontinuous distribution have to be accounted for by some such means. 
But whilst sufficient for the scanty settlers of true oceanic islands, they
cannot be held seriously to account for the rich fauna of a large
continent, over which palaeontology shows us that the immigrants have
passed like waves.  It should also be borne in mind that there is a great
difference between flotsam and jetsam.  A current is an extension of the
same medium and the animals in it may suffer no change during even a long
voyage, since they may be brought from one litoral to another where they
will still be in the same or but slightly altered environment.  But the
jetsam is in the position of a passenger who has been carried off by the
wrong train.  Almost every year some American land birds arrive at our
western coasts and none of them have gained a permanent footing although
such visits must have taken place since prehistoric times.  It was
therefore argued that only those groups of animals should be used for
locating and defining regions which were absolutely bound to the soil. 
This method likewise gave results not reconcilable with each other, even
when the distribution of fossils was taken into account, but it pointed to
the absolute necessity of searching for former land-connections regardless
of their extent and the present depths to which they may have sunk.

That the key to the present distribution lies in the past had been felt
long ago, but at last it was appreciated that the various classes of
animals and plants have appeared in successive geological epochs and also
at many places remote from each other.  The key to the distribution of any
group lies in the configuration of land and water of that epoch in which it
made its first appearance.  Although this sounds like a platitude, it has
frequently been ignored.  If, for argument's sake, Amphibia were evolved
somewhere upon the great southern land-mass of Carboniferous times
(supposed by some to have stretched from South America across Africa to
Australia), the distribution of this developing class must have proceeded
upon lines altogether different from that of the mammals which dated
perhaps from lower Triassic times, when the old south continental belt was
already broken up.  The broad lines of this distribution could never
coincide with that of the other, older class, no matter whether the
original mammalian centre was in the Afro-Indian, Australian, or Brazilian
portion.  If all the various groups of animals had come into existence at
the same time and at the same place, then it would be possible, with
sufficient geological data, to construct a map showing the generalised
results applicable to the whole animal kingdom.  But the premises are
wrong.  Whatever regions we may seek to establish applicable to all
classes, we are necessarily mixing up several principles, namely
geological, historical, i.e. evolutionary, with present day statistical
facts.  We might as well attempt one compound picture representing a
chick's growth into an adult bird and a child's growth into manhood.

In short there are no general regions, not even for each class separately,
unless this class be one which is confined to a comparatively short
geological period.  Most of the great classes have far too long a history
and have evolved many successive main groups.  Let us take the mammals. 
Marsupials live now in Australia and in both Americas, because they already
existed in Mesozoic times; Ungulata existed at one time or other all over
the world except in Australia, because they are post-Cretaceous;
Insectivores, although as old as any Placentalia, are cosmopolitan
excepting South America and Australia; Stags and Bears, as examples of
comparatively recent Arctogaeans, are found everywhere with the exception
of Ethiopia and Australia.  Each of these groups teaches a valuable
historical lesson, but when these are combined into the establishment of a
few mammalian "realms," they mean nothing but statistical majorities.  If
there is one at all, Australia is such a realm backed against the rest of
the world, but as certainly it is not a mammalian creative centre!

Well then, if the idea of generally applicable regions is a mare's nest, as
was the search for the Holy Grail, what is the object of the study of
geographical distribution?  It is nothing less than the history of the
evolution of life in space and time in the widest sense.  The attempt to
account for the present distribution of any group of organisms involves the
aid of every branch of science.  It bids fair to become a history of the
world.  It started in a mild, statistical way, restricting itself to the
present fauna and flora and to the present configuration of land and water. 
Next came Oceanography concerned with the depths of the seas, their
currents and temperatures; then enquiries into climatic changes,
culminating in irreconcilable astronomical hypotheses as to glacial epochs;
theories about changes of the level of the seas, mainly from the point of
view of the physicist and astronomer.  Then came more and more to the front
the importance of the geological record, hand in hand with the
palaeontological data and the search for the natural affinities, the
genetic system of the organisms.  Now and then it almost seems as if the
biologists had done their share by supplying the problems and that the
physicists and geologists would settle them, but in reality it is not so. 
The biologists not only set the problems, they alone can check the offered
solutions.  The mere fact of palms having flourished in Miocene Spitzbergen
led to an hypothetical shifting of the axis of the world rather than to the
assumption, by way of explanation, that the palms themselves might have
changed their nature.  One of the most valuable aids in geological
research, often the only means for reconstructing the face of the earth in
by-gone periods, is afforded by fossils, but only the morphologist can
pronounce as to their trustworthiness as witnesses, because of the danger
of mistaking analogous for homologous forms.  This difficulty applies
equally to living groups, and it is so important that a few instances may
not be amiss.

There is undeniable similarity between the faunas of Madagascar and South
America.  This was supported by the Centetidae and Dendrobatidae, two
entire "families," as also by other facts.  The value of the Insectivores,
Solenodon in Cuba, Centetes in Madagascar, has been much lessened by their
recognition as an extremely ancient group and as a case of convergence, but
if they are no longer put into the same family, this amendment is really to
a great extent due to their widely discontinuous distribution.  The only
systematic difference of the Dendrobatidae from the Ranidae is the absence
of teeth, morphologically a very unimportant character, and it is now
agreed, on the strength of their distribution, that these little arboreal,
conspicuously coloured frogs, Dendrobates in South America, Mantella in
Madagascar, do not form a natural group, although a third genus,
Cardioglossa in West Africa, seems also to belong to them.  If these
creatures lived all on the same continent, we should unhesitatingly look
upon them as forming a well-defined, natural little group.  On the other
hand the Aglossa, with their three very divergent genera, namely Pipa in
South America, Xenopus and Hymenochirus in Africa, are so well
characterised as one ancient group that we use their distribution
unhesitatingly as a hint of a former connection between the two continents. 
We are indeed arguing in vicious circles.  The Ratitae as such are
absolutely worthless since they are a most heterogeneous assembly, and
there are untold groups, of the artificiality of which many a zoo-
geographer had not the slightest suspicion when he took his statistical
material, the genera and families, from some systematic catalogues or
similar lists.  A lamentable instance is that of certain flightless Rails,
recently extinct or sub-fossil, on the isalnds of Mauritius, Rodriguez and
Chatham.  Being flightless they have been used in support of a former huge
Antarctic continent, instead of ruling them out of court as Rails which,
each in its island, have lost the power of flight, a process which must
have taken place so recently that it is difficult, upon morphological
grounds, to justify their separation into Aphanapteryx in Mauritius,
Erythromachus in Rodriguez and Diaphorapteryx on Chatham Island. 
Morphologically they may well form but one genus, since they have sprung
from the same stock and have developed upon the same lines; they are
therefore monogenetic:  but since we know that they have become what they
are independently of each other (now unlike any other Rails), they are
polygenetic and therefore could not form one genus in the old Darwinian
sense.  Further, they are not a case of convergence, since their ancestry
is not divergent but leads into the same stratum.

THE RECONSTRUCTION OF THE GEOGRAPHY OF SUCCESSIVE EPOCHS.

A promising method is the study by the specialist of a large, widely
distributed group of animals from an evolutionary point of view.  Good
examples of this method are afforded by A.E. Ortmann's ("The geographical
distribution of Freshwater Decapods and its bearing upon ancient
geography", "Proc. Amer. Phil. Soc." Vol. 41, 1902.) exhaustive paper and
by A.W. Grabau's "Phylogeny of Fusus and its Allies" ("Smithsonian Misc.
Coll." 44, 1904.)  After many important groups of animals have been treated
in this way--as yet sparingly attempted--the results as to hypothetical
land-connections etc. are sure to be corrective and supplementary, and
their problems will be solved, since they are not imaginary.

The same problems are attacked, in the reverse way, by starting with the
whole fauna of a country and thence, so to speak, letting the research
radiate.  Some groups will be considered as autochthonous, others as
immigrants, and the directions followed by them will be inquired into; the
search may lead far and in various directions, and by comparison of
results, by making compound maps, certain routes will assume definite
shape, and if they lead across straits and seas they are warrants to search
for land-connections in the past.  (A fair sample of this method is C.H.
Eigenmann's "The Freshwater Fishes of South and Middle America", "Popular
Science Monthly", Vol. 68, 1906.)  There are now not a few maps purporting
to show the outlines of land and water at various epochs.  Many of these
attempts do not tally with each other, owing to the lamentable deficiencies
of geological and fossil data, but the bolder the hypothetical outlines are
drawn, the better, and this is preferable to the insertion of bays and
similar detail which give such maps a fallacious look of certainty where
none exists.  Moreover it must be borne in mind that, when we draw a broad
continental belt across an ocean, this belt need never have existed in its
entirety at any one time.  The features of dispersal, intended to be
explained by it, would be accomplished just as well by an unknown number of
islands which have joined into larger complexes while elsewhere they
subsided again:  like pontoon-bridges which may be opened anywhere, or like
a series of superimposed dissolving views of land and sea-scapes.  Hence
the reconstructed maps of Europe, the only continent tolerably known, show
a considerable number of islands in puzzling changes, while elsewhere, e.g.
in Asia, we have to be satisfied with sweeping generalisations.

At present about half-a-dozen big connections are engaging our attention,
leaving as comparatively settled the extent and the duration of such minor
"bridges" as that between Africa and Madagascar, Tasmania and Australia,
the Antilles and Central America, Europe and North Africa.  (Not a few of
those who are fascinated by, and satisfied with, the statistical aspect of
distribution still have a strong dislike to the use of "bridges" if these
lead over deep seas, and they get over present discontinuous occurrences by
a former "universal or sub-universal distribution" of their groups.  This
is indeed an easy method of cutting the knot, but in reality they shunt the
question only a stage or two back, never troubling to explain how their
groups managed to attain to that sub-universal range; or do they still
suppose that the whole world was originally one paradise where everything
lived side by side, until sin and strife and glacial epochs left nothing
but scattered survivors?

The permanence of the great ocean-basins had become a dogma since it was
found that a universal elevation of the land to the extent of 100 fathoms
would produce but little changes, and when it was shown that even the 1000
fathom-line followed the great masses of land rather closely, and still
leaving the great basins (although transgression of the sea to the same
extent would change the map of the world beyond recognition), by general
consent one mile was allowed as the utmost speculative limit of subsidence.
Naturally two or three miles, the average depth of the oceans, seems
enormous, and yet such a difference in level is as nothing in comparison
with the size of the Earth.  On a clay model globe ten feet in diameter an
ocean bed three miles deep would scarcely be detected, and the highest
mountains would be smaller than the unavoidable grains in the glazed
surface of our model.  There are but few countries which have not be
submerged at some time or other.)

CONNECTION OF SOUTH EASTERN ASIA WITH AUSTRALIA.  Neumayr's Sino-Australian
continent during mid-Mesozoic times was probably a much changing
Archipelago, with final separations subsequent to the Cretaceous period. 
Henceforth Australasia was left to its own fate, but for a possible
connection with the antarctic continent.

AFRICA, MADAGASCAR, INDIA.  The "Lemuria" of Sclater and Haeckel cannot
have been more than a broad bridge in Jurassic times; whether it was ever
available for the Lemurs themselves must depend upon the time of its
duration, the more recent the better, but it is difficult to show that it
lasted into the Miocene.

AFRICA AND SOUTH AMERICA.  Since the opposite coasts show an entire absence
of marine fossils and deposits during the Mesozoic period, whilst further
north and south such are known to exist and are mostly identical on either
side, Neumayr suggested the existence of a great Afro-Son American mass of
land during the Jurassic epoch.  Such land is almost a necessity and is
supported by many facts; it would easily explain the distribution of
numerous groups of terrestrial creatures.  Moreover to the north of this
hypothetical land, somewhere across from the Antilles and Guiana to North
Africa and South Western Europe, existed an almost identical fauna of
Corals and Molluscs, indicating either a coast-line or a series of islands
interrupted by shallow seas, just as one would expect if, and when, a
Brazil-Ethiopian mass of land were breaking up.  Lastly from Central
America to the Mediterranean stretches one of the Tertiary tectonic lines
of the geologists.  Here also the great question is how long this continent
lasted.  Apparently the South Atlantic began to encroach from the south so
that by the later Cretaceous epoch the land was reduced to a comparatively
narrow Brazil-West Africa, remnants of which persisted certainly into the
early Tertiary, until the South Atlantic joined across the equator with the
Atlantic portion of the "Thetys," leaving what remained of South America
isolated from the rest of the world.

ANTARCTIC CONNECTIONS.  Patagonia and Argentina seem to have joined
Antartica during the Cretaceous epoch, and this South Georgian bridge had
broken down again by mid-Tertiary times when South America became
consolidated.  The Antarctic continent, presuming that it existed, seems
also to have been joined, by way of Tasmania, with Australia, also during
the Cretaceous epoch, and it is assumed that the great Australia-Antarctic-
Patagonian land was severed first to the south of Tasmania and then at the
South Georgian bridge.  No connection, and this is important, is indicated
between Antarctica and either Africa or Madagascar.

So far we have followed what may be called the vicissitudes of the great
Permo-Carboniferous Gondwana land in its fullest imaginary extent, an
enormous equatorial and south temperate belt from South America to Africa,
South India and Australia, which seems to have provided the foundation of
the present Southern continents, two of which temporarily joined
Antarctica, of which however we know nothing except that it exists now.

Let us next consider the Arctic and periarctic lands.  Unfortunately very
little is known about the region within the arctic circle.  If it was all
land, or more likely great changing archipelagoes, faunistic exchange
between North America, Europe and Siberia would present no difficulties,
but there is one connection which engages much attention, namely a land
where now lies the North temperate and Northern part of the Atlantic ocean. 
How far south did it ever extend and what is the latest date of a direct
practicable communication, say from North Western Europe to Greenland? 
Connections, perhaps often interrupted, e.g. between Greenland and
Labrador, at another time between Greenland and Scandinavia, seem to have
existed at least since the Permo-Carboniferous epoch.  If they existed also
in late Cretaceous and in Tertiary times, they would of course easily
explain exchanges which we know to have repeatedly taken place between
America and Europe, but they are not proved thereby, since most of these
exchanges can almost as easily have occurred across the polar regions, and
others still more easily by repeated junction of Siberia with Alaska.

Let us now describe a hypothetical case based on the supposition of
connecting bridges.  Not to work in a circle, we select an important group
which has not served as a basis for the reconstruction of bridges; and it
must be a group which we feel justified in assuming to be old enough to
have availed itself of ancient land-connections.

The occurrence of one species of Peripatus in the whole of Australia,
Tasmania and New Zealand (the latter being joined to Australia by way of
New Britain in Cretaceous times but not later) puts the genus back into
this epoch, no unsatisfactory assumption to the morphologist.  The apparent
absence of Peripatus in Madagascar indicates that it did not come from the
east into Africa, that it was neither Afro-Indian, nor Afro-Australian; nor
can it have started in South America.  We therefore assume as its creative
centre Australia or Malaya in the Cretaceous epoch, whence its occurrence
in Sumatra, Malay Peninsula, New Britain, New Zealand and Australia is
easily explained.  Then extension across Antarctica to Patagonia and Chile,
whence it could spread into the rest of South America as this became
consolidated in early Tertiary times.  For getting to the Antilles and into
Mexico it would have to wait until the Miocene, but long before that time
it could arrive in Africa, there surviving as a Congolese and a Cape
species.  This story is unsupported by a single fossil.  Peripatus may have
been "sub-universal" all over greater Gondwana land in Carboniferous times,
and then its absence from Madagascar would be difficult to explain, but the
migrations suggested above amount to little considering that the distance
from Tasmania to South America could be covered in far less time than that
represented by the whole of the Eocene epoch alone.

There is yet another field, essentially the domain of geographical
distribution, the cultivation of which promises fair to throw much light
upon Nature's way of making species.  This is the study of the organisms
with regard to their environment.  Instead of revealing pedigrees or of
showing how and when the creatures got to a certain locality, it
investigates how they behaved to meet the ever changing conditions of their
habitats.  There is a facies, characteristic of, and often peculiar to, the
fauna of tropical moist forests, another of deserts, of high mountains, of
underground life and so forth; these same facies are stamped upon whole
associations of animals and plants, although these may be--and in widely
separated countries generally are--drawn from totally different families of
their respective orders.  It does not go to the root of the matter to say
that these facies have been brought about by the extermination of all the
others which did not happen to fit into their particular environment.  One
might almost say that tropical moist forests must have arboreal frogs and
that these are made out of whatever suitable material happened to be
available; in Australia and South America Hylidae, in Africa Ranidae, since
there Hylas are absent.  The deserts must have lizards capable of standing
the glare, the great changes of temperature, of running over or burrowing
into the loose sand.  When as in America Iguanids are available, some of
these are thus modified, while in Africa and Asia the Agamids are drawn
upon.  Both in the Damara and in the Transcaspian deserts, a Gecko has been
turned into a runner upon sand!

We cannot assume that at various epochs deserts, and at others moist
forests were continuous all over the world.  The different facies and
associations were developed at various times and places.  Are we to suppose
that, wherever tropical forests came into existence, amongst the stock of
humivagous lizards were always some which presented those nascent
variations which made them keep step with the similarly nascent forests,
the overwhelming rest being eliminated?  This principle would imply that
the same stratum of lizards always had variations ready to fit any changed
environment, forests and deserts, rocks and swamps.  The study of Ecology
indicates a different procedure, a great, almost boundless plasticity of
the organism, not in the sense of an exuberant moulding force, but of a
readiness to be moulded, and of this the "variations" are the visible
outcome.  In most cases identical facies are produced by heterogeneous
convergences and these may seem to be but superficial, affecting only what
some authors are pleased to call the physiological characters; but
environment presumably affects first those parts by which the organism
comes into contact with it most directly, and if the internal structures
remain unchanged, it is not because these are less easily modified but
because they are not directly affected.  When they are affected, they too
change deeply enough.

That the plasticity should react so quickly--indeed this very quickness
seems to have initiated our mistaking the variations called forth for
something performed--and to the point, is itself the outcome of the long
training which protoplasm has undergone since its creation.

In Nature's workshop he does not succeed who has ready an arsenal of tools
for every conceivable emergency, but he who can make a tool at the spur of
the moment.  The ordeal of the practical test is Charles Darwin's glorious
conception of Natural Selection.


XVIII.  DARWIN AND GEOLOGY.

By J.W. JUDD, C.B., LL.D., F.R.S.

(Mr Francis Darwin has related how his father occasionally came up from
Down to spend a few days with his brother Erasmus in London, and, after his
brother's death, with his daughter, Mrs Litchfield.  On these occasions, it
was his habit to arrange meetings with Huxley, to talk over zoological
questions, with Hooker, to discuss botanical problems, and with Lyell to
hold conversations on geology.  After the death of Lyell, Darwin, knowing
my close intimacy with his friend during his later years, used to ask me to
meet him when he came to town, and "talk geology."  The "talks" took place
sometimes at Jermyn Street Museum, at other times in the Royal College of
Science, South Kensington; but more frequently, after having lunch with
him, at his brother's or his daughter's house.  On several occasions,
however, I had the pleasure of visiting him at Down.  In the postscript of
a letter (of April 15, 1880) arranging one of these visits, he writes: 
"Since poor, dear Lyell's death, I rarely have the pleasure of geological
talk with anyone.")

In one of the very interesting conversations which I had with Charles
Darwin during the last seven years of his life, he asked me in a very
pointed manner if I were able to recall the circumstances, accidental or
otherwise, which had led me to devote myself to geological studies.  He
informed me that he was making similar inquiries of other friends, and I
gathered from what he said that he contemplated at that time a study of the
causes producing SCIENTIFIC BIAS in individual minds.  I have no means of
knowing how far this project ever assumed anything like concrete form, but
certain it is that Darwin himself often indulged in the processes of mental
introspection and analysis; and he has thus fortunately left us--in his
fragments of autobiography and in his correspondence--the materials from
which may be reconstructed a fairly complete history of his own mental
development.

There are two perfectly distinct inquiries which we have to undertake in
connection with the development of Darwin's ideas on the subject of
evolution:

FIRST.  How, when, and under what conditions was Darwin led to a conviction
that species were not immutable, but were derived from pre-existing forms?

SECONDLY.  By what lines of reasoning and research was he brought to regard
"natural selection" as a vera causa in the process of evolution?

It is the first of these inquiries which specially interests the geologist;
though geology undoubtedly played a part--and by no means an insignificant
part--in respect to the second inquiry.

When, indeed, the history comes to be written of that great revolution of
thought in the nineteenth century, by which the doctrine of evolution, from
being the dream of poets and visionaries, gradually grew to be the accepted
creed of naturalists, the paramount influence exerted by the infant science
of geology--and especially that resulting from the publication of Lyell's
epoch-making work, the "Principles of Geology"--cannot fail to be regarded
as one of the leading factors.  Herbert Spencer in his "Autobiography"
bears testimony to the effect produced on his mind by the recently
published "Principles", when, at the age of twenty, he had already begun to
speculate on the subject of evolution (Herbert Spencer's "Autobiography",
London, 1904, Vol. I. pages 175-177.); and Alfred Russel Wallace is
scarcely less emphatic concerning the part played by Lyell's teaching in
his scientific education.  (See "My Life; a record of Events and Opinions",
London, 1905, Vol. I. page 355, etc.  Also his review of Lyell's
"Principles" in "Quarterly Review" (Vol. 126), 1869, pages 359-394.  See
also "The Darwin-Wallace Celebration by the Linnean Society" (1909), page
118.)  Huxley wrote in 1887 "I owe more than I can tell to the careful
study of the "Principles of Geology" in my young days."  ("Science and
Pseudo Science"; "Collected Essays", London, 1902, Vol. V. page 101.)  As
for Charles Darwin, he never tired--either in his published writings, his
private correspondence or his most intimate conversations--of ascribing the
awakening of his enthusiasm and the direction of his energies towards the
elucidation of the problem of development to the "Principles of Geology"
and the personal influence of its author.  Huxley has well expressed what
the author of the "Origin of Species" so constantly insisted upon, in the
statements "Darwin's greatest work is the outcome of the unflinching
application to Biology of the leading idea and the method applied in the
"Principles" to Geology ("Proc. Roy. Soc." Vol. XLIV. (1888), page viii.;
"Collected Essays" II. page 268, 1902.), and "Lyell, for others, as for
myself, was the chief agent in smoothing the road for Darwin."  ("Life and
Letters of Charles Darwin" II. page 190.)

We propose therefore to consider, first, what Darwin owed to geology and
its cultivators, and in the second place how he was able in the end so
fully to pay a great debt which he never failed to acknowledge.  Thanks to
the invaluable materials contained in the "Life and Letters of Charles
Darwin" (3 vols.) published by Mr Francis Darwin in 1887; and to "More
Letters of Charles Darwin" (2 vols.) issued by the same author, in
conjunction with Professor A.C. Seward, in 1903, we are permitted to follow
the various movements in Darwin's mind, and are able to record the story
almost entirely in his own words.  (The first of these works is indicated
in the following pages by the letters "L.L."; the second by "M.L.")

From the point of view of the geologist, Darwin's life naturally divides
itself into four periods.  In the first, covering twenty-two years, various
influences were at work militating, now for and now against, his adoption
of a geological career; in the second period--the five memorable years of
the voyage of the "Beagle"--the ardent sportsman with some natural-history
tastes, gradually became the most enthusiastic and enlightened of
geologists; in the third period, lasting ten years, the valuable geological
recruit devoted nearly all his energies and time to geological study and
discussion and to preparing for publication the numerous observations made
by him during the voyage; the fourth period, which covers the latter half
of his life, found Darwin gradually drawn more and more from geological to
biological studies, though always retaining the deepest interest in the
progress and fortunes of his "old love."  But geologists gladly recognise
the fact that Darwin immeasurably better served their science by this
biological work, than he could possibly have done by confining himself to
purely geological questions.

From his earliest childhood, Darwin was a collector, though up to the time
when, at eight years of age, he went to a preparatory school, seals, franks
and similar trifles appear to have been the only objects of his quest.  But
a stone, which one of his schoolfellows at that time gave to him, seems to
have attracted his attention and set him seeking for pebbles and minerals;
as the result of this newly acquired taste, he says (writing in 1838) "I
distinctly recollect the desire I had of being able to know something about
every pebble in front of the hall door--it was my earliest and only
geological aspiration at that time."  ("M.L." I. page 3.)  He further
suspects that while at Mr Case's school "I do not remember any mental
pursuits except those of collecting stones," etc..."I was born a
naturalist."  ("M.L." I. page 4.)

The court-yard in front of the hall door at the Mount House, Darwin's
birthplace and the home of his childhood, is surrounded by beds or
rockeries on which lie a number of pebbles.  Some of these pebbles (in
quite recent times as I am informed) have been collected to form a
"cobbled" space in front of the gate in the outer wall, which fronts the
hall door; and a similar "cobbled area," there is reason to believe, may
have existed in Darwin's childhood before the door itself.  The pebbles,
which were obtained from a neighbouring gravel-pit, being derived from the
glacial drift, exhibit very striking differences in colour and form.  It
was probably this circumstance which awakened in the child his love of
observation and speculation.  It is certainly remarkable that "aspirations"
of the kind should have arisen in the mind of a child of 9 or 10!

When he went to Shrewsbury School, he relates "I continued collecting
minerals with much zeal, but quite unscientifically,--all that I cared
about was a new-NAMED mineral, and I hardly attempted to classify them." 
("L.L." I. page 34.)

There has stood from very early times in Darwin's native town of
Shrewsbury, a very notable boulder which has probably marked a boundary and
is known as the "Bell-stone"--giving its name to a house and street. 
Darwin tells us in his "Autobiography" that while he was at Shrewsbury
School at the age of 13 or 14 "an old Mr Cotton in Shropshire, who knew a
good deal about rocks" pointed out to me "...the 'bell-stone'; he told me
that there was no rock of the same kind nearer than Cumberland or Scotland,
and he solemnly assured me that the world would come to an end before
anyone would be able to explain how this stone came where it now lay"! 
Darwin adds "This produced a deep impression on me, and I meditated over
this wonderful stone."  ("L.L." I. page 41.)

The "bell-stone" has now, owing to the necessities of building, been
removed a short distance from its original site, and is carefully preserved
within the walls of a bank.  It is a block of irregular shape 3 feet long
and 2 feet wide, and about 1 foot thick, weighing probably not less than
one-third of a ton.  By the courtesy of the directors of the National
Provincial Bank of England, I have been able to make a minute examination
of it, and Professors Bonney and Watts, with Mr Harker and Mr Fearnsides
have given me their valuable assistance.  The rock is a much altered
andesite and was probably derived from the Arenig district in North Wales,
or possibly from a point nearer the Welsh Border.  (I am greatly indebted
to the Managers of the Bank at Shrewsbury for kind assistance in the
examination of this interesting memorial:  and Mr H.T. Beddoes, the Curator
of the Shrewsbury Museum, has given me some archaeological information
concerning the stone.  Mr Richard Cotton was a good local naturalist, a
Fellow both of the Geological and Linnean Societies; and to the officers of
these societies I am indebted for information concerning him.  He died in
1839, and although he does not appear to have published any scientific
papers, he did far more for science by influencing the career of the school
boy!"  It was of course brought to where Shrewsbury now stands by the
agency of a glacier--as Darwin afterwards learnt.

We can well believe from the perusal of these reminiscences that, at this
time, Darwin's mind was, as he himself says, "prepared for a philosophical
treatment of the subject" of Geology.  ("L.L." I. page 41.)  When at the
age of 16, however, he was entered as a medical student at Edinburgh
University, he not only did not get any encouragement of his scientific
tastes, but was positively repelled by the ordinary instruction given
there.  Dr Hope's lectures on Chemistry, it is true, interested the boy,
who with his brother Erasmus had made a laboratory in the toolhouse, and
was nicknamed "Gas" by his schoolfellows, while undergoing solemn and
public reprimand from Dr Butler at Shrewsbury School for thus wasting his
time.  ("L.L." I. page 35.)  But most of the other Edinburgh lectures were
"intolerably dull," "as dull as the professors" themselves, "something
fearful to remember."  In after life the memory of these lectures was like
a nightmare to him.  He speaks in 1840 of Jameson's lectures as something
"I...for my sins experienced!"  ("L.L." I. page 340.)  Darwin especially
signalises these lectures on Geology and Zoology, which he attended in his
second year, as being worst of all "incredibly dull.  The sole effect they
produced on me was the determination never so long as I lived to read a
book on Geology, or in any way to study the science!"  ("L.L." I. page 41.)

The misfortune was that Edinburgh at that time had become the cockpit in
which the barren conflict between "Neptunism" and Plutonism" was being
waged with blind fury and theological bitterness.  Jameson and his pupils,
on the one hand, and the friends and disciples of Hutton, on the other,
went to the wildest extremes in opposing each other's peculiar tenets. 
Darwin tells us that he actually heard Jameson "in a field lecture at
Salisbury Craigs, discoursing on a trap-dyke, with amygdaloidal margins and
the strata indurated on each side, with volcanic rocks all around us, say
that it was a fissure filled with sediment from above, adding with a sneer
that there were men who maintained that it had been injected from beneath
in a molten condition."  ("L.L." I. pages 41-42.)  "When I think of this
lecture," added Darwin, "I do not wonder that I determined never to attend
to Geology."  (This was written in 1876 and Darwin had in the summer of
1839 revisited and carefully studied the locality ("L.L." I. page 290.)  It
is probable that most of Jameson's teaching was of the same controversial
and unilluminating character as this field-lecture at Salisbury Craigs.

There can be no doubt that, while at Edinburgh, Darwin must have become
acquainted with the doctrines of the Huttonian School.  Though so young, he
mixed freely with the scientific society of the city, Macgillivray, Grant,
Leonard Horner, Coldstream, Ainsworth and others being among his
acquaintances, while he attended and even read papers at the local
scientific societies.  It is to be feared, however, that what Darwin would
hear most of, as characteristic of the Huttonian teaching, would be
assertions that chalk-flints were intrusions of molten silica, that fossil
wood and other petrifactions had been impregnated with fused materials,
that heat--but never water--was always the agent by which the induration
and crystallisation of rock-materials (even siliceous conglomerate,
limestone and rock-salt) had been effected!  These extravagant "anti-
Wernerian" views the young student might well regard as not one whit less
absurd and repellant than the doctrine of the "aqueous precipitation" of
basalt.  There is no evidence that Darwin, even if he ever heard of them,
was in any way impressed, in his early career, by the suggestive passages
in Hutton and Playfair, to which Lyell afterwards called attention, and
which foreshadowed the main principles of Uniformitarianism.

As a matter of fact, I believe that the influence of Hutton and Playfair in
the development of a philosophical theory of geology has been very greatly
exaggerated by later writers on the subject.  Just as Wells and Matthew
anticipated the views of Darwin on Natural Selection, but without producing
any real influence on the course of biological thought, so Hutton and
Playfair adumbrated doctrines which only became the basis of vivifying
theory in the hands of Lyell.  Alfred Russel Wallace has very justly
remarked that when Lyell wrote the "Principles of Geology", "the doctrines
of Hutton and Playfair, so much in advance of their age, seemed to be
utterly forgotten."  ("Quarterly Review", Vol. CXXVI. (1869), page 363.) 
In proof of this it is only necessary to point to the works of the great
masters of English geology, who preceded Lyell, in which the works of
Hutton and his followers are scarcely ever mentioned.  This is true even of
the "Researches in Theoretical Geology" and the other works of the
sagacious De la Beche.  (Of the strength and persistence of the prejudice
felt against Lyell's views by his contemporaries, I had a striking
illustration some little time after Lyell's death.  One of the old
geologists who in the early years of the century had done really good work
in connection with the Geological Society expressed a hope that I was not
"one of those who had been carried away by poor Lyell's fads."  My surprise
was indeed great when further conversation showed me that the whole of the
"Principles" were included in the "fads"!)  Darwin himself possessed a copy
of Playfair's "Illustrations of the Huttonian Theory", and occasionally
quotes it; but I have met with only one reference to Hutton, and that a
somewhat enigmatical one, in all Darwin's writings.  In a letter to Lyell
in 1841, when his mind was much exercised concerning glacial questions, he
says "What a grand new feature all this ice work is in Geology!  How old
Hutton would have stared!"  ("M.L." II. page 149.)

As a consequence of the influences brought to bear on his mind during his
two years' residence in Edinburgh, Darwin, who had entered that University
with strong geological aspirations, left it and proceeded to Cambridge with
a pronounced distaste for the whole subject.  The result of this was that,
during his career as an under-graduate, he neglected all the opportunities
for geological study.  During that important period of life, when he was
between eighteen and twenty years of age, Darwin spent his time in riding,
shooting and beetle-hunting, pursuits which were undoubtedly an admirable
preparation for his future work as an explorer; but in none of his letters
of this period does he even mention geology.  He says, however, "I was so
sickened with lectures at Edinburgh that I did not even attend Sedgwick's
eloquent and interesting lectures."  ("L.L." I. page 48.)

It was only after passing his examination, and when he went up to spend two
extra terms at Cambridge, that geology again began to attract his
attention.  The reading of Sir John Herschel's "Introduction to the Study
of Natural Philosophy", and of Humboldt's "Personal Narrative", a copy of
which last had been given to him by his good friend and mentor Henslow,
roused his dormant enthusiasm for science, and awakened in his mind a
passionate desire for travel.  And it was from Henslow, whom he had
accompanied in his excursions, but without imbibing any marked taste, at
that time, for botany, that the advice came to think of and to "begin the
study of geology."  ("L.L." I. page 56.)  This was in 1831, and in the
summer vacation of that year we find him back again at Shrewsbury "working
like a tiger" at geology and endeavouring to make a map and section of
Shropshire--work which he says was not "as easy as I expected."  ("L.L." I.
page 189.)  No better field for geological studies could possibly be found
than Darwin's native county.

Writing to Henslow at this time, and referring to a form of the instrument
devised by his friend, Darwin says:  "I am very glad to say I think the
clinometer will answer admirably.  I put all the tables in my bedroom at
every conceivable angle and direction.  I will venture to say that I have
measured them as accurately as any geologist going could do."  But he adds: 
"I have been working at so many things that I have not got on much with
geology.  I suspect the first expedition I take, clinometer and hammer in
hand, will send me back very little wiser and a good deal more puzzled than
when I started."  ("L.L." I. page 189.)  Valuable aid was, however, at
hand, for at this time Sedgwick, to whom Darwin had been introduced by the
ever-helpful Henslow, was making one of his expeditions into Wales, and
consented to accept the young student as his companion during the
geological tour.  ("L.L." I. page 56.)  We find Darwin looking forward to
this privilege with the keenest interest.  ("L.L." I. page 189.)

When at the beginning of August (1831), Sedgwick arrived at his father's
house in Shrewsbury, where he spent a night, Darwin began to receive his
first and only instruction as a field-geologist.  The journey they took
together led them through Llangollen, Conway, Bangor, and Capel Curig, at
which latter place they parted after spending many hours in examining the
rocks at Cwm Idwal with extreme care, seeking for fossils but without
success.  Sedgwick's mode of instruction was admirable--he from time to
time sent the pupil off on a line parallel to his own, "telling me to bring
back specimens of the rocks and to mark the stratification on a map." 
("L.L." I. page 57.)  On his return to Shrewsbury, Darwin wrote to Henslow,
"My trip with Sedgwick answered most perfectly," ("L.L." I. page 195.), and
in the following year he wrote again from South America to the same friend,
"Tell Professor Sedgwick he does not know how much I am indebted to him for
the Welsh expedition; it has given me an interest in Geology which I would
not give up for any consideration.  I do not think I ever spent a more
delightful three weeks than pounding the north-west mountains."  ("L.L." I.
pages 237-8.)

It would be a mistake, however, to suppose that at this time Darwin had
acquired anything like the affection for geological study, which he
afterwards developed.  After parting with Sedgwick, he walked in a straight
line by compass and map across the mountains to Barmouth to visit a reading
party there, but taking care to return to Shropshire before September 1st,
in order to be ready for the shooting.  For as he candidly tells us, "I
should have thought myself mad to give up the first days of partridge-
shooting for geology or any other science!"  ("L.L." I. page 58.)

Any regret we may be disposed to feel that Darwin did not use his
opportunities at Edinburgh and Cambridge to obtain systematic and practical
instruction in mineralogy and geology, will be mitigated, however, when we
reflect on the danger which he would run of being indoctrinated with the
crude "catastrophic" views of geology, which were at that time prevalent in
all the centres of learning.

Writing to Henslow in the summer of 1831, Darwin says "As yet I have only
indulged in hypotheses, but they are such powerful ones that I suppose, if
they were put into action but for one day, the world would come to an end."
("L.L." I. page 189.)

May we not read in this passage an indication that the self-taught
geologist had, even at this early stage, begun to feel a distrust for the
prevalent catastrophism, and that his mind was becoming a field in which
the seeds which Lyell was afterwards to sow would "fall on good ground"?

The second period of Darwin's geological career--the five years spent by
him on board the "Beagle"--was the one in which by far the most important
stage in his mental development was accomplished.  He left England a
healthy, vigorous and enthusiastic collector; he returned five years later
with unique experiences, the germs of great ideas, and a knowledge which
placed him at once in the foremost ranks of the geologists of that day. 
Huxley has well said that "Darwin found on board the "Beagle" that which
neither the pedagogues of Shrewsbury, nor the professoriate of Edinburgh,
nor the tutors of Cambridge had managed to give him."  ("Proc. Roy. Soc."
Vol. XLIV. (1888), page IX.)  Darwin himself wrote, referring to the date
at which the voyage was expected to begin:  "My second life will then
commence, and it shall be as a birthday for the rest of my life."  ("L.L."
I. page 214.); and looking back on the voyage after forty years, he wrote;
"The voyage of the 'Beagle' has been by far the most important event in my
life, and has determined my whole career;...I have always felt that I owe
to the voyage the first real training or education of my mind; I was led to
attend closely to several branches of natural history, and thus my powers
of observation were improved, though they were always fairly developed." 
("L.L." I. page 61.)

Referring to these general studies in natural history, however, Darwin adds
a very significant remark:  "The investigation of the geology of the places
visited was far more important, as reasoning here comes into play.  On
first examining a new district nothing can appear more hopeless than the
chaos of rocks; but by recording the stratification and nature of the rocks
and fossils at many points, always reasoning and predicting what will be
found elsewhere, light soon begins to dawn on the district, and the
structure of the whole becomes more or less intelligible."  ("L.L." I. page
62.)

The famous voyage began amid doubts, discouragements and disappointments. 
Fearful of heart-disease, sad at parting from home and friends, depressed
by sea-sickness, the young explorer, after being twice driven back by
baffling winds, reached the great object of his ambition, the island of
Teneriffe, only to find that, owing to quarantine regulations, landing was
out of the question.

But soon this inauspicious opening of the voyage was forgotten.  Henslow
had advised his pupil to take with him the first volume of Lyell's
"Principles of Geology", then just published--but cautioned him (as nearly
all the leaders in geological science at that day would certainly have
done) "on no account to accept the views therein advocated."  ("L.L." I.
page 73.)  It is probable that the days of waiting, discomfort and sea-
sickness at the beginning of the voyage were relieved by the reading of
this volume.  For he says that when he landed, three weeks after setting
sail from Plymouth, in St Jago, the largest of the Cape de Verde Islands,
the volume had already been "studied attentively; and the book was of the
highest service to me in many ways..."  His first original geological work,
he declares, "showed me clearly the wonderful superiority of Lyell's manner
of treating geology, compared with that of any other author, whose works I
had with me or ever afterwards read."  ("L.L." I. page 62.)

At St Jago Darwin first experienced the joy of making new discoveries, and
his delight was unbounded.  Writing to his father he says, "Geologising in
a volcanic country is most delightful; besides the interest attached to
itself, it leads you into most beautiful and retired spots."  ("L.L." I.
page 228.)  To Henslow he wrote of St Jago:  "Here we spent three most
delightful weeks...St Jago is singularly barren, and produces few plants or
insects, so that my hammer was my usual companion, and in its company most
delightful hours I spent."  "The geology was pre-eminently interesting, and
I believe quite new; there are some facts on a large scale of upraised
coast (which is an excellent epoch for all the volcanic rocks to date
from), that would interest Mr Lyell."  ("L.L." I. page 235.)  After more
than forty years the memory of this, his first geological work, seems as
fresh as ever, and he wrote in 1876, "The geology of St Jago is very
striking, yet simple:  a stream of lava formerly flowed over the bed of the
sea, formed of triturated recent shells and corals, which it has baked into
a hard white rock.  Since then the whole island has been upheaved.  But the
line of white rock revealed to me a new and important fact, namely, that
there had been afterwards subsidence round the craters, which had since
been in action, and had poured forth lava."  ("L.L." I. page 65.)

It was at this time, probably, that Darwin made his first attempt at
drawing a sketch-map and section to illustrate the observations he had made
(see his "Volcanic Islands", pages 1 and 9).  His first important
geological discovery, that of the subsidence of strata around volcanic
vents (which has since been confirmed by Mr Heaphy in New Zealand and other
authors) awakened an intense enthusiasm, and he writes:  "It then first
dawned on me that I might perhaps write a book on the geology of the
various countries visited, and this made me thrill with delight.  That was
a memorable hour to me, and how distinctly I can call to mind the low cliff
of lava beneath which I rested, with the sun glaring hot, a few strange
desert plants growing near, and with living corals in the tidal pools at my
feet."  ("L.L." I. page 66.)

But it was when the "Beagle", after touching at St Paul's rock and Tristan
d'Acunha (for a sufficient time only to collect specimens), reached the
shores of South America, that Darwin's real work began; and he was able,
while the marine surveys were in progress, to make many extensive journeys
on land.  His letters at this time show that geology had become his chief
delight, and such exclamations as "Geology carries the day," "I find in
Geology a never failing interest," etc. abound in his correspondence.

Darwin's time was divided between the study of the great deposits of red
mud--the Pampean formation--with its interesting fossil bones and shells
affording proofs of slow and constant movements of the land, and the
underlying masses of metamorphic and plutonic rocks.  Writing to Henslow in
March, 1834, he says:  "I am quite charmed with Geology, but, like the wise
animal between two bundles of hay, I do not know which to like best; the
old crystalline groups of rocks, or the softer and fossiliferous beds. 
When puzzling about stratification, etc., I feel inclined to cry 'a fig for
your big oysters, and your bigger megatheriums.'  But then when digging out
some fine bones, I wonder how any man can tire his arms with hammering
granite."  ("L.L." I. page 249.)  We are told by Darwin that he loved to
reason about and attempt to predict the nature of the rocks in each new
district before he arrived at it.

This love of guessing as to the geology of a district he was about to visit
is amusingly expressed by him in a letter (of May, 1832) to his cousin and
old college-friend, Fox.  After alluding to the beetles he had been
collecting--a taste his friend had in common with himself--he writes of
geology that "It is like the pleasure of gambling.  Speculating on first
arriving, what the rocks may be, I often mentally cry out 3 to 1 tertiary
against primitive; but the latter have hitherto won all the bets."  ("L.L."
I. page 233.)

Not the least important of the educational results of the voyage to Darwin
was the acquirement by him of those habits of industry and method which
enabled him in after life to accomplish so much--in spite of constant
failures of health.  From the outset, he daily undertook and resolutely
accomplished, in spite of sea-sickness and other distractions, four
important tasks.  In the first place he regularly wrote up the pages of his
Journal, in which, paying great attention to literary style and
composition, he recorded only matters that would be of general interest,
such as remarks on scenery and vegetation, on the peculiarities and habits
of animals, and on the characters, avocations and political institutions of
the various races of men with whom he was brought in contact.  It was the
freshness of these observations that gave his "Narrative" so much charm. 
Only in those cases in which his ideas had become fully crystallised, did
he attempt to deal with scientific matters in this journal.  His second
task was to write in voluminous note-books facts concerning animals and
plants, collected on sea or land, which could not be well made out from
specimens preserved in spirit; but he tells us that, owing to want of skill
in dissecting and drawing, much of the time spent in this work was entirely
thrown away, "a great pile of MS. which I made during the voyage has proved
almost useless." ("L.L." I. page 62.)  Huxley confirmed this judgment on
his biological work, declaring that "all his zeal and industry resulted,
for the most part, in a vast accumulation of useless manuscript."  ("Proc.
Roy. Soc." Vol. XLIV. (1888), page IX.)  Darwin's third task was of a very
different character and of infinitely greater value.  It consisted in
writing notes of his journeys on land--the notes being devoted to the
geology of the districts visited by him.  These formed the basis, not only
of a number of geological papers published on his return, but also of the
three important volumes forming "The Geology of the voyage of the
'Beagle'".  On July 24th, 1834, when little more than half of the voyage
had been completed, Darwin wrote to Henslow, "My notes are becoming bulky. 
I have about 600 small quarto pages full; about half of this is Geology." 
("M.L." I. page 14.)  The last, and certainly not the least important of
all his duties, consisted in numbering, cataloguing, and packing his
specimens for despatch to Henslow, who had undertaken the care of them.  In
his letters he often expresses the greatest solicitude lest the value of
these specimens should be impaired by the removal of the numbers
corresponding to his manuscript lists.  Science owes much to Henslow's
patient care of the collections sent to him by Darwin.  The latter wrote in
Henslow's biography, "During the five years' voyage, he regularly
corresponded with me and guided my efforts; he received, opened, and took
care of all the specimens sent home in many large boxes."  ("Life of
Henslow", by L. Jenyns (Blomefield), London, 1862, page 53.)

Darwin's geological specimens are now very appropriately lodged for the
most part in the Sedgwick Museum, Cambridge, his original Catalogue with
subsequent annotations being preserved with them.  From an examination of
these catalogues and specimens we are able to form a fair notion of the
work done by Darwin in his little cabin in the "Beagle", in the intervals
between his land journeys.

Besides writing up his notes, it is evident that he was able to accomplish
a considerable amount of study of his specimens, before they were packed up
for despatch to Henslow.  Besides hand-magnifiers and a microscope, Darwin
had an equipment for blowpipe-analysis, a contact-goniometer and magnet;
and these were in constant use by him.  His small library of reference (now
included in the Collection of books placed by Mr F. Darwin in the Botany
School at Cambridge ("Catalogue of the Library of Charles Darwin now in the
Botany School, Cambridge".  Compiled by H.W. Rutherford; with an
introduction by Francis Darwin.  Cambridge, 1908.)) appears to have been
admirably selected, and in all probability contained (in addition to a good
many works relating to South America) a fair number of excellent books of
reference.  Among those relating to mineralogy, he possessed the manuals of
Phillips, Alexander Brongniart, Beudant, von Kobell and Jameson:  all the
"Cristallographie" of Brochant de Villers and, for blowpipe work, Dr
Children's translation of the book of Berzelius on the subject.  In
addition to these, he had Henry's "Experimental Chemistry" and Ure's
"Dictionary" (of Chemistry).  A work, he evidently often employed, was P.
Syme's book on "Werner's Nomenclature of Colours"; while, for Petrology, he
used Macculloch's "Geological Classification of Rocks".  How diligently and
well he employed his instruments and books is shown by the valuable
observations recorded in the annotated Catalogues drawn up on board ship.

These catalogues have on the right-hand pages numbers and descriptions of
the specimens, and on the opposite pages notes on the specimens--the result
of experiments made at the time and written in a very small hand.  Of the
subsequently made pencil notes, I shall have to speak later.  (I am greatly
indebted to my friend Mr A. Harker, F.R.S., for his assistance in examining
these specimens and catalogues.  He has also arranged the specimens in the
Sedgwick Museum, so as to make reference to them easy.  The specimens from
Ascension and a few others are however in the Museum at Jermyn Street.)

It is a question of great interest to determine the period and the occasion
of Darwin's first awakening to the great problem of the transmutation of
species.  He tells us himself that his grandfather's "Zoonomia" had been
read by him "but without producing any effect," and that his friend Grant's
rhapsodies on Lamarck and his views on evolution only gave rise to
"astonishment."  ("L.L." I. page 38.)

Huxley, who had probably never seen the privately printed volume of letters
to Henslow, expressed the opinion that Darwin could not have perceived the
important bearing of his discovery of bones in the Pampean Formation, until
they had been studied in England, and their analogies pronounced upon by
competent comparative anatomists.  And this seemed to be confirmed by
Darwin's own entry in his pocket-book for 1837, "In July opened first
notebook on Transmutation of Species.  Had been greatly struck from about
the month of previous March on character of South American fossils..."
("L.L." I. page 276.)

The second volume of Lyell's "Principles of Geology" was published in
January, 1832, and Darwin's copy (like that of the other two volumes, in a
sadly dilapidated condition from constant use) has in it the inscription,
"Charles Darwin, Monte Video.  Nov. 1832."  As everyone knows, Darwin in
dedicating the second edition of his Journal of the Voyage to Lyell
declared, "the chief part of whatever scientific merit this journal and the
other works of the author may possess, has been derived from studying the
well-known and admirable "Principles of Geology".

In the first chapter of this second volume of the "Principles", Lyell
insists on the importance of the species question to the geologist, but
goes on to point out the difficulty of accepting the only serious attempt
at a transmutation theory which had up to that time appeared--that of
Lamarck.  In subsequent chapters he discusses the questions of the
modification and variability of species, of hybridity, and of the
geographical distribution of plants and animals.  He then gives vivid
pictures of the struggle for existence, ever going on between various
species, and of the causes which lead to their extinction--not by
overwhelming catastrophes, but by the silent and almost unobserved action
of natural causes.  This leads him to consider theories with regard to the
introduction of new species, and, rejecting the fanciful notions of
"centres or foci of creation," he argues strongly in favour of the view, as
most reconcileable with observed facts, that "each species may have had its
origin in a single pair, or individual, where an individual was sufficient,
and species may have been created in succession at such times and in such
places as to enable them to multiply and endure for an appointed period,
and occupy an appointed space on the globe."  ("Principles of Geology",
Vol. II. (1st edition 1832), page 124.  We now know, as has been so well
pointed out by Huxley, that Lyell, as early as 1827, was prepared to accept
the doctrine of the transmutation of species.  In that year he wrote to
Mantell, "What changes species may really undergo!  How impossible will it
be to distinguish and lay down a line, beyond which some of the so-called
extinct species may have never passed into recent ones" (Lyell's "Life and
Letters" Vol. I. page 168).  To Sir John Herschel in 1836, he wrote, "In
regard to the origination of new species, I am very glad to find that you
think it probable that it may be carried on through the intervention of
intermediate causes.  I left this rather to be inferred, not thinking it
worth while to offend a certain class of persons by embodying in words what
would only be a speculation" (Ibid. page 467).  He expressed the same views
to Whewell in 1837 (Ibid. Vol. II. page 5.), and to Sedgwick (Ibid. Vol.
II. page 36) to whom he says, of "the theory, that the creation of new
species is going on at the present day"--"I really entertain it," but "I
have studiously avoided laying the doctrine down dogmatically as capable of
proof" (see Huxley in "L.L." II. pages 190-195.))

After pointing out how impossible it would be for a naturalist to prove
that a newly DISCOVERED species was really newly CREATED (Mr F. Darwin has
pointed out that his father (like Lyell) often used the term "Creation" in
speaking of the origin of new species ("L.L." II. chapter 1.)), Lyell
argued that no satisfactory evidence OF THE WAY in which these new forms
were created, had as yet been discovered, but that he entertained the hope
of a possible solution of the problem being found in the study of the
geological record.

It is not difficult, in reading these chapters of Lyell's great work, to
realise what an effect they would have on the mind of Darwin, as new facts
were collected and fresh observations concerning extinct and recent forms
were made in his travels.  We are not surprised to find him writing home,
"I am become a zealous disciple of Mr Lyell's views, as known in his
admirable book.  Geologising in South America, I am tempted to carry parts
to a greater extent even than he does."  ("L.L." I. page 263.)

Lyell's anticipation that the study of the geological record might afford a
clue to the discovery of how new species originate was remarkably
fulfilled, within a few months, by Darwin's discovery of fossil bones in
the red Pampean mud.

It is very true that, as Huxley remarked, Darwin's knowledge of comparative
anatomy must have been, at that time, slight; but that he recognised the
remarkable resemblances between the extinct and existing mammals of South
America is proved beyond all question by a passage in his letter to
Henslow, written November 24th, 1832:  "I have been very lucky with fossil
bones; I have fragments of at least six distinct animals...I found a large
surface of osseous polygonal plates...Immediately I saw them I thought they
must belong to an enormous armadillo, living species of which genus are so
abundant here," and he goes on to say that he has "the lower jaw of some
large animal which, from the molar teeth, I should think belonged to the
Edentata."  ("M.L." I. pages 11, 12.  See "Extracts of Letters addressed to
Prof. Henslow by C. Darwin" (1835), page 7.)

Having found this important clue, Darwin followed it up with characteristic
perseverance.  In his quest for more fossil bones he was indefatigable.  Mr
Francis Darwin tells us, "I have often heard him speak of the despair with
which he had to break off the projecting extremity of a huge, partly
excavated bone, when the boat waiting for him would wait no longer." 
("L.L." I. page 276 (footnote).)  Writing to Haeckel in 1864, Darwin says: 
"I shall never forget my astonishment when I dug out a gigantic piece of
armour, like that of the living armadillo."  (Haeckel, "History of
Creation", Vol. I. page 134, London, 1876.)

In a letter to Henslow in 1834 Darwin says:  "I have just got scent of some
fossil bones...what they may be I do not know, but if gold or galloping
will get them they shall be mine."  ("M.L." I. page 15.)

Darwin also showed his sense of the importance of the discovery of these
bones by his solicitude about their safe arrival and custody.  From the
Falkland Isles (March, 1834), he writes to Henslow:  "I have been alarmed
by your expression 'cleaning all the bones' as I am afraid the printed
numbers will be lost:  the reason I am so anxious they should not be, is,
that a part were found in a gravel with recent shells, but others in a very
different bed.  Now with these latter there were bones of an Agouti, a
genus of animals, I believe, peculiar to America, and it would be curious
to prove that some one of the genus co-existed with the Megatherium:  such
and many other points depend on the numbers being carefully preserved." 
("Extracts from Letters etc.", pages 13-14.)  In the abstract of the notes
read to the Geological Society in 1835, we read:  "In the gravel of
Patagonia he (Darwin) also found many bones of the Megatherium and of five
or six other species of quadrupeds, among which he has detected the bones
of a species of Agouti.  He also met with several examples of the polygonal
plates, etc."  ("Proc. Geol. Soc." Vol. II. pages 211-212.)

Darwin's own recollections entirely bear out the conclusion that he fully
recognised, WHILE IN SOUTH AMERICA, the wonderful significance of the
resemblances between the extinct and recent mammalian faunas.  He wrote in
his "Autobiography":  "During the voyage of the 'Beagle' I had been deeply
impressed by discovering in the Pampean formation great fossil animals
covered with armour like that on the existing armadillos."  ("L.L." I. page
82.)

The impression made on Darwin's mind by the discovery of these fossil
bones, was doubtless deepened as, in his progress southward from Brazil to
Patagonia, he found similar species of Edentate animals everywhere
replacing one another among the living forms, while, whenever fossils
occurred, they also were seen to belong to the same remarkable group of
animals.  (While Darwin was making these observations in South America, a
similar generalisation to that at which he arrived was being reached, quite
independently and almost simultaneously, with respect to the fossil and
recent mammals of Australia.  In the year 1831, Clift gave to Jameson a
list of bones occurring in the caves and breccias of Australia, and in
publishing this list the latter referred to the fact that the forms
belonged to marsupials, similar to those of the existing Australian fauna. 
But he also stated that, as a skull had been identified (doubtless
erroneously) as having belonged to a hippopotamus, other mammals than
marsupials must have spread over the island in late Tertiary times.  It is
not necessary to point out that this paper was quite unknown to Darwin
while in South America.  Lyell first noticed it in the third edition of his
"Principles", which was published in May, 1834 (see "Edinb. New Phil.
Journ." Vol. X. (1831), pages 394-6, and Lyell's "Principles" (3rd
edition), Vol. III. page 421).  Darwin referred to this discovery in 1839
(see his "Journal", page 210.)

That the passage in Darwin's pocket-book for 1837 can only refer to an
AWAKENING of Darwin's interest in the subject--probably resulting from a
sight of the bones when they were being unpacked--I think there cannot be
the smallest doubt; AND WE MAY THEREFORE CONFIDENTLY FIX UPON NOVEMBER,
1832, AS THE DATE AT WHICH DARWIN COMMENCED THAT LONG SERIES OF
OBSERVATIONS AND REASONINGS WHICH EVENTUALLY CULMINATED IN THE PREPARATION
OF THE "ORIGIN OF SPECIES".  Equally certain is it, that it was his
geological work that led Darwin into those paths of research which in the
end conducted him to his great discoveries.  I quite agree with the view
expressed by Mr F. Darwin and Professor Seward, that Darwin, like Lyell,
"thought it 'almost useless' to try to prove the truth of evolution until
the cause of change was discovered" ("M.L." I. page 38.), and that possibly
he may at times have vacillated in his opinions, but I believe there is
evidence that, from the date mentioned, the "species question" was always
more or less present in Darwin's mind.  (Although we admit with Huxley that
Darwin's training in comparative anatomy was very small, yet it may be
remembered that he was a medical student for two years, and, if he hated
the lectures, he enjoyed the society of naturalists.  He had with him in
the little "Beagle" library a fair number of zoological books, including
works on Osteology by Cuvier, Desmarest and Lesson, as well as two French
Encyclopaedias of Natural History.  As a sportsman, he would obtain
specimens of recent mammals in South America, and would thus have
opportunities of studying their teeth and general anatomy.  Keen observer,
as he undoubtedly was, we need not then be surprised that he was able to
make out the resemblances between the recent and fossil forms.)

It is clear that, as time went on, Darwin became more and more absorbed in
his geological work.  One very significant fact was that the once ardent
sportsman, when he found that shooting the necessary game and zoological
specimens interfered with his work with the hammer, gave up his gun to his
servant.  ("L.L." I. page 63.)  There is clear evidence that Darwin
gradually became aware how futile were his attempts to add to zoological
knowledge by dissection and drawing, while he felt ever increasing
satisfaction with his geological work.

The voyage fortunately extended to a much longer period (five years) than
the two originally intended, but after being absent nearly three years,
Darwin wrote to his sister in November, 1834, "Hurrah! hurrah! it is fixed
that the 'Beagle' shall not go one mile south of Cape Tres Montes (about
200 miles south of Chiloe), and from that point to Valparaiso will be
finished in about five months.  We shall examine the Chonos Archipelago,
entirely unknown, and the curious inland sea behind Chiloe.  For me it is
glorious.  Cape Tres Montes is the most southern point where there is much
geological interest, as there the modern beds end.  The Captain then talks
of crossing the Pacific; but I think we shall persuade him to finish the
coast of Peru, where the climate is delightful, the country hideously
sterile, but abounding with the highest interest to the geologist...I have
long been grieved and most sorry at the interminable length of the voyage
(though I never would have quitted it)...I could not make up my mind to
return.  I could not give up all the geological castles in the air I had
been building up for the last two years."  ("L.L." I. pages 257-58.)

In April, 1835, he wrote to another sister:  "I returned a week ago from my
excursion across the Andes to Mendoza.  Since leaving England I have never
made so successful a journey...how deeply I have enjoyed it; it was
something more than enjoyment; I cannot express the delight which I felt at
such a famous winding-up of all my geology in South America.  I literally
could hardly sleep at nights for thinking over my day's work.  The scenery
was so new, and so majestic; everything at an elevation of 12,000 feet
bears so different an aspect from that in the lower country...To a
geologist, also, there are such manifest proofs of excessive violence; the
strata of the highest pinnacles are tossed about like the crust of a broken
pie."  ("L.L." I. pages 259-60.)

Darwin anticipated with intense pleasure his visit to the Galapagos
Islands.  On July 12th, 1835, he wrote to Henslow:  "In a few days' time
the "Beagle" will sail for the Galapagos Islands.  I look forward with joy
and interest to this, both as being somewhat nearer to England and for the
sake of having a good look at an active volcano.  Although we have seen
lava in abundance, I have never yet beheld the crater."  ("M.L." I. page
26.)  He could little anticipate, as he wrote these lines, the important
aid in the solution of the "species question" that would ever after make
his visit to the Galapagos Islands so memorable.  In 1832, as we have seen,
the great discovery of the relations of living to extinct mammals in the
same area had dawned upon his mind; in 1835 he was to find a second key for
opening up the great mystery, by recognising the variations of similar
types in adjoining islands among the Galapagos.

The final chapter in the second volume of the "Principles" had aroused in
Darwin's mind a desire to study coral-reefs, which was gratified during his
voyage across the Pacific and Indian Oceans.  His theory on the subject was
suggested about the end of 1834 or the beginning of 1835, as he himself
tells us, before he had seen a coral-reef, and resulted from his work
during two years in which he had "been incessantly attending to the effects
on the shores of South America of the intermittent elevation of the land,
together with denudation and the deposition of sediment."  ("L.L." I. page
70.)

On arriving at the Cape of Good Hope in July, 1836, Darwin was greatly
gratified by hearing that Sedgwick had spoken to his father in high terms
of praise concerning the work done by him in South America.  Referring to
the news from home, when he reached Bahia once more, on the return voyage
(August, 1836), he says:  "The desert, volcanic rocks, and wild sea of
Ascension...suddenly wore a pleasing aspect, and I set to work with a good-
will at my old work of Geology."  ("L.L." I. page 265.)  Writing fifty
years later, he says:  "I clambered over the mountains of Ascension with a
bounding step and made the volcanic rocks resound under my geological
hammer!"  ("L.L." I. page 66.)

That his determination was now fixed to devote his own labours to the task
of working out the geological results of the voyage, and that he was
prepared to leave to more practised hands the study of his biological
collections, is clear from the letters he sent home at this time.  From St
Helena he wrote to Henslow asking that he would propose him as a Fellow of
the Geological Society; and his Certificate, in Henslow's handwriting, is
dated September 8th, 1836, being signed from personal knowledge by Henslow
and Sedgwick.  He was proposed on November 2nd and elected November 30th,
being formally admitted to the Society by Lyell, who was then President, on
January 4th, 1837, on which date he also read his first paper.  Darwin did
not become a Fellow of the Linnean Society till eighteen years later (in
1854).

An estimate of the value and importance of Darwin's geological discoveries
during the voyage of the "Beagle" can best be made when considering the
various memoirs and books in which the author described them.  He was too
cautious to allow himself to write his first impressions in his Journal,
and wisely waited till he could study his specimens under better conditions
and with help from others on his return.  The extracts published from his
correspondence with Henslow and others, while he was still abroad, showed,
nevertheless, how great was the mass of observation, how suggestive and
pregnant with results were the reasonings of the young geologist.

Two sets of these extracts from Darwin's letters to Henslow were printed
while he was still abroad.  The first of these was the series of
"Geological Notes made during a survey of the East and West Coasts of South
America, in the years 1832, 1833, 1834 and 1835, with an account of a
transverse section of the Cordilleras of the Andes between Valparaiso and
Mendoza".  Professor Sedgwick, who read these notes to the Geological
Society on November 18th, 1835, stated that "they were extracted from a
series of letters (addressed to Professor Henslow), containing a great mass
of information connected with almost every branch of natural history," and
that he (Sedgwick) had made a selection of the remarks which he thought
would be more especially interesting to the Geological Society.  An
abstract of three pages was published in the "Proceedings of the Geological
Society" (Vol. II. pages 210-12.), but so unknown was the author at this
time that he was described as F. Darwin, Esq., of St John's College,
Cambridge"!  Almost simultaneously (on November 16th, 1835) a second set of
extracts from these letters--this time of a general character--were read to
the Philosophical Society at Cambridge, and these excited so much interest
that they were privately printed in pamphlet form for circulation among the
members.

Many expeditions and "scientific missions" have been despatched to various
parts of the world since the return of the "Beagle" in 1836, but it is
doubtful whether any, even the most richly endowed of them, has brought
back such stores of new information and fresh discoveries as did that
little "ten-gun brig"--certainly no cabin or laboratory was the birth-place
of ideas of such fruitful character as was that narrow end of a chart-room,
where the solitary naturalist could climb into his hammock and indulge in
meditation.

The third and most active portion of Darwin's career as a geologist was the
period which followed his return to England at the end of 1836.  His
immediate admission to the Geological Society, at the beginning of 1837,
coincided with an important crisis in the history of geological science.

The band of enthusiasts who nearly thirty years before had inaugurated the
Geological Society--weary of the fruitless conflicts between "Neptunists"
and "Plutonists"--had determined to eschew theory and confine their labours
to the collection of facts, their publications to the careful record of
observations.  Greenough, the actual founder of the Society, was an ardent
Wernerian, and nearly all his fellow-workers had come, more or less
directly, under the Wernerian teaching.  Macculloch alone gave valuable
support to the Huttonian doctrines, so far as they related to the influence
of igneous activity--but the most important portion of the now celebrated
"Theory of the Earth"--that dealing with the competency of existing
agencies to account for changes in past geological times--was ignored by
all alike.  Macculloch's influence on the development of geology, which
might have had far-reaching effects, was to a great extent neutralised by
his peculiarities of mind and temper; and, after a stormy and troublous
career, he retired from the society in 1832.  In all the writings of the
great pioneers in English geology, Hutton and his splendid generalisation
are scarcely ever referred to.  The great doctrines of Uniformitarianism,
which he had foreshadowed, were completely ignored, and only his
extravagances of "anti-Wernerianism" seem to have been remembered.

When between 1830 and 1832, Lyell, taking up the almost forgotten ideas of
Hutton, von Hoff and Prevost, published that bold challenge to the
Catastrophists--the "Principles of Geology"--he was met with the strongest
opposition, not only from the outside world, which was amused by his
"absurdities" and shocked by his "impiety"--but not less from his fellow-
workers and friends in the Geological Society.  For Lyell's numerous
original observations, and his diligent collection of facts his
contemporaries had nothing but admiration, and they cheerfully admitted him
to the highest offices in the society, but they met his reasonings on
geological theory with vehement opposition and his conclusions with
coldness and contempt.

There is, indeed, a very striking parallelism between the reception of the
"Principles of Geology" by Lyell's contemporaries and the manner in which
the "Origin of Species" was met a quarter of a century later, as is so
vividly described by Huxley.  ("L.L." II. pages 179-204.)  Among Lyell's
fellow-geologists, two only--G. Poulett Scrope and John Herschel (Both
Lyell and Darwin fully realised the value of the support of these two
friends.  Scrope in his appreciative reviews of the "Principles" justly
pointed out what was the weakest point, the inadequate recognition of sub-
aerial as compared with marine denudation.  Darwin also admitted that
Scrope had to a great extent forestalled him in his theory of Foliation. 
Herschel from the first insisted that the leading idea of the "Principles"
must be applied to organic as well as to inorganic nature and must explain
the appearance of new species (see Lyell's "Life and Letters", Vol. I. page
467).  Darwin tells us that Herschel's "Introduction to the Study of
Natural Philosophy" with Humboldt's "Personal Narrative" "stirred up in me
a burning zeal" in his undergraduate days.  I once heard Lyell exclaim with
fervour "If ever there was a heaven-born genius it was John Herschel!")--
declared themselves from the first his strong supporters. Scrope in two
luminous articles in the "Quarterly Review" did for Lyell what Huxley
accomplished for Darwin in his famous review in the "Times"; but Scrope
unfortunately was at that time immersed in the stormy sea of politics, and
devoted his great powers of exposition to the preparation of fugitive
pamphlets.  Herschel, like Scrope, was unable to support Lyell at the
Geological Society, owing to his absence on the important astronomical
mission to the Cape.

It thus came about that, in the frequent conflicts of opinion within the
walls of the Geological Society, Lyell had to bear the brunt of battle for
Uniformitarianism quite alone, and it is to be feared that he found himself
sadly overmatched when opposed by the eloquence of Sedgwick, the sarcasm of
Buckland, and the dead weight of incredulity on the part of Greenough,
Conybeare, Murchison and other members of the band of pioneer workers.  As
time went on there is evidence that the opposition of De la Beche and
Whewell somewhat relaxed; the brilliant "Paddy" Fitton (as his friends
called him) was sometimes found in alliance with Lyell, but was
characteristically apt to turn his weapon, as occasion served, on friend or
foe alike; the amiable John Phillips "sat upon the fence."  Only when a new
generation arose--including Jukes, Ramsay, Forbes and Hooker--did Lyell
find his teachings received with anything like favour.

We can well understand, then, how Lyell would welcome such a recruit as
young Darwin--a man who had declared himself more Lyellian than Lyell, and
who brought to his support facts and observations gleaned from so wide a
field.

The first meeting of Lyell and Darwin was characteristic of the two men. 
Darwin at once explained to Lyell that, with respect to the origin of
coral-reefs, he had arrived at views directly opposed to those published by
"his master."  To give up his own theory, cost Lyell, as he told Herschel,
a "pang at first," but he was at once convinced of the immeasurable
superiority of Darwin's theory.  I have heard members of Lyell's family
tell of the state of wild excitement and sustained enthusiasm, which lasted
for days with Lyell after this interview, and his letters to Herschel,
Whewell and others show his pleasure at the new light thrown upon the
subject and his impatience to have the matter laid before the Geological
Society.

Writing forty years afterwards, Darwin, speaking of the time of the return
of the "Beagle", says:  "I saw a great deal of Lyell.  One of his chief
characteristics was his sympathy with the work of others, and I was as much
astonished as delighted at the interest which he showed when, on my return
to England, I explained to him my views on coral-reefs.  This encouraged me
greatly, and his advice and example had much influence on me."  ("L.L." I.
page 68.)  Darwin further states that he saw more of Lyell at this time
than of any other scientific man, and at his request sent his first
communication to the Geological Society.  ("L.L." I. page 67.)

"Mr Lonsdale" (the able curator of the Geological Society), Darwin wrote to
Henslow, "with whom I had much interesting conversation," "gave me a most
cordial reception," and he adds, "If I was not much more inclined for
geology than the other branches of Natural History, I am sure Mr Lyell's
and Lonsdale's kindness ought to fix me.  You cannot conceive anything more
thoroughly good-natured than the heart-and-soul manner in which he put
himself in my place and thought what would be best to do."  ("L.L." I. page
275.)

Within a few days of Darwin's arrival in London we find Lyell writing to
Owen as follows:

"Mrs Lyell and I expect a few friends here on Saturday next, 29th
(October), to an early tea party at eight o'clock, and it will give us
great pleasure if you can join it.  Among others you will meet Mr Charles
Darwin, whom I believe you have seen, just returned from South America,
where he has laboured for zoologists as well as for hammer-bearers.  I have
also asked your friend Broderip."  ("The Life of Richard Owen", London,
1894, Vol. I. page 102.)  It would probably be on this occasion that the
services of Owen were secured for the work on the fossil bones sent home by
Darwin.

On November 2nd, we find Lyell introducing Darwin as his guest at the
Geological Society Club; on December 14th, Lyell and Stokes proposed Darwin
as a member of the Club; between that date and May 3rd of the following
year, when his election to the Club took place, he was several times dining
as a guest.

On January 4th, 1837, as we have already seen, Darwin was formally admitted
to the Geological Society, and on the same evening he read his first paper
(I have already pointed out that the notes read at the Geological Society
on Nov. 18, 1835 were extracts made by Sedgwick from letters sent to
Henslow, and not a paper sent home for publication by Darwin.) before the
Society, "Observations of proofs of recent elevation on the coast of Chili,
made during the Survey of H.M.S. "Beagle", commanded by Captain FitzRoy,
R.N."  By C. Darwin, F.G.S.  This paper was preceded by one on the same
subject by Mr A. Caldcleugh, and the reading of a letter and other
communications from the Foreign Office also relating to the earthquakes in
Chili.

At the meeting of the Council of the Geological Society on February 1st,
Darwin was nominated as a member of the new Council, and he was elected on
February 17th.

The meeting of the Geological Society on April 19th was devoted to the
reading by Owen of his paper on Toxodon, perhaps the most remarkable of the
fossil mammals found by Darwin in South America; and at the next meeting,
on May 3rd, Darwin himself read "A Sketch of the Deposits containing
extinct Mammalia in the neighbourhood of the Plata".  The next following
meeting, on May 17th, was devoted to Darwin's Coral-reef paper, entitled
"On certain areas of elevation and subsidence in the Pacific and Indian
Oceans, as deduced from the study of Coral Formations".  Neither of these
three early papers of Darwin were published in the Transactions of the
Geological Society, but the minutes of the Council show that they were
"withdrawn by the author by permission of the Council."

Darwin's activity during this session led to some rather alarming effects
upon his health, and he was induced to take a holiday in Staffordshire and
the Isle of Wight.  He was not idle, however, for a remark of his uncle, Mr
Wedgwood, led him to make those interesting observations on the work done
by earthworms, that resulted in his preparing a short memoir on the
subject, and this paper, "On the Formation of Mould", was read at the
Society on November 1st, 1837, being the first of Darwin's papers published
in full; it appeared in Vol. V. of the "Geological Transactions", pages
505-510.)

During this session, Darwin attended nearly all the Council meetings, and
took such an active part in the work of the Society that it is not
surprising to find that he was now requested to accept the position of
Secretary.  After some hesitation, in which he urged his inexperience and
want of knowledge of foreign languages, he consented to accept the
appointment.  ("L.L." I. page 285.)

At the anniversary meeting on February 16th, 1838, the Wollaston Medal was
given to Owen in recognition of his services in describing the fossil
mammals sent home by Darwin.  In his address, the President, Professor
Whewell, dwelt at length on the great value of the papers which Darwin had
laid before the Society during the preceding session.

On March 7th, Darwin read before the Society the most important perhaps of
all his geological papers, "On the Connexion of certain Volcanic Phenomena
in South America, and on the Formation of Mountain-Chains and Volcanoes as
the effect of Continental Elevations".  In this paper he boldly attacked
the tenets of the Catastrophists.  It is evident that Darwin at this time,
taking advantage of the temporary improvement in his health, was throwing
himself into the breach of Uniformitarianism with the greatest ardour. 
Lyell wrote to Sedgwick on April 21st, 1837, "Darwin is a glorious addition
to any society of geologists, and is working hard and making way, both in
his book and in our discussions."  ("The Life and Letters of the Reverend
Adam Sedgwick", Vol. I. page 484, Cambridge, 1890.)

We have unfortunately few records of the animated debates which took place
at this time between the old and new schools of geologists.  I have often
heard Lyell tell how Lockhart would bring down a party of friends from the
Athenaeum Club to Somerset House on Geological nights, not, as he carefully
explained, that "he cared for geology, but because he liked to while the
fellows fight."  But it fortunately happens that a few days after this last
of Darwin's great field-days, at the Geological Society, Lyell, in a
friendly letter to his father-in-law, Leonard Horner, wrote a very lively
account of the proceedings while his impressions were still fresh; and this
gives us an excellent idea of the character of these discussions.

Neither Sedgwick nor Buckland were present on this occasion, but we can
imagine how they would have chastised their two "erring pupils"--more in
sorrow than in anger--had they been there.  Greenough, too, was absent--
possibly unwilling to countenance even by his presence such outrageous
doctrines.

Darwin, after describing the great earthquakes which he had experienced in
South America, and the evidence of their connection with volcanic
outbursts, proceeded to show that earthquakes originated in fractures,
gradually formed in the earth's crust, and were accompanied by movements of
the land on either side of the fracture.  In conclusion he boldly advanced
the view "that continental elevations, and the action of volcanoes, are
phenomena now in progress, caused by some great but slow change in the
interior of the earth; and, therefore, that it might be anticipated, that
the formation of mountain chains is likewise in progress:  and at a rate
which may be judged of by either actions, but most clearly by the growth of
volcanoes."  ("Proc. Geol. Soc." Vol. II. pages 654-60.)

Lyell's account ("Life, Letters and Journals of Sir Charles Lyell, Bart.",
edited by his sister-in-law, Mrs Lyell, Vol. II. pages 40, 41 (Letter to
Leonard Horner, 1838), 2 vols.  London, 1881.) of the discussion was as
follows:  "In support of my heretical notions," Darwin "opened upon De la
Beche, Phillips and others his whole battery of the earthquakes and
volcanoes of the Andes, and argued that spaces at least a thousand miles
long were simultaneously subject to earthquakes and volcanic eruptions, and
that the elevation of the Pampas, Patagonia, etc., all depended on a common
cause; also that the greater the contortions of strata in a mountain chain,
the smaller must have been each separate and individual movement of that
long series which was necessary to upheave the chain.  Had they been more
violent, he contended that the subterraneous fluid matter would have gushed
out and overflowed, and the strata would have been blown up and
annihilated.  (It is interesting to compare this with what Darwin wrote to
Henslow seven years earlier.)  He therefore introduces a cooling of one
small underground injection, and then the pumping in of other lava, or
porphyry, or granite, into the previously consolidated and first-formed
mass of igneous rock.  (Ideas somewhat similar to this suggestion have
recently been revived by Dr See ("Proc. Am. Phil. Soc." Vol. XLVII. 1908,
page 262.).)  When he had done his description of the reiterated strokes of
his volcanic pump, De la Beche gave us a long oration about the
impossibility of strata of the Alps, etc., remaining flexible for such a
time as they must have done, if they were to be tilted, convoluted, or
overturned by gradual small shoves.  He never, however, explained his
theory of original flexibility, and therefore I am as unable as ever to
comprehend why flexiblility is a quality so limited in time.

"Phillips then got up and pronounced a panegyric upon the "Principles of
Geology", and although he still differed, thought the actual cause doctrine
had been so well put, that it had advanced the science and formed a date or
era, and that for centuries the two opposite doctrines would divide
geologists, some contending for greater pristine forces, others satisfied,
like Lyell and Darwin, with the same intensity as nature now employs.

"Fitton quizzed Phillips a little for the warmth of his eulogy, saying that
he (Fitton) and others, who had Mr Lyell always with them, were in the
habit of admiring and quarrelling with him every day, as one might do with
a sister or cousin, whom one would only kiss and embrace fervently after a
long absence.  This seemed to be Mr Phillips' case, coming up occasionally
from the provinces.  Fitton then finished this drollery by charging me with
not having done justice to Hutton, who he said was for gradual elevation.

"I replied, that most of the critics had attacked me for overrating Hutton,
and that Playfair understood him as I did.

"Whewell concluded by considering Hopkins' mathematical calculations, to
which Darwin had often referred.  He also said that we ought not to try and
make out what Hutton would have taught and thought, if he had known the
facts which we now know."

It may be necessary to point out, in explanation of the above narrative,
that while it was perfectly clear from Hutton's rather obscure and involved
writings that he advocated slow and gradual change on the earth's surface,
his frequent references to violent action and earthquakes led many--
including Playfair, Lyell and Whewell--to believe that he held the changes
going on in the earth's interior to be of a catastrophic nature.  Fitton,
however, maintained that Hutton was consistently uniformitarian.  Before
the idea of the actual "flowing" of solid bodies under intense pressure had
been grasped by geologists, De la Beche, like Playfair before him,
maintained that the bending and folding of rocks must have been effected
before their complete consolidation.

In concluding his account of this memorable discussion, Lyell adds:  "I was
much struck with the different tone in which my gradual causes was treated
by all, even including De la Beche, from that which they experienced in the
same room four years ago, when Buckland, De la Beche(?), Sedgwick, Whewell,
and some others treated them with as much ridicule as was consistent with
politeness in my presence."

This important paper was, in spite of its theoretical character, published
in full in the "Transactions of the Geological Society" (Ser. 2, Vol. V.
pages 601-630).  It did not however appear till 1840, and possibly some
changes may have been made in it during the long interval between reading
and printing.  During the year 1839, Darwin continued his regular
attendance at the Council meetings, but there is no record of any
discussions in which he may have taken part, and he contributed no papers
himself to the Society.  At the beginning of 1840, he was re-elected for
the third time as Secretary, but the results of failing health are
indicated by the circumstance that, only at one meeting early in the
session, was he able to attend the Council.  At the beginning of the next
session (Feb. 1841) Bunbury succeeded him as Secretary, Darwin still
remaining on the Council.  It may be regarded as a striking indication of
the esteem in which he was held by his fellow geologists, that Darwin
remained on the Council for 14 consecutive years down to 18