The History of Civilization

The Earth before History

The History of Civilization

In the Section of this Series devoted to Pre-History and Antiquity are
included the following volumes : —

/. Introduction and Pre-History

♦Social Organization ....

The Earth Before History .

Prehistoric Man .....

Language : A Linguistic Introduction to History

A Geographical Introduction to History

Race and History

From Tribe to Empire .
♦Woman's Place in Simple Societies
♦Cycles in History
♦The Diffusion of Culture .
♦The Migration of Symbols .
♦The Foundations of Western Civilization

W. H. R. Rivers

E. Perrier

J. de Morgan

J. Vendryes

L. Febvre

E. Pittard

A. Moret

J. L. Myres

J. L. Myres

G. Elliot Smith

D. A. Mackenzie

V. G. Child e

II The Early Empires

The Nile and Egyptian Civilization
♦Colour Symbolism of Ancient Egypt
Chaldaeo-Assyrian Civilization .
The Aegean Civilization

A. Moret
D. A. Mackenzie
. L. Delaporte

G. Glotz

* An asterisk indicates that the volume does not form part of the French collection " L'Evolution
de l'Humanite " (of which the present work is No. i of the First Section), published under the
direction of M. Henri Berr, Editor of the " Revue de Synthese Historique ".

A full list of the Series will be found at the end of this volume.

T5 H A

The

Earth before History

Man's Origin and the Origin of Life

By
EDMOND PERRIER

Late Professor of Comparative Anatomy at the Musium d' 'LListoire Katurelle,
Alembre de FAcadc'mie des Sciences et de PAcadc'mie de Mididne.

NEW YORK

ALFRED A. KNOPF

1925

Translated by

PAUL RADIN, Ph.D.

Late Associate Professor of Anthropology in the University of California,

and

V. C. C. COLLUM

Printed in Great Britain by Stephen Austin fir5 Sons, Ltd., Hertford.

GENERAL INTRODUCTION

rT~r[\'0 circumstances, quite different in nature, make the
1 present time particularly favourable for the writing of a
Universal History : on the one hand, the development of
historical studies, and, on the other, the growth of world-conditions
in which all countries share.

For almost a century now an ever increasing number of
students — anthropologists, historians, archceologists — have been
extending, with commendable patience, their researches along all
lines and into the most remote corners of man's past. The
tremendous mass of detailed knowledge thus accumidated was
bound eventually to force upon scholars the necessity for some kind
of synthesis, and tJiis need has made itself felt most imperatively
in a desire for some co-ordinating point of view from which it
wovdd be possible to dominate Time.

Yet the work of the historians, no matter how impartial it
may appear, does not merely respond to intetfftl laws but is
also subject to external influences to a certain extent. If, for
instance, any particular trait may be regarded as characteristic
of our present epoch it is the human solidarity encountered all
over the earth. Our planet seems to have shrunk in size through
the rapidity of communication and civilized nations have
developed such intimate relations either between one another or
through intensive colonization, with less developed peoples, that,
as in an organism, everything seems to be inter-connected.
To-day we have a world-politics, a world-economics, a world-
civilization. This visible spatial and temporal unity in human
groups invites us to reflect upon the role which the universal
factor has played from the beginnings of time.

Thus, apart from the works devoted to facts and individuals,
to countries, peoples, and successive epochs, we have the Earth
and Humanity left as objects that must be studied.

In Germany, during the years preceding the war, the study of
universal history flourished — under the name of " Weltge-

vi THE EARTH BEFORE HISTORY

schichte ". In that home of erudition and adventurous synthesis,
where a balance between " micrography " and metaphysics is
seldom achieved, the arduous labour of historians and a pre-
occupation with world affairs have resulted in the appearance of
numerous works, unequal in importance and interest, which
endeavoured to satisfy, and at the same time have stimulated, the
demand for universal history. Some of these volumes are merely
collections of chapters, compilations without unity, others are
systematized to an excessive degree ; some are co-operative, and
are the result of more or less definite collaboration, others represent
the enterprise, rash though it may have been, of one man. Yet all
possess merits, whatever be the criticism to which they lend them-
selves. But there is room for a new synthesis, for a vast
enterprise, on new foundations, which shall include Humanity ,
from its origins, and the Earth as a whole.

The work which this introductory volume is to inaugurate
will have the following special features :

It will have a real unity : not merely the unity of its subject —
history in its entirety — but unity of plan, firmly binding
together all the various parts ; and also unity of the
activating ideas. The problem with which we are faced is how
to prevent incoherence and yet to avoid the opposite error of
over-systematizatiou. In the present state of our knowledge,
a single individual cannot accomplish this task alone, and even
to organize it he must exercise very great discretion. Certain
ideas will run through the whole enterprise, but they will not be
dominating theories thrust upon the collaborators, and, through
them, upon the facts ; rather will they be experimeyital ideas,
hypotheses pervading the whole work, and subjected' to the control
of actual facts by unfettered investigation, allowing complete
autonomy to the collaborators. Our undertaking is thus something
in the nature of a vast experiment, to be gradually undertaken
under the eyes of the public to the great profit, as we hope, of
historical science ; and the ideas put forward will emerge from
the test either confirmed or rectified.

Within this unity of the whole each part will have its own
unity. The series has not been planned in terms of large collective
volumes, grouping together more or less unconnected chapters
written by various collaborators, but as independent volumes of
moderate size. The number of these will, therefore, be considerable,

GENERAL INTRODUCTION vii

since they will correspond to the great problems and the organic
divisions of history ; and each, as far as this is possible, will be
entrusted to a single scholar of recognized authority. Each will
be an independent work, will carry the imprint of one personality ,
and will be the more interesting in that it will have been written
with greater freedom and pleasure. Each volume will have its
own life ; so too will a given group of volumes, and they will thus,
from different view-points, form a whole within a whole, partial
syntheses within a total synthesis. Our task, in short, is to
combine the advantages of an historical encyclopedia with those
of a continuous history of human evolution.

Having thus indicated the general characteristics of our
enterprise, let us proceed to the principles which will govern the
undertaking as a whole, and to the general character of the volumes
themselves.

To unite Science and Life : such is the formula which
expresses the ideal we desire to attain.

This series is to be essentially a work of scholarship. Not
only will it offer the most authoritative knowledge, but this
knowledge will be amply documented — as we shall shortly explain.
Any learned synthesis, which gives results without indicating
the sources, presupposes an act of faith, since it does not facilitate
verification and must in a way appear to lead to stagnation in
research, since it does not provide ihe impetus to proceed further.
But if we set forth an inventory of the work accomplished we can
not only indicate all that remains to be done but procure the
means for accomplishing it. From the standpoint of scholarship ,
then, our undertaking will at once mark achievement and provide
a point of departure for work still to be done.

But the aim of the series is not merely to be erudite : it is also
to be scientific in the full sense of that term. Scholarship may
enable us to prepare and assemble materials : it is science alone,
however, that brings order into them. Indeed, one of the most
subtle problems confronting the human mind is that concerned
with the scientific nature of history. To arrange facts in series,
in traditional compartments, to recount the lives of individuals
or of peoples, this has nothing to do with science — for its proper
work is to generalize and to elicit principles of explanation.

Without claiming that the method of scientific synthesis can

viii THE EARTH BEFORE HISTORY

actually be fixed for history in any definite fashion, it may be
assumed — at least, as a tentative hypothesis — that the facts of
which human evolution is woven, can be grouped in three quite
distinct orders. The first are the contingent, the second the
necessary, and the third those that relate to some inner logic. We
shall try to make use of and to harmonize the very diverse explana-
tions that have been attempted, by endeavouring to show that the
whole content of human evolution falls into these general divisions
of contingency, necessity, and logic. It seems to us that by this
tripartite division, history receives both its natural articulation
and its whole explanation. Indeed, this classification opens up
a deeper view of causality. It invites us to probe into the mass of
historical facts and to attempt to disentangle three kinds of causal
relations : mere succession, where the facts are simply determined
by others : relations that are constant, where the facts are linked
to others by necessity : and internal linkage, where the facts are
rationally connected with others. On this view of the nature of
the causes operating in history, a synthesis may not appear
easy, but it is at least conceivable. We have developed this
methodological hypothesis x at length elsevohere ; here we would
merely summarize briefly its general bearings.

For societies to take form and to endure they must submit to
certain special and necessary conditions which we call institutions.
Wherever a society exists there are institutions — at any rate,
in outline. We encounter the same fundamental institutions
everywhere, although under different forms ; but this diversity
is not unlimited in its characteristics, a fact that is to be
explained, in part, by the differences existing in the very
structure of societies — that is to say, in the number of social
units and their concentration or density. " Sociology," when it
is conscious and scientific looks upon societies merely as such.
The proper work of the sociologist is the study of social organiza-
tion from the comparative point of view. In order the better to
define its essential functions as translated into institutions, and
in order to determine the connexions of these functions with the
social structure and their reciprocal inter-relationships , it isolates
the social element. This is one of the aspects of historical
synthesis, yet only one. A complete historical synthesis brings
this element, these necessities or social laws, into renewed contact

1 La Synthesc en Histoire : Essaz critique et theorique, fan's, 1911

GENERAL INTRODUCTION ix

with the other elements of history, elements neglected and, indeed,
often denied by the pure sociologist.

It is also desirable in any attempt to differentiate between
various explanatory elements to make the following distinction.
Even if institutions are always a social construction, so to speak,
and bear the stamp of society, it does not follow from this that
they always express the specific necessities of society or respond
to actual functions. Not everything which, in the course of the
life of society, takes on an institutional form is essentially social.

The juridico-political function is an essential characteristic of
society and it differentiates itself into political, juridical, and
moral elements ; its only reason for existence is in, and for,
society, of which in fact it forms the chief support, fust as
economic institutions correspond to the personal necessities of
the individual — the necessities of subsistence, of enjoyment,
and of luxury — so we may speak of an economic function of
society ; theoretically it might even be considered as primary,
for society can only be organized by giving to these needs of the
individual a more secure and complete satisfaction by appropriate
means and by substituting, to a great extent, co-operation and
division of labour for individual effort. But we cannot accurately
speak of a mental or (esthetic function of society, although institu-
tions have been built up with art and science in view. Society
does not think. Mental development as well as (esthetic — from
the most rudimentary technique to the efflorescence of philosophy,
science, and art — rests essentially on the faculties of the individual :
it is human not social. Of course, this human development is
only possible within society. Between the human and the social
there is constant action and reaction, and with the very beginnings
of thought we are confronted by the problem of the nature of
this interrelation between the individual — as a thinking being —
and society. It develops particularly with that very complex
group of phenomena which we call religious. But in spite of
appearances we believe it to be as impossible to speak of a religious
function of society as of a mental or (esthetic one. Religion
consists fundamentally of a connected system of beliefs and
practices related to a given milieu and to forces surrounding and
transcending those of man : in other words, it is an inter-
pretation of the objects by which human activity tends to be
regulated. It gives expression to the most profound anxieties of
developing thought and amalgamates them with the most varied

x THE EARTH BEFORE HISTORY

psychical elements. It is human in essence— but strongly
socialized. The possession of specific institutions does not suffice
for religion ; it must also enter into the various functions of
social life. In short it consolidates into one unified whole the
social bond and simple primitive mentality — consolidating the
one by means of the other. In thus strengthening thought,
however, it at the same time confines and tends to constrain it ;
and, moreover, the individual endeavours either to transform
the religious institutions or, to a certain extent, to free himself
from them ; it is to this effort that art, philosophy and science
specifically owe their development.

If, then, the study of the social factor is at the basis of
historical synthesis, since society is man's necessary milieu
and a constant and regular element in history, it is just as
clear that the evolution of society, as such, as well as its com-
plications, only become intelligible when considered in the light
of other factors. It is therefore necessary to introduce that
" logical " factor which has already been so much abused, under
the terms "finality" and "Idea", by philosophic historians,
and the factor of contingency, of which purely descriptive
historians have made too exclusive and complacent a use ; the
latter being also known as the principle of change as such,
fortuitous or directed.

Contingencies modify the structure of human society ; they
either react on them or influence them directly. Their number
in history is infinite, but they can be brought together under
cer ain general categories : accidental happenings, the role of
the individual as individual, temporary collective arrangements,
and ethnic and geographical conditions. Neither the categories
themselves nor the contingencies within each category are of
equal interest to the historian who is concerned with explanation.
Their importance is determined by the extent and the duration
of their action : surroundings races, and epochs can be grouped
from the point of view of human evolution ; individuals and
events can be selected from the same standpoint ; some are
insignificant, others important. Our mind can only dominate
and systematize the past by resorting to elimination — just as
chance has unfortunately done with remote epochs. But we
must consign again to oblivion something of what has been
selected.

It is when we thus reject negligible events that Vie role of

GENERAL INTRODUCTION xi

" logic ' in the life of societies is best realized. The logical
factor is explanatory in the deepest sense of the word. It is
what gives to evolution its real continuity, its inner law ; it is
from their connexion with it and exactly to the degree in which
they either serve or contradict logic that contingent happenings
derive their actual value. They lead to others : but it is the logical
factor which alone produces new events : it alone is creative.
The principle from which all logic proceeds, the real motive force
of history — as of life — can only be discovered, it seems to us, in
the tendency of a human being to maintain and expand his
Personality. Life is not a passive and empty thing. It is
tendency and memory. When sticcessful it retains the means
that led to its success. Logic, strictly speaking, is the profitable
use of mind ; in the broader sense, however, it is that activity
which conforms to the fundamental tendencies of the being who
employs appropriate means. Springing from the inner core of
life the logical activity ends by both in co-operation and in struggle,
but expands more in the form of social instinct than as egotism ;
in short it creates society itself.

Once society has been formed and endowed with specific laws,
the principle that gave it birth continues to aid in its development.
The same logic that laid the foundation for the social organism
produces in large measure the inner phenomena of crisis and
reform, of political, juridico-moral and economic evolution. It
manifests itself in the external activity of social groups and
in inter-social connexions by means of various phenomena, all of
vital historical interest. There is, for instance, the phenomenon
of " migration ", to explain which it is not enough to give an
account of the pressure of geographical surroundings, but which
through a " Will to Change " , gives expression to that restlessness
which craves for a better existence, to the desire for a habitat
favourable to life, and, undoubtedly also, to an ambition to
enlarge the sphere of the known and to secure a larger possession
of the earth. There is the phenomenon of " Imperialism " —
which tends, by a " Will to Growth " , to seize possession, for
divers purposes, of a larger or smaller part of humanity. It has,
moreover, various types, some more violent, others of a more
assimilative nature. There are finally the phenomena of
" receptivity ", of " renaissance ", of international " co-opera-
tion " — which, by a " Will to Culture ", tend to unite societies,
across space and time, in order that they may conquer nature and

xii THE EARTH BEFORE HISTORY

adapt it to human needs, and to render them more and more at
one through the creation and multiplication of " values " of all
kinds.

In connexion with the manifestations of this social logic
which concerns either the inner life or the external activity of
societies — there arises a very important and subtle question and
one which has already presented itself in regard to mental
evolution, namely the role of the individual and his relation to
society. We have seen that mental development introduced
into social organization elements that were human in origin —
that is to say, individual — and remodelled the " Institutional "
form without, however, entirely depriving the individual of his
specific faculty of thinking. Indeed, in addition to being the
agent of mental logic, the individual is also, it seems, the agent
of social logic. These institutions which appear as something
objective and with a large measure of constraining force, these
actions of the group which spring apparently from a collective
will, do not entirely escape the consciousness of the individual.
In fact, what is the " social consciousness " — if we would not
be duped by words — except the representation of society in the
consciousness of individuals ? Even the most striking phenomena
of social life, those that arise from what might be called " herd
conditions ", admit of an active participation of the individual,
however effaced this may seem to be. In these states — which are
essentially affective — although the individual representations
are sharpened and have become harmonized through a common
emotion, and although, to a certain degree, a unity of consciousness
can be temporarily realized, individuals are always found
who unquestionably respond in a high degree to the needs of the
group as regards canalizing and directing the manifestation : they
are, in consequence, not simple elements of society but true
social agents. But apart from these " herd " manifestations —
which for numerous reasons have become less and less frequent in
the course of history — can it be said that the representation of
society has been especially unequal in intensity or in precision
in the minds of different individuals ? Society, let me repeat,
does not think : it is the individual who thinks. He can, however,
also be more than a social agent : an initiator, a social inventor.
Mental and social logic have the same profound source and here
they meet. Born of the success of activity, thought in the individual
concerns itself with serving action and perfecting social life.

GENERAL INTRODUCTION xiii

It is difficult to deny the practical efficacy of ideas : we should
rather endeavour to determine it.

In fine, to unravel the complicated skein of causality : to
distinguish the "accidental" or the "crude facts" of history, the
institutions or the social necessities, the needs or the fundamental
causes that flower in the form of ideas within reflective thought :
to study the play of these diverse elements — contingent, necessary,
and logical — their reciprocal action and what may be called the
rearrangement of causes : this should constitute the essential
object of this synthesis. We must take care not to promise too
much. Universal history — because of its extent, its complication,
its lacuna?, and the necessity for co-operation — does not permit
a complete solution of these problems. Studies more limited in
scope and at the same time more intensive alone can furnish
decisive demonstrations. But for special studies to be suitably
directed it is useful to have before us the general tendency of
history as a whole. That is why we shall try, in the main at
any rate, to make our work the opposite of unilateral, to neglect
none of the explanatory elements, but yet, by careful arrangement,
to give to each its proper part. In distributing the subject-matter
and in deciding upon the volumes to be included, certain hypotheses,
dictated by the whole scope of the work, were, indeed, paramount.
They have been indicated at the outset and will appear at different
places in the introductions, but they will serve merely as a bond —
and that only discreetly. It would not be wise to rely on it unduly.
Let it be remembered that the collaborators are free and that
their liberty of action alone can give full value to this enterprise.
This is no pre-arranged experiment — merely a simple experiment
" to see ", as Claude Bernard said. It is not a question of solving
problems at all costs but rather of stating them and of introducing
into tmiversal history the leaven of true science.

*

* *

Although profoundly scientific in intention this series will not,
for that reason, be any the less alive. It has been supposed,
quite erroneously , that the introduction of science into history
is opposed to life, that the resurrection of the past is the privilege
of art. It is analysis which reduces the past to a dust-heap of
facts ; what erudition collects is saved not from death but from
oblivion. Synthesis resurrects the past, otherwise than does
intuition, and better. Its task as defined by Michelet, " the

xiv THE EARTH BEFORE HISTORY

resurrection of the whole of life not merely in its surface aspects
but in its inner and deeper organisms ", cannot be fulfilled by
genius ; but science can accomplish it by deepening its theory
of causality and endeavouring, through its synthesis, to reconstitute
the interplay of causes.

It is this purpose, then, that animates our work : to render
intelligible by the study of its causes, and to enable us to follow
that progressive movement — not continuously and absolutely
progressive, but as a whole and from certain points of view —
which gives meaning to the life of humanity. Facts of every
category — isolated by special historical accounts and forming in
general histories a mosaic of juxtaposed chapters — will all be
considered in relation to the permanent needs and individual
character of different societies. These societies, on the other
hand, will be considered not for themselves but in their relation
to the great transformations of humanity. We would not make
of them entities or idols. But it is the way in which life changes
and develops in human societies that constitutes the specific
object of historical science. This is all that is meant, in short,
by " civilization " or " culture ", both handy and rather vague
words. We shall not deprive ourselves of the use of the word
" civilization " : and since we cannot begin with a precise
definition we shall in these volumes give it its broad meaning —
the increasing complexity of life — relying upon the work itself
to indicate what is essential in this complex whole and how the
true line of progress is to be determined.

From the point of view of an ideal presentation, a practical
difficulty presents itself. The publications will follow as far as
possible the order of the general plan. It woidd have been easier,
after the plan of the work had once been decided upon, to publish
the volumes as soon as they were completed without reference to
any order : but we should then have produced not a real work ;
we should only have formed a collection. On the principle
adopted, however, the authors and the public will take a more
lively interest in the enterprise. Each author will be in a position
to adjust his work to those volumes nearest in scope, no matter
how strong the personal element, and thus make his contribution
fit into the whole. There are undoubtedly subjects whose position
is not strictly determined : but apart from a very limited number
of cases, the volumes will appear in the order arranged, and, in
particular, that one series will not overlap another.

GENERAL INTRODUCTION xv

By a series, we understand a group of volumes composed from
different points of view, and on this a few words of explanation
are necessary.

The divisions of universal history in their time relations,
represent a very delicate problem which the Germans call
" Periodisierung der W eltgeschicJite ", and here many kinds of
mistakes and prejudices must be avoided. Chronological divisions
are handy and even necessary compartments ; but pushed too far,
a pre-occupation with chronology tends, on the one hand, to split
up the study of regions and peoples and, on the other hand, to
bring on to the same plane phenomena of unequal importance
from the cultural point of view (Lavisse and Rambaud). If
chronology is subordinated to geographical and ethnical interests
the thread is broken : we simply get a collection of histories for
different regions of the world (Helmolt), or for different
peoples (Duruy, Oncken, Heeren, Uckert, von Giesebrecht, and
Lamprecht) , and not a universal history. If, on the other hand,
chronology is subordinated to logic the woof is knit too tight,
and we get a metaphysical synthesis and not a science of history.
The purely logical divisions — whether through the choice of
centres of civilization or of preponderating races, they ascribe
to humanity a succession of periods enclosed as it were the one
within the other (the Philosophy of history, Hegel), or
give all peoples a succession of identical periods (Lamprecht) ;
whether they terminate in a continuous progress (German
philosophers) or in an eternal recurrence (Vico) with or without
progress — are all arbitrary, undesirable and condemned : but
they are always reappearing, doubtless because they correspond to
some element of historical reality.

We, for our part, shall attempt to reconcile these various
interests. We shall have four large chronological sections :
Introduction (pre-hi story and proto-history) and antiquity ;
Christian origins and the Middle Ages ; the Modern era ; and
the Contemporary era. Each of these sections will comprise almost
the same number of volumes although they will embrace shorter
and shorter periods. This economy can be easily justified owing
to the inequality of the resources at our disposal for the investiga-
tion of these periods and the practical utility afforded
respectively by their study.

In these sections, the secondary divisions and, in turn, their
units, will be so arranged as to satisfy, as far as this is possible,

xvi THE EARTH BEFORE HISTORY

the interests of geography, ethnography — or the psychology of
peoples — and logic. The pre-occupation with the whole as such,
with human evolution, will no doubt be constantly in evidence :
mid from the very nature of things this will become increasingly
Prominent since, as we remarked before, human solidarity becomes
more and more manifest as we proceed : but light will be
■thrown, in the course of our work, at the opportune moment and
in the measure desired, upon those portions of the earth and upon
those peoples whose influence makes itself felt, and becomes
preponderant. As to logic, if our conception of causality occupies
too large a place it will yet be admitted that it has been entirely
freed from its metaphysical and a priori nature : it has become
merely one of the positive elements of history whose role is to be
determined. Moreover, is not the fundamental principle of
division here of an internal nature ? Is it not derived from the
complex nature of historical causality ? As we have already
indicated, our principal care will be to lay particular stress on the
effect of great events, the pressure of social necessities, the profound
influence of psychic factors, of needs and ideas, and thus to
■bring into relief not the continuity of progress but the three-fold
play of the permanent causes and the results of their continuous
operation.1

Our work, although it will have all the utility of an
Encyclopaedia, will, as we shall see, be something quite different.
If it is true that a little science sterilizes history, a good deal of
science ought to endow it with life. The pre-occupation with
general and permanent causes, which enhances the worth of even
the most modest research, will give our synthesis not only its full
dignity but its full interest, and an element of dramatic attraction.
We are concerned, in other words, with reconstructing the road
along which humanity has travelled ; the path which a blind
instinct, obscure influences, and a variety of circumstances have
forced it to take ; and in so doing we are attempting to understand
why this path has been pursued. Along the ages, through the

1 After the main outlines of the plan had been sketched, I submitted it to the
judgment of friends, and I have also sought the advice of specialists in assigning
the various volumes. Although firmly adhering to the initial lines laid down,
I have profited by the experience of numerous scholars and the suggestions of
the most diverse types of men. I would like to mention among those who have
been most intimately associated in the work of elaboration my friends Paul
Lorquet, L. Barrau-Dihigo, Lucien Febvre, and Abel Rey. To these and others
the plan owes some of its merits : for its defects I alone assume full
responsibility.

GENERAL INTRODUCTION xvii

efforts, ambitions, struggles, and the diverse fates of groups, in
spite of stumblings, detours, and setbacks — Humanity progresses.
Its horizon, as we advance, becomes higher : it endeavours with
the aid of the historian to adjust itself in time and space, to take
cognizance of itself, to know more in order to do more. A n enterprise
like ours is consequently a living thing. And though it is the
duty of the historian as a scholar to collect facts and to study
their causes objectively and dispassionately, yet he has the right
as a man to develop an enthusiasm for his work and impart to it
an inner fire.

Since our work must possess this living character a final
problem confronts us. Shall we content ourselves with the text
alone and absolutely reject the picture or shall we utilize illustra-
tions and thus give the text an additional vital interest ?

Illustration has its dangers. A few pictures scattered through
a volume give it a more attractive, perhaps a more unacademic
aspect but do not necessarily heighten its value. Numerous
illustrations, on the other hand, generally end by dominating
the volume, impose upon it a definite size and definite proportions
so that we run the risk of reducing the text to a mere commentary.
Nevertheless, we admit that illustrations have their merits. The
resurrection of the inner and deeper life of the past calls in some
measure for a visualization of individuals and their surroundings.
Michelet is the " visualizer " not merely of souls but also of
forms. If, then, it is opportune to replace a dangerous psycho-
logical intuition by methodical research into causes, it is perhaps
equally opportune to replace or help a dangerous imaginative
vision by forcing it to look upon authentic pictures.

Whenever, therefore, the text would seem to be obscure and
incomplete without this aid, useful illustrations will be found in
the proper place. In certain volumes which demand a larger
number, plates can be added in an appendix. In the main,
however, the role of the illustration will always remain an
accessory one.

II

Each volume, as we have said, is to have its own interest and
its own unity.

Each will constitute, for a given period or for a given historical

problem, an inventory of what has been and what still remains

to be accomplished.

b

xviii THE EARTH BEFORE HISTORY

Each volume will contain a Bibliography : not exhaustive,
of course, but sufficiently complete to furnish students with the
necessary data for obtaining additional information. The works
mentioned in this Bibliography will be numbered ; and in the
notes references will be made as far as possible by means of
numbers — one for the bibliographical item, one for the volume
of the work, and, if necessary, a number for the page. Placed
one after another, and separated simply by commas, these
references can be multiplied without encroaching upon or
encumbering the book itself.

By this means we shall be able to realize our double purpose
of satisfying the demands of science and helping the student,
and of addressing ourselves, at the same time, to the large
cultivated public interested in human destinies. The presenta-
tion of the results attained in language as clear and as vivid
as possible will occupy the bulk of the pages. The amateur in
history will find an advantage in this : he will even escape the
involuntary distraction produced by notes which are immediate' y
intelligible. In order to be useful our numbered references will
necessitate a study of the Bibliography ; but the author will thus
be able, in an economical manner, to justify the essential parts
of his text, and the historically minded reader, if he so desires,
to considt the sources with a minimum of effort, whether in order
to verify the contents or to extend the work beyond the point
where the author has left it.

Works without references, syntheses where, at the best, the
Bibliography is found at the beginning or at the end of the
chapters, without running notes, are quite popular to-day, in
Germany and elsewhere, and represent a reaction against the
abuse of erudite annotation. But this opposite excess appears
to us also dangerous. Under such anti-scientific conditions we
are forced to take the author at his word. But no matter how
scrupulous he may be, an author will often allow himself to group
facts artificially, to present hypotheses as certitudes. As far as
facts or the explanation of facts are concerned, the certain, the
probable, the possible ought, of course, to be carefully graded and
be so offered for criticism.

The bearings of each work and what still remains to be done
will be touched on in the last chapter of every volume in an
arresting manner. The object aimed at will be to show the lacunce
still existing, the questions which arise in the various fields in

GENERAL INTRODUCTION xix

connexion with the different periods of history, the publications
that are urgent and the researches, explorations, and excavations
which, by furnishing new facts, might possibly clear up obscure
points. These concluding chapters will thus offer many
advantages. Not only will they furnish specialists with
useful hints, but they will, at the same time, offer numerous
subjects for treatment and give many individuals with indefinite
but praiseworthy desires, ample opportunity for effectively
employing themselves. It is to be hoped that this general survey
of the historical field may lead to a better organization of effort,
to a more advantageous division of labour, and direct some of the
surplus workers with which certain subjects are encumbered
toward the neglected regions of science.

Our inventory will even be of profit to the merely curious
public : it will provide a sane notion of the present and future
conditions of historical studies. No one, of course, is to imagine
that in this synthesis history has been completed. History is in
the making : it exists as a knowledge of the past obtained
through learned research, as an explanation of the past through
the study of causes. Our knowledge of the past, quite incomplete
to-day, will, in fact, always remain so in spite of constant progress ;
what has existed, what has lived, what has been created and then
destroyed by time, of all this only an infinitesimal part can possibly
be evoked. But the scientific problems raised by the past will
gradually become more definite and in the course of investigations
still to be determined may eventually be solved. That is how the
public, no less than the historians, ought to conceive scientific
history or synthesis — as the determination and gradual solution
of limited problems relating to a subject that is itself without
limitations and in part unknowable.

Ill

Our enterprise may thus be of great value to further decisive
progress in the study of human evolution. Its object is the proper
arrangement of labour and the elaboration of a true scientific
method with the purpose of initiating the public into the more
serious and engrossing aspects of history as a whole. In the
natural sciences, laboratory research, however technical and
ungrateful it may be, always results in theories or in a practical
outcome to which the public cannot remain indifferent : and, for

xx THE EARTH BEFORE HISTORY

that reason, there is abundance of encouragement for those who
cultivate these fields. On the other hand, because of its over-
erudite and insufficiently scientific character, history as presented
by learned historians has become an arid speciality, in which the
public manifests no interest — accepting in their place anecdotal
and romantic works put together by clever popularizers in the guise
of true history.

Thanks to the eminent collaborators who have co-operated in
this undertaking, things may perhaps be changed for the better.
Our programme is vast and our ambition must appear to
many over-sanguine. But we must take the risk. It is obvious
that a desire for action, a confidence in the spontaneous forces
of life have been revived amongst us. There would be a dis-
quieting side to this if, as some tell us, it has taken an anti-
intellectualistic turn. It is essential that this need for action,
this revival, should also manifest itself in intellectual courage.
Life expands with knowledge. And an historic science under-
stood in a living manner — the consciousness of humanity springing
from reflection is necessary to direct the tumultuous powers of
instinct.

Henri Berr.

FOREWORD TO THE FIRST SERIES

/T is not our purpose to justify the plan of our first Section
taken as a whole ; it arose of itself. We shall preface
each Series with such explanations as seem useful.

With regard to the first volume, we may observe that its object
is not merely to give a resume of all we know concerning human
origins carried back as far as possible into the past. It is as
much an introduction to history itself as to the problems of
History.

The justification for its inclusion is that it connects History
in the strict and accepted sense of the word with History as
understood in its broader sense of linking the evolution of
Humanity with the evolution of Life on the Earth and with the
evolution of our planet in the Universe. It enables us to find
a proper " place " for humanity so that its destiny does not seem
like a mere adventure or an unrelated episode. To attain this
it was above all essential to exhibit the great natural forces and
the permanent factors, which in explaining the Earth and
Life will explain, at the same time, the evolution of Man and
of Society.

We shall thus see how the " milieu " of our history was formed
in the stellar system : in this milieu, detached from the Sun
though still dependent on it, we shall perceive life arising —
apparently through the action of the Sun itself. We shall see
its first tentative advances in all directions and its experiments
with the most diverse forms. We shall see it subjected to the
complex influences of different habitats, of innumerable vicissitudes
and of its own inner properties : to heredity, that conservative
principle which may also become an agent of change, and to
tendency, an active principle expressing itself in the faculty of
assimilation and of association more efficiently than in struggle :
and realizing every sort of improvement, until finally, with the
human form, we reach that decisive advance — the development of
the brain.

xxii THE EARTH BEFORE HISTORY

It is an immense subject demanding a richness and an
exceptional variety of knowledge, together with a rare power of
synthesis such as perhaps only the author of this volume possesses.
The man who in 1881 wrote " Les Colonies animates et la
formation des organismes " , who occupied the professorial Chair
of Lamarck, and always "followed with the deepest interest the
attempts of the transformist doctrine to provide an explanation
of the living world ", that man, at the summit of his great career
was well qualified to establish, in this vigorous epitome, a biological
bond of union between the physical sciences and history.

We need not be surprised that this volume does not entirely
conform to the type we have outlined, that its Bibliography is so
restricted, and finally that the concluding chapter does not indicate
the gaps in our knowledge. The Bibliography and the list of
the problems to be solved would be infinite were they not strictly
limited in the case of a subject covering, as it does, millions of
years.

In a general way, in the volumes of this first Series, the
subjects, on account of their extent and complexity , do not lend
themselves to quite the same treatment as that of the more properly
historical volumes which follow.

Henri Berr.

CONTENTS

PAGE

General Introduction (by Henri Berr) . . v

Foreword to the First Series (by Henri Berr) xxi

Part I. THE FORMATION OF THE EARTH . i

Chap.

I. The Birth of the World .... 3

II. Transformations of Land or Water . 15

III. The Sun and Climatic Variation . . 38

Part II. THE PRIMITIVE FORMS OF LIFE . 57

Chap.

I. The Appearance of Life .... 59

II. The Genealogical Basis of Organic

Differentiation ..... 74

III. The Genesis of the Typical Forms of the

Plant Kingdom ..... 96

IV. Primitive Animal Forms .... 112

V. Attitudinal Changes and Structural

Modifications 126

VI. The Peopling of the Open Sea, the Ocean

Depths, and the Land Masses . . 146

' >

■

I '-> >' ^

XXIV

THE EARTH BEFORE HISTORY

FAGE

3 ART

III. TOWARDS THE HUMAN FORM

. 197

^HAP.
I.

Life in the Primary Period

• 199

II.

Life in Secondary Times .

• 243

III.

Life in Tertiary Times.

. 28l

IV.

The Human Form ....

• 317

Conclusion .....

• 325

Maps .......

• 333

Bibliography

• 337

Index ......

• 34i

MAPS

I. The Conformation of Land and Sea in the
Northern Hemisphere at the Beginning

of the Primary Period. . . . 333

II. The Continents of the Cambrian Epoch . 334

III. The Earth of the Jurassic Period . . . 335

IV. The Earth of the Nummulitic Period . . 336

PART I

THE FORMATION OF THE EARTH

CHAPTER I

The Birth of Our World

ALL that we know of the extent of the universe has been
revealed to us by the light of the stars. At a speed of
186,000 miles a second the light of the nearest of these stars
takes about two years to reach us. We do not know how far
removed the furthest of them is ; we cannot even affirm that
their distance is inversely proportional to their brilliance, nor
can we say how many figures would be necessary to express
this distance in miles. Whatever the nature of light may be
we are at all events certain that it cannot reach us from those
stars unless it is borne by that " unknown something " which
fills space. It was once believed that this unknown medium was
the substance of light itself. To-day, however, there are strong
reasons for assuming that this medium exists in its own right.
It has been named the ether, and has been pictured as composed
of particles so small that in comparison with them an atom is
enormous. These particles are capable of oscillating around a
fixed point from which they can deviate only very slightly,
and these regular oscillations, propagated in the ether
as ripples are propagated in water when a stone is dropped
into it, constitute light. The light of the sun and of the various
stars maintain vibrations in the ether, which cross each other
in every direction without mingling, but they are not alone in
traversing it, for the ether is the scene of tremendous agitations.
Through its medium the stars attract each other and the sun-
spots influence our magnetic needles, and there is even a
question whether it is not actually the substratum of matter.
Contrary to a belief that seemed at one time to be final, the
study of radium has demonstrated that matter is neither
eternal nor immutable. Atoms of radium destroy themselves
spontaneously and give rise to helium and hydrogen. This
destruction liberates a sufficient quantity of energy to act
at a distance, through the ether, upon other atoms.

4 FORMATION OF THE EARTH

Lord Rayleigh believed that in the series of elements drawn up
by Mendeleef those having the greatest atomic weight are
broken up in this way and that the atoms of the lighter metals
are their residues. Silver, in this way, can be transformed into
lead, lead into carbon, thorium into bismuth, and gold,
perhaps, into copper. Thus atoms can be transformed and
broken up and made to disappear.

Since matter can be transformed, and even be made to dis-
appear, we have the right to ask how it was able to appear.
The phenomena produced in a Crookes' tube, through the
walls of which X-rays are able to escape, had practically
demonstrated that atoms of matter were far from being
simple entities. Among the various hypotheses as to their
constitution we may at least accept this — that they are formed
of infinitely small masses of matter charged with positive
electricity,1 around which, like satellites round a planet,
revolve a very large number of corpuscles, infinitely more
minute, whose mass is 1,000 to 2,000 times less than that of an
atom of ttydrogen, the smallest known quantity of matter.2
These corpuscles, called electrons, are charged with negative
electricity. What, however, do we mean when we say that a
thing is charged with such and such a kind of electricity ?
Simply that these electrified bodies are centres of attraction
or repulsion for other bodies ; that is to say, that they are
capable of determining movement ; which they could not
do if they were not themselves the theatre of movement. To
pass from this to the admission that the electrons and the
positive corpuscles are nothing but limited areas of ether and
the centre of an active eddying movement, and that
electricity is nothing but a manifestation of this vortical
motion, is but a step. The nature of electricity then depends
simply upon the direction of this movement. Molecular
attraction, gravity, attraction of any kind, in brief, are also
the consequences of this same movement.

If the stars are subject to this attraction, it is because its
action, like light, is propagated through the medium of the
ether, a medium which also transmits the Roentgen rays, the
invisible rays of the infra-red and ultra-violet regions of the

1 II, 218. [In these notes the black Ivoman numerals refer to the
Bibliography ; the Arabic numerals to the pages of the works quoted.]

2 I, 15.

THE BIRTH OF OUR WORLD 5

spectrum, the Hertzian waves — the agents of wireless
telegraphy — and the vibrations due to the destruction of
radium and of analogous bodies ; so that the substance which
fills space is uninterruptedly traversed by waves of all
descriptions of which actually we know only a part. These
spread out in every direction, and in impinging on one another
ought, strictly speaking, to give birth to vortical movements
analogous to those of which atoms are the theatre, and thus
originate matter.

But what we so far positively know of this movement is that
it did not develop out of nothing. Every movement is the
product of some former movement and the result of the trans-
formation of that movement.

We do not know, and probably we never shall know, what
was the nature of the initial motion from which came the
electrons, with their negative charges of electricity, and the
elements charged with positive electricity around which they
revolve, thus forming the first elements of matter. Not long ago
it was believed that motion, like matter, was eternal ; that it
could change its modality ; be transmitted from one body to
another according to certain laws ; affect the whole mass of a
body, or merely disturb its molecules, producing, in this case,
heat ; and the demonstration of an equivalence between the
mechanical work done and heat produced, foreshadowed by
Carnot and determined by Joule, Mayer, Hirn, and Tyndall,
apparently gave a very solid scientific foundation to this idea.
Therefore, it would be useless to demand what may have
been the origin of force. An ether completely permeated with
motion and identical with it would thus originate all the forces
which eventually would return to it and be lost in it, after
having animated matter. To-day, however, we are not quite
so certain of this eternity of motion.

Let us now return to intelligible things. We can see vaguely
that a large number of elements, capable of becoming matter,
were able to come together in certain regions of space and there
form a kind of tight network *■ across the path of infinitely
small particles which the repulsive force of already existent
stars projects constantly into space. These particles travel at
a tremendous speed, and, according to Svante Arrhenius, are

1 III, 16.

6 FORMATION OF THE EARTH

charged with negative electricity. They are arrested at the
surface of the network, where their tension increases till they
finally launch across the whole extent of its surface electric
discharges which would illuminate it, just as such discharges
illuminate a Crookes' tube. This would have been the origin of
the nebulae whose temperature, in spite of their phosphorescent
condition, would be more than 200 degrees below zero. The
spectrum of these nebulae shows bands of helium, hydrogen,
and certain apparently special elements. When a particle of
matter, however small, penetrates such a nebula, a fragment
of a broken star, for example, like those which form
meteorites, it at once becomes a centre of attraction towards
which the particles of the nebula hurl themselves and eddy
round it, developing at the same time a terrifically high
pressure and a very intense heat. The cold and phosphorescent
nebulae thus become transformed into a gaseous and in-
candescent mass, a kind of vast flame convulsed by movements
of incredible violence, at first entirely disordered. Gradually,
however, out of this very disorder, out of the collisions and
partings which ensue, a kind of harmony is born. These internal
movements become, so to speak, classified ; some are reduced
to simple vibrations propagated in the form of different
radiations across the ether far removed from the nebula ;
others are fused in a single rapid rotatory movement, dragging
along with them the entire mass of the nebula, compelling
it to revolve at a prodigious speed around a single ideal axis.
It must be admitted that, strictly speaking, the original
diversity of the movements divides the nebular mass into
several unequal parts, each whirling around on its own account,
with a translatory movement which is transformed into a
rotatory movement of the small masses around the larger
ones by which they will be attracted. It is thus that a system of
luminaries such as the multiple stars might have arisen directly.
For our solar system, however, Laplace was led to another
hypothesis, grandiose in its simplicity.

The incandescent nebula would, in his view, consist only of
a spheroidal mass revolving in its entirety, at an inconceivable
speed, round an axis. In conformity with the laws of centrifugal
force this mass, by reason of its speed, would assume an
ellipsoidal form such as that of the earth. The region corre-
sponding to the equatorial zone would then, at the successive

THE BIRTH OF OUR WORLD 7

epochs of its cooling, break away and form a series of rings
comparable to those of Saturn. On account of their more rapid
cooling these rings would become condensed, the different
substances of which they consisted separating from one another
on account of their coefficient of specific heat and the difference
between their melting and solidification points, and each ring
having thus become distinct would break off. Since, however,
the larger masses attract the smaller, the whole process would
end in the formation of a globe revolving around the principal
mass with a speed equal to that of the molecules of the ring
after its isolation, but with an orbit of the same form and
dimensions as that of the original ring. Thus the solar system
would arise, and its stars scattered in the sky would all represent
a more or less faithful repetition of the same process with the
exception of the multiple stars which consist of many suns
moving round one another in complex orbits.

These stars are not distributed in a haphazard order. Along-
side of the nebulae which possess such a vaporous consistency
as to be considered simple stars in process of formation, there
are others that only present a nebulous aspect when examined
by a slightly magnifying telescope. The more powerful
instruments show them to be formed of an infinite number of
brilliant points which are manifestly stars. In these nebulae
thousands, perhaps millions, of stars comparable to our solar
system are assembled ; and they are probably the furthest
away of all. Now these nebulae frequently have the regular
form of rings. We live in the midst of one of these rings, the
Milky Way, and the beautiful stars of our firmament are merely
those scattered through the nebular region nearest the sun.

At this point it may be asked whether beyond what we are
able to see, there is really nothing else ; whether there are not
other universes separated from us by an absolute unbridgeable
void, for could it, indeed, be bridged, it would not be a void ;
and also whether these universes are not made of an ether
different from our own where our physical laws would have to
be replaced by entirely different ones. This, however, we shall
never know ; we shall never obtain even a hint of the answer
and we must therefore be content to remain enclosed within
our own universe, which is already of vast dimensions. It is
the only one which we have any chance of knowing.

Had we announced only half a century ago that we should

8 FORMATION OF THE EARTH

some day know of what the stars and the sun were made and
whether the atmosphere of the planets was or was not charged
with aqueous vapour, so daring a prophecy would have been
regarded as the product of a deranged imagination. Yet such
knowledge has been attained, and it is light itself which has
furnished us with this information. Everyone knows that if
a very narrow ray of white light is allowed to impinge on a
triangular crystal prism, perpendicularly to one of its faces,
it changes its direction in traversing the prism and, in emerging,
spreads out fanwise, the rays as they shade insensibly into one
another being of different colours, and the same colours always
following on in the same order. Beginning with that part of the
fan furthest from the original direction we have the following :
Violet, indigo, blue, green, yellow, orange, red. We arrange
them in this order instead of the reverse, because the names of
the colours then form a word series easily remembered. Violet
is the colour with the greatest refractability, red with the least.
This fan, whose colours seem to form a magnificent brilliant
band when a white screen is placed in its path, is called the solar
spectrum. If the ray is sufficiently fine and the prism thick
enough for the opening of the fan to be of considerable size,
black lines and dark bands are seen in the spectrum. These are
the Frauenhofer lines, which justly bear the name of the German
physicist who discovered them. On the other hand, the French
physicist, Foucault, had pointed out that the spectrum of
metals at white heat was not continuous ; that it was composed
of lines and of brilliant patches. A little later in Germany,
Kirchoff and Bunsen showed that if a beam of continuous
white light is made to pass across a dark metallic vapour such
as incandescent carbon emits, its spectrum shows dark lines
exactly corresponding to the brilliant lines which would be
found in the spectrum of the metal emitting the vapour. In
other words, from the point of view of luminous intensity, a
reversed spectrum of this metal is obtained. Now, on comparing
the Frauenhofer lines with the brilliant lines of the spectra
of various metals, they were found to be exactly super-
imposable, thus indicating the presence of these metals in
the solar atmosphere. The study of this atmosphere charged
with metallic vapours has been carried very far by the work of
the French astronomer, Jannsen, and has demonstrated that
all the elements therein contained are found also on the earth.

THE BIRTH OF OUR WORLD 9

But for some time it was supposed that one element was to be
excepted which appeared to exist only in the sun and had for
that reason been called helium. Helium, however, has now
been discovered on the earth as one of the products of the dis-
integration of radium, and, since the discovery of its origin,
it has played a considerable role in the speculations of
physicists. The study of the spectra of stars has not revealed
any special bodies. Those of the nebulae have given us onty two,
nebulium and archonium ; so we reach the conclusion that
our whole universe is made up of the same substances, which
is, so to speak, quite natural if atoms are merely ether animated
by certain vortical movements.

It is still more natural that the substance of the different
planets should be identical, on the hypothesis that they have
come from the sun, as Buff on already believed, and as has
been accepted by all astronomers since Laplace. The origin
of these stars is not due to chance ; it occurred at definite
periods which seem to correspond to successive phases of the
contraction and cooling of the sun. During the period in which
they were formed the elements composing the sun were already
arranged in the order of their increasing density and in what
might be called that of their viscosity. The most distant
planets, the first in all probability to be formed, are very large
and very light, and since they remained in a molten state for
a very long time they themselves gave birth to a large number
of satellites, that is, to numerous moons.1 These planets are
Neptune, Uranus, Saturn, and Jupiter. Then, suddenly, come
the denser and smaller planets, with only a small number of
satellites : Mars, the Earth, Venus, and Mercury. Between
these two groups and within the same orbit, revolve a great
number — almost a thousand — of small stars, the asteroids.
It may be conjectured that between Jupiter and Mars there
once was a planet containing so large a proportion of light
matter similar to that of the larger planets, or of heavy matter
similar to that of the planets analogous to the earth, that
since all these substances contracted unequally in cooling, the
planet broke up like a piece of glass of heterogeneous origin
in the fire ; and that these fragments were then scattered
along the whole length of its orbit. This hypothesis

IV, 6.

io FORMATION OF THE EARTH

seems to be confirmed by the position occupied by the ring of
asteroids. In fact, the distance of the different planets from the
sun is controlled by a law formulated by the astronomer Bode,
of Berlin, which may be set forth as follows, if we take as the
point of departure not the sun but the last of the planets to
be formed, Mercury : —

The distances of the planets from Mercury form a geometrical
progression whose first term is 3 and ratio 2.

That is to say, the distances are to one another as the
following numbers :—

Venus Earth Mars Jupiter Saturn.

3 3x2 = 6 6x2 = 12 12x2= 24 24x2=48 48x2 = 96

This law, first established by observation, was rediscovered in
1867 through computation. As the astronomer Heinrichs has
shown, it is due to the progressive condensation, regular and
proportional to time, of the solar nebula, and is of such a nature
that it also links together both the distances of the planets from
the sun and the epochs of their formation. Now, in this series
the planet corresponding to the number 24 is represented by
the ring of asteroids. This ring therefore corresponds to a
planet. It is also possible that the asteroids are not the result
of the rupture of a planet but of a ring which once encircled
the sun as Saturn is encircled to-day.

Although the various planets are only formed of substances
found on the earth, it does not necessarily follow that each
one contains all of them, still less that it contains them all in
the same proportions. Their differences in density even force
us to assume, that this could not be the case. If, for instance,
we take water as the unit of density, we find that of Neptune
to be 17, that of Uranus i'5, and that of Jupiter 1*3. These
densities are only slightly higher than that of water, scarcely
equal to that of sugar, and much lower than that of glass.
Saturn, indeed, is so light that if there were a basin large
enough to hold it, it would float on the water. The density
of Mars on the other hand is 3*9, that of the Earth 5*5, Venus
4'4, and Mercury 6'5. These four planets may contain more or
less of the heavy metals, and may have a more or less extensive
atmosphere ; but their densities approximate too closely for
us not to assume that the same simple elements would be found
there. The lightness of the planets outside the ring implies a

THE BIRTH OF OUR WORLD n

predominance of metalloids and of alkaline or earthy metals
the compounds of which are the lightest of all. The compounds
of the alkaline metals are almost soluble ; we may, therefore,
assume that the seas of these planets are far more saline than
ours, a fact which, as we shall see later on, is not without its
consequences.

The present incandescent state of the sun's surface, and the
immense hydrogen flames that dart out from it, imply that its
entire mass has an extremely high temperature ; it is even
probable that it is in a molten state, and that its brilliancy
is due to solid scoria floating on the surface of the molten
mass. At the time when these planets were formed the
temperature of the sun could not have been lower than it is
to-day ; it is therefore certain that the sun was in a liquid,
if not a gaseous state, when the planets were detached. Their
distinctly spherical form and even their flattening at the poles
confirm this hypothesis. It is only much later, when the
atmospheric gases were freed, that their surface consolidated.
Such, at least, is what happened on the earth. Water then
formed a part of the atmosphere, the earth's surface being still
too hot for it to exist in a liquid state ; and as the surface cooled
the water gradually became precipitated, and the vaporous
atmosphere covering it became clearer. Venus, which is younger
than the Earth, nearer to the Sun, and for these reasons hotter,
is still in a phase where clouds absolutely conceal its surface ;
it therefore reflects toward us the bright light which wins such
admiration for the evening star, and shines even in a sky
illuminated by the rays of the sun — although the firmament
is masked for its own inhabitants who, according to the
pertinent observation of Henri Poincare, are perhaps still
unaware of the existence of the stars. Mars, on the contrary,
being smaller and twice our age, while Venus is only half, has
acquired an atmosphere of extreme limpidity.

Jupiter, which is enormous in comparison with the Earth,
being 1,279 times larger, has cooled less rapidly, but it is
further away from the sun, and eight times older than our
Earth ; it is possible that water is being precipitated on its
surface, and that it has long since formed oceans like ours
whence rise clouds which seem to be distributed in bands
parallel to the equator by winds comparable to our trade-

12 FORMATION OF THE EARTH

winds and counter trade-winds. It is possible that a ring like
that of Saturn is beginning to be outlined on its surface. The
existence of Saturn's ring is unquestionably connected with the
extreme lightness of the substances which constitute it and
which have yielded without resistance to the centrifugal
action arising from its rotation. The peculiar nature of these
distant planets and the fact that their birth goes back to so
distant a past that we can form no idea of it, prevents us from
being able to draw any very great profit from their study in
reconstituting the history of our globe.

The gradual cooling of the Earth did not merely bring about
the separation of water from the atmosphere and its
condensation upon the surface. It led in course of time to a
whole series of modifications in the relations of the waters and
the solid crust. Undoubtedly the Earth at first was absolutely
spherical and was covered with a layer of water of probably
uniform depth. Air, water, and earth formed three concentric
spheres ; the solid terrestrial crust itself covering the central
mass, which remained burning and molten. The cooling
gradually disturbed the regularity of this geometrical arrange-
ment. Being homogeneous and contracting rapidly like all
liquids, the central mass would soon have separated itself from
the solid crust, and have left a void below, if the crust had not
been distorted so as to limit its capacity.

The contraction of a cooling solid is, in fact, much slower
than that of a liquid, and the solid covering, for that reason,
would be unable to follow as quickly in its own contraction that
of the liquid mass which it covers ; it would collapse if it were
not distorted. Perhaps such a collapse occurred more than once
before distortion ; possibly both had taken place together.
This we shall probably never know, but it is of little importance.
Whatever really happened it can be shown by a very simple
geometrical calculation that, given equal surfaces, the solid
with the greatest volume is a sphere, while that whose volume
is smallest is a tetrahedron ; and therefore the crust, merely
through the process of cooling, must have tended to change
from a spherical form to that of a triangular pyramid with
four sides, whose four apices and the edges nearest to them
must have projected above the water. From that moment
continents and deep oceans must have existed. The sea, as the
Bible says, was separated from the dry land. At first sight it looks

THE BIRTH OF OUR WORLD 13

as though the present disposition of the continents and seas
confirms this calculation : 1 the North Pole is occupied by a
sea covering the base of the pyramid ; at the South Pole a
continent indicates the apex opposite the base ; the Eurafrician
continent represents one of the lateral levellings ; the two
Americas correspond to the second, and the Australasian
continent separated from Europe by the Aralo-Caspian
depression (the bed of an ancient sea) represents the third.
These three continental masses widen towards the north, and
duly become narrower towards the south. And, further,
while the earth revolves on its axis, each of its meridians
revolves in a given period, through an equal angle.
But in order to revolve through an equal angle the points
nearest the equator have to traverse an arc much greater than
those near the poles, and they therefore move much more
rapidly in a tangential direction. If, however, one part of this
meridian sinks, the sunken points will move faster than they
should, and will be in advance of the projecting points with their
markedly retarded movement. The continents would thus
have to twist their apices toward the east ; and this torsion,
evident as regards America, would lead to a rupture in the
central portions. This would explain the existence of the
Mediterranean and Caribbean Seas ; and also the separation
of the Australian continent from Asia. All this, unfortunately,
must necessarily have taken place not in our days, but at the
very beginning of the contraction of the earth's crust. It is
always possible that the initial arrangement of the continents
and seas began by conforming to this irreproachable calculation;
but since then other causes have supervened which have
modified the course of events. The oldest geographies extant
yield no trace of tetrahedral arrangement, and the present
disposition of land and water, which seems to conform to the
calculation, is of relatively recent date. This conformity is a
sort of anachronism. We have therefore had to abandon with
regret, and only after many efforts to save it, that mathematical
explanation, so seductive at first sight, known as the tetra-
hedral theory. The contours of the continents, their extent,
and their altitude have changed many times. Areas long
continuous have been cut up into many smaller ones ; isolated

1 V, 55, 1245.

14 FORMATION OF THE EARTH

islands, on the other hand, have become united to one another,
and then attached to the continents nearest to them ; and the
vast regions thus formed have again been divided up by the
invading waters. Plants and animal organisms which once
lived together have become isolated from one another as a
result ; species enclosed in regions separated by seas have been
able to spread from one to the other as soon as a land-bridge
appeared, and to pass from one sea to another as soon as they
were connected by straits. The evolution of life is intimately
bound up with these slow and peaceful terrestrial " revolu-
tions ", which, in fact, have been merely an evolution which
we shall have to study before we can examine the evolution
of life.

CHAPTER II
Transformations of Land and Water

NOWHERE have we been able to reach the primary solidified
crust of the earth. For a long time it was believed that
this crust was represented by rocks which, in part, date back to
a very great antiquity, such, for instance, as the granitoid and
the gneisses, forming, almost of themselves, enormous areas such
as the central plateau of France. It has, however, been shown
that, in spite of appearances to the contrary, we have here, too,
simply rocks deposited by water, and not all of the same age.
Though some of them are to be classed with the oldest rocks
known, others, identical in their mineralogical constitution
and structure, are more recent and are discovered at different
levels in analogous conditions. When the rocks laid down
horizontally as sediment were folded by lateral pressure, it
was near the bottom of these concave folds that granitoid rocks
belonging to the same age as the sedimentary beds were found.
From this we may infer that they were the result of a trans-
formation of sedimentary rocks in a partly molten state
violently compressed, and more or less altered either by gaseous
or liquid infiltrations, and, through this two-fold action,
crystallized. We call these rocks metamorphosed ; and meta-
morphosis is of very general occurrence. It caused the formation
of gneiss and granite whenever sedimentary rocks were com-
pressed and folded, so that rocks once called primitive are seen
to have lost that quality.1

It is none the less true that the oldest portions of the globe
now emergent consist essentially of these rocks, whose thickness
in certain places is more than fifteen thousand metres. This fact
alone enables us to gauge the time required for such deposits
to be laid down, especially if we consider that these deposits,
by no means compact at first, have achieved the homogeneity
which we find in gneiss.

1 VI, 172.

16 FORMATION OF THE EARTH

The oldest gneiss and granite is always found in the con-
cavities of stratified layers folded by terrific lateral compression,
and these folds are usually alternately concave and convex,
constituting what geologists call synclines and anticlines.

The anticlines are naturally highly elevated, and correspond
to the summits of the mountain chains formed by this
crumpling. These chains were not formed by a single action.
The solid crust of the earth, being compelled to follow the
contour of the molten sphere, which, owing to the gradual
cooling of the globe, contracted more swiftly, became folded
in such a way as to preserve its surface intact while at the same
time it shrank and diminished in volume. Contrary, however,
to geometrical conjecture, from that epoch at which the earth
becomes accessible to our observation, the continents did
not form prominences directed towards the meridians, as the
tetrahedral theory would have us believe, but rather rings or
bands oriented parallel with the equator. This is either
because the centrifugal force resulting from the rotation of the
earth has contributed to their formation or because the cooling,
always more intense at the poles, has caused the formation of
powerful barriers that could resist a thrust in the direction of
the poles, tangentially to the meridians. The first of these
bands was formed near the North Pole ; we do not know
whether there was another corresponding to it at the South
Pole, the southern hemisphere being to-day largely concealed
beneath the ocean. It was in the course of its formation that
the Circum-polar gneisses were folded ; the direction of these
folds indicates the position of the oldest of the mountain
chains, the Hnronian, so-called because the traces it has left
of its existence are particularly visible in the neighbourhood of
Lake Huron in the American continent ; but it once extended
from thence to Greenland, northern Scandinavia, and Siberia.
Later it was surrounded by a second chain, situated more to
the south, called the Caledonian because it is definitely recogniz-
able in the Grampian Hills of Scotland ; it extends into
Scandinavia, and appears again in the Green mountains of
Vermont, in the State of Maine and in the Appalachians.
Still later, and always further to the south, rose the Hercynian
chains, whose name recalls the vast Hercynian forest, which in
the time of Caesar covered the mountains of the Black Forest,
the Harz, the Erzgebirge, and the Riesengebirge, and extended

LAND AND WATER 17

also across the Vosges from Lorraine to the central plateau
and Brittany. These mountain chains sent branches into
Spain as far as Seville and the Meseta in one direction ; and,
striking across Bohemia, reached as far as the Urals below the
Carpathians and the Balkans, radiating into Asia from the
Altai Mountains to the Gulf of Petchili, Tonkin, Annam, and
Cambodia, and reappearing again in Australia, in Brazil, and
the neighbourhood of Canada. Finally, we have a fourth, more
southerly series of folds of still later origin, corresponding to
the Balkans, the Alps, the Jura, the Carpathians, the Pyrenees,
the Apennines, the Atlas mountains, the Caucasus, the
Himalaya, the warped massif of southern and eastern China,
and the mountains which skirt Indo-China on both sides,
and, stretching out in a median chain in the Malay peninsula,
betray their presence by the numerous volcanic islands of the
Pacific. These folds then extend to the western coast of
America, and, following the ocean, to North America and
Alaska, winch they reach as far as Terra del Fuego in a southerly
direction.

The Alpine-Himalayan chains are the highest in the world,
and attain in the Himalaya a height of 8,840 metres ; eternal
snows accumulate on their summits, while vast glaciers move
slowly down the entire length of their high valleys. In their
vicinity, too, there are volcanoes, distributed so thickly
along the coasts of the Pacific as to surround this ocean with
what has been called its girdle of fire ; and it is either at the foot
or the side of these mountains that earthquakes most frequently
occur. All this is evidence of recent origin. The older mountains
have been worn down, corroded and levelled by atmospheric
agencies. It requires all the ingenuity of the geologist to
reconstruct them by a study of the strata folded when they
formed, and which to-day are like the buried foundations of a
ruined city. A geographer limiting himself to a study of the
earth's surface would hardly suspect their existence. They,
too, once possessed glaciers, traces of which are found even on
the oldest gneiss, but the actual remains of the original
Hercynian ridges have been reduced by the wear and tear of
time to hills of too modest a height for snow to remain long in
temperate regions. The volcanoes indicate that quite recent
fractures still persist along the flanks of recently formed folds,
leaving a free passage for the molten matter within the earth.

18 FORMATION OF THE EARTH

Similar fissures rent the Hercynian and Caledonian folds, and
lava beds and streams, remains of ancient molten lava, are
found in many places ; but these have solidified so that all
the openings from which these fiery torrents issued are now
permanently closed. Stratified deposits at first horizontal,
which were raised to form the flanks of ancient mountain chains,
have either slid over one another or been completely inverted ;
the enormous masses thus dislocated have gradually reached
considerable distances at times from the place of their origin,
carrying along with them debris from the projecting folds
encountered. Elsewhere the stratified rock has been broken
vertically along the line of fissure whose two edges had changed
their relative levels, constituting a. fault. All this gargantuan
task was not, of course, accomplished without sudden shocks
causing earthquakes. To-day, however, all is consolidated, and
in equilibrium, and only in the vicinity of relatively young
mountain chains are seismic shocks still felt.

Theoretically the order of the superposition of the layers
horizontally deposited by the waters should indicate their
relative age. When these layers have been forced up vertically,
folded, reversed, compressed, or carried away by cataclysms,
this determination becomes more difficult ; but it is the business
of stratigraphers to overcome these difficulties. They are almost
always successful, and have developed, in conjunction with
stratigraphy, a new science, that of tectonics, the special object
of which is the study of the different agencies operating in the
laying down of strata in different localities. When these layers
have been pushed up vertically or folded, then raised above
the water and once more submerged, the waters flowing back
over their old domain cover it with horizontal strata oriented
in a direction different from that of the tilted strata. This
discordance indicates clearly that there were ground move-
ments before the new layer was deposited, and if these are
also in their turn folded, the discordancy persists, thus showing
that the terrain was lifted up on two different occasions. It
was by starting from these principles, so very simple in theory
but often difficult of application, laid down in former days by
Elie de Beaumont, that geologists succeeded in determining
the relative age of mountains and arrived at the conclusion
that there had been four series of folds whose distribution we
have briefly indicated.

LAND AND WATER 19

This work of orogenesis, or mountain building, characterizes

the great geological epochs, and the formation of one series of

folds generally required an entire epoch for its consummation.

The era in which the Huronian chain was formed is generally

known as the pre-Cambrian ; while the era extending from the

origination of the Caledonian folding to the completion of the

Hercynian, is known as the Primary. A long period of relative

calm — the Secondary — followed. Orogenic disturbances

continued in Tertiary times, and resulted in the formation of

the Alpine and Alpine-Himalayan folds. Strictly speaking,

one might concede that this third period has not yet come to an

end, since the orogenic movement characteristic of it still

continues. We can, indeed, point to movements indicative of

the rising up of the land on many of our coasts, as on the

Saintonge coast ; x or of its sinking, as in the Bay of

Douarnenez. Earthquakes frequently occur at those points

of the globe clearly connected with the intersection of mountain

chains ; volcanic craters are numerous, active and quite

evidently associated, in regions where levelling is still

proceeding. But the present, or Quaternary Epoch, was

marked by an event to which we naturally attach the greatest

importance, namely Man's effective appearance as the master

of the earth ; the beginning of this dominance coincides with

a climatic condition which is regarded as closing the tertiary

epoch — a lowering of the temperature which over and over

again permitted a prodigious extension of glaciers. This

glacial period was unquestionably the consequence of tertiary

orogenic phenomena, which, by raising high peaks on the

surfaces levelled during Secondary times, and by modifying

the distribution of continents and oceans, favoured the

accumulation of great masses of snow, augmented every winter

on the summits of the vast chains of newly formed mountains.

From a geological view-point, no new factor was involved,

except perhaps at the beginning of the period of erosion

of the Alpine chains. But we naturally attach particular

importance to phenomena so intimately linked with our own

history, and all geologists, for that reason, regard the era

in which the human species began to assume an important

1 The movements found in such regions, it is true, are rather equilibratory,
and belong to the category of epirogenetic movements, thanks to which the
sea covers zones of subsidence which it abandons and re-occupies alternately.

20 FORMATION OF THE EARTH

place among living beings as a distinct period in the earth's
history.

Each of the eras just defined has been divided into many
periods corresponding alike to the formation of certain parts of
the great folds briefly described above, to a certain phase in the
evolution of life, or to specific characteristics of the deposits
then formed. We shall confine ourselves to enumerating these
in the order of their formation, beginning with the oldest.
Their names will be so many landmarks to which we can relate
the various developments to be recorded in connexion with the
evolution of life on our planet.

The oldest known deposits have been completely trans-
formed into crystalline rocks or mica schists in which traces
only of fossils have been discovered. They belong to a pre-
Cambrian era, in which two periods are recognized : the
Archaean and the Algonkian. It is followed by the primary
epoch, comprising five periods : i, the Cambrian whose deposits
contain the earliest well-characterized remains of living beings ;
2, the Silurian ; 3, the Devonian ; 4, the Carboniferous, whose
rich vegetation produced the most important coal deposits of
our country ; 5, the Permian, which immediately precedes the
secondary period.

The secondary period, in its turn, is divided into three great
periods : 1, the Triassic, the period of transition ; 2, the
Jurassic, during which enormous coral reefs such as those
encountered to-day in tropical regions were formed along our
coasts ; 3, the Cretaceous, in which the oceans were deepened
and a fine calcareous ooze formed on their floor which later
became chalk.

Finally, the Tertiary era, which witnessed the appearance
and multiplication of animals more and more similar to those
of our own times, has been subdivided into two great periods
according to the proportion of animals with representatives
still existing encountered in their fauna : the Eogene or
Nummulitic, during which the sea was full of very simple
organisms, which formed disc-shaped shells — nummulites — and
the Neogene period, rich in animals of our present fauna.
These periods have been again divided into two subdivisions :
the Eogene, into the Eocene and Oligocene, and the Neogene
into the Miocene and Pliocene. Sometimes another, the
Pleistocene, corresponding to the quaternary, is added.

LAND AND WATER 21

The mountain chains whose main outlines we have just
traced, did not attain their high altitudes without producing
vast modifications in the level of the adjacent regions. In fact,
they rest upon enormous continental bases ; as a rule, they are
on the border line marking the separation of the continents of
one epoch from those of a preceding one, so that where the
continental barriers are missing, as along the American littoral
of the Pacific, we are led to think there once existed a continent
which has since disappeared.

We shall now endeavour to reconstruct, on the basis of the
above principles, the distribution of the continents and oceans
at the various geological epochs. The first continents to emerge
from the seas, as has already been indicated, were arranged
in the Northern Hemisphere in two principal semi-circles,
of which the larger part has since then been submerged ;
the first constituting the Palaearctic continent was not very
far from the South Pole and the second near the Equator.

The Circumpolar coronet x broke up into four massifs or
barriers arranged around the Pole like the petals of a flower :
1, the Canadian barrier in North America ; 2, Greenland ;
3, the Finno-Scandinavian barrier, including Scandinavia and
Finland; 4, the Siberian massif. They formed at first, no doubt,
a continuous half-moon, divided up by the sinking
of certain portions in a meridianal direction. Their
present distribution does not date back far beyond our own
epoch. These four massifs had already been subjected to
folding before any additional strata had been deposited upon
them. They may have been temporarily submerged, but they
have remained constant ever since the folding they underwent
precedent to the subsequent geological periods, so that all the
later deposits formed on their levelled surface have remained
horizontal. Their folding shows that they underwent a process
of corrugation at a very early period, resulting in the formation
of mountain chains which quickly lost all traces of relief. It
was these mountains, the oldest raised up on the earth's surface,
which formed the Huronian chain.

Another continent extended from about ioo° W. long, to
1650 E. long., roughly resembling a huge spitted bird with
folded wings (see Map II), with the equator representing the
spit, the head towards the East, and with a huge wattle

1 IX, 486, Map I.

22 FORMATION OF THE EARTH

depending from it. The back of the bird roughly corresponds
to 300 N. lat., its breast to 400 S. lat., and the top of its
head to 900 N. lat. The end of its beak was placed 1250 E.
long, by 550 N. lat. An arm of the sea, comparable to a vast
river, separated this continent from the Palaearctic and united
the two sides of an immense ocean, occupying and generally
exceeding in size the site of the present Pacific Ocean, which
seems to have persisted, at least in the form of a girdle round
the hypothetical Pacific Continent, through all the geological
epochs. The equator cut the body of the bird into two almost
equal parts, and the bird covered the whole of the Isthmus of
Panama, spreading westwards over Venezuela, Colombia,
Ecuador, Peru, and Brazil, and connecting this American
portion with Africa, which, together with Arabia, it completely
enveloped. It stretched eastwards beyond Madagascar, and
to the mouth of the Indus. Spain, the north of Italy, France,
the British Isles, nearly all Germany, Finland, and Scandinavia
were submerged beneath the waters of the arm of the trans-
versal sea behind the neck of the bird which ran along the north
coast of Africa and the frontiers of Turkey and Austria, while
the head covered the whole of Russia and nearly all China, the
forehead and the beak extending obliquely from the Gulf of Obi
to the north of Korea. The wattle, contained naturally between
the two gulfs, covered India and Indo-China, and united all the
islands of the Indian Archipelago, linking one part with, the
Asiatic coast and the other with northern Australia. At that
time there was neither Atlantic (except for the transversal
channel separating the two large continental belts) nor
Mediterranean, North Sea, Red Sea, nor Persian Gulf. Chile,
Argentina, Patagonia, and all eastern Siberia, including Japan,
were submerged.

The geography just sketched corresponds to what geologists
call the Cambrian period ; it succeeded the pre-Cambrian, in
which the rocks, afterwards becoming the northern granites
and gneisses, were laid down. These granites and gneisses,
during this period, formed a primary system of rocks — the
Archaean, covered again by the mica-schists and sedimentary
sandstone which constitute the Algonkian system. It is in these
Algonkian deposits that the first traces of living organisms
have been discovered. They are rare, and it is difficult to
determine to what forms of life the traces or remains belong ;

LAND AND WATER 23

but in the Cambrian deposits there appears a very complete
fauna which the famous geologist Joachim de Barrande
regarded as the oldest of all, and to which he gave the name of
primordial fauna.

The sea at that time occupied an area almost equal to that
which it occupies to-day ; the diminution of the earth's
diameter has since then perhaps increased its depth to a certain
extent, but it was probably very little different then from what
it is to-day. The transversal inter-continental channel was a
kind of English Channel, and not very deep, its coasts rose in
a very gentle slope, for we still find on the surface of the sand-
stone traces known as ripple-marks, left on the sand by the
action of the waves. The west coast of America was, so to
speak, staked out by three islands running parallel to its future
coast, and practically occupying the site of the Rocky
Mountains of Canada, the Sierra Nevada, and the Chilean
Andes. In the same way a southern peninsula of the Pal«-
arctic continent outlined the future Appalachians up to the
neck of the isthmus connecting the persisting area of emersion
called by Suess the Canadian barrier, with the continental
mass of which it formed the western and southern extremity.
The sea had abandoned the region of the Great Lakes situated
between Canada and the United States (Map I).

Thenceforward these new lands were subjected to erosion ;
the crystalline rocks became decomposed by the action of the
sea ; and sands were deposited at the foot of the cliffs that
were later to be transformed through the action of iron salts
and iron oolitic carbonates x into red sandstone, such as that
of Saint-Remy (Calvados), Segre (Maine-et-Loire) , Nucic
(Bohemia), the South of Spain, Saint-Leon (Sardinia),
Krivorrog (Southern Russia), and those, somewhat later,2
of Clinton, in New York, and Lake Michigan, and which are
accompanied by deposits formed in salt lagoons, such as gypsum
and rock-salt, which reappear in all geological periods in places
where the sea has receded.3

The oceans, however, had extended their domain in both
hemispheres towards the equator ; the inter-continental
channel or inland sea extended over the north of Africa —
which had risen above the water up to that point — as far as

1 Ordovician. 2 Gothlandian. 3 IX, 490.

24 FORMATION OF THE EARTH

the Sahara,1 but had receded from Scandinavia and Finland,
which remained united to Canada, and almost the whole of
Russia ; while the southern ocean invaded the south of Africa
and a large part of Brazil. These changes were only temporary ;2
the sea reconquered Russia, the north of Scandinavia and
Germany, almost all Europe, Siberia, China, and the greater
part of the two Americas, except the east of Canada, which
remained united to Scandinavia. Only Scandinavia, Central
Africa, India, western Australia, and eastern China emerged
from the sea.

It is also generally admitted that after this epoch a vast
continent occupied the Pacific. After having worn down the
coasts of the Palaearctic continent and washed away from them
the portions which became the Old Red Devonian sandstone,
the sea to the south of this continent dried up ; 3 a zone of
lagoons was formed there which laid down deposits of gypsum
and salt, in which the bitumen of the White Sea, found in
even greater abundance in the Appalachians, and between
Hudson Bay and British Columbia, was produced, doubtless
from decomposing animal remains.

The Hercynian folding coincides with the period during
which the beds of coal, so useful to industry to-day, were
successively laid down in the estuaries and lakes of these
different regions. Their formation continued during the first
part of the Secondary period. The uplifting of the land accom-
panying the gradual formation of the Hercynian chains
drained the sea first from Scotland,4 then from the south of
England, Belgium, and the north of France,5 and finally from
the Central Plateau.6 At the beginning of this period there
existed three large continental masses separated by as many
seas ; the transversal sea of the preceding epochs, which
persisted in a more or less modified form, and two others of
which one was oriented along the meridians. The Arctic
continent still linked up Scandinavia, Greenland, and Canada,
and formed the Canadian-Scandinavian plateau ; 7 a second
continent corresponded to modern Siberia and a part of modern
China, constituting the Siberian plateau ; a third extended

1 Coblentzian. 2 Eifelian.

3 Frasnian. 4 Dinantian deposits.

6 Westphalian deposits. 6 Stephanian deposits.

7 CI. Map V.

LAND AND WATER 25

without a break from that part of Africa south of the Sahara
to South America on the one hand, and to India and the north
of Australia on the other ; this was the Equatorial or Gondwana
continent. The transversal sea covered all Europe except
Scandinavia and the north of Africa. In this vast channel
called the Central Mediterranean by Neumayer, the Mesogean
by M. Douville, and Tethys by Suess, a transversal island
emerged consisting of Italy, the Balkan countries, and Southern
Russia. This sea then became shallower and there emerged 1
Wales, Holland, Normandy and the Ardennes region, Morvan,
the southern part of the Central Plateau with the Vosges,
Franconia united to Bohemia, Italy, the Balkan countries,
the Caucasian region, comprising the south of Russia and the
Urals — all forming as many islands separated by shallow
channels. The straits between the Gallo-Dutch and the
Ardenno-Norman islands were occupied by warm and limpid
waters. Coral reefs x bordered the coasts already established,
though more to the west, during the Devonian period. These
limpid waters created the Dinantian or " mountain lime-
stones ". To the south of the Gallo-Dutch island there
was another strait separating it from Morvan and the Central
Plateau. The southern border of this strait was the seat of great
volcanic activity and was probably dominated by high
mountains, whose erosion products, mixed with carboniferous
substance, are found everywhere at their feet. Not long after,
these newly emerged islands became covered by magnificent
vegetation, the debris of which accumulated in the straits
and drove out the corals. It was at this time that the coal-
bearing areas of Scotland, the rich coalbeds of Lothian and
of Dalkeith, and those of northern France and Belgium were
successively laid down. Whereas in Silesia, where four arms of
the sea converged, a vast chain of mountains arose which was
at once subjected to intense erosion, which filled the geosyncline
situated at the base of the chain, and on the point of sinking
at the time, with debris to a depth of 14,000 metres. A similar
basin was formed in the neighbourhood of Moscow (Map III).
Mountains, however, continued to rise. The Hercynian
chain extended across Spain, the Central Plateau, Brittany,
the Vosges, the Black Forest, and Saxony. There were glaciers

1 Dinantian.

26 FORMATION OF THE EARTH

at certain points in the Alpine x region. Two long parallel
islands corresponded to the Rocky Mountains of California,
and to the west coast of Mexico ; a vast continent extended to
the north, linking up the whole of the west of North America,
the islands bordering the Arctic region, Greenland, Scandinavia,
the British Isles, the west of France, Spain, Morocco, and
Algeria ; all this formed the Canadian-Scandinavian plateau
separated by an arm of sea — the Fusulina Sea 2 — from the
Siberian plateau. Italy constituted the nucleus of a large
island.

The inland sea was thus pushed far southwards where it was
bordered by the Afro-Brazilian plateau uniting Central
America and the Equatorial Republics, the whole of Central
Africa, Arabia, India, and the western part of Indo-China,
including the Malay peninsula. To the north-east of this
continent was attached a T-shaped peninsula, of which the
western arm, passing through north Italy and closing the
inland sea on the west, was linked with Spain ; the other arm
of the T corresponded to the Caucasus, and included the Black
Sea and the entire central part of the Caspian Sea, terminating
to the south of and slightly beyond it towards the east of the
Sea of Aral. The other peninsula, situated in the south-east,
united Indo-China to Australia, which had almost entirely
emerged, and to the east of which a large island contained the
north of Borneo and the whole Malay Archipelago. Finally,
to the south of the Afro-Brazilian plateau there was another
continent, separated from it by a second inland sea and uniting
Patagonia to the African Cape region and to Madagascar,
beyond which it extended considerably. The T-shaped
peninsula was separated from the Scandinavian region of the
Canadian-Scandinavian plateau by an arm of the sea, with
parallel shores running from east to west and terminating in
three divergent branches like the toes of a bird's foot. It was
in these gulfs and along the coasts of this arm of the sea that
the vegetable debris was accumulated which formed the coal
beds of Scotland, the great coalfields of the south of England,
Belgium, northern France, Bohemia, Upper Silesia, and
Moravia (where the strata attain a thickness of 154 metres),

1 Westphalian.

2 The Fusulinas are Protozoa in the shape of minute spindles, characteristic
of carboniferous seas and belonging to the class of Foraminifera.

LAND AND WATER 27

and finally the Donetz coalfield in Russia, where this arm
rejoined the ocean.

The secondary period opens with the Trias. It was an epoch
of comparative calm during which the ocean probably
experienced slow oscillations, the continents either increasing
or shrinking in size ; but there was no more crumpling on a
scale that could raise long mountain chains thousands of metres
high ; on the contrary, it was the period in which the
Hercynian chain was destroyed. The general configuration of
the continents and the seas was but little different from that
just described. During the Triassic epoch all the northern
continents were united ; only the north-west of Siberia,
Alaska, and the western side of the United States and Mexico
remaining submerged. A vast ocean, bounded on the south by
the Pacific continent, occupied the site of the present North
Pacific. The Gondwana continent was greatly extended ;
to the north, separating it from the North Atlantic, there was
a large channel representing the inland sea or Tethys of the
preceding age. Two arms of the sea flowing between the Pacific
continent and the west coast of America on the one hand, and
the east coast of Asia on the other, united the Tethys to an
Arctic ocean, which continued its course southwards between
the Pacific continent and the equatorial continent of Gondwana.
These long channels alternately widened and narrowed in
certain places, which was responsible for the three series of
littoral deposits of the French Trias in the future Rhone
valley, which gives the name Trias to the general deposits of
this epoch.

This general arrangement lasted throughout the Jurassic
period ; the North Atlantic continent persisted throughout,
although the sea nibbled at its coasts from time to time during
the lower Oolic epoch. It was only from the Oxfordian
epoch onwards that a depression in the Ural region separated
it from the new Sino-Siberian continent to winch it had been
united during the Permian. This last remained above water
throughout this period, except for the eroded coasts in the
extreme north of Siberia and in Borneo during the Lias, the
coast of Okutsk up to the Bajocian and the whole northern
part of Siberia up to the Portlandian. The Gondwana continent
was likewise cut in two by a depression in the region of

28 FORMATION OF THE EARTH

Mozambique, the two halves becoming the Afro-Brazilian and
the Australo-Indo-Madagascan continents.1 Between these
two continents and the two northern ones the transversal
sea, already alluded to as the Central Mediterranean or Tethys,
grew larger. It occupied the exact site of the future Alpine
folds. It is probable that the hypothetical Pacific continent
still existed, and that the Tethys extended from the western
to the eastern site of the present Atlantic, being prolonged
towards the seas bordering it on the eastern coast.

We now come to the Cretaceous period.2 At its commence-
ment the northern part of the North Atlantic continent
(King Charles Land, Spitzbergen, east Greenland) was
invaded by the ocean ; an arm of the sea separated the Sino-
Siberian continent from the Scandinavian barrier ; in the Afro-
Brazilian continent the sea reached and submerged southern
Abyssinia, the Somali coast, and the southern part of Cape
Colony. Almost all the Australo-Indo-Madagascan continent,
except the Kateh district and western Australia, was left intact.
The arm of the sea which had united the Caribbean Sea to
the Tethys in Triassic and Jurassic times still existed. This
epoch might be called the Eocretaceous, and the following
epochs the Mesocretaceous and Neocretaceous.

During the Mesocretaceous period the sea abandoned the
Arctic regions just enumerated. The sea arm which had
divided the Scandinavian barrier from the Sino-Siberian
continent and the sea to the north of Siberia, and part of the
ocean encircling the Pacific continent, dried up ; but the
waters invaded the western coast of the Canadian barrier,
certain parts of Scotland, Ireland, Brittany, Bohemia, and
Spanish and Moroccan Meseta, thus forming a communication
between the Tethys and the Gulf of Guinea. The ocean entirely
covered Syria, Arabia, the Sahara, the Sudan, the Africa
coasts from the equator to the Cape, the north-east of Brazil,
the north and south-east of the Indian peninsula, the plateau
of Assam, Queensland, and the west coast of Madagascar.
The Tethys continued to spread to the south of the North
Atlantic and the Sino-Siberian continents, establishing a
common marine fauna for the Asiatic and the present
Mediterranean regions. One of its arms, passing between the

i Map III. 2 VI, 135S, 1359.

LAND AND WATER 29

North Atlantic and the Sino-Siberian continents, linked the
Tethys with the Arctic Ocean, at least during the second part
of this period ; and it also communicated with the Antilles 1
in such a way as to encircle an Atlantis. The Afro-Brazilian
continent, from this epoch onwards, was divided into two by
the immersion of a vast area corresponding to the South
Atlantic. Madagascar and India still remained united. This
disposition of land and water persisted throughout the
Neocretacean period, when the sea advanced a little further
in some regions, as in the Baffin Sea where a bay appeared,
the north-east coast of Brazil and the neighbourhood of
Pondicherry, and possibly isolated Madagascar for a short
time (Map IV).

With the Tertiary period and the upraising of the Alpine-
Himalayan chains we rapidly approach present geographical
conditions, so markedly different from those which we have
just described. During a part at least of the Eogene or
Nummulitic period,2 Europe and North America were still
united in one vast continent, the rest of Europe
remaining an archipelago whose principal islands, as during the
Secondary era, were Scotland, Ireland and W'ales, Brittany,
the Central Plateau, and Spanish Meseta. These islands,
separated by shallow branches of the sea, were inter-
mittently reunited, and were even connected by a genuine
Atlantis to North America. In any case a gulf of the Arctic
ocean penetrated to the heart of Europe, covering what is
now the North Sea, the Paris basin, and the south of
England. The Afro-Brazilian continent still persisted.
Madagascar was still united with India, but Australia from this
time onwards was separated from it, and the Indo-Madagascan
continent itself was separated by a strait from the Afro-
Brazilian. It is probable that the Pacific continent had already
begun to collapse, but the sinuous marine ring surrounding it
was momentarily raised and later transformed into a land of
lagoons, or perhaps a shallow sea, communicating with the
Tethys by a channel separating North from South America.

At the beginning of the Tertiary period the Southern sea still
covered the site of the Pyrenees and Alps, as well as a part of
Spain, all North Africa, Italy, Turkey, Greece, Asia Minor,

1 X, 134. 2 Map IV.

30 FORMATION OF THE EARTH

Persia, the region now occupied by the Himalaya, and extended
as far as China. This was the Nummulitic sea, so called because
it contained enormous quantities of fossil nummulites, coin-
shaped, slightly bi-convex, and somewhat resembling the
ancient liards. A gulf, which soon filled up, extended over
the Paris basin. It was now that the Pyrenees began to emerge
between France and Spain. The sea spread further into the
Paris basin, finally submerging Beauce, while certain reaches
extended to the Central Plateau, and also covered the basin
of the Gironde. England then stretched eastwards to Boulogne ;
the Paris basin was inundated, and the English Channel, of
which there were already signs, although narrower than at
present, communicated with the North Sea. Soon, however,
the level of the sea subsided and enormous freshwater lakes
replaced it in the central parts of France, Spain, and Switzer-
land. This was the Oligocene period, which immediately
followed the Miocene. The freshwater lakes occupying central
France now filled up, and the Alps and the Himalaya attained
their greatest altitudes. The sea finally abandoned the basin
of the Seine, but, on the other hand, invaded those of the
Loire, the Gironde, and the Rhone. Brittany became an
island, was separated from the rest of France ; England, on
the other hand, was joined to the continent, from which it had
been isolated in the preceding epoch. Throughout the rest of
the Tertiary period England remained united at first to Artois,
whose south-east coasts were washed by the lake that had
occupied the basin of Paris. In the Miocene period this became
free from water ; the English Channel was driven back to the
west of Cotentin, and England, to a large extent, was connected
with what was to become Normandy and Artois.1 This large
area was only an isthmus in the Pliocene period, and was cut
during the Quaternary period, thus opening the Pas de Calais to
the ocean which was to become the Atlantic and which already
separated Europe from America and Africa from Brazil.

The general configuration of land and sea had already
become stabilized somewhat earlier, during the Pliocene period.
Some regions like Brittany were rather less hemmed in by the
sea, which, on the other hand, advanced further along the
entire west coast of the Atlantic from Brittany to Spain and

1 X, 168.

LAND AND WATER 31

along the littoral of the Gulf of Lions, where it invaded the whole
valley of the Rhone as far as la Bresse, then occupied by a large
lake. The straits of Gibraltar, the Dardanelles, and the
Bosphorus were formed at this time.

The Earth thenceforth became what we know it to-day.
No doubt modifications still continue. We know that at the
present day certain coastlines are becoming submerged, while
others are rising. Scandinavia has been regarded as subject to
a sort of sea-saw movement, but this opinion is not strongly
held to-day.1 The south coast of Brittany and the west coast of
France are sinking beneath the Atlantic ; the Channel Islands
have become separated from the continent within historic
times ; the town of Ys has been engulfed by the waters of the
Bay of Douarnenez ; certain parts of the Italian coast have
become raised, and numerous regions where earthquakes and
volcanic eruptions still take place clearly indicate that the
activity of the earth's crust has not yet ceased. All these
changes, however, are so gradual and of such slight extent that
geographers' maps are scarcely modified. Events moved just
as leisurely in earlier times, and the greatness of the changes
that have taken place is not to be explained by those
tremendous cataclysms of which Cuvier has given us so
grandiose a description at the beginning of his discourse on
the Revolutions of the Earth, but rather by the extreme
duration of the geological periods in which they occurred.
This great duration, already invoked by astrologers in support
of their cosmogonic conceptions — this stupendous length of
time which Cuvier accused Lamarck of abusing in the interests
of transformism, may be accepted as an established fact to-day.
Attempts have been made to measure it in figures by taking
various phenomena into consideration, but in spite of the
hypotheses put forward to enable this to be done, and in spite
of the objections of the last partisans of the chronology of
Biblical commentators, to whom Cuvier lent the support of his
remarkable erudition, the agreement between the results arrived
at from very different starting-points, bearing no relation to one
another, is such that it is impossible to escape from the evidence
that the interval between two geological periods represents a
stupifying succession of centuries. Time itself has been the
great architect of the transformations of the earth.

1 V, 656.

32 FORMATION OF THE EARTH

It is only since the discovery of radium that we have been
able, by a simple calculation, to approach the question of the
age of the earth, or, speaking more accurately, the age of some
of the minerals constituting its solid crust. Strutt has drawn
attention to the fact that some of these minerals contain at
the same time uranium, itself radio-active, and a certain
proportion of a substance resulting from the decomposition of
uranium, viz. helium. He has calculated that n million
years are necessary for a gramme of uranium-oxide to produce
a cubic centimetre of helium. From the quantity of helium a
mineral contains we can thus arrive at an estimate of the
quantity of uranium it possessed at the time of its formation,
and the time necessary for the transformation of this uranium
into helium. The calculation yields 622 million years for the
zirconium in the archsean rocks of Ontario ; 145 million years
for certain Devonian hematites ; 400 million years for some
minerals, and only 40 million years for others. On the other
hand, certain Swedish and American rocks yield figures of
1,300 and 1,400 million years, and specimens from Colombo, in
Ceylon, reach 1,600 million years. These different figures enable
11s to determine the age of the terrainin which the buried minerals
analysed are found, and thus to calculate the time that has
•elapsed between the geological periods corresponding with the
laying down of the different strata. It may be, of course, that
the differences are in part due to the fact that the minerals
■examined are not found in conditions equally favourable for
the preservation of helium.

A further problem has been propounded, namely the date of
the appearance of life on the earth, which must necessarily have
been subsequent to that at which the temperature of the earth's
surface fell below 100 degrees. Lord Kelvin was the first to
interest himself in this problem, and arrived at an approximate
solution by treating the earth, for the purpose of calculation,
.as a homogeneous ball brought to a red heat and then allowed
to cool. According to this hypothesis, which is very far
removed, it is true, from the actual facts, Lord Kelvin,
according to the secondary hypothesis favoured, found the
answer to vary between 20 and 100 million years. But the
calculation can be made in another way by reckoning the time
necessary for the different geological layers to be formed. We
:are assuming, of course, that during the geological periods which

LAND AND WATER 33

preceded our own, the rapidity with which sediments were laid
down was the same as that of to-day. As we have only the
vaguest notion of the reduction in thickness undergone by the
oldest deposits during their transformation into gneiss, it is
quite likely that estimates made by tins procedure are too low
and that the error due to this fact will compensate, in large
measure, for possible exaggerations due to a difference in the
rapidity with which certain deposits are formed. On the basis
of the foregoing facts, Dana estimated the duration of the
primary period as 15 million years ; that of the secondary
as 4 million, and that of the tertiary as i| million years,
making the total of 20 millions at which Lord Kelvin
had already previously arrived. The duration of our present
period has been calculated from an entirely different starting-
point. The Niagara River, emerging from Lake Erie, originally
fell, after a short course, into Lake Ontario. But gradually the
cliff from whose height it falls has been eaten away ; thus
the Falls to-day are n kilometres distant from the lake.
Taking as his basis the rate at which the cliff is retreating
to-day, Lapparent estimated the duration of our present
epoch as 40,000 years. This estimate is confirmed if we measure
the present rate of increase of coral reefs and try to discover
how long it has taken to unite to the peninsula of Florida
the four coral reefs attached to its primitive coasts ; this has
required 35 to 40,000 years. The calculation of the time
necessary for the formation of the present peat-bogs gives the
same results. We may, therefore, regard it as exceedingly likely
that about 40,000 years have elapsed since man began to spread
over the earth.

From the agreement of all these facts we may at least
conclude that the surface of the earth has been solidified
for from 1 to 2,000 million years. Other calculations
indicate that it is at least a trillion years since the earth was
separated from the sun and that life is already an extremely
ancient phenomenon.

The prodigious changes which have occurred in the course of
ages in the configuration of the continents and the seas has
necessarily influenced the mean temperature of any given
region. According to whether the sea washing the coasts was
in extensive communication with tropical or polar waters, its
temperature rose or fell, and that of the adjacent continent

34 FORMATION OF THE EARTH

became mild or rigorous and the climate humid or dry. The
climate was in part also conditioned by the altitude of the
mountains. The Caledonian and Hercynian chains were com-
pletely levelled during the primary and secondary periods ;
but from the inclination to one another of the layers
constituting the two opposite faces, where the distance from one
another is known, of an anticlinal fold, we can compute the
height to which the summit of this fold was once raised, and we
thus discover that the ridges of these chains rose to a height
of many thousand metres as in the case of the present
Himalaya. These high mountains were covered with an eternal
garment of snow, as in our own time. Glaciers, of which traces
can be seen even in the Archaean period, moved down their
valleys and so cooled the air. At all epochs, therefore, there
have been relatively cold and relatively hot regions, and, in
consequence, winds and tempests, rain and snow. But all this
is true even of tropical regions to-day, and we shall see that a
tropical climate dominated the world for a long time. It is
tempting to attribute this to the fact, incontestable to-day,
that the internal heat of the earth, still considerable no doubt,
is more markedly felt through a solid crust where it is least
thick. Since the appearance of life on the earth, however,
this internal heat does not seem to have played any great
role. As a matter of fact, we possess no means of calculating
how much the earth's temperature rises at the centre. In the
deep wells of mines, where the temperature has been studied,
it has been found to increase steadily as one descends ; but
it does so in a surprisingly capricious manner. The term
geothermic degree has been given to the number of metres
corresponding to a rise of temperature of i degree. In the
mines of Sperenberg, which are among the deepest, the
geothermic degree has been measured every 200 metres to a
depth of 2,500 metres. It varies from 16 to 140 metres. An
attempt has been made to combine these observations by a
formula of the second degree. The formula is as follows,
S being the depth in metres and T the temperature (Reaumur).

T = 70 18 + o, 0,12983572 S — o, 00000125791 S2

This gives us the amazing result that freezing point would be
reached at a depth of 3,420 metres if the temperature continued
to obey it at this depth. But however variable laws may be, a

LAND AND WATER 35

continuous rise of temperature cannot change to a fall which
eventually reaches freezing point. Assuming that the
geothermic degree remains constant and equal at 100 degrees,
a figure not far from the observed mean, the temperature of
the earth's centre situated at a depth of 6,350,000 metres would
be found to be 63,500 degrees — which is quite a different
matter, but manifestly impossible, for this would be higher than
the temperature attributed to the surface of the sun.

These contradictory data suffice to show how little we should
know of the interior constitution of the earth if it were not for
other facts which have recently come to l.'ght. The study of the
lava from volcanic eruptions has led to the assumption that
below the solid crust or lithosphere there exists a continuous
molten mass, the Pyrosphere, constituted by a magma
containing iron and magnesium. This becomes increasingly
homogeneous as the depth increases, tending to approach, in
composition, that of silicate of iron and magnesium, which
mineralogists call peridot.1 Peridot, deeply situated, is always
associated with iron. This association is exactly reproduced
in the meteorites studied by Daubree and M. Stanislas Meunier,
and has led them to consider these as the scattered debris of
a star, or possibly a residual planet, approximately con-
temporaneous in origin with the earth, formed at the expense
of the sun, and with an orbit crossing ours periodically.2 The
composition of these meteorites may therefore be compared to
that of the earth's core called the barysphere. This barysphere,
in the main, would be formed by a metallic iron associated with
nickel, a sort of steel. In this way the resemblance of its
properties to those of a magnet and its power of directing a
compass would be explained. Nickel-steel would thus be the
essential metal and constitute the universal basis of the earth's
crust.

The study of earthquakes has corroborated this conclusion
in a manner as unexpected as it is exact. After numerous
more or less clumsy attempts, an automatic registering
apparatus has been constructed of such a degree of sensibility

1 The chemical formula of peridot is (MgO.FeO)2Si02.

2 It is difficult to assume that this star was a former satellite of the earth
like the moon. The debris of such a satellite would have formed a ring round
the earth or would have revolved round it like the moon, before falling
to its surface as soon as its tangential acceleration had sufficiently slackened.
This does not seem to be the case with meteorites which occur in " swarms "
whose orbit rather resembles that of comets.

36 FORMATION OF THE EARTH

as to record earthquakes produced in any part of the globe,
however distant, and even when they take place in the greatest
depths of the sea. A vertical pendulum, suitably constructed,
describes the horizontal components, and a horizontal
pendulum the vertical. The curves registered by the apparatus,
undulatory like those described on a revolving cylinder coated
with lampblack by a needle fixed to a freely vibrating scale,
are remarkably uniform. For each shock they fall into three
divisions, which differ solely in the length and amplitude of
waves and are inscribed in succession. From the time taken for
the registration of these vibrations and from what we know,
through the experiments of Wertheim, of the mode of trans-
mission of vibrations through solid bodies, Lord Rayleigh
concluded that the first and second parts of the curve represent
respectively transverse and longitudinal vibrations trans-
mitted across the barysphere, the third series of vibrations
and the last to arrive being transmitted across the earth's
crust or lithosphere. Now the speed of the transmission of the
first two series of undulations, 9, 6, and 5 kilometres per second,
indicates that these latter have been transmitted across a
medium more rigid than steel. The maximum density of this
medium, as calculated by Roche, would be 10, 6, and, at most,
a little greater than that of iron — 7, 7. These correspondences
are somewhat disturbing in view of the diversity of the con-
siderations involved, all bringing us back to the same
assumption — that the earth's core may well be solid and consist
essentially of iron. It must not be forgotten, however, that all
the metals heavier than iron, especially those that combine
with difficulty with metalloids, such as gold and platinum,
are very probably at least as largely represented in the bary-
sphere as in the lithosphere, and that, on the other hand, the mode
of transmission of luminous vibrations across the interstellar
ether equally leads us to assume a medium " more rigid than
steel ", without implying, however, that it is solid in the sense
in which we understand that term. The term " rigidity " simply
means that the molecules of the body considered can be
displaced only with difficulty and have an active tendency to
return to the position from which they have been dislodged.
As far as the barysphere is concerned, the rigidity of its sub-
stance appears to be due to the tremendous pressure to which
it is subjected and which maintains the molecules in place

LAND AND WATER 37

without giving us any information as to their nature or their
temperature. Under such colossal pressure probably the heat
can no longer affect the mobility of the molecules : all bodies
must appear rigid and solid. The distinctions made on the
earth's surface between the various states of bodies no longer
have any significance in these central regions.

However that may be, if the internal heat makes itself
so little felt on the earth's surface to-day, we may perhaps also
assume that it had very little influence during the epoch in
which the first consolidated layer could support sediments
more than 20,000 metres thick, as was already the case at the
beginning of the primary period, not long before the first
appearance of life. From that time onward climates have been
determined by action from without the earth, and this action
can only have been that of the sun — whose intervention we
must now study.

CHAPTER III

The Sun and Climatic Variation

AFTER giving birth to our planet the sun continued to be
so closely linked with it, as with the other planets also,
that the more we increase our knowledge of those links the
more they justify the worship it has inspired in diverse forms
in so many of the peoples of antiquity. From the sun our
earth, in addition to its material constitution, received and
retains both its inner heat and the movements which cause it
to revolve on its own axis and ceaselessly describe its vast
elliptical orbit. From these movements night and day and
the regular succession of the seasons take their existence,
manifestations of the tutelage in which we are still held
subject by the father of stars — held chained, indeed, by the
mysterious bond of attraction within his resplendent mantle
of gold and purple radiance.

Nothing takes place on our earth without the intervention of
the sun. It penetrates the waters of the sea, scattering their
molecules till they become invisible and then draws them up
into the air, where they are left to unite and form clouds.
It is the sun that, by heating unequally the different regions of
the earth, generates the moisture-laden winds whence fall the
fertilizing rains that permitted life to appear on the
continents. And it is the sun that induces in the living web
of the plant's texture the chlorophyll, the green substance
which, when activated by its rays, combines water with
carbonic acid and liberates the oxygen consumed by animals,
thus performing the miracle of producing sugar and starch.
These are called by the chemists carbo-hydrates, because they
are composed entirely of water and carbon, and constitute
the first and only source of all food, whether for animal or
plant.

The sun alone, therefore, can maintain life on the earth. It
determines the conditions of its development equally on land
and sea. Innumerable green microscopic algae float on the
surface of the sea in calm and clear weather ; and at the bidding

SUN AND CLIMATIC VARIATION 39

of the sun they create the food which allows them to multiply
rapidly. They themselves furnish the inexhaustible provender
which attracts the countless infusoria and the minute, almost
microscopic, larvae of marine animals of every sort : worms,
starfish, sea-urchins, and the small crustaceans which form the
interminable army of Copepods — in a word, the whole minute
world of life that swarms unceasingly near the surface of waters
penetrated by light, and to which the Jena naturalist, Haeckel,
gave the name of plankton, including thereby the algse them-
selves. The herrings, sardines, and mackerel, in their search for
the Copepods they delight in, are themselves pursued by the
various tunnies and bonitos ; and these in turn are hunted by
porpoises, sharks, and even dolphins. When the weather is
clear and the temperature favourable all this teeming life is
clearly visible, fishing is fruitful and happiness and prosperity
reign among the fishermen. But when the sky is overcast and
the winds raise waves and trouble the waters, the debris so
fatal to the transparency of the ocean is stirred up, and the
plankton at once flees from the sullied surface, descending to
calmer zones, attracting in its wake all those creatures that
live at its expense. Herring, sardine, and mackerel become
rare ; the fisherfolk can no longer gain their livelihood ; and
the sound of their lamentations is heard even in Parliament
itself.

All this is the work of the sun. Its activity does not, however,
end here. By creating the winds that carry the clouds into the
upper regions of the atmosphere, whence they fall in due course
in the form of rain, the heat of the sun becomes changed into
motion. The water which falls on the high mountain chains
and streams down their slopes gradually wears them away ;
and this continuous action, however slight it be, produces a
prodigious effect. The mountains of 7 or 8 thousand metres in
height that formed the Huronian chain, and the younger
Caledonian chain, have been completely levelled to the ground by
this erosion, which may be said to be also the work of the sun.
On the sun, too, depends the energy of watercourses, the energy
developed by waves in their assault on the land, and the energy
that lies hidden in the depths of the earth in the form of coal,
for the sun is the principal builder of vegetable tissues. And as
plants, children of the sun, directly or indirectly, are the only
source from which animals derive the foods upon which they

40 FORMATION OF THE EARTH

subsist, the animals owe to the sun their very power of move-
ment. The rustling of the leaves as they are stirred by the
wind, the devastations that follow in the wake of cyclones ;
the gentle ripples formed by light breezes on the surface of
placid waters, like the colossal waves raised by tempests ;
the tranquil course of rivers, like the impetuous violence of
torrents — all are the sun's work, just as is the clumsy progress
of the earth-worm, the fleetness of the gazelle or the bold
flight of the eagle. The song of the elves in The Midsummer
Night's Dream, as they pray that "never harm, nor spell,
nor charm " may disturb the slumbers of their queen is
a prayer to the sun, which causes both thunder and the song of
birds, and all the sounds to be heard on earth. In the opinion of
meteorologists even the spots on the sun's surface influence our
atmosphere ; the dry and rainy periods being supposed to
vary with the number of spots observed. These spots reach a
maximum every eleven years, which thus corresponds exactly
to our rainy cycles, and it has been even assumed, perhaps too
rashly, that this maximum also coincides with a period of
frequent earthquakes.

Night and day and the periodic recurrence of the seasons
depend equally upon the sun, just as does the existence of
diurnal and nocturnal animals, which pass the day or the night,
as the case may be, in periods of alternating rest and
activity. To the sun, finally, is due the increase of life through-
out all Nature in the spring, and the tendency of all organisms
to multiply, each according to its kind. The sun, then, governs
all activity on our globe ; and, in accordance with the
distribution of its heat and light, all the movement that
animates the atmosphere and the seas, all the phenomena of
life, are regulated. We must, therefore, examine in detail the
various relations that unite us to the sun, and the way in which
these relations have been modified in the course of centuries, as
well as the changes which the sun itself has undergone.

The earth exhibits numerous types of motion ; it turns on
its own axis, and the duration of that rotation is called by
astronomers a day ; the axis upon which it revolves is a straight
line fixed with reference to the earth, and the stationary points
on its surface which represent the extremities of this imaginary
line are known as the Poles ; the plane perpendicular to this
axis, which passes through the centre of the earth and which

SUN AND CLIMATIC VARIATION 41

cuts the surface along a great circle, is called the equator. The
earth, moreover, moves round the sun and describes an ellipse,
of which it occupies one of the foci ; the time required for
this journey constituting the unit of measurement is called a
year. The ellipse described by the earth is called its orbit, and
the plane of the orbit the ecliptic. If the earth's axis of rotation
were perpendicular to the ecliptic the equator would be
situated in this plane, and every part of the globe would then
always be illuminated for exactly one half the time occupied
by the rotation. The term day is usually limited in its
application in ordinary language, and refers not to the
astronomical day but to the fraction of that day during which
a given place is illuminated. On the hypothesis of a coincidence
of the plane of the equator with that of the ecliptic the days on
the earth's surface would be equal to the nights. But this is not
so. The two planes indicated actually form an angle of
230 27' 21". Now it can easily be shown by simple geometrical
methods, that on account of this inclination, those parts of
the earth, which are situated on the equator are the only ones
where the days and nights are of exactly the same length
throughout the year. At either Pole, on the other hand, it is
night for six months, and also day for six months, the day of
one of the Poles coinciding with the night of the other, and
conversely.

For all points of the earth situated on a small circle whose
distance from the Pole can be measured by an arc 230 27' 21",
there is a consecutive day and night period of 24 hours at the
moment when the plane of the terrestrial axis and the
perpendicular which passes through the centre of the earth
also passes through the centre of the sun. That moment is
called the solstice. Polar circles is the name given to the small
circles that fulfil these conditions for either Pole. For all
points situated between these circles and the Poles, the
duration of the day and the night is longer than that of an
astronomical day and all these points are situated within the
frigid zones. On each side of the equator, a small circle, also
situated at a distance of 230 27' 21" from the equator, marks
off the region where every point sees the sun twice a year
exactly vertical, i.e. at its zenith, that being the moment in
which the days and nights in the arctic circles are equal to the
astronomical day. This is the torrid zone, and the small circles

42 FORMATION OF THE EARTH

limiting it on each side of the equator are the tropics, or as
they are sometimes called, the inter-tropical zone. Between
the tropics and the Polar circles extend the temperate zone,
where the duration of light and darkness is always less than one
terrestrial revolution and where the sun never reaches its
zenith.

At the particular moment in which the plane of projection
of the earth's axis to that of the ecliptic is perpendicular to
the line joining the centre of the earth to the centre of the sun,
the days and nights are equal at all points of the globe, and this
is called the equinox. From this moment onwards, we have
inequality between the duration of day and night in both
hemispheres, the nights becoming longer in one and shorter
in the other. In one case we are passing from autumn to winter,
and in the other from spring to summer. The culminating point
of the hot season, which we call summer, coincides with that
particular instant, which lies half-way between the two
equinoxes, that is to say, at the summer solstice, and the same
holds for the winter solstice. In our hemisphere the hot season
coincides with the period in which the earth is approaching
the height of its orbit furthest from the sun. It is the duration
of the day and not the proximity of the sun which raises the
temperature. As the length of the day is the same in the two
hemispheres, the summer of the southern hemisphere is a little
hotter than in the northern, the earth then being nearer the
sun than it is during our summer. The year is consequently
divided into four seasons, spring, summer, autumn, and
winter.

These facts are not as definitely fixed as might at first be
supposed. The terrestrial axis does not remain parallel to
itself. It describes a cone with a sinuous contour round a line
perpendicular to the ecliptic, whilst the orbit itself is revolving
in its own plane. These combined movements cause the line
of equinoxes passing through the centre of the orbit to turn,
in the plane of this orbit, 62" per year, just as if it were going to
meet the earth, thus gradually advancing the period of the
equinoxes. The procession of the equinoxes requires 21,000
years to make one complete rotation. The duration of the
seasons itself varies periodically, and under conditions at
present prevailing in our hemisphere the spring-summer
period lasts eight days longer than the autumn-winter period.

SUN AND CLIMATIC VARIATION 43

There is consequently a slight rise in temperature to the
advantage of the former. The converse occurs every 10,500
years.

The eccentricity of the earth's orbit is also subject to very
important variations : to-day it is -gV- But it can increase to
Tj5 ; that is to say, the orbit may be extended by the earth
going further from the sun than it does to-day, and also by
coming nearer to it ; and this would lead, of necessity, to a
greater difference between the hot and the cold season than
that prevailing to-day, especially if the line of the solstice
coincided with the major axis of the orbit. Conversely, if the
eccentricity were zero, that is to say, if the terrestrial orbit
became circular, a possible contingency, and the earth remained
the same distance from the sun throughout the year, the
seasons would be less marked than they are to-day. Such
alternations must actually have occurred in the course of the
millions of years represented by geological periods. But we may
go further and say that in the present phase of our planetary
system, the angle formed by the plane of the equator and the
ecliptic varies only within narrow limits, from about 210 59'
to 34° 36'. These two planes cannot coincide, which would
eliminate the seasons. But other astronomical conditions
affect the position of the earth's axis ; every change in the shape
of the earth, which is not rigid, and every modification in the
distribution of the matter which composes its mass, may bring
about a displacement of the axis of rotation in relation to the
surface, or, to put it otherwise, a displacement of the line of
the Poles, and may, in consequence, fundamentally alter the
climates of different regions of the globe. It has even been
supposed that a greater accumulation of ice at one of the
Poles than at the other can produce such an effect.

Neither has the sun itself remained unchanged. After the
earth was detached from it the sun continued to shrink both
as a result of cooling and because it had thrown off two other
planets, Venus and Mercury, which naturally Jed to a reduction
in its size. It would be sufficient for the sun to have an apparent
diameter of 470 to cause the lighted area of the earth greatly
to exceed that of the unlighted,1 instead of their being equal
as is the case to-day. Under those conditions, however, the
long solar nights would disappear and there would be no more

1 Vbis, 32.

44 FORMATION OF THE EARTH

seasons. In the twenty million years during which life has
existed on the earth, such climatic changes must actually have
occurred.1 The computations of Blandet have led us to assume
that during these twenty million years the diameter of the sun
has decreased by one-half. When life began on earth the sun
was so large that there was hardly any night at all. The work
of J. Bosler 2 suggests that through radiation alone the sun
must have lost in thirty million years a mass equivalent to
that of the earth. This diminution, together with modifications
in the longitude of the earth, would bring about a slowing down
of the earth's motion equivalent by the end of the same time
to a retardation of 36 hours for the seasons. The temperature
of the sun, therefore, must have correspondingly diminished
since the commencement of life. Scientists are not agreed as
to its temperature at the present moment. M. Violle reduces
it to 2,500 degrees, Lord Kelvin places it at 14,000, and
M. Le Chatelier stops at an intermediate figure, 7,500 degrees.
6,000 degrees is regarded as the most probable figure.

Whatever the facts may have been, the diminution of the
solar temperature must have changed the nature of the light
emitted. To-day the sun is, in fact, a yellow star. We know
that there are white and blue stars in the firmament which
are hotter. The sun must once have belonged to one of these
categories. The light which it then sent the earth was richer
in chemically active rays — in blue or violet, or invisible ultra-
violet rays. The energy of such light was then much greater
and quite different from the solar light of to-day. It must
consequently have produced on the earth chemical phenomena
now impossible. We shall have recourse to this important fact
later on ; for the present, however, we may conclude that at
a period not far distant relatively to the duration of the
geological epochs, the sun was of sufficiently great dimensions
to render the climate of those regions of the earth, corresponding
to those now above water, quite different from what it is to-day.
As to that, however, there are reasons nearer at hand thanks to
which frequent changes of climate must have occurred in the
same place. What determines climatic characters to-day is
the altitude above sea-level, the proximity of high mountain
chains covered with eternal snow and glaciers, and the position
relative to the sea of these mountain chains whence hot or cold
1 IX, 122. 2 XI.

SUN AND CLIMATIC VARIATION 45

winds blow according as the air reaching them and carried to
lower levels is dry or moist ; and, finally, the distance from
the sea, and the variable temperature in its vicinity depending
on whether it is in open communication with warm equatorial
water or the cold oceans of polar regions.

We have seen how, in the course of geological periods, mighty
mountain chains were formed and then gradually levelled ;
their gradual elevation to great heights little by little cools
the climate at their base, whilst around them the reciprocal
effects of continents on islands, and land masses on seas, change
incessantly. So that not only have there everywhere been
slow yet ceaseless modifications in the general nature of
meteorological phenomena, but all that was accomplished by
the agency of the sun's energy on the earth has also undergone
consecutive changes of aspect.

The study of plant and animal fossils by palaeontologists
would seem to support all that has been said above as to
climatic changes. To-day there are animals and plants peculiar
to cold countries, and others to temperate and hot countries.
Conifers, birches, and analogous trees constitute the stock
type of vegetation found on high mountains and more or less
polar regions ; annuals and caducous trees abound in temperate
regions ; tree-ferns, cycads, palms, monocotyledons with large
flowers, spices, such as the cinnamon, the clove, etc., at once
evoke the idea of tropical countries, just as coral reefs and
the greater shell-fish immediately suggest tropical seas. It is
generally held to-day that, in warm climates only, can such
creatures nourish as crocodiles among the greater reptiles, birds
such as parrots, and mammals such as the elephant, rhinoceros,
hyena, panther, lion, tiger, and monkey. We judge the climate
of a region by the presence among its fossils of the remains of
plants or animals analogous to whose habitat is known to-day.
The method is far from unimpeachable, and the misadventure
which befell even Cuvier should be enough to warn us
to proceed in this direction with the greatest caution. The
elephant was regarded by Cuvier as belonging to a warm
climate ; so that the discovery of the bodies of mammoths
with flesh and hair still preserved, in the Siberian ice, seemed to
him to prove that this country once enjoyed a tropical climate.
To explain the presence of elephants buried in the ice he did
not hesitate to assume that, owing to some miraculous

46 FORMATION OF THE EARTH

cataclysm, a tropical climate had been instantaneously trans-
formed into a glacial one. Mammoths were simply hairy
elephants adapted to life in arctic countries, where they lived
together with the rhinoceros and other species of animals
whose representatives to-day are found only in tropical
climates.

In fact, living organisms are exceedingly untrustworthy
guides to climate for two reasons : —

1. Since they were produced successively only, the first
organisms achieved spread over the whole globe without
difficulty, with the result that the flora and fauna then
presented a homogeneity giving the impression of great
similarity in the conditions of existence, because we are accus-
tomed to see a close correlation between these conditions,
when they are diverse, and the presence of certain animal
and plant groups. This is the case, for instance, for the ferns,
horse-tails, club-mosses, conifers, and cycads which throughout
the Primary Period constituted the flora of continents that
possessed no flowering plants at that time. The same holds
true for the Trilobites, cartilaginous fish, and carapaced
Batrachians then dominating the fauna.

2. The same fauna can both adapt itself to and resist climatic
conditions of the most varied kind.

The tiger, for instance, is encountered in the high cold
plateaux of Tibet. Father Armand David also found monkeys
and parrots there, and M. Lefebvre, in his excellent book
Chaleur animate et bioenergetique, has described how he
succeeded in getting a Cercopithecus to live under snow.1
Finally our domestic animals prove the extent to which an
animal organism can adapt itself to the most varied conditions
of existence.

Moreover, glaciers have again and again left traces which
give us more precise information on the regions invaded by
extreme cold than living organisms have given about heat.
It is thus that the presence of glaciers during the Algonkian
epoch, at a time when the oldest gneisses had hardly been formed,
has been traced in Ontario, in the region between Lake Superior
and Temiscaming forest, and in Minnesota, Michigan,
Spitzbergen, and the Cape of Good Hope. It was the period

1 XII, 407.

SUN AND CLIMATIC VARIATION 47

in which the Caledonian chain attained its greatest height.
At that date there were not only polar glaciers, but glaciers
comparable to those which, later on, marked the approach of
the quaternary period subsequent to the formation of the
Alpine-Himalayan chain. These glaciers were perpetuated at
the base of the Cambrian formations in Norway, in the Yang-
tse district, in India, at Simla, and in the south of Australia.
This, as we have already pointed out, is no reason why
we should believe that the climate became cold at this epoch ;
for even to-day there are glaciers below the equator.

With these reservations we may here summarize the con-
clusions reached by geologists as to the climates of the different
geological epochs.

The temperature of the seas seems to have been uniform
during the Cambrian Period, and, in fact, there is no reason for
assuming — at least, if at that time the orbit of the earth had
not become markedly flattened — that this temperature was
lower then than during the Silurian epoch that followed. The
abundance of corals found at all latitudes in the Silurian seas
does indicate warm waters, since the secretion of calcareous
matter by marine organisms increases in activity as the
temperature rises. No traces of Silurian glaciers have been
discovered, but this may simply mean that erosion had levelled
the Caledonian mountain chain to such an extent that its
mountains no longer accumulated eternal snows upon their
summits. There is nothing to suggest that conditions changed
during the Devonian Period, though glaciers have been traced
at the Cape of Good Hope. On the contrary, corals continued
to nourish all round the North Atlantic continent in the region
corresponding to the site of the later Hercynian chain in the
Central Plateau, Bohemia, etc. In addition, the abundance of
red sandstone, whose colour corresponds to that produced
in our day in desert regions under the influence of powerful
solar radiation, seems to indicate that in those regions
temperate to-day the sun's power was then far greater than it
is now. The glaciers of the Cape of Good Hope have even
suggested the possibility of the South Pole having become
displaced by 6o°, but if this were true the same ought to hold
for the North Pole, and no indication of such a displacement
exists. We must admit, then, that the glaciers of the Cape of
Good Hope were the result of a local phenomenon, namely,

48 FORMATION OF THE EARTH

the presence in this area of a high mountain chain during the
Devonian epoch. These mountains, after a period of
quiescence, seem to have extended to other parts of South
Africa, India, and Australia. At any rate, during the second
half of the Carboniferous Period in which the coal deposits
were formed, enormous glaciers, uniting at certain points,
developed on the slopes of the high mountains in the southern
portion of the huge continent of Gondwana, which then com-
prised Brazil, Africa, Madagascar, India, New Guinea, and
the western portion of Australia, and whose southern coast
was washed by the southern ocean.

It was also at this time that the Hercynian chain arose on
the North Atlantic continent, which was then washed by the
tropical Tethys or Central Mediterranean Sea. Both in the
North Atlantic and the Gondwana continents the land
vegetation assumed, during the first part of the Carboniferous
epoch, an importance it had not hitherto possessed. The
uprising of the Hercynian range and the volcanic eruptions
accompanying it troubled the ocean waters. The corals
abandoned these shores and retired to the north, to the region
of Dinant in Belgium, the Pennine chain in England, and even
the neighbourhood of the Pole. The temperature of the sea
in this area, therefore, did not fall below 20°, the temperature
essential for the development of coral reefs to-day. The
Hercynian chain soon attained its greatest altitude ; its slopes
became covered with a rapidly growing vegetation of the non-
flowering plant families, whose only representatives to-day are
modest herbaceous plants, such as club-moss, the selaginaceae,
and horse-tails, or those whose flowers are still in an
undeveloped stage, such as conifers. The torrents rushing down
these mountain slopes became powerful streams, which
uprooted trees and carried them to lakes and wide estuaries
where they collected and helped to form coalfields such as
those in the south of England, the north of France, and
Belgium. At the foot of these slopes, in vast marshes, there
grew also plants with long underground stems, ferns, and
cycads, whose leaves, dead branches, and trunks then
accumulated where they were and led to the formation of coal-
fields of another type, such as those of the Central Plateau,
for instance. The richness of these deposits is such that it was
at one time believed, owing to an illusion comparable to that

SUN AND CLIMATIC VARIATION 49

which the idea of cataclysms created in the mind of Cuvier,
that an exceptionally high temperature and an especially
humid atmosphere charged with carbonic acid were essential
to their origin. Nothing of the kind, however, was required.
It needed only slopes capable of supporting a dense vegetation,
a uniform temperature, and a normally humid atmosphere,
to permit the rapid and continuous growth of vegetation. And,
in fact, there is not the slightest trace, in cross-sections of tree-
trunks of this period, of those concentric circles which in the
cross-section of contemporaneous trees indicate yearly growth
in obedience to the seasons. During the Carboniferous Period
the earth enjoyed a perpetual spring, somewhat mitigated in
high latitudes, recalling those regions which to-day are repre-
sented in Europe by the Alps with their perpetual snows and
glaciers. All this accords with the hypothesis of a then greater
solar diameter. The absence of flowering plants must have
caused a greater uniformity in the vegetation than there is
to-day, and the newness of the land flora also explains why there
was as yet so little differentiation into species. The same plants,
in fact, were distributed over the entire North Atlantic
continent. A similar uniformity characterized the whole
Gondwana continent ; but their flora is entirely distinct.
The relatively poor flora of the Gondwana, known as the
Glossopteris flora, seems to suggest, especially in the south, a
lower mean temperature than that of the North Atlantic
continent, at least, if the vegetation of this continent was not of
more recent origin. This flora later extended to other regions.
At the end of this epoch the beautiful flora of the North
Atlantic continent began to become impoverished. The climate
then no longer allowed an abundant vegetation. Over a large
part of northern Germany, the southern Alps, eastern Russia,
and the United States, heavy rains, sweeping along with them
into the sands, now transformed into sandstone, chemical
substances which they dissolved, alternated with long periods
of drought and heat which gave to these sandstones the colour
so characteristic of desert formations. The species that were
typical of the North Atlantic continent could not protect them-
selves against the invasion of the more resi stent species from
the Gondwana continent which had not had to endure the
test of a dry heat comparable to that of the present Sahara.
This period of impoverishment in the northern flora coincides

50 FORMATION OF THE EARTH

with the Permian Period. It probably then gave rise to
phenomena analogous to those which have produced the
Gobi desert at the foot of the Tibetan massif.

We now approach the beginning of the Secondary Period,
the Trias, during which, it appears, the height of the Hercynian
mountain chain had been considerably reduced, either through
long-continued erosion or local subsidences. The mountains,
which play so great a role in atmospheric condensation, having
been markedly levelled, glaciers seem to have disappeared and
the rains to have become less abundant. The dry and hot
climate of certain regions during the Permian epoch appears
to have become general, or, at least, more extended.

Although local differences in the mean temperature existed,
nothing indicates that at this period there were climatic zones
comparable to those existing now. Until positive proof is
forthcoming that, at this epoch, the earth's axis approached
a position normal to the ecliptic, with which periodic variations
of position are inconsistent, and also that at that time its orbit
approximated to that of a circle, we must assume, as has been
pointed out, that the apparent diameter of the sun was very
much greater than it is to-day. A very slight decrease in this
diameter, without the axis of the earth changing its position,
would be sufficient to cause the appearance of polar zones,
separated by a torrid zone that was, in fact, very extensive,
for there still existed at this period reefs and islands formed of
madreporic coral in certain areas of Europe corresponding to
Alsace, the north of France, and Wales. This torrid zone seems
to have been characteristic of the climate of the Jurassic
Period.

Throughout this quiescent Secondary Period, during which
not a single chain of mountains was raised, and in which the
slow action of erosion continued, nothing could have been
produced suddenly — neither glaciers in the deep valleys nor
violent atmospheric condensations ; but a slow retreat of
coral formations towards the south indicates a gradual
restriction of the torrid zone and a compensating appearance of
temperate zones towards the polar regions.

Corals long persisted in Alsace, in Switzerland, in the cantons
of Argovie and Fribourg, and in the Jura, whilst in Lorraine
they formed reefs twenty metres in thickness. The flora

SUN AND CLIMATIC VARIATION 51

extending from lat. 500 to lat. 710, however, was a temperate
one, and annual alternations of temperature are indicated in
the trunks of certain conifers, notably in those discovered in
Graham's Land on the edge of the Vancouver Straits, and in
the Araucaris by the concentric rings known in the conifers
and dicotyledonous trees of our country, but which are absent
in trees of the torrid zone. Thus there were evidently seasons
in the polar regions, which, however, continued to enjoy
a very mild climate throughout the Jurassic Period, whereas a
tropical climate persisted in what are the present temperate
regions. For if the corals disappeared suddenly in the north of
the Central Plateau, doubtless as the result of a change in the
direction of the currents, they appear again in the Tethys,
beginning at Poitou, and also, somewhat later, in the
Ardennes, and still later near Trouville, on the eastern frontier
of Lorraine, to the north of Morvan, at Bourges, Sancerre,
and even extend to Yorkshire ; while in the Jura they lasted
still later.

These conditions changed very quickly in the Cretaceous
Period which followed. The corals were entirely replaced in
the Mediterranean area by the Rudistae, peculiar lamelli-
branch molluscs, which also congregated in immense reefs
and came from warm waters, though they accommodated
themselves to a lower temperature. Caducous dicotyledons
made their appearance and developed more and more in the
northern regions. The temperature, however, continued, if
not very high, at least mild and fairly constant as it is to-day
on the coasts of Brittany, for the bread-fruit tree and various
cycads flourished side by side with small-flowered dicotyledons,
such as Willows, Poplars, Birches, Oaks, Walnuts, Plane-trees,
and Figs, and evergreens like Ivy and Oleander. Some
gamopetalous forms — the Viburnum, and even mono-
cotyledons were associated with them.

During the Nummulitic Period, which marks the beginning of
the Tertiary epoch, Greenland and Spitzbergen still retained
a very rich flora, and even kept it through the Neogene Period
that followed, which clearly demonstrates that the polar
regions had not as yet experienced any considerable decrease
in temperature. The temperature indeed was almost that of
the present Mediterranean lands. Grinnel Land, in lat. 820,
had the climate the Vosges have to-day ; poplars, birches,

52 FORMATION OF THE EARTH

silver-fir, and water-lilies flourished there. In Greenland,
in lat. 700, magnolias flourished. A little later, during the
Oligocene Period, in the area corresponding to our present
temperate regions, there was now a mixed flora, now a
localization of temperate flora and tropical flora, indicating
that the vegetation had come under the influence of the
temperature of the coastal currents. On the other hand, the
nature of the arctic flora in the Neogene Period points to a very
definite increase of cold in these regions. It was in this period
that the largest of our existing mountain chains was formed,
and, as in the case of the formation of the Caledonian and
Hercynian chains, glaciers soon made their appearance.

The plants of the warm climates gradually moved south and
were replaced by trees with caducous foliage, bearing witness
to an alternation of cold and warm seasons. The camphor-
tree, however, still flourished at a latitude of 510, and palms
at 500 ; the flora was identical from lat. 380 to lat. 540 — from
Serbia to Finland.

By the time that the Alpine-Himalayan chain had attained
a great altitude the Oligocene epoch was in full sway. The
presence of these large massifs conduced to condensation, and
the summer became rainy ; but the winter still remained
warm. Along the shores of Lake Constance there was a climate
like that of Madeira and the south of Japan ; the mean
temperature of the shores of the Sea of Okhotsk was about
190. But a period of erosion and settling followed for the new
mountain chains. Torrential rains, caused by their very
height, ravaged their slopes, cutting deep valleys, and there was
a tremendous extension of glaciers.

This brings us to the beginning of the Quaternary Period,
which witnessed man's conquest of the soil. During this
period, apart from the changes in land elevation due to the
formation of mountain chains, it seems that extensive
continental areas experienced alternate elevation and settling
movements constituting what are known as epirogenic
movements. During the periods of upraising, the glaciers that
had formed in the valleys of the high ranges extended very far,
only to retreat again during the epochs of settling. The climate
naturally became colder in the neighbourhood of the glaciers,
but in regions distant from them it still remained mild.

SUN AND CLIMATIC VARIATION 53

These periods of alternate invasion and retreat of the glaciers
are called glacial and inter-glacial periods, and have helped
to mark the stages of man's history. At that time the /Egean
communicated with the Black Sea. After an initial lowering of
temperature in the Pliocene, the climate became less rigorous :
the Hippopotamus, Rhinoceros, Elephant, Lion, and Hyena,
all of them animals to-day confined to tropical areas, flourished
in southern France. The glaciers, however, once more gained
the ascendancy (the Munsterian age), and spread over one-
seventh of the whole land area of the globe, a total of twenty
to twenty-five million square kilometres. In the United States
they reached 400 lat., somewhere in the neighbourhood of
New York ; in Europe they extended as far as lat. 500, and
covered England, North Germany, Scandinavia, and Russia
up to the Vorona. The prehistoric x Mammoth and Rhinoceros,
whose descendants to-day are practically hairless, were then
provided with a coat of woolly hair. When the ice retreated
Lemmings were to be found near the glaciers, and further
southwards Reindeer, arctic Hare, and arctic Fox. In fact, the
fauna of the Steppes reached as far as the Pyrenees. The
temperature subsequently became somewhat warmer and the
air drier (the climate of the tundras). This was the age of the
reindeer, which in the period following was temporarily to be
driven northwards, to reappear at the end of the Pleistocene
and again to descend to lat. 430.

To what are we to ascribe these variations of temperature
that brought about four successive glacial invasions ?
Formerly, when it was generally assumed that there had been
only one glacial period, the explanation of Croll and Geikie
sufficed which postulated a gradual lengthening and flattening
of the earth's orbit. But the existence of several glacial periods
renders this hypothesis of little avail as an explanation. It is
also contradicted by the fact that the glacial period would thus
seem to have made its appearance simultaneously in both
hemispheres. A periodicity connected with sun spots has been
suggested, but the period of duration of such spots is far too
short, and it is therefore probable that local phenomena were
entirely responsible.

Local phenomena, however, have played but a secondary
r61e in the earth's history, and then only for short periods.

1 Middle Pleistocene or Magdalenian.

54 FORMATION OF THE EARTH

They are dominated by two outstanding facts : First, that as
far as our observation can be extended, that is to say during
a period of nearly twenty million years, the polar caps retained
a climate resembling that of the Mediterranean to-day ; for
this to be the case it would be essential that they should have
been almost permanently illuminated by the sun. Secondly,
the torrid zone, on the other hand, had remained constant in
climate ever since the origin of life, but it had gradually
decreased in extent, and there had been a very slow but con-
tinuous cooling of the polar regions, whose climate, having
become rigorous and glacial, was preserved in regions
corresponding to our present temperate zone. This we can
explain only in one way, by admitting a progressive shrinking
of the solar disc, and it is therefore to this dominating cause
that those other and secondary conditions appertain that have
given to the Pleistocene Period the variety of characters
peculiar to it.

It is therefore the sun which has guided the evolution of the
earth. The sun has shown himself to be the great artist who
can repeat over and over again the forms of living creatures,
and who is himself the creator of every variety of living form.
The periodic alterations in the earth's orbit and the
inclination of the axis to the ecliptic, mentioned at the
beginning of this chapter, have undoubtedly played their part
here, too, so that if geologists and astronomers could be
induced to co-operate in their researches into these questions,
it might be possible, by exhaustive discussion of the testimony
gathered by each, to find some method of explaining the
principal geological events and arriving at an accurate
chronology. The calculations of astronomers themselves do
not take into consideration all the facts of the problem, for
they have specifically studied the consequences of those events
that, on the supposition of stationary stars, relate to the
influences they exercise upon one another. Everything relating
to modifications in the form and constitution of the earth
escapes their calculations, though these modifications must
have been relatively greater than those acting on the sun,
owing to the smaller size of the earth. These modifications may
have intervened to increase the inclination of the earth's axis
of rotation to the ecliptic, or to have rendered it perpendicular
to the same without changing the geographical position of the

SUN AND CLIMATIC VARIATION 55

Poles, and this would have sufficed to bring about a complete
alteration in the seasons, or even to have caused their dis-
appearance. They might equally well have altered the
geographical position of the Poles without increasing the
periodic modifications of the inclination of the earth's axis
to the ecliptic. It is, however, only after the inadequacy of
explanations based on astronomical calculations has been
demonstrated that these new data can be studied to advantage.1

1 For questions relating to climate see Febvre's Geographical Introduction
to History.

PART II

THE PRIMITIVE FORMS OF LIFE

CHAPTER I

The Appearance of Life

OF all the problems with which man's mind has wrestled the
most perplexing is that concerned with the origin of life,
embracing as it does the problems of humanity's own origin.
Even before science came into being, the most daring thinkers
of every age attempted to find some explanation for it, as the
forms of life, among which we ourselves occupy the most exalted
position, confront us on all sides in a far more insistent manner
than even the phenomena of wind and weather. Our ancestors
had to move about in enormous forests where they encountered
powerful adversaries, against which they had continually to
measure their strength. Only from the other living creatures
which surrounded them could they obtain all that was necessary
for the maintenance of life, and only by a constant struggle
could they wrest these necessities from their rivals and at the
same time defend their own lives. So long as man imagined
a Creator under human form he supposed the gods to be the
creators of all living things — of plants or animals just as we
see them around us, of germs destined to evolve according to
the process which could be observed every day in the
germination of seeds and the hatching of eggs. No further
explanation was required. As time went on it was thought that
natural forces were in themselves capable of causing
germination, or even that certain substances in the course of
fermentation, under the action of the sun's rays, either in the
secret depths of the ocean or in the bosom of the earth — so
often regarded as the great mother of all being — were capable
of forming themselves into organisms. To this, the doctrine of
spontaneous generation, Joly, Archimede, Pouchet and Musset
attempted to give scientific form. It was the doctrine that
Aristotle had already advanced ; it had been accepted by
Lamarck ; defended against Pasteur by scientists such as
Musset, Joly and Pouchet, favoured by the medical men,
extolled by the most materialistic philosophers, it finally took
on, in the nineteenth century, a quasi-scientific air.

60 PRIMITIVE FORMS OF LIFE

It must be admitted that though the remarkable
experimental researches of Pasteur opened up unforeseen
perspectives to medicine and surgery and provided curative
art with a new kind of precision and new methods with
inexhaustible possibilities, they were, at the same time, the
source of endless difficulties for the scientific philosophy of the
day. One unquestionably correct idea prevailed — that every
phenomenon was preceded by causes which definitely and
inevitably determined it. Claude Bernard had introduced
into physiology the notion of determinism in living phenomena,
and had thus destroyed the older doctrine of vitalism, which
excluded such phenomena from the working of the ordinary
laws of physical chemistry. Vitalism once discarded, the
phenomena of life had perforce to be attributed to these normal
natural forces. It was readily admitted that living matter,
composed as it is of carbon, hydrogen, oxygen, nitrogen, and
traces of various other simple elements might well have arisen
and could be reconstructed in the same way as other simpler
chemical compositions. Huxley, we know, even believed in the
existence of one single substance, the physical basis of life,
and to this he gave the name of protoplasm, a name which
has managed to survive. The German dreamer, Oken, founder
of a so-called Philosophy of Nature, which, in the early nineteenth
century created quite a stir on the other side of the Rhine, had
already postulated the existence of a primordial slime, in which
all life had its origin. Huxley at one time thought that he had
really discovered it in the slime of the oceanic depths ; he
called it Bathybius haeckeli, and, in spite of Huxley's sub-
sequent abandonment of the notion, the impenitent naturalist
of Jena continued to insist on the real existence of this spiritual
god-child of his,1 though Huxley himself recognized it as being
only a mineral precipitate of gelatinous appearance, which
arises when distilled alcohol is poured into sea-water containing
organic matter in suspension.

Thus the new thinkers argued that if protoplasm really
existed, and if it was only an especially complex chemical
compound possessing special properties by reason of its
complexity, it might be obtained artificially by appropriate
chemical processes. The ill-success of chemists in their
attempts to reconstruct even a nitrogenous substance like

1 XV, 165.

THE APPEARANCE OF LIFE 61

albumen, the simple white of an egg, possessing no life,
might be nothing more than a temporary check. Had not
Berthelot, for instance, succeeded in combining carbon directly
with hydrogen and nitrogen, had he not formed synthetic
sugar ; and had not chemists before, during and after his day
succeeded in obtaining an infinite number of substances which
had once been regarded as the exclusive and peculiar work of the
life-force itself ? Directly the chemists could understand the
constitution of nitrogenous substances such as albumen —
and the most skilful were at work upon it — was there not every
likelihood that its reconstruction would be achieved ? And,
finally, if protoplasm was merely one of these substances,
endowed with specific instability and a particular capacity for
combination, was it indeed foolhardy to believe that this, too,
would some day appear in the retorts and test-tubes of the
chemists ? It would unquestionably emerge as an indefinite
and amorphous mass, but could it not be given the form and the
perpetuating activity which would make a living organism ? . . .
All this beautiful dream the experiments of Pasteur threatened
to destroy at one blow. If, indeed, the free play of forces and
substances was incapable of producing living matter, if it was
necessary in order to account for its formation to have recourse
to a direct act of creation, why not then admit with Cuvier the
direct creation of all living beings and consequently the fixity of
species ? To accept the foolish theory of spontaneous generation
was to undermine that whole doctrine of evolution which had
proved so satisfactory to man's reason and had, moreover,
been substantiated by so many facts.

As the difficulties in the way of reconstructing living
substances appeared to be invincible, the idea soon occurred
to some to explain its advent as from another world. In 1821
de Montlivault decided that life-germs from other planets,
perhaps those furthest removed from us, had been brought
thence to our earth — no one could tell how, for no winds existed
in the interplanetary spaces to carry dust from one to another.
These germs had developed on earth and given rise to the first
living organisms. In 1853 the hypothesis of de Montlivault was
taken up again and developed by Count Keyserling. Life, he
said, is eternal, like the world itself ; but in the course of ages
changes its habitat. Germs travel unceasingty from one stellar
system to another, quicken into being those stars ready to

62 PRIMITIVE FORMS OF LIFE

receive them, reanimate life in places where some premature
catastrophe has destroyed it, and enrich it where it already
exists by bringing with them greater variety. Thus, on our earth,
a fauna extinct at the end of one geological period was replaced
by a new one at the beginning of the following epoch, and this
phenomenon was repeated over and over again. However, as
we said before, the means by which these germs made the
journey had still to be discovered. In 1865 Count de Salles-
Guyon opined that they must come to us in meteorites or
thunderbolts. But this presupposed a disintegrated planet
endowed with a tremendous wealth of life. Richter and
Cohn preferred the idea of cosmic dust or comets travelling
through vast spaces and sowing life as they go. The great
physicists Helmholtz and Lord Kelvin accepted this hypothesis,
and also the master of the French botanical school, Philippe
Van Tieghem.1 But the germs of life did not come from the
planets alone ; they could come also from the stars ; and there-
fore they must be considered non-combustible. In 1872,
indeed, Preyer did not hesitate to attribute to them this
marvellous property. He gives the name of Pyrozoa to creatures
born of these germs and able to resist fire. Strange as it may
seem, the great physicist, Arrhenius, likewise accepted the
idea of insemination by the stars by means of spores analogous
to the reproductive cells of algae and mushrooms, which spores
possessed tremendous power of resistance to the extreme cold
of abyssmal space. These minute germs, he declared, were
scattered through space by the centripetal force of the stars,
which also threw out such a quantity of minute dust around
the sun that it formed what we call its corona, a phenomenon
easily visible during total eclipses. Germs of this degree of
minuteness mav conceivablv exist, for there are manv microbes
that can pass through porcelain and are invisible to the ultra-
microscope. However, Paul Becquerel has demonstrated 2
that certain ultra-violet rays kill them ; a low temperature
certainly augments their power of resistance, but in the end
they succumb. This demonstration completely destroys the
hypothesis of an extra-planetary insemination, unless we assume
that germs coming from other planets possess a constitution
peculiar to themselves. However, in the very first place, this

1 XIII, 982. 2 XVII.

THE APPEARANCE OF LIFE 63

hypothesis was self-destructive. In actual fact it solved no
problem at all. Wherever the germs of life may have come from,
it remains to explain how they originated in another world ;
the difficulty has merely been relegated to a farther sphere.

All living organisms, moreover, consist of atoms of the same
nature. Carbon, hydrogen, nitrogen, and oxygen must at least
be present. These exist on the earth, as well as on other planets
that have passed, are still passing, or will pass through the same
stages of evolution. Why, it may be asked, should these
elements have united outside our earth and yet have remained
separate here ? This would indeed be contrary to the
fundamental principle of all science — that the same causes
always produce the same effects. If at any particular phase
in the evolution of the planets some sort of life has succeeded
in manifesting itself, the earth should be no exception to the
general rule. The task before us therefore is to investigate
fearlessly how, at some particular moment in the past, life
originated on this planet of ours, whereas now it can pass
only from one living organism to its successors. But, before
undertaking this task, we must first arrive at some agreement
as to what it is that constitutes living matter.

It is not to be regarded as some special substance in which
life resides and which constitutes its unique and necessary
basis, something like an essentially unstable chemical com-
pound in a condition of perpetual change. On the contrary, it
consists of an assemblage of chemical compounds with sensitive
reactions which allow us, even during their living state, clearly
to differentiate and characterize them. Foremost among these
compounds are those which bear so much resemblance in their
constitution to the white of an egg that they have received the
name of albuminoid compounds. They consist of carbon,
hydrogen, nitrogen, oxygen, and a small quantity of some fifth
body : sulphur, phosphorus, or another substance. With these
so-called quaternary compounds are associated, in greater
or less quantities, ternary compounds consisting only of carbon,
hydrogen, and oxygen. Some of them contain more hydrogen
than is requisite for the formation of water in combination with
oxygen, while others can be considered as the result of a union
of carbon and water ; these latter are called carbo-hydrates. To
the first belongs the group of fats : sugars, dextrine, starch,
cellulose, etc., belong to the carbo-hydrates. None of these

64 PRIMITIVE FORMS OF LIFE

substances has a simple constitution. The molecule CH20,
which represents the least complex of the carbo-hydrates,
develops very high powers in organic carbo-hydrates, so that
their formula is given by (CH20)n+pH20. Thus glucose has
the formula C6H1206 ; the starches and cellulose C5Hn05
and cane sugar C12H22On.

The fats are more complex : tristearine, for example, has
the formula :

C3H5 (C18H3502)3 = C57Hno06.

But the highest degree of complexity is obtained by the
albuminoid substances. For instance, the constituent part of
the blood corpuscles of the dog has the formula : —

^72 6 -"-11 7 lO 21 4-N 19 1^3'

The exponential numbers in these formulae indicate the
number of atoms of carbon, hydrogen, oxygen, nitrogen, and
sulphur that enter into the constitution of the bodies
represented. For example,

A molecule of glucose contains 24 atoms.
A molecule of tristearine 153 atoms.

A molecule of albumen 2,305 atoms.

A molecule of albumen, then, is a structure almost a hundred
times as large as a molecule of glucose, and more than thirteen
times as complex as a molecule of fat. It might be compared
with a house of cards, or, at least with one of those fragile
towers which children build with dominoes, and which the
slightest shock will overthrow. However small any mass of
living matter may be, it, nevertheless, contains a certain
number of these molecules, as well as sugars, starches, and fats,
all of which may exist side by side without any alteration so
long as they are not exposed to the influence of the oxygen in
the air, a most powerful disintegrating agent, or mixed with
certain other also exceedingly active substances called soluble
ferments, diastases or enzymes.

Ferments are chemical compounds which can be dissolved,
precipitated, and then dissolved again ; they pass through
filters slowly, and, as they do not absorb nourishment, they
cannot be described as living substances, although they ?ose
all their activity when subjected to heat above 100 \ They
then appear to perish. They possess the property of acting

THE APPEARANCE OF LIFE 65

upon certain organic substances, the carbo-hydrates, fats, and
the albuminoid substances in particular, causing fundamental
changes, and themselves undergoing transformations so slight
in character that some experimentalists have thought they are
not modified at all by their activity. Certainly the influence they
exert is entirely out of proportion to the amount of their own
substance that is altered and the enormous mass of substance
they transform. There is an exceedingly large number of these
ferments acting respectively on the carbo-hydrates {diastases)
on the fats {lipases) or on albumens. Each one possesses its
own specific action — decomposition, hydration, dehydration,
oxidation, reduction, coagulation, or dispersion, and though
simple, they suffice to displace, transform or break up complex
organic substances. Each ferment frequently has some counter-
ferment which neutralizes what it has accomplished ; some are
only active when associated with others which assist them ;
frequently they possess a reversible activity, and are capable
under certain circumstances of reconstituting the bodies they
have destroyed.1 They are frequently poured into the body of
the organism by glands outside of which their action takes place,
but they also mix with other associated substances to form a
vital element, and their very presence suffices to stimulate the
activity of substances that would otherwise remain inert.
Through their agency, associated organic substances undergo
unceasing interchanges and reciprocal modifications in the
presence of the oxygen of the air and the water impregnating
them. The larger organic molecules break down, so to speak,
upon the others ; but it is the characteristic of life that in this
disintegration the more complex substances split up the simpler
and annex the broken-down fragments, so that the unceasing
process of decomposition is yet balanced by a building-up and
an actual increase of the substance brought into action. This
increase is called nutrition, and its natural consequence is
reproduction.

Life, thus understood, is not the work of a single substance,
but rather a result of the reciprocal reactions of a certain
number of definite substances. These, moreover, are not
without individuality. They appear in a relatively small
number of groups, which in all living organisms seem to possess
the same fundamental chemical structure although they differ

1 I, 664.

66 PRIMITIVE FORMS OF LIFE

in detail. The fundamental substance of the blood corpuscles,
the green colouring matter of plants, the chromatin that plays
such an outstanding part in the nutrition of the anatomical
elements, the pigments, etc., all have a composition which may
vary sometimes in kind, as Armand Gautier has demonstrated
in connexion with the vine and various kinds of catechu, or
from one variety to the other, but all belong to the same
chemical type.

Hence we no longer seek to solve the problem of life-creation
by looking for a special substance that is to represent " the
physical basis of life ", as Huxley believed, but by studying
synthetic processes by which substances that in themselves
may be commonplace and inactive, such as carbo-hydrates,
fats, albuminoids, and ferments may be grouped or altered
in nature. The turn recently taken by organic chemistry in
reproducing artificially all those substances formerly believed
to be the exclusive work of life, and the achievement of
Marcellin Berthelot in producing synthetic sugar from
hydrogen, carbon, and oxygen, justifies us in believing that the
problem is not insoluble, and that, if the albuminoids still resist
our attempts, their resistance will not be of long duration.
However, we have yet a more delicate problem to solve — how
to compound the recipe of different substances that must be
combined if life is to be produced and maintained. This is a
task of particular difficulty, as we do not yet possess any precise
data on the constitution of those combinations in which
infinitesimal traces of certain bodies can bring about
fundamental changes. Yet what we are unable to achieve
was done spontaneously in the beginning. If we are to suppose
that elements capable of producing life when they come into
contact with each other were formed at a given moment under
influences still to be determined, they must have met and
combined in all sorts of proportions, and the most complex
combinations must have taken place as well as the most simple.
Those that fulfilled the particular condition under which the
reciprocal reactions of substances, accidentally brought
together, led to an increase in the quantity of the total, con-
stituted the earliest forms of living matter ; and we may
admit that such masses of living matter were at first
quite amorphous and of unlimited dimensions. Now there
exists a certain albuminoid substance which, when mixed

THE APPEARANCE OF LIFE 67

with other albuminoids, possesses the property of forming from
the carbon dioxide of the air and from water-vapour the
carbo-hydrates that represent the most important primary
foods. This substance is chlorophyll, the green colouring-
matter of plants. After the carbo-hydrates have once been
formed, the albuminoids already existing and the ferments
accompanying them utilize the carbo-hydrates in the
manufacture of new quantities of albuminoid substances,
including chlorophyll. It is therefore through the agency of
chlorophyll that life can be perpetuated, and this leads us to
think that the first masses of living matter were green, and if
they still existed would be classed in the vegetable kingdom.

Water-vapour and carbonic acid from the air are unable
to penetrate any organic compound except through the
surface. It is therefore very important that the latter should
develop as far as possible. Under the most propitious con-
ditions this result could be achieved by a pulverization of the
initial mass into small globules and microscopic granules such
as those formed on the moist trunk of trees by Protococcus
viridis. After they have attained a certain size these granules
multiply by fission. This is the origin of the cellular consti-
tution of living creatures. A pulverulent form like that of
Protococcus results no doubt from certain advantages it
presents in respect of nutrition. This we may well believe on
the grounds that certain organisms such as the tan mould
(Fuligo septicum), which do not absorb nourishment through
their surface, but introduce into their substance digestible
food particles, are able to form gelatinous masses, two to
three decimetres in diameter and two or three centimetres
in thickness, and can move themselves about by crawling.

It is possible that the animal and vegetable kingdom might
already have been differentiated in this fashion. The green
colouring-matter of the plants, chlorophyll, cannot combine
atmospheric carbon dioxide and water-vapour, and at the
same time eliminate oxygen, except by the action of the
sun's rays. This process can be accomplished by living matter
only through a surface that is free and exposed to the light.
Nothing, however, prevents the soluble carbo-hydrates from
penetrating the entire living mass if they are present in sufficient
quantity, or, consequently, prevents the nutrition of which they
are the basis from taking place, at some part far removed from

68 PRIMITIVE FORMS OF LIFE

the surface and from the light. There we see the first signs of
the method of nutrition adopted by animals. Oken's hypothesis
of a primeval slime (Urschleim) , out of which all animals and
plants have developed, is not therefore untenable. Organisms
in the form of a simple mass of slime are, indeed, so exceptional
that in all probability it was only after the pulverulent form
had been developed that the separation of the two kingdoms
took place, by means of a process analogous to that which we
have just described.

The multiplication in situ, by fission, of these green granules,
each one enveloped in a membrane formed by the exudation
of carbo-hydrates not utilized in nutrition, must have sufficed
to form a thick layer of vegetable powder which the solar
light was finally unable to penetrate. The multiplication of
vegetable powder would be none the less continuous because
the nutrition had not been interrupted. Chlorophyll is only
produced under the influence of those invisible 1 or luminous
radiations which form the solar spectrum. These rays are
excluded as soon as the powdery mass has become sufficiently
thick, but this does not prevent excess soluble carbo-hydrates,
washed down by the dew, for instance, from passing into the
deeper layers. These deep-sunken granules, if sufficient in
number, continue to envelop themselves in cellulose and to feed
by absorbing dissolved substances, but they form no more
chlorophyll. Plants of this kind, which have no chlorophyll,
are known as fungi. Underneath these, in our hypothetical
layer of living granules, the carbo-hydrates are scarcer and
are completely absorbed during nutrition ; the granules
build no more cellulose exudate, and the living slime remains
free and mobile, as in the case of tan mould. Since
it translates the stimuli it receives into visible movements it
must consequently be sensitive. Mobility and sensitivity are
characteristics of the animal kingdom, which thus appear as
a degraded condition of primitive plant-life, to which is linked
such forms of mixed origin as the fungi. Mobility and
sensibility, however, have enabled the animals to come into
their own by other means, and to raise themselves to the
highest manifestations of life.

1 It can be formed by the infra-red rays alone in various species of
microscopic algas (Chlorella, Dictyosphezrium, Hormococcus, Pleurococcus,
etc.), ferns, certain conifers, bulbous plants like onions or parasites like the
mistletoe.

THE APPEARANCE OF LIFE 69

Thus we see how the mere process of nutrition has sufficed
to decompose our hypothetical layer of living granules into
three strata : a green one corresponding to the algae, a colourless
one containing granules enveloped in cellulose corresponding
to the fungi, and one with free granules, corresponding
to the animals.

The knowledge we possess to-day thus permits us to form a
logical idea of the conditions necessary for the appearance of
life, alike for the formation of the animal and vegetable
kingdoms, without presupposing the interference of anything
but ordinary chemical or physical phenomena, or appealing
to any but the simplest considerations — which to some people
may appear even too simple. Natural laws, however, are always
simple. It is only our mind that loves to surround itself with
mystery and complication.

It may naturally be asked why those cells which do not form
chlorophyll when they are in the dark should not again develop
the power to do so when they are brought into contact with
light. But it is a general rule that a function which is not
exercised disappears, and the faculty of making chlorophyll
can disappear even in the higher parasitic plants like Monotropa,
the broom-rapes, and orchids of the genus Neottia, just as in
the underground roots of ordinary plants.

One particularly tantalizing problem remains. If life has
developed on earth in the manner here indicated, why does
living substance no longer continue to form ? The conditions
under which life is being actually maintained on earth suggest
the direction in which many look to find an answer to this
question. Herbivorous animals obtain their food exclusively
from plants ; carnivora live on the flesh of the herbivora ;
thus they, too, in the final analysis, are nourished exclusively
by plants. Fungi, too, are dependent upon plants, to which
they are parasites, either directly or through the medium of
animals. Green plants are thus the great purveyors of nutrition
to all other living organisms. They themselves obtain their
mineral and nitrogenous food from the earth, and the
indispensable carbo-hydrates from the atmosphere, but they
can do this only by means of the sun's rays. Hence it is the
sun, and the sun alone, that ultimately supports life on earth.
If this is true, and it is indeed incontestable, we are naturally
led to ask whether it was not the sun likewise that originated

70 PRIMITIVE FORMS OF LIFE

life ; whether certain of its rays are not capable or, above all,
were not formerly capable of producing directly those com-
binations that enter into the constitution of all living matter.
Then we see how Daniel Berthelot and Gaudechon obtained
synthetic carbo-hydrates by the reciprocal action of carbon
dioxide and water, in the absence of any chlorophyll and
solely under the influence of ultra-violet rays emanating from
a tube of mercury vapour. The same rays enabled them to
obtain formamides through their action on a mixture of carbon
dioxide and ammonia gas. Formamide is the simplest of the
quaternary substances, of which the albuminoids are the most
complicated, and a combination of which constitutes the proto-
plasm which uses the carbo-hydrates as a food. Here we are on
the path that ought to lead us to the origin of life. At any rate,
it has been demonstrated that if certain ultra-violet rays kill
spores, others, on the contrary, are capable in themselves of
producing combinations which were for a long time believed
to be possible only if certain organic substances were already
present ; and it is these very rays that do in fact penetrate
our atmosphere.1

After giving his results, Berthelot adds : " The fundamental
reason for the efficacy of ultra-violet rays seems to be their
extremely high temperature. The higher the temperature of
the source rises, the richer it becomes in ultra-violet rays.
And when the reflection of a mercury-arc is projected upon that
of the solar disc we recognize by the physical phenomenon of
the displacement of the lines in the spectrum that the
temperature of this arc is greater than that of the sun." Now
it is certain that the portion occupied by ultra-violet in the
solar spectrum was at one time greater than it is to-day.
The sun, in fact, belongs to the group of yellow stars— A returns,
ai of Centaur, the Polar star, etc. It is now already colder than
Procyon and Canopus, which also belong to the yellow stars.
The sun was unquestionably, at some distant epoch, far hotter
than it is to-day ; we can even reconstruct the various stages
through which it has passed by studying the white and bluish
stars that are by far the hottest of all. Some of the white
stars, such as the majority of those in Orion and the Pleiades,
Regulus, the p of Centaur, Deneb, etc., are evidently the seat
of electrical discharges produced under very special conditions ;

1 XVIII.

THE APPEARANCE OF LIFE 71

others, again, are distinguished by the abundance of helium
and hydrogen present in their atmosphere, indications of
tremendous radio-activity. The bluish-white stars are even
hotter ; the ultra-violet portion of their spectra is very
extensive, and includes radiation of particular intensity and
of unknown origin, and the presence of helium in their
atmosphere implies that they are also the seat of important
radio-active phenomena.1

During the period when the sun was passing through these
various stages, the chemical activities taking place on earth
under its influence must have been more numerous and
emphatically more powerful than they are to-day. The ultra-
violet radiation was of greater extent than in our mercury
vapour lamps to-day, and the chemical combinations this
radiation was capable of stimulating must have been far more
varied than those which we can bring about to-day, and which
would be a necessary condition for the appearance of life.
Ultra-violet radiation emanating from the sun and capable of
penetrating our atmosphere was then able to achieve results
which the irradiation of the present epoch is no longer capable
of accomplishing unaided. Thus it is that we can explain the
lack of spontaneous generation in our own day. Moreover,
the earth itself, during that far-off period, was at a different
stage. It was possessed of greater radio-activity, and its
atmosphere contained hydrogen, helium, and perhaps other
elements developing from the disintegration of various simple
substances, at that particular stage which chemists call the
nascent state, during which their chemical affinities were
higher ; hence we have another reason why combinations
impossible to-day could then have been produced. It must have
been from quaternary substances, more complex than the
formic amides, that the true albuminoid substances developed.
After the simplest of these had been obtained, the formation
of the others became a purely chemical phenomenon. The
researches of P. Schiitzenberger, A. Kossel, E. Fischer, L. C.
Maillard, and others, on the constitution of albuminoid
substances, essential factors in chemical life, at any rate,
have thrown considerable light on the constitution of the
quaternary substances. A preponderating part in their constitu-
tion is played by the amino-acids, formed by an acid agent

1 XIX, 306.

72 PRIMITIVE FORMS OF LIFE

resulting from the union of oxygen with carbon (COOH), and
a basic agent resulting from the union of hydrogen with
nitrogen NH2. These two agents are united in a single molecule
without, however, being neutralized in their respective
functions. From this it follows that the acid agent of the
molecule continues to " attract the basic substances that are
within its range, and the basic agent to attract the acid
substances ". 1 When the basic substances are derived from
another amino acid a new body is produced by the elimination
of a molecule of water so constituted as to regenerate, at the
expense of substances annexed, the acid function of the
primitive body. The same holds true for the basic function
when it is this which co-operates in the elimination of a molecule
of water. As the result of this double interplay, compounds of
any degree of complication whatsoever can be obtained, and
thus we may entertain some hope of being able to construct
the enormous, unstable molecules with reciprocal reactions
which give rise to the chemical phenomenon of life. The school
of Fischer has already obtained substances analogous to the
peptones into which the albuminoid food substances are first
resolved in the course of digestion. With the aid of these
peptides we ought to be able to reconstruct the substances from
which the peptones come, and obtain the peptides them-
selves by methods more akin to those employed by living
beings. This is what a number of chemists have attempted :
Balbiano, Trasciatti in Italy, and Maillard in France. By means
of a suitably induced reaction from pure glycerine and amino
acids, Maillard has succeeded in obtaining bodies with a strong
resemblance to peptones, to caseine, and to keratin substances
which are the albuminoid substances par excellence. It is
probable that by substituting sugars and alcohols for glycerine
we might obtain other results equally as important. It is
true that a temperature of 1700 to 1800 would be required
to accelerate the reactions, but these can be obtained at lower
temperatures if other accelerators are employed. The diastases,
which are simply albuminoids of a nature still inadequately
determined, and which are known to act especially by hydration
and dehydration, appear to be capable of doing this work. If,
therefore, it is true that all these substances might have arisen

1 L. C. Maillard, " Recherche du mecanisme naturel des formations
albuminoi'des ", Presse medicate, 17. Fev. 1912.

THE APPEARANCE OF LIFE 73

unaided through the mere action of diverse radiations
emanating from the sun or from radio-active bodies, then we
can understand how it was that certain of these combinations
might have represented the first living substances.

The question of the first appearance of life returns, then,
like the whole subject of physiology, to the domain of physical
chemistry. Life arose during conditions which we can now
mentally reconstruct, and which still unquestionably persist
in some stellar systems, but which have disappeared from the
solar system, never to return. The faculty of giving birth to
living matter gradually became the province of living beings
alone, as the solar radiations and the radio-activity of the earth
became feebler, but it has not always been their exclusive
privilege. Physical astronomy, disclosing to us the stages
of this impoverishment in stars of different ages and of different
size, has brought Pasteur's conclusions into harmony with
reason, and discredited all those hypotheses — so daring but
so contrary to the scientific spirit — of a semination of life on
the earth by germs of unknown origin coming from the great
Beyond.

Under what form, then, did the first living organisms
manifest themselves ? The earliest fossils we know date from
a period so much later than the first appearance of life on earth,
and so many forms have disappeared during the metamorphosis
of archaic formations that palaeontology cannot aid us in this
respect. However, the ties that unite the actual living forms
are such that one form can be deduced from the other, on the
hypothesis that they are the outcome of a natural evolution, with
laws which can be precisely stated. These laws, in turn, permit
us to reconstruct with great verisimilitude the different stages
through which their various predecessors have passed. After
this primary period, palaeontology can provide us with land-
marks and the means of checking the inferences we draw from
the study of the structure and the embryogenetic development
of beings now living, and of the modifications to which they are
susceptible. This matter will form the subject of the next
chapter.

CHAPTER II
The Genealogical Basis of Organic Differentiation

IN spite of the many millions of years that have elapsed since
the first appearance of life on earth, and even since the
arrival of organisms with definite forms transmitted from
generation to generation, so many simple types still persist
that we can obtain an impression of sequence in living beings,
complete from the initial forms onwards. This is one of the
most astonishing facts that confront naturalists. It is true that
innumerable secondary series connected with the complete
cycle have disappeared, but the chain itself has been left
sufficiently intact to render its reconstruction comparatively
easy. The unicellular organisms which seem to possess the
simplest form next to the " primeval slime ", in which life
can manifest itself, still abound in both the animal and
vegetable kingdoms. Among the very oldest fossils we find
not only bacteria but Globigerince and Orbulince, similar to
those which now float upon the surface of the seas far distant
from the coasts. We can trace sponges closely related to the
beautiful Hexactinellidse, with their skeletons of elegant
opalescent lacework, that are still dredged from the waters of
the coasts of Japan and the Philippines, and from the deepest
parts of our own seas ; we also find polyps ; segmented
forms which have been conserved, in their general character at
least, in the Limuli of the Moluccas, Japan, and the Antilles, as
well as in the Estherida?, Nebalidae, and in the species of Cypris
of our oceans or fresh waters ; and, finally, Lingula and other
unsegmented Brachiopods, which are highly modified
descendants of annelid worms. Echinoderms are also en-
countered— of very special types, it is true, and molluscs with
shells, already differentiated into the three present classes of
Cephalopods, Gasteropods, and Lamellibranchs, of which the
Octopus, Snail, and Oyster are the best-known present day
examples, so far removed from the primitive types that we

ORGANIC DIFFERENTIATION 75

only cite them here in order to give a clear idea of the nature of
these classes.

The comparatively abrupt appearance of so many organic
forms has sometimes been regarded as evidence against the
evolutionary theory. Again and again it has been proved that
a new flora and fauna have suddenly appeared in some
geological stratum after the complete disappearance of older
ones preserved in the strata immediately antecedent, and the
most ardent disciples of Cuvier considered this an unanswerable
argument in favour of the hypothesis of independent creations.
Alcide d'Orbigny succeeded in computing twenty-seven
catastrophic phenomena of such a kind. However, it has been
possible to show that in many cases layers now directly super-
posed in certain localities were at one time separated by inter-
mediate strata containing transitional forms, or else to establish
the fact that the higher layer was laid down only after
a long period of subsidence, during which the lower layer had
been subjected to considerable erosion. Hence the argument is
destroyed. On the other hand, we have been able to follow,
through long periods of time, continuous successions of forms
which are manifestly derived from one another, but which
might have been regarded as distinct species had they been
considered by themselves. This, for instance, is the case with
the spiral Ammonites of the Secondary Period, so thoroughly
studied by Neumayer, Mosjisowic, Douville, Haug, and
others ; with Planorbidse of the Miocene lake at Steinheim
in Wurtember^, of Paludinidae of the great Pliocene lakes of
Slavonia and many others. We are consequently justified in
assuming that every apparently sudden displacement of one fauna
and flora by another is really the result of some interference
in the deposits, whether of short or long duration, often due to
a sudden subsidence which occurred between two apparently
consecutive periods, corresponding to the two faunas and floras
which appear to succeed each other. In connexion with the
differences we observe between them, we do not know what part
may have been played by transformations in situ and well-
authenticated migrations of animals and plants from one region
to another.

Palaeontology teaches us as little about the origin of life as
it does about the origin of organic types or the causes that have
produced them. Its sadly defective data can be of use only in

76 PRIMITIVE FORMS OF LIFE

verifying the laws deduced from a strict comparison of living
forms and from the careful study of the possible influence
exerted upon them by exterior environment, either in their
adult forms or in the course of embryonic development.

The laws thus formulated have as rigorous and as absolute
a character as those which control physical and chemical
phenomena. After they have once been established in a
definitive manner, the past history of each one of the main
groups of living organisms can be reconstructed and the various
phases of this past linked to preceding causes. Thus we may
eliminate the valueless hypotheses and illusory philosophical
conceptions which have so long concealed the true explanation
of facts under false principles purporting to be axioms. Such
erroneous notions are to be found in Leibnitz's principle of
continuity — the Natura non facit s alius of Linnaeus — Geoffroy
Saint-Hilaire's law of unity in the plan of organic form in the
animal kingdom, Cuvier's theory of unity, even as limited to
the main branches, Charles Bonnet's " ladder of being ",
Blainville's Degeneration of Types, etc. These premature
conclusions based on limited observation, satisfied human
reason only at a time when science could not pretend to explain
the nature of living organisms, in the proper sense of the term.

Darwin x made admirable use of instinct and of sexual
selection to explain the preservation, diffusion and even perhaps
the exaggeration of useful characters. He could offer an explana-
tion of the adaptation of animals and plants to the conditions of
their existence, an adaptation so close that it gave rise to the
notion of their predestination for these. He could explain the
splitting up of the zoological and botanical series into species
separated by seemingly unbridgable gaps. But his theories did
not go so far as to determine the causes that made the
distinctive characters appear.

Darwin did not even broach the problem of the significance
of structural types as they are now called, in either the vegetable
or animal kingdom. Later on Weismann 2 assigned a mysterious
function, in the evolution of organisms, to the living sub-
stance which mainly constituted the reproductory cells for
which he claimed a constitution different from that of the
body-cells. This substance he called the germen, or germ

1 XXIV and XXV. * XXVI.

ORGANIC DIFFERENTIATION yy

plasm, and regarded it as the sole depository of the forces
regulating the evolution of organisms. The other substance,
the soma or body-plasm, although distributed throughout
the whole body, he considered as a protection provided
for the needs of the germ-plasm, to protect it against
the action of the external environment, to whose in-
fluences alone it yields. It is quite evident that such a
conception is the absolute negation of every scientific
explanation of living organisms, and it is indeed strange that
no one should have perceived how the facts upon winch it
rests, far from serving as a starting-point for a general theory
of evolution, were actually the specific result of a modification
of embryogenetic processes concerning which we shall shortly
have more to say. We have more reason to dwell on the
important modifications that organisms exhibit under the
influence of numerous internal secretions and of certain
substances introduced from outside, such as the secretions of
a number of parasites x or the poison injected by the sting of
particular insects,2 which have led us to postulate the existence
of special substances, the hormones,3 which stimulate the
various organs to react upon one another at a distance, and
thus maintain the necessary solidarity within the organism.
The hormones and the parasitic secretions constitute the
mechanism of this reciprocal adaptation of organisms, the
importance and range of which I pointed out in 1881, in the
following terms : — 4

" The direct causes for division of labour and the
modifications connected with it in the associated merids are
found in large measure, as in the case of the plastids, in the
social life itself. Whenever two or more organisms enter into
constant relations with each other, modifications of a more or
less important nature take place in each of them."

In making use of the term social life, we come to the question
that dominates the entire evolution of living beings, namely, the
nature of that mechanism regulating the constitution of the long
series of organisms, which begins with the first minute living
things and culminates in types that are so far removed from the
original starting-point in size, form, complexity of structure,

1 The wasps of the Terebrantia series, for example, producing the galls
of the corn blight, etc.

1 Galls produced by Cynipidae. ■ XXIII and XXV. « XXVIII, 710.

78 PRIMITIVE FORMS OF LIFE

variety of functions, and in intellectual manifestations. As
usual, a number of a priori ideas at first obscured the meaning of
the facts. Because our own personality has always been regarded
as an indivisible unit, and as indeed this word " individual ",
so often used to designate ourselves, has come to mean just
that — i.e. an indivisible personality — we experience some
difficulty in recognizing that this individuality was not achieved
at the first attempt, hence the resulting inevitable conclusions
meet with some resistance, even from people of distinguished
intelligence. Even if we admit that in the beginning things
might have happened otherwise, practically all organisms that
have passed the stage of the primitive living slime are to-day
constructed along similar lines and have attained their
definitive structure in the same way. We might add that the
exceptional cases that have been discovered, such as the Algse of
the Siphonese family, the Fungi of the Myxomycetes group, the
Infusoria of the genus Salinella of Semper, can all be easily
referred to the same general principles.

The outstanding facts which we cannot possibly ignore may
be reduced to these four propositions : —

i. Every organism, be it animal or vegetable, is formed by
the assemblage of elements, generally microscopic in size,
possessing a similar fundamental constitution, and known as
cells, anatomical elements, or, more recently, plastids.

2. Some organisms exist that consist of but a single plastid,
and in nature to-day a multitude of forms, constituted by an
increasingly complex association of plastids, form a chain linking
together these isolated plastids, and the most complex organisms.

3. Every living being starts from a single plastid, the egg,
and only attains its final complexity through repeated division
of the first plastid and those arising from it.

4. The plastids that live as independent units divide as soon
as they have attained a certain size, in just the same way as
those destined to constitute organisms ; the only difference is
that the plastids resulting from this subdivision separate
from one another as soon as they are formed, whereas they
remain contiguous when they form part of an organism.

This is equivalent to saying that the higher organisms
are exclusively formed by the gradual association of an
increasingly large number of plastids. Through this union they
unquestionably lose a certain amount of their independence,

ORGANIC DIFFERENTIATION 79

but in spite of this they conserve a large measure of
individuality. It has always been known that certain parts of
a plant could be separated from the plant itself without dying,
and that if placed in propitious conditions could subsequently
give birth to a new plant. As early as 1740-4 1 Trembley
showed that the freshwater Hydra could be dismembered in
a similar manner, and since then it has been discovered that
sponges, polyps, and all ramiform organisms possess this
property. Transplantation of tissues and grafting have even
succeeded as completely with the higher animals as with plants,
and within recent times Dr. Alexis Carrel has succeeded in
maintaining life and promoting growth in pieces of connective
tissue, even nerves, under proper artificial conditions, without
the aid of any organism.2 This directly proves the independence
of anatomical units as Claude Bernard had deduced from his
physiological experiments.

This independence still appears in the course of embryo-
genetic development. The first phases of this development
consist in division of the egg into two elements, then four, eight,
etc., all of which are quite alike as long as the egg does not
contain a large quantity of nutritive material and as long as
they are not so numerous as to necessitate an arrangement into
superposed layers. These units are called blastomeres. They
resemble the egg itself. Certain eggs, when violently shaken,
divide into the two original blastomeres, and each one of them
develops independently and produces an embryo differing
from the normal one only in being half its size.3

Such a separation of blastomeres can take place
spontaneously but accidentally, even in man. The egg then
develops two exact counterparts, always of the same sex, and
in the case of the mammals, possessing only one placenta.
What is purely accidental in man is of normal occurrence
among such mammals as the armadillos, the carapaced
Edentata of South America. The egg of the nine-banded
Armadillo always divides in such a manner as to produce four
of a sex at the same time ; 4 and that of the hybrid Armadillo

1 XXVIII.

2 XXIX.

3 Driesch (XXX) experimented thus on the eggs of the Sea-urchin and
of A mphioxus, and Bataillon (XXXI) has done the same for the Lamprey.

4 De Morgan, XXXII, for a highly specialized fish belonging to the
Malacopterygii.

So PRIMITIVE FORMS OF LIFE

to produce seven, eight, or nine 1 at a time. To cite a more
extreme instance, if the fertilized egg of the sea-urchin is
placed in water deprived of calcium, as in Herbst's experiment,
the first thirty-two blastomeres can separate and develop in-
dependently, and produce the beginnings of as many as thirty- two
embryos. Such a division is produced naturally in the embryo of
certain minute four-winged flies, akin to the wasps, and which
might indeed be considered as lilliputian wasps. The larvae
of these insects, minute in size but already highly organized,
develop either within other larvae imprisoned in galls, the larvae of
certain mosquitoes, the Cecidomyia, or more frequently in very
small common caterpillars, like those of the moths of the genus
Hyponomeutia which live on the spindle-wood. The parasitical
caterpillars always contain a multitude of larvae. As many as
three thousand have been counted, and for a long time naturalists
were puzzled as to why there was no intermediate condition be-
tween the presence of vast numbers of parasites and complete
immunity, since the fertilized fly itself contains not more than a
hundred eggs. The problem was solved by Marchal.2 The em-
bryos of the majority of insects are enclosed in a sac, the amnion,
derived like them from a cellular membrane, the blastoderm,
formed by the division of the nucleus of the egg. In the case of
the minute parasites in question, the egg commences by
dividing into two halves, one of which develops into the amnion
and the other, generally, into a single embryo. In certain
species, however, the elements that are destined to form the
embryo separate and develop independently, so that ten,3
two hundred,4 or even three thousand larvae,5 varying with the
species, may be born from a single egg. The blastomeres, in
this case, retain their likeness throughout a large number of
fissions.

In those eggs containing reserve substances what happens
is quite different ; this has led to embryogenetic conceptions
that are entirely erroneous, because the facts were generalized
without reference to their causes.

1 Von Jehring had in 18S5-6 already concluded from this the disjunction
of the egg, a fact that was later confirmed by Miguel Fernandez in 1909 (XXXIII) .

2 XXXIV.

3 Polygnotus minntus, the parasite of the Cecidomyidae (Marchal).

4 Encyrtus (Ascidiaspis) fusicollis, the parasite of the caterpillar
of Hyponomeutia of the spindle-wood (Marchal).

5 Litomastix, the parasite of the caterpillars of the nocturnal butterflies
of the genus Plusia (Silvestris).

ORGANIC DIFFERENTIATION 81

After their first division, the blastomeres are often very
unequal ; the smaller, clearer, and more transparent being
formed of almost undiluted living substance, the granular and
larger opaque one contains practically all the alimentary
reserve. This large blastomere continues to divide unequally,
and forms new small, translucent blastomeres, but, at the same
time, the original itself divides in a leisurely fashion into other
blastomeres which remain granular and much larger than the
clear ones. The embryo, consequently, is made up of two kinds
of blastomeres, which are necessarily conjoint and mutually
dependent on the larger for the supply of the nutritive substances
which are needed for the increase and division of the smaller.
From that time the embryo forms a unit, still susceptible of sub-
division into cellular agglomerations possessing both elements
and capable of developing into distinct individuals. The egg
of certain Bryozoa,1 after segmentation, can still subdivide
into any number of groups of blastomeres up to a hundred,
each of which is capable of producing a larva. The embryos
of some species of Lumbricus even divide regularly into halves
before producing the succession of segments that constitute
the worm. In exceptional cases this division may still be
partially realized in the embryos of higher animals, and it is to
this that many kinds of double monstrosities owe their origin.
But, as a rule, after a very short time it becomes impossible
to separate the different parts of the embryo from one another,
and each blastomere, from the time it is formed, appears to
have a particular destination. Some seem to be charged with
the duty of forming the anterior portion of the body, others
the middle portion, and still others the posterior ; some belong
to the left side, others to the right ; some are utilized for the
ventral side, others for the dorsal ; each blastomere playing a
distinct part in the building up of the tissues and organs of
the different parts of the body. If one of these particular
elements is suppressed, its place is not then taken by the others ;
the tissues and the organs that should develop from it do not
appear ; they are suppressed with it ; l if displaced, it does its
own work in the new place imposed on it. The embryo thus
resembles a building made of stones, which have been prepared
in advance to occupy one fixed place and no other. Potentially
it contains all the different parts of the future adult individual,

1 Experiments of Wilson.

82 PRIMITIVE FORMS OF LIFE

and nothing else. Each part corresponds to a particular portion
of the egg, and even the substance of the egg itself is sub-
divided in such a way that we can say it possesses an anterior
and posterior end, a dorsal and ventral region, and a left and
right side, corresponding exactly to the equivalent parts of
the embryo. But, between this kind of egg and an egg capable
of producing numerous embryos, there are all kinds of inter-
mediate forms. This determination of the functions of the
blastomeres, by virtue of which, as soon as each becomes an
individual unit, it is destined to occupy a place in a definite
portion of the body, which it cannot then leave and for which
it must form tissues and organs, does not, of course, represent
the initial condition of all embryogenetic development. It
has been gradually evolved step by step, giving to embryo-
genetic phenomena a precision which leads in turn to a
maximum rapidity in development. This is merely one
particular aspect of the phenomena of embryogenetic acceleration
or tachy 'genesis, which have played so great a part in the
evolution of organisms, and which have been so long neglected,
though it is impossible to understand anything about the
history of living forms or the determination of their origin
without taking these phenomena into consideration. It is
quite evident that if, reversing the actual order of the facts,
we consider the normal embryological type to be an egg in which
everything is determined beforehand, nothing but a miracle
could have created it, and we should not need to look further for
explanation. This notion has frequently recurred with fatal
results in the philosophic biology which either takes man as its
point of departure or as the model for the entire animal
kingdom. But just as there are some blastomeres in the egg
which are destined for different functions according to the rank
they occupy in the sequence of the egg's bipartitions and to the
position this imposes, so there are others which are not of
direct service in building up the body and are held in reserve,
to develop later. The most important of these latent organic
elements are those which, in many animals such as the Rotifers,
Daphnia, and various small insects, enter into the formation
of the reproductive elements. They may become isolated from
the very first segmentation, and thus constitute true
blastomeres. It is because his conclusions were based on these
specialized examples, which he took as representative of the

ORGANIC DIFFERENTIATION 83

primordial conditions of generation — in other words because he
reversed the entire order of facts — that Weismann believed
himself justified in considering the plasma constituting the
generative organs — the germen or germ-plasm — as distinct
from the plasma constituting the organs of the body proper,
the somatic plasm or soma. Upon this distinction he built up
his whole system, a veritable pyramid resting on its apex —
but we need not pursue the matter further.

The elements thus separated may evolve with varying
rapidity, and produce others more or less specialized, such as
those of the genital ducts and others that retain their primitive
character of blastomeres. The latter are naturally capable of
developing without impregnation into new individuals. This
explains most cases of parthenogenesis occurring in minute
insects such as plant-lice, the cochineal insects and Cynips,
occasionally complicated by viviparity, and liable to occur even
in larvae, such as those of the Diptera of the genus Cecidomyia.

At the same time these reserve elements are not exclusively
destined to produce the genital apparatus ; they may belong
to any part of the embryonic body, and thus as in embryos
produced from predetermined blastomeres, represent that
particular portion of the body and none other. Thus Kiinckel
d'Herculais and Weismann have shown that in each of the
segments of insect larvae subject to complete metamorphosis
there are gathered together in the form of folds of the skin cer-
tain neutral elements to which the first of these naturalists gave
the name of Jiistoblasts, and the second imaginal discs.
They are destined either to replace outworn elements of the
larvae, or to produce those new tissues or organs which give the
adult animal a form often very different from that of the larva,
thus constituting an actual metamorphosis. The fact that these
histoblasts represent only that particular segment of the body
with which they are connected, tends, moreover, to establish
the individuality of these segments. This idea has its
importance in the explanation of organic evolution.

We may postulate that the ultimate cause of this evolution
lies in the power acquired by the earliest microscopic organisms
to unite and to form a body destined to acquire tremendous
possibilities ; if further we may conceive that each element
in such an association retains a considerable degree of
independence, yet modifies itself in a special way according to

84 PRIMITIVE FORMS OF LIFE

influences derived from external environment or from neigh-
bours which pervade and penetrate it with their excretory
products, continually modifying even their common medium
to suit their nutritive needs ; then nothing would be more
natural than that considerable variety should therefore develop
in the characters and properties of the elements associated in
the same body. Furthermore, from this variety there would
naturally arise among the inter-related elements a more or less
notable degree of solidarity, since, though each organism lives
for its own sake, the medium or ensemble in which they live is
their common achievement, and can scarcely be reconstructed
without them. But when a group of elements capable of living
together and multiplying, or a single element, the egg, capable
of absorbing nourishment and multiplying in an independent
fashion, becomes detached from this association, how does it
happen that the new elements become diversified, and in both
cases, whatever the external conditions may be, are grouped
in such a way as to form another organism similar in all its
details to that from which they were separated originally ?

With regard to this point, we are forced back upon
hypotheses whose phenomena, however, may be submitted
to close analysis, thus circumscribing the ground we have to
cover. Every modification affecting any predetermined part
of the body expresses itself in a change either in the constitution
of its elements or of their mode of nutrition, activity or number.
In every case the products excreted are themselves changed
qualitatively or quantitatively. These products can be poured
directly into the interior " environment ", i.e. into the blood,
or the liquid that takes its place in the lower animals, and this
environment then experiences a modification correlative to that
of the portion of the body modified. These products may also
pass immediately into contiguous elements, which they modify,
and which in their turn modify the parts with which they are in
contact ; and these modifications may then proceed, stage by
stage, till they reach the reproductive cells, which in the first
case are modified at the beginning because of their immersion
in an interior medium itself having undergone modification.
However, it is difficult to admit that so intimate a correlation
exists between the interior medium and the various parts of
the body, that the modifications of the latter should be re-
echoed in the reproductive cells through the agency of this

ORGANIC DIFFERENTIATION 85

medium and thus be reproduced exactly, each in its relative
situation. The second hypothesis is more plausible, but it
assumes that the reproductive cells succeed in evolving only
when all the characters of the organism to which they belong
are developed. It is true (except in rare cases) that it is at
maturity that the reproductive cells of animals become ready
to develop — and any exceptions to this rule are either apparent
only or explicable by the phenomena of tachygenesis. Among
the structural cells, the most active agents of transformation
are those which direct the phenomena of nutrition and thus
play the principal part in building up form ; these belong to the
category of soluble ferments. If the very extensive action of
these ferments is reversible, and they prove capable, under
certain circumstances, of rebuilding what they have destroyed,
and if the reproductive cells contain some ferments of this
nature, they ought to be capable of building up again, according
as the division of the blastomeres increases, the series of
substances composing the elements through which they had
originally passed in order to attain the egg-stage. Accordingly
as the new elements appear, they will assume the form and the
properties of the various parental elements.

Is there anything in the structure of the reproductive cells
that would lend support to this hypothesis ? In order to answer
this question we must now show exactly how the structure
of body-building cells and reproductive cells is common to both
at the beginning of their existence.

Every structural cell, as we know, is made up of a mass of
protoplasm (a mixture of various substances) protected by or
innocent of a membrane ; in the centre of this cell is a delicate
vesicle isolated from other substances, which constitutes
the nucleus. The most remarkable substance within the
nucleus itself is that which has received the name of chromatin x
because it possesses a special ability to fix colouring matter
and particularly ammoniacal carmine. During the period of
bipartition and multiplication of cells, the chromatin
contained in the nucleus normally arranged in the form
of a network, shrinks into a sinuous ribbon, the loops
of which, constant in number — with rare exceptions
— for all the cells of organisms of the same species, soon

1 xpcu^a, colour.

86 PRIMITIVE FORMS OF LIFE

separate from one another forming as many distinct bodies,
the chromosomes. The number of chromosomes is generally
even. Throughout the entire animal and vegetable king-
doms the cells that are later to give rise to the ova and
spermatozoa, as the case may be, divide twice in succession,
in such a fashion that down to the last division in the case of
animals, and to the penultimate division in the case of plants,
the chromosomes, instead of splitting before the cell divides
and then distributing themselves equally between the two
resulting new cells, form two equal groups without preliminary
fission. The number of the chromosomes in the germ cells
is consequently less by half than that in the somatic cells.
The penetration of the spermatozoon within the ovum re-
establishes the proper number of chromosomes and makes the
fecundated ovum the first complete, normal body-unit, which
will produce others by bipartition.

From the above it appears that in order to make use of the
reserve materials it has accumulated, which distinguish it
from the male element, the ovum must possess a predetermined
quantity of chromatin. Thus, chromatin must be the active
substance which controls the digestion of the reserves in the
structural cells. The experiments which Balbiani performed
long ago on Infusoria, and which many investigators have
since repeated, seem to confirm this view completely. The
chromatin can only perform this digestive function with the
aid of ferments no doubt associated with other secretions,
affecting by their quantity and quality the nature of the
elements formed later, and determining the separation
previously described.

A proof of this influence exerted by chromatin is furnished
by the observation of what occurs in the case of certain
insects possessing spermatozoa of two kinds, where either half
the spermatozoa contain one chromosome more than the others l
or where one half contains a chromosome much larger than the
others.2 In both cases ova fecundated by the spermatozoa
richest in chromatin produce females, the others males. This
fact acquires even greater significance if it be recalled that the

1 Moths ; Cockroaches, Hemiptera of the genera Pyrrhocoris, Protenor,
A nasa, A lydus, etc.

2 Hemiptera of the genera Lygceus, Caenus, Euschistus ; coleoptera of the
genus Tenebrio ; the domestic fly.

ORGANIC DIFFERENTIATION 87

eggs of bees which develop without fertilization always produce
males.

It is not our purpose here to study the problem of sex-
determination ; it must suffice if we have shown the importance
of the part played by the chromatin and indicated the bearing
it has upon a clear conception of the phenomena of heredity.
Furthermore, if in certain cases, most frequent in connexion with
insects, sex is determined from the time of the fecundation of
the egg and is specifically connected with certain conditions
in the formation of the spermatozoa, and even if this
determination in other cases is precocious, that is no reason
why we should assume that it is impossible to influence sex-
determination, or that we should abandon the problem
forthwith.

Summing up, we may assert that the evolution of the ovum
can be classed as a phenomenon of nutrition. The reappearance
of the characters of parents in their offspring is called heredity.
No true explanation of the matter has yet been given. All that
has been asserted about it is either pure hypothesis or a begging
of the question, and the best that we can do for the present is
to attempt to narrow down the conditions in which heredity
first could have arisen, and once established, those in which it
functions.1

After what has been said of the theory of Weismann we
need not stop here to discuss his rejection of the inheritance
of acquired characters. This rejection is meaningless. It
must be admitted that living organisms have been modified
since the beginning of time ; that they have only been modified
by the acquisition of new characters, and that had these
characters not been hereditary, their modifications would not
have been preserved. The only problem with which we need
concern ourselves is to find out how these new characters have
been acquired. They have not arisen of their own accord —
unless we are face to face with a miracle — and yet, on the other
hand, it is undeniable that drought, humidity, a stronger or
weaker wind-action, heat, light, and even electricity can
modify, either temporarily or permanently, the individual
characters of living beings, be they animals or plants. The
nature of the food consumed and its superabundance or
scarcity have a still greater influence. If we cannot yet afford

1 XXXVII.

88 PRIMITIVE FORMS OF LIFE

to claim as much for the use or disuse of every organ, at least
it cannot be denied that exercise does expand the muscles and
create new habits.

The organism possesses within itself the various causes for
those chemical modifications which are so important. Every
cell in the body, from the very fact that it feeds and is active,
exudes around it substances which then become diffused
throughout the entire body and consequently make their
activity felt in varying degrees throughout the whole. Apart
from the modifications that may arise from the mere mode of
functioning, every organ, by the very act of functioning, tends
to modify the whole organism in some particular manner.
The substances by means of which it acts unquestionably
possess certain elective affinities for some particular element,
but, in the case of animals, they may have a general influence
upon the organism either by direct diffusions or by way of the
nervous system. For instance, they may augment or diminish
its size, as in the case of acromegaly due to disturbance of the
function of the pituitary body. They may act also upon a
particular tissue or organ, or on some particular system or
apparatus, thereby exercising a local influence changing the
relative proportions of organs, thus modifying the external
form of the body. Armand Gautier x has shown that the
morphological characters of different varieties of vines corre-
spond to modifications in the chemical composition of their
pigments, which, although all belonging to the same chemical
type, differ in the number and the composition of the radicals
constituting them. The reproductive organs are to be reckoned
among those in which chemical action is most vigorous.
We know, for instance, what extensive modifications
they may bring about in reproductive leaves and the
leaves which surround them — petals, sepals, bracts, and
in Poinsetia, even in a certain number of its ordinary
leaves. Analogous modifications have been observed on
the reproductive rami of hydroid polyps,2 and the gay
" bridal dress " which many Worms, Fish, Batrachians,
Reptiles, and Birds put on at the breeding season has
often been described. The coincidence between the formation

1 LXVI.

2 Corbullidae of Aglaoahenia, phylactocarps of Lytocarpus, Medusas of
Campularia and gymnoblastic Hydras.

ORGANIC DIFFERENTIATION 89

or maturation of the sexual cells, and the appearance of
this brilliant ornamentation is so general that there must be
a correlation of cause and effect ; and since the reproductive
cells are here the active ones, it is quite probable that either
they or the interstitial glands derived from them are to be
considered as the exciting cause of the modifications that the
organism presents during the period of reproduction. Pursuing
this line of thought, we are perhaps justified in asking if the
wings, new forms and brilliant colours characterizing adult
insects at the moment of their sexual maturity were not
originally their nuptial apparel. On the other hand, it might
be urged that the mating plumage, which in the male of some
birds, ruff, white heron, etc., only occurs in the courting
season, becomes permanent in others (cocks, pheasants,
peacocks, etc.) from the time when the males become adult
and that there are numbers of species in which the brilliant
adornments of the males are gradually taken on by
the females, as in the case of the Kingfisher family
and that of the small blue Butterflies of our own fields,
Argus or Polyommatus. This gives us a sound reason for
assuming that a character temporarily acquired under
influences peculiar to one sex, can persist when the influences
determining it have ceased and can subsequently, through
heredity, become extended to the other sex.

Whatever be the cause or the aggregation of causes that has
led to a modification of an organism, for that modification to
be inherited it is necessary that the cause or the causes that
have determined it should act directly or indirectly upon the
germ cells. But it is also necessary that the modification the
reproductive cells experience be of such a nature as to react
in its turn upon those elements arising from them and thus,
by means of a series of successive releases, succeed in
establishing the new character. But how can this series of
releases be initiated with the regularity familiar to us ? If it
be remembered that the toxins injected into an organism
generally stimulate the formation of antitoxins with opposite
properties, we may regard it as probable that the active
substances contained within the ovum may be able to
reconstitute gradually the substances whose successive
modifications have caused their own formation, and thus
the reappearance of the characters to which they correspond.

■go PRIMITIVE FORMS OF LIFE

Recent researches, moreover, have shown that the action
of radiation on organic compounds is often reversible, and
E. Bourquelot and Bridel have demonstrated that in the
same way ferments are generally able, under certain con-
ditions, to reconstruct what they have destroyed.1 It
would seem that we may attribute heredity to a similar
reversibility. This statement is not, of course, an ex-
planation of the phenomena of heredity, but it does permit
us to get a glimpse of how these phenomena arose ; opens
the way to accurate research, and allows us from the outset
to eliminate as useless those hypotheses which demand almost
supernatural, or, at least, intangible agencies. Yves Delage,
in his book on Heredity, entered into a learned discussion of all
these questions, which will probably be solved only by
extremely minute investigations in the bio-chemical laboratory.
However that may be, if we consider heredity with regard
to its effects and not its causes, we shall all agree in attributing
to it the function of maintaining, in the lineage of organisms,
the characters acquired under the influence of determined
causes after these causes have themselves ceased to act. At
first sight, consequently, it would appear to be an essentially
conservative force, but for this very reason it creates the gravest
difficulties for all investigations into the causes determining
the characters of living beings, simply because heredity main-
tains these characters under conditions manifestly incapable
of producing them, and with which they may even be com-
pletely out of harmony. But that is not all : even when these
organisms continue to live under the conditions which have
determined their characters, the characters appear when the
causes are incapable of acting as, for instance, during
embryonic life ; or, if the characters are periodic, they may
occur out of their appropriate season. Thus it happens that the
correspondence between the journeys of migratory birds and
variations in temperature is relative only. Accustomed as
naturalists are to observe organic characters and embryonic
phenomena generally without finding it possible to trace them
back to definite external causes, and powerless as they are to
give irrefutable proof of the existence of any causes they may
suspect, they have ceased to be interested in the search for
any explanation, and have declared this search to be vain, if

1 LXVII, 63.

ORGANIC DIFFERENTIATION 91

not positively unscientific. Or sometimes in place of ex-
planations they have accepted certain a priori conceptions,
stated in the form of general laws borrowed from some
philosophical system or relegated to the sphere of Nature's
unfathomable mysteries. It is, indeed, owing to the difficulties
which heredity puts in the way of all explanations, that the
doctrine of special creation has arisen and persisted, contrary
to all reason.

However, the function of heredity is not limited to the mere
conservation of characters, apart from the causes that have pro-
duced them. In the very act of conserving it must accumulate
them. This it is that Etienne Geoffroy Saint-Hilaire so
clearly perceived when he asserted that the embryos of the higher
animals reproduce the permanent forms of lower animals, i.e.
that they manifest, one after another, the characters acquired
by their various ancestors, which they must have inherited —
if, with Geoffroy Saint-Hilaire, we accept the theory of
evolution. The same truth is expressed with less precision
by the somewhat mystical formula of Antoine Serre, a disciple
of Geoffroy Saint-Hilaire : " Transcendental anatomy is only
a transitory comparative anatomy, just as comparative
anatomy is only a transcendental permanent anatomy." What
he called transcendental anatomy we now call embryogeny.
As we can study comparative anatomy only by considering the
series of forms, beginning with the simplest, that is to say the
oldest, and working up to the most complex, which are the
most recent, we come face to face with the formula of Haeckel,
which differs from the preceding ones only in its adaptation to
modern ideas : " The embryogeny of living organisms is
merely an abbreviated recapitulation of their genealogy."

If we were to take this formula literally it would merely be
necessary to take the final expression of each organic series and
study it from the initial egg-stage to its full term of life, in order
to obtain an exact recapitulation of the entire past history of
the organisms now living on earth. True, we should still have
to reconstruct subsidiary lines that have now become extinct,
but we should be able to do this by means of the comparative
study of fossils as they succeeded one another. An accurate
knowledge of the laws determining the evolution of the series
actually represented to-day would permit us to fill the gaps with
extinct series, of which only a few fragments have been found.

92 PRIMITIVE FORMS OF LIFE

Unfortunately, it is not quite so simple as this, for
within those apparently innocent words of Haeckel's formula —
"abbreviated recapitulation" — are concealed such insidious
pitfalls that Haeckel himself could not avoid them, and
could not even succeed in showing us where to look for them.

As we have already stated, the duration of life on earth is to
be reckoned in millions of years, and a similar length of time
must be assumed for existing species to have acquired their
special characters. Now the maximum period required for the
development of an individual animal, apart from size, does not
exceed two years, and certain very complex insects complete
their term of life, including their metamorphoses, in a few
weeks. In the one case as in the other, the abbreviation of
descent that takes place in embryogeny is simply stupendous.
It is, moreover, exceedingly unequal, even in closely related
species. There are instances in which a young animal is hatched
with only a small portion of its body developed : the other parts
are then successively formed without cessation of the normal
life-activity. There is consequently always a possibility that
the successive forms which the creature assumes will represent
ancestral forms, or at least forms which suggest them. To the
modes of development which fulfil this condition we give the
name of patrogony. However, even here the abbreviation is so
great, and the ancestral forms succeed one another so rapidly,
that they are telescoped into one another, so to speak, and the
successive shapes assumed by the embryo may be considered
only as analogous to ancestral forms and not their exact
reproduction. The general trend of evolution is here indicated,
not its detail.

In some species related to those described above the young
animal emerges, if not in possession of its final form, at all
events provided with all the parts of its body. The develop-
ment then takes place so quickly that the parts of the
body which were formed successively in the preceding case,
here appear to be formed simultaneously ; thus the course of
evolutionary development can be so modified, and the forms
assumed by the embryo recall the ancestral forms so little that,
if at any given moment we were to free it from its protecting
envelope, the organism would be unable to lead an independent
existence. This is the case with all vertebrates except
Amphioxus. We call this greatly accelerated embryogenetic

ORGANIC DIFFERENTIATION 93

development tachygony. In the same series of organisms it is
possible to find all the steps intermediate between tachygony
and patrogony. This gradual embryogenetic acceleration
we have already termed tachy genesis.1

Alike in the case of patrogony and tachygony the embryo
is subjected to the influence of the actual conditions under
which its development takes place. These tend to make it
vary from the ancestral forms, and may impose upon it forms
quite different from those of the embryos of species that have
developed under other conditions. These adaptive modes of
development, which may be recognized by the great variety
of characters that the embryos of related species present, are
distinguished under the name armogony,2 and the phenomenon
of adaptation to the conditions of development that determine
them can thus be called armogenesis. Armogenesis can both
complicate and simplify patrogony. Thus, pelagic embryos
living in the open sea often acquire organs which are not
present in the littoral patrogonic embryos ; on the other hand,
the larvae of insects which live parasitically lose the legs and
even the masticatory organs found in free larvae. Moreover,
the very simplified tachygonic embryos of mammals develop
a special organ, the placenta, which has nothing to do with
ancestral forms.3

It might perhaps be surprising that armogenesis, while
modifying embryonic forms, should not lead to important
modifications in the final form they are to assume. Giard has
endeavoured to explain this paradox by resorting to
comparison with mechanical laws. Comparisons, however, are
not reasons. In reality it is the elements held in reserve in the
interior of the body, the highest expression of which is found in
the histoblasts of insects and Nemerteans, which mould
the permanent form after the disappearance of armogonic
organs, because these reserves have escaped from the
influence of external actions and have preserved intact the

1 LXXVIII, 149.

1 From ap/xos joint or app-i] union and consequently adaptation and
yovos, generation. I have hitherto employed the word armozogony from the
verb app.6£a> " I harmonize," but it does not express the facts any better,
and is too long.

3 It should, of course, be remembered that the words patrogenesis,
tachygenesis, and armogenesis by no means designate a special active
cause found only in living beings, but the totality of the causes and
mechanisms, still too little known, which give rise to the diverse modes of
organic development.

94 PRIMITIVE FORMS OF LIFE

stored-up hereditary characters which they received from the
ovum.

Armogenesis has consequently only a secondary importance
in the evolution of organisms. Not so, however, tachygenesis.
We have demonstrated elsewhere that it furnishes us with an
explanation of the resemblance of the evolutionary develop-
ment in the female and the male cells.1 Its influence on
the morphology of living beings is just as great. By virtue
of the independence of the structural cells giving rise to the
tissues, the organs, and even the areas of the body, this
influence affects the different parts in various ways, modifies
their relationships and their proportions, and induces trans-
positions and fusions, to which Etienne Geoffrey Saint-Hilaire
had already appealed when he tried to explain how unity in
the plan of composition did not necessarily exclude variety
in the details of organization. It thus becomes an instrument
of modification, all the more powerful since in the course of
embryonic development a veritable struggle for existence
takes place, in a narrow field of battle, so to speak, between all
the structural cells and all the tissues and organs which they
constitute as well as between the various body areas themselves.

If armogenesis tends to bring embryos into intimate relation
with the environment in which they develop, tachygenesis,
on the contrary, tends to alter these relations more and more,
and to accentuate the dissociation between causes and effects
which heredity in its purely conservative aspect had already
begun to accomplish. Fortunately, this dissociation is generally
gradual. In each series the lower forms most frequently present
a patrogonic form of development, in which essential characters
are conserved in the tachygenetic forms. This permits us, on
the one hand, to distinguish the links which connect characters
and the causes capable of producing them, and, on the other
hand, to eliminate, by explaining the facts upon which they
might be based, any possible objections to the inferences
suggested by the analysis of the modes of development most
closely akin to patrogony. This work of weeding out and
classifying embryogenetic phenomena had never been done
in a methodical manner until I attempted it in the embryo-
logical section of my Traite de Zoologie.2 For this reason it has

1 XXXVIII 330.

3 XLIII, 567, 624, 961, 1605, 2251, 2565.

ORGANIC DIFFERENTIATION 95

not hitherto been possible to extract from embryogeny all
the data it affords on the subject of the origin of living forms ;
for this reason no light has been shed in particular on the
perfectly commonplace causes which determine the formation
of the great organic types. Indeed, so accustomed have we
become to regarding these facts as miraculous phenomena
that the explanations we shall make are liable to the reproach
of being over-simple. Mystical or purely verbal explanations
have been treated with more respect, as if there were any causes
operating around us other than commonplace causes. The world
tends to forget that all the progress we have made in geology
within the last few generations is due to the abandonment of
old doctrines based on miraculous cataclysms, universal floods,
and other " world revolutions ", in favour of the careful
investigation of actual cause and effect, to which Buff on and
Lamarck had already devoted themselves before Sir Charles
Lyell systematized them.

The oldest known geological period, the Archaean, was
actually of longer duration than the whole Primary Period, and
witnessed the formation of deposits which are still more than
20,000 metres thick, despite the levellings and metamorphic
transformations they have undergone. Yet if we wish to recon-
struct the forms of life which probably prevailed so long ago,
the inadequacy or, indeed, the total absence of palaeontological
documents compels us to fall back upon the data supplied
by existing forms. As we have already observed, the lowest of
these are so simple that we can hardly conceive of any simpler.
If there be any general theory which establishes a connexion
between these simple beings and the most complicated
organisms we know, and leaves no gaps in the chain, that theory
will possess the best chance of being applicable to fossil as
well as to living forms. Consequently it will add precision
to our work in linking the first with the second, interpreting
the inadequate remains left to us, and filling in the lacunae
between the forms that have persisted. It will also frequently
guard us against judging by appearances in determining the
date when these forms first appeared. Such a theory would be
synonymous with an explanatory genealogy of living forms,
which we are now about to outline. This question can only be
broached, however, after the principles we have just expounded
have been well established.

CHAPTER III
The Genesis of the Typical Forms of the Plant Kingdom

IF the ingenuity of the naturalists has been tirelessly exer-
cised on all matters relating to the problems of variability
in living forms, it has turned aside from any explanation of
factors which are fixed and stable. All variations of detail have
been studied with the most painstaking care ; botanists have
been at the greatest pains to note the slightest modifications
in the form and colour of flower-petals, in the contour of leaves,
in the abundance or scarcity of hairs ; they have made careful
and sometimes ultra-minute distinctions in the case of Briars
and Vines, for instance, between species and sub-species ;
between spontaneous, geographic or merely topographic,
cultivated or wild races, varieties and sudden, heritable
variations, fluctuations, etc. The zoologists have been
hardly less energetic in studying the smallest variations. They
have made violent onslaughts upon the old classification —
striped, spotted and piebald animals, and have even sub-
divided the African Elephants, because their ears and
tails are not exactly alike. Interesting as it may be to
study the variability of details, all this is certainly not
so important as the causes that have led to the development
of animals and plants on the lines of those marvellously
persistent types which Cuvier called embranchements (main
divisions) ; or as the reasons for differentiation between
plants and animals.

The latter question has been broached before. Plants take
their special character from the fact that every one of their
essential parts is enclosed in a rigid cellulose membrane,
preventing any movement and consequently any external sign
of sensibility. This membrane may temporarily be missing, as
in the case of the zoospores and the antherozoids or
reproductive cells of certain algae and fungi. It may only be
present for a time, and then only around the spores or repro-
ductive cells, as in the case of slime-fungi or Myxomycetes,

TYPICAL FORMS OF PLANT KINGDOM

97

but its mere existence, however brief, authorizes us in classing
the organism as a plant. Certain organisms throughout their
whole lives may resemble either zoospores of Algae or Fungi, or
else myxomycetes, and differ only in the complete absence of
the formation of a cellulose membrane. It is these forms which
link up the vegetable and animal kingdoms. Here the
differentiation between the two is quite artificial, though it
is legitimate to consider these ambiguous forms — devoid as
they are of the positive characters that distinguish true plants —
as members of the animal kingdom ; the more so as the absence
of cellulose, a negative feature, goes with that mobility which
is a positive character of animal organisms. Because of that
very immobility imposed on their cells by this rigid membrane
of cellulose, the evolution of plants has been relatively simple.
When isolated, these cells appear in the form of rounded
granules,1 rods,2 spindles,3 crescents,4 spirals,5 etc. They can
be juxtaposed so as to form chains,6 networks,7 small solid
cubes,8 and fans supported on a stem,9 or even spherical
masses capable of swimming 10 whenever the cells of which they
are built up are furnished, as in Volvox, with vibratile flagella.
Generally they are placed end to end so as to form those inter-
lacing green filaments called confervas, which abound in fresh
water. Analogous filaments, welded together in parallel lines
and giving rise to lateral branches, form the body or thallus of
Char a. Cells that are more or less polyhedral and dissimilar in
shape arranged in several layers, can build up laminated or
even massive structures of large dimensions such as those that
form the varecs of our coasts, the great marine Laminaria
many metres long, or those enormous floating Macrocystis
found in southern waters, which can spread out their branches
over more than a hundred metres. Plants thus formed entirely
of cells almost alike in structure and juxtaposed are subdivided
into two groups : Algae, when they are coloured green by
chlorophyll ; and Fungi, when, devoid of chlorophyll, they live
at the expense of other organisms — as animals, in their very
different way, are also compelled to do.

In spite of their homogeneous structure, Algae may exhibit

1 Micrococcus, Protococcus, etc.

Naviculcc.

Spirilla?, spirochaetes.

Hydrodictyon.

Gomphonema.

2 Bacilli, bacteria.

4 Closterium.

6 Nostoc.

8 Merista.

10 Volvox.

H

98 PRIMITIVE FORMS OF LIFE

a high degree of complexity. Certain forms attach themselves
to submarine rocks by means of processes like the roots of
higher plants ; or the body of the plant may elongate into a
cylindrical cord resembling a stem with lateral ramifications,
sometimes flattened, which might therefore be called leaves.
We would be tempted to assume that Algae such as these
having become terrestrial, were metamorphosed as a group
into plants analogous to those that grow in our fields to-day,
were it not that the mechanism of their origin is apparently
more complicated.

Fungi, obviously later in origin than Algae, but dominated in
their evolution by the necessity to lead a parasitic life, have not
attained such a high degree of complexity. Their most highly
developed forms consist of elongated filaments variously inter-
twined, and wound in places, which become attached to one
another and come up out of the ground, or erect themselves upon
the surface of the plants in which they have developed, and
finally spread out to form that cap-shaped fructifying organ which
we know so well both as a delicious food and a deadly poison.

The terrestrial plants which form the group of the Mosses,
always very modest in size, still bear a close resemblance to the
Algae as regards their structure. In the class of Muscineae, to
which they belong, we can even trace gradations between a
flattened thallus in the form of a continuous lamina found in
certain Hepaticae, and the thallus of those Mosses which exhibit
a small cylindrical stem bearing leaves laterally. Only the
root is absent.

In the case of the Mosses, however, reproduction has taken
a special line which tachygenesis will modify in the higher
plants by making it pass through successive stages, each of
which will be characteristic of some main branch. The lower
Algae generally reproduce themselves by means of corpuscles,
which we call zoospores, provided with minute paddles,
whip-like threads or waving cilia, enabling them to swim.
In these Algae the zoospores are all alike, in others,
however (Ulothrix, Tetraspora), they can, according to
circumstances, either remain alike in character and give birth
singly to new algae, or take on two different forms : one large-
sized, which accumulates reserve substances in its protoplasm,
the other small, and without these reserves. A large zoospore
can then only develop into a new alga if it first unites with a

TYPICAL FORMS OF PLANT KINGDOM 99

small one. This is the beginning of sexual reproduction, and we
call the large zoospore female, the small one male. The first
is sometimes known as an oosphere, and the second as an
antherozoid. In the seaweeds the oosphere is enormous and
immobile ; the antherozoid alone is active ; there are no
zoospores — reproduction is always sexual. Finally, in certain
Algae, the zoospores are replaced by immobile asexual
cells called spores, formed in special organs known as sporangia.
In the case of the Mosses these two kinds of reproduction are
combined, and alternate with perfect regularity. In the early
spring each small moss-stem expands at its extremity into
a delicate rosette of leaves, among which two kinds of minute
cups can be distinguished. The first, known as archegonia,
contain the immobile oosphere, and the second, known as
antheridia, are filled with very active antherozoids. Each
oosphere is soon fecundated by an antherozoid. Without
leaving its archegonium it develops into a small new plant
made up exclusively of a filament ending in an ovoid capsule
or sporangium, filled with spores. These spores, scattered over
the humid soil, develop into filaments similar to those of
the Confervas ; upon these grow the buds, which eventually
become new Moss plants.

The method of reproduction found in the Mosses is retained in
those plants, frequently large in size, which belong to the three
classes of Ferns, Club-mosses, and Horse-tails, and together form
the division of the vascular Cryptogams. Here the method of
growth becomes complicated. The body of the plant generally
consists of a stem which creeps along the surface or under the
ground, at times almost indefinitely, and which is called a
rhizome. On this rhizome two kinds of ramifications grow in
opposite directions ; one sort moves upward towards the light and
forms leaves, and the other, pushing deeper into the ground,
forms roots — which here make their first appearance. Through
files of elongated cells, ranged end to end in a straight line, water
charged with salts absorbed from the soil finds its way upward
to the leaves, where it becomes charged with the sugar they
have formed, and makes its way back again to the roots.
This circulating water is the sap, and the long lines of cells
which provide its paths represent the vascular system of the
plant, an arrangement which is also here observed for the first
time, and which has earned for the Ferns, Club-mosses, and

ioo PRIMITIVE FORMS OF LIFE

Horse-tails their name of vascular Cryptogams. When a cluster
of leaves develops at the same point on the rhizome, these
leaves become adherent and form a secondary stem, which
grows erect, as with the tropical tree-ferns, and probably also
at first with the Horse-tails with verticillate leaves. In the case
of the Mosses, it is the leafy stem which bears the organs of
sexual reproduction, and also a kind of accessory plant fixed
on this leafy stem which furnishes the sporangia and the spores.
In the vascular Cryptogams we find a singular reversal of the
dimensions of the sexual and the asexual plants that alternate
regularly in the development of Mosses, and up till the present
no intermediate condition has been found to fill the gap
separating the latter from the Cryptogams. The sporangia
are, indeed, borne on the large leaves of the Ferns and on the
leaves of the accessory stems of the Club-moss and the Horse-
tails ; the spores arising from these sporangia give birth only
to a leaf-like shoot without roots, resembling the thallus of the
Hepaticse and known as the prothallus. This pro thallus bears
archegonia, each containing an oosphere, and antheridia which
produce antherozoids. Every fecundated oosphere gives rise
to a new leaf -bearing stem.

The same process takes place in the three classes of Ferns,
Club-mosses, and Horse-tails : in all three there are parallel
modifications of reproduction, due to tachygenesis and to the
gradual transformation of the normal method of reproduction
into another more accelerated method, characteristic of the
gymnospermous Phanerogams. From this we can draw the
inference that it is certainly tachygenesis which transformed the
vascular Cryptogams into gymnospermous Phanerogams, though
probably each class of Cryptogams has passed over separately to
the gymnospermous condition, and given rise to special types of
the latter. Indeed, the Cycads, with their large leaves, seem to
be connected with the Ferns ; the Conifers, with their small
leaves arranged spirally, with the Club-mosses ; and the
Gnetaceae, with their small whorled leaves, with the Horse-tails.

However that may be, the course of tachygenesis in the three
classes of Cryptogams is the same.

i. The dimensions of the prothallus are reduced and instead
of developing outside the spore, they develop inside it.

2. The sporangia, instead of being identical in form, are
divided into two groups : the macrosporangia, which produce

TYPICAL FORMS OF PLANT KINGDOM 101

a small number of large spores, and the microsporangia, which
produce a large number of small spores. The large spores only
give rise to female prothalli bearing archegonia, and the small
spores only to male prothalli bearing antheridia.

3. In the spore-producing tissue of the macrosporangia the
spores cease to be individualized and invested with their pro-
tective membrane. This tissue remains neutral ; the archegonia
are directly formed there, and each one is itself reduced to
an oosphere surmounted by four or eight cells representing
the neck. In the microsporangia, on the contrary, the spores
become individualized, but the prothallus which they contain
consists simply of three cells of which one, the generative,
can give rise by subdivision to eight or ten small cells
(Microcycas colocoma of Cuba), each producing two
antherozoids, or the generative cell can itself directly produce
two antherozoids only (Cycas, Ginkgo).

4. Lastly the antherozoids cease forming their helicoid
band of waving cilia and are reduced to a simple nucleus.

These modifications can already be produced without
changing the form of the vegetative system, as Grand 'Eury
has observed in certain fossil Ferns. They are characteristic
of the reproductive system of gymnospermous Phanerogams,
but the names of the various parts we have just enumerated
must in this case be changed, because the reproductive system
of Gymnosperms was at first compared with that of Angio-
sperms, for which botanists have created a special terminology.
Thus, the macrosporangium becomes the ovule ', the tissue
corresponding to the prothallus, the endosperm, and the
archegonia are the small bodies, each corresponding to an
embryo sac. The microsporangia, in their turn, become the
pollen sacs, and the microspores the pollen grains. At the same
time the modified leaf that bears the macrosporangia becomes
the carpel, and that which bears the microsporangia, the
stamen.

The transformation of gymnospermous Phanerogams into
Angiosperms is accomplished very simply by a renewed
progress of tachygenesis. The carpels, instead of remaining
spread open, and leaving the ovules unprotected, as in the
Gymnosperms,1 which derive their name from this fact, are

1 From yvfivos naked and ontpfia grain.

102 PRIMITIVE FORMS OF LIFE

rolled up in a cone-shaped receptacle so as to conceal the
ovules, and it is thus their name of Angiosperm arises. At the
same time the prothallus is still further reduced in the ovule ;
the cell which gives rise to it, and which is called the embryo
sac, increases in size ; the nucleus generally undergoes only
three successive subdivisions, which give rise to eight nuclei ;
two of these nuclei fuse into a single one occupying the centre
of the embryo sac, three others are arranged at its base,
and the last three at the top, where they form the basis of an
equal number of cells. Of these three cells one only is trans-
formed into an oosphere ; the others remain sterile, and all
traces of the archegonia are lost. The microspores or pollen
grains do not themselves contain more than two nuclei, one of
which is subdivided to form two others, the last relics of the
antherozoids.

Anyone who has followed this evolution must realize that it
is the characters produced by tachygenesis which distinguish
the three large groups of Rhizophytes or plants possessed of
roots and vessels : the Cryptogams, the Gymnosperms, and
the Angiosperms. It is evident that these three classes
successively developed their characters in the order we have
just indicated, and could have appeared on our earth in no
other order. Tachygenesis, however, goes still further in the
Angiosperms. The reproductive leaves of the same sex are all
grouped together in the Gymnosperms, and arranged in a
tight spiral, forming what we know as a cone ; there are both
female and male cones, generally found on the same tree ;
hence the conifers are said to be monoecious. The Angio-
sperms, like the Gymnosperms from which they are directly
derived, ought to have " flowers " reduced to the essential
parts ; those of the same sex ought to be grouped together,
either on the same tree or on two separate trees. This actually
occurs in the large family of the Amentacese, which group their
flowers in unisexual catkins, or sometimes reduce them, as in
the case of certain willows, to two stamens protected by a
simple scale.

How was it possible for catkins to evolve into true flowers, as
botanists understand the term ? Flowers of the highest type
consist of four whorls. Two are of sterile leaves : these are the
calyx, whose leaves generally remain green, and the corolla,
whose leaves are usually coloured. The two other whorls are

TYPICAL FORMS OF PLANT KINGDOM 103

fertile, and are always arranged in the same order, a whorl
of male leaves or stamens, above the corolla, and a whorl of
female leaves or carpels, formed at the end of the floral branch.
At first sight the mechanism of this transformation is
not apparent ; however, in the light of what we already know
of the nature of the sexes, it is possible to make a good guess.
In the first place sex is not, as we might be tempted to judge
from ordinary observation, something absolute. We have seen
that the difference between the male and the female cells is
essentially a difference of aptitude for nutrition. This difference
can be aggravated by an increase or decrease of nutrition in the
individuals producing these cells. A simple transplantation
often suffices to change Thladianta dubia (Blavet), Trice-
nosperma ficifolia, Dioscorea canariensis, and Clematis hilarii
(Spegazzini, 1900), from the female to the male sex. The same
result has been obtained by cutting off the head of a willow
(Salix caprcea, Haacke, 1896). The contrary transformation has
been obtained also in willows (Klein, 1896) : Edmond Bordage
saw the same thing take place in a papaw on Reunion Island
(1898) ; Hariot (1902) and Davaul (1903) announced that this
phenomenon is habitually produced in the palms of the oases
of Southern Algeria by longitudinally splitting from the centre
to the sheath all the leaves of stems two or three years old.
Moreover, in a series of the most exact and ingenious
experiments, Blaringhem x has obtained the most startling
results. Dividing the young female stems of Mercucialis and
of Spinach, he saw shoots arise each bearing male and female
flowers, and thus he transformed a dioecious plant into a
monoecious one. He was able to go even farther, and obtained
hermaphrodite flowers by mutilating the stalks of the male
hemp. His experiments on Maize also proved the influence of
nutrition upon these phenomena. Maize-stalks, as we all know,
terminate in a plume of male ears which becomes characterized
at an early stage ; later on female ears, enveloped in large
bracts, appear at the flower-axil of the stalk, like lateral
branches. It may be observed that the male tuft forms at the
stage when the young maize-stalk is only growing small roots ;
consequently its nutrition is not very active and tachygenesis
makes it develop too soon. The female ears, on the contrary,

1 XXXIX, 124.

104 PRIMITIVE FORMS OF LIFE

develop when the stalk is at its full activity. With this in mind,
Blaringhem cut the Maize-stalks at different stages of growth,
thus suppressing the first male ear and a large part of the stalk
that had borne it at the exclusively male stage. This stalk was
replaced by numerous lateral shoots, which can be considered
as new stalks. If the section of the original stalk took place
when the roots were only partially developed, that is to say,
under the conditions which produce the male plume of this
stalk, all the shoots likewise terminated in a plume exclusively
male. If the section was delayed till the roots developed,
an increasing number of female flowers appeared on the terminal
crowns of certain shoots. If he waited till the approach of the
period of maximum growth of the stalk, which was obviously
the period in which the roots exhibited great nutritive activity,
the terminal plumes of a certain number of shoots bore only
female flowers. Finally, if the section was made during or
after the blossoming period, all the shoots terminated in a
head of female flowers. Blaringhem succeeded equally well in
obtaining the transformation of female ears into male ones.
All that was necessary was to twist the stalk below the terminal
bud, thus arresting its development. The lateral buds benefited
by the nourishment which the other would have absorbed,
and grew actively. Instead of forming a short thick crown,
with flowers exclusively female, they elongated at the expense
of their width, tended to ramify like the male ear, and finally
produced a certain number of male flowers. The same result
can be obtained even more consistently by twisting either the
peduncle of the female ear itself in the process of development,
or the same ear at a certain point of its length. In the latter
case the twisted portion, being less well nourished, produces
male flowers.

The influence of nutrition on sex is thus quite evident. But
these operations are not confined to sex determination in
flowers ; they also confer upon the seeds arising therefrom
a special aptitude for getting nutriment. If we go on to plant
the seeds obtained from a male ear, the terminal ear of the
young stalks issuing from them would normally contain both
male and female flowers ; a new factor comes in in the
development of these new growths — heredity.

It is even possible to make new organs appear in the flower,
which, of course, also implies that they can be suppressed.

TYPICAL FORMS OF PLANT KINGDOM 105

Blaringhem succeeded, in the case of maize, in adding carpels
to the male flowers in which the stamens remained intact, and
thus obtained hermaphrodite flowers. This is probably what
happens in the analogous transformations observed in the
unisexual flowers of a certain number of other plants.1

Thus we have made our first point :—

The sex of flowers is clearly a function of their nutrition, and not
determined in advance — at least, in a certain number of cases.
The fundamental identity of the phenomena of reproduction in
animals and plants is a no less incontestable fact, and we are
consequently justified in appealing from what is obvious in the
one kingdom to its application to the other. There are, as we
shall see, groups of hermaphrodite animals, but while
hermaphroditism is the rule in the higher plants, it is the
exception in animals, which indicates that its appearance is of
later origin, and explains why its causes can be more easily
understood.

The conditions under which hermaphroditism has been ob-
served in the Animal Kingdom agree in establishing the fact that
it, too, is connected with some disturbance in nutrition, which
leads to the disappearance of the males and the transformation
of the females into hermaphrodites. This hermaphroditism is
brought about in a particular way ; the cells destined to produce
germ-cells are formed early and make their first appearance
during the period of growth ; when they are competing with
the somatic cells in the process of multiplication they evolve in
the direction of masculinity ; when maturity is attained, how-
ever, they are enabled to appropriate all the nutritive
substances, and then evolution is towards the female sex.
There is no simultaneity in the development of the two kinds
of germ-cells, except, perhaps, for a short transitional period in
certain animals such as the Oyster,2 which begins as a male and
then becomes a female. This process is called protandrous
hermaphroditism. The converse may take place, but it is
extremely rare. Among the Cirripedes and the Nematodes
we often find supernumerary and useless males, which persist as
though to serve as witnesses of the mechanism that produces
hermaphrodi tism . We are thus j ustified in thinking that the same
may hold true in the Vegetable Kingdom ; that under new
conditions of nutrition, as in the case of vegetation which had

1 Trianosperma, Dioscorea, Clematis. 2 XII.

106 PRIMITIVE FORMS OF LIFE

at first been possible only in very humid or even marshy soil,
and which was transplanted to dry soil, the male catkins,
always present in Gymnosperms and the Amentaceae, have dis-
appeared from the latter, and the female catkins alone have
persisted and become hermaphrodite. From this fact alone,
the explanation of the habitual form of flowers becomes easy.
We may assume that the hasty and precipitate formation of
fertile leaves, stamens, and carpels in a floral bud which is
undergoing especially rapid development has caused the dis-
appearance of the rudimentary infertile leaves which generally
accompany them, and which in the cone of the Gymnosperms
are mingled with them in various ways. These leaves, as a matter
of fact, are represented by little scales in the Plane-tree catkin,
and by little knobs in the case of the Willows and the Poplars ;
they are completely absent in the female catkins of the Birch,
in all those of the Myricinacese, and in the Oaks, Hazels,
Chestnuts, and the ordinary and white Beeches. Here the
catkin is protected by other infertile leaves called bracts,
grouped together by their bases and forming the cup for nuts
like the acorn (that of the hazel-nut surmounted by long leaf-
like appendages), the bur of the chestnut, the beech-mast, and
the envelope of the fruit of the horn-beam. In these plants,
almost all of them large trees or bushes, the flowers still possess
neither calyx nor corolla. Although they also demonstrate the
contingent character of the accessory parts of the flower, we need
not be concerned with those cases in which, as in many groups
of Monocotyledons, Juncaceae, Cyperaceae, Gramineae, Naia-
daceae,and Lemnaceae, the perianth, normally developed in other
plants, has become reduced and finally abortive. The instance
of the Arums is particularly interesting, because it shows
how the reduced perianths of flowers grouped in an ear can
be replaced by a huge bract capable of taking on the aspect of
the most brilliant perianth.

Let us imagine a female catkin composed entirely of fertile
leaves, protected at its base by sterile bracts, which, under
unaccustomed conditions of nutrition, such as must have
frequently occurred when plants became more exclusively
terrestrial, is subjected to an accelerated development. The
first fertile leaves formed in the course of the elongation of
the catkin, those that occupy its base, will compete for their
nutrition with the catkin itself. As in the protandrous

TYPICAL FORMS OF PLANT KINGDOM 107

hermaphroditism of animals, these will become reduced to the
state of male flowers, that is to say, stamens ; only the fertile
leaves at the top of the catkin, those that represent the final
growth, preserve their female sex, and become carpels with
their ovules. Thus we have the actual flower of the
dicotyledons, as it is schematically represented and as it is
described in all the classical works on botany, with its carpels
in the centre forming the gyncecium or pistil ; a ring of stamens
forming the andrcecium, and a ring of sterile leaves constituting
the perianth. The latter is usually double, and comprises the
coloured leaves of the corolla and the green leaves of the calyx.
In order to explain this fact, we must turn to another order of
considerations. The elaboration of the germ-cells does not take
place without the resultant formation of special compounds,
waste products evacuated by these cells and thus coming into
contact with others contiguous to them, either by absorp-
tion or by way of a circulatory system. Zoologists and
physicians have long been aware of the influence exerted upon
the organism by these internal secretions, as they are called
to-day, and we have already indicated to what degree they are
capable of modifying the form, size, and the colour of the
organs they penetrate, especially those which form part of the
secondary sexual characters. So far as colour is concerned,
this action may be spent entirely in modifying the corolla,
but sometimes it is extended to the calyx, which then becomes
petaloid, notably in many Monocotyledons (Colchiaceae,
Liliaceae, Asparagoideae, Orchidaceae, etc.), and can even
succeed in modifying the bracts (various Sages) or the leaves
(Poinsetia).1

Naturally, if flowers have originated thus, the earliest of them
ought to preserve some traces of the primitive elongation of the
catkins and the indeterminate number of their constituent
elements : sepals, petals, stamens, and carpels ought to have been
numerous at the beginning, because of their common origin, and
to have approximated to one another by gradual transitions.

1 It may happen, of course, that the cause for these phenomena is just the
reverse, and that the coloured bracts, the petaloid calices, and the petals owe
their particular development to the fact that they have arrested in their passage
the foods which the fertile leaves have attracted toward themselves, and thus
profited by additional nourishment ; but if this were so we might well ask why
these parts do not themselves become fertile. Experiment or chemical
analvsis must be left to decide this.

108 PRIMITIVE FORMS OF LIFE

These conditions are certainly fulfilled in a large number of
flowers, at any rate in certain of their parts, the andrcecium
or the gyncecium, of which the multiple elements are arranged
in spiral form like the scales of a pine-cone around its
axis. The Magnolias, the white Water-lilies {Nymphcea alba) , the
Camelias, and the Cactus also have such helicoidal flowers with
numerous elements, in which we can trace the development of
the sepals into petals (Camelia) or petals into stamens
(NymphcBa). In roses the leaves develop into sepals, and
although the latter are only five in number, they are gradually
modified. The number of petals is also five, all resembling
each other. The stamens, arranged in three whorls, are
always twenty in number, the carpels indeterminate, and
arranged spirally inside a cup hollowed out in the extremity
of the stem-axis. In the Strawberry, Raspberry, and Black-
berry, on the contrary, the axis protrudes, but the carpels have
the same arrangement. The calyx and the corolla are in whorl
formation, and the parts are all equal in the case of
the Buttercups, Anemones, Clematis, etc., but the stamens and
carpels are many in number. The latter become reduced in
number and fuse with one another, while the stamens remain
numerous, in the Poppy. Finally, all is regularized, tachy-
genesis shortens the axis which supports the various parts
of the flower ; parts of the same nature then arise
simultaneously, and their helicoidal arrangement disappears
completely ; sepals, petals, stamens, carpels, form so many
whorls of which the parts, equal in number, alternate from one
whorl to another. The flower is then said to be isomerous. The
last reduction of all affects the gyncecium, which may be formed
from carpels less in number than the corresponding parts of
the other whorls.

Once the flower has been thus evolved, other causes can
modify it ; it can, for example, pass from the whorl form
to one symmetrical about one plane, as in the Papilionaceae ;
but, above all, under the influence of tachygenesis, the
parts of the same whorls may be formed so quickly that
they grow into one another, and the dialypetalous corolla
becomes gamopetalons. This fundamental division of the
Dicotyledons, which everyone recognizes, would thus appear to
be the result of such a process of tachygenesis. It is
tachygenesis, moreover, which in both these two series has

TYPICAL FORMS OF PLANT KINGDOM 109

led to the concrescence of all the carpels with the base of the other
floral organs, and hence has determined the achievement of the
so-called inferior ovary. Thus, in each of the two subclasses
of Dialypetalae and Gamopetalce, two orders can be
distinguished, one with superior ovaries and one with inferior.
This makes it clear that the gamopetalous Dicotyledons could
not have appeared until after the dialypetalous.

We have now reached a delicate point. The older botanists,
having failed to take into consideration these facts, from
which we have just drawn so many inferences, or, may be,
having failed to realize them, were guilty of an error of
judgment which certain present-day botanists are inclined
to revive. There is a widespread opinion that the
Monocotyledons are lower than the Dicotyledons, and must
have appeared first, and many ingenious attempts have been
made to establish this fact. But the moment we apply to the
flowers of the Monocotyledons the incontrovertible principles
that result from the study of the Dicotyledons, we are
immediately convinced that far from being primitive flowers
they are the most highly developed of all. In the first place,
like the flowers of the highest Dicotyledons, with very few
exceptions,1 they are almost all isomeric and constructed on
type 3, that is to say, they have three sepals, three petals,
three or six stamens, and three carpels. They are among the
most brilliant. Frequently the calyx is as magnificent, or even
more so, than the corolla — a rare thing among Dicotyledons.
Often, as in many of the Orchids,2 they are arranged symmetri-
cally to the median plane in such a way as to resemble bees or
butterflies. Sometimes the andrcecium undergoes a reduction
that bears witness to an alteration of the general type,
subsequent to the achievement thereof. The Mono-
cotyledons with small flowers, such as the rushes, sedges, and
grasses, are not more primitive than the others because
their flower is small and green. They are isomeric like them,
and the flower of the Gramineae has undergone profound
modifications of this isomeric type, which is recent in itself.

The relatively advanced character of the Monocotyledons

1 The Centrolepideae, indigenous in Australia, and the plants of the
Lemnaceae, and the Naiadacese families, all either floatingor submerged, inwhich
this very specialized manner of life goes along with an undeniable degeneration
of the flower.

2 Fly Orchis, Bee Orchis, Hornet Orchis, etc.

no PRIMITIVE FORMS OF LIFE

is therefore proved by the structure of their flowers ; the con-
trary idea has arisen because the structure of their stalk
resembles, in certain respects, that of the vascular Cryptogams.
But the Monocotyledons are angiospermous plants which can
only have acquired this character by passing through the
Gymnosperm stage, and the stalk of the known Gymno-
sperms has developed far beyond the primitive stem-
structure of the vascular Cryptogams. Consequently the
explanation of this feature must be sought elsewhere. The
Monocotyledons appear to have lived originally in humid or
marshy soil, or even in the water, as is indicated by their
smooth, simple, thick, parallel-veined leaves. Many are still in
this condition. We have but to cite the Rush, Sedge,
Rice, Iris, Arum Lily, Marsh Reeds, Bamboo, Eel-grass,
Pond-weed, Duckweed, etc. Even Palms, contrary to the
popular notion, are not found in the desert but in the well-
watered oases of the desert, which is not the same thing at all.
The stems of the ancestors of monocotyledonous plants, being
ill-supported in the soft soil, as we shall see, assumed a
recumbent position in the ground and became transformed into
rhizomes, like those of the vascular Cryptogams, and it is
upon this rhizome that the aerial stems were formed again by
a process analogous to that which forms the stalk of Mosses
and Horse-tails — which they thus resemble quite naturally.
These marshy plants are most favourably situated for
fossilization. It is not surprising, therefore, that they
should have been more easily preserved than the
Dicotyledons, and that they should even be found in strata that
have not as yet furnished any Dicotyledons. Lignier has
actually described under the name of PropaUnophylla the basal
parts of Jurassic leaves that he believes to have belonged to the
group of Monocotyledons.

It would be useless to attempt to systematize the forms,
essentially variable according to their circumstances, of
Fungi, Algae, Hepaticae, and even Mosses. Their organic unity
is scarcely higher than that of the plastids ; all the parts of the
body, complicated as it appears, have the same value ; none
of them can be considered as having any particular
individuality. It is very different when we come to analyse
the vascular plants. If we look at the trunk of a Tree-fern,
a Cycad, or a Palm, it would seem evident, at first view, that

TYPICAL FORMS OF PLANT KINGDOM in

it is formed by the growing together of the petioles of the leaves,
and there has been much discussion of this theory. Dicotyle-
donous plants are in a different case. Here the stem does not de-
velop from the leaf, but seems, on the contrary, to have produced
it. Hence the conclusion that the apparent formation of the trunk
from concrescent petioles was illusory. Perhaps it would have
been more logical to take as the starting-point the obvious
indications furnished by Ferns, and then to find out how the
initial method of trunk formation was able to give rise to a
structure characteristic of the trunk of Gymnosperms and
dicotyledonous Angiosperms. This indication provided by the
Ferns, Cycads, and Palms carries us further still. We have
only to examine the young branch of a Conifer to get on the
track of it. Without entering deeply into the problem we may
point out that the order of formation of the organs is often
altered by tachygenesis, and that where organs of independent
origin are fused into one, as more than one example will prove,
the new organ resulting from their fusion is formed, in the
course of embryogenetic development, before those parts that
have remained independent, thus appearing to be formed
at their expense. This is notably the case with the primitive
kidney or pronephros of Vertebrates. This observation gives
its value to Goethe's theory. He believed that every plant
is an association of leaves, and every leaf a kind of individual
which by its own indefinite repetitions forms the whole plant,
and by transforming itself gives rise to all the parts of the flower.
What Goethe divined from the study of flowering plants alone
has since then been demonstrated by the study of the vascular
Cryptogams. There the leaves, all alike at first and equally
capable of bearing sporangia, subsequently divide into two
types with distinct forms, the sterile leaves and the fertile
leaves. In the case of Club-mosses and Horse-tails, these leaves
form in groups around the end of the branches or stems and
hence presage the formation of the cones on the Conifers, which,
in their turn, shadow forth the flower.

CHAPTER IV

Primitive Animal Forms
Branched and Segmented Animals

/^\WING to their aptitude for changing their form and
^S moving about, those members of the animal kingdom
reduced to a single structural element or plastid, acquired a
variety of forms infinitely greater in number than that which
we find at the corresponding stage in the Vegetable Kingdom.
Furthermore, these plastids, having once become associated,
modified each other reciprocally and became mutually
dependent much more quickly than the vegetable plastids.
Hence, we do not find in the Animal Kingdom, alongside of
unicellular beings which constitute the large group of Protozoa
corresponding to the simplest structural type, creatures of larger
size possessing the homogeneous structure encountered in the
Algae and the higher Fungi. We pass suddenly from the
Protozoa to organisms already complicated ; the Protozoa,
however, possess an infinite variety of forms and abound every-
where. They are divided into three large groups, the Rhizopoda,
Infusoria, and Sporozoa.

The body substance of the first has a consistency so
nearly akin to that of water that the surface of the mass
responds to the least attraction ; it is constantly being
flocculated, fringed, or lobed, and the temporary amoebic
protrusions that emerge from its mass are called pseudopodia,
that is, false feet. These pseudopodia, if they are ex-
tensively ramified, may have the delicate ramifications
fused together. Thus, they become surrounded by a kind
of living network. Two classes of these reticulated Rhizo-
poda have played a great part in all Geological Periods,
and are still abundant in all our seas ; these are the Radiolaria
with a skeleton, which is often silicious, and the Foraminifera,
with a shell that is generally calcareous. The first float on the
water, and their skeletal debris is found as far back as the
Algonkian deposits ; the second group live nearer or actually

PRIMITIVE ANIMAL FORMS 113

at the bottom of the sea. They have formed, practically unaided,
deposits of great thickness at different epochs. In the less
important Rhizopods the pseudopodia do not fuse ; in the
Amoeba they take the form of simple rounded lobes.

We come thus to the Infusoria, which alter their shape
but little, and move with the aid of permanent processes
known as vibratile flagella when they are long and few in
number, and waving cilia when they are short, numerous, and
arranged like a fleece or in fringes. The Infusoria have left no
fossil traces. Some Flagellates, however, are interesting because
certain bodies which resemble them in all respects, are charged
with the duty of promoting the circulation of water in the
internal canals of Sponges. This is the only case in which so
marked a resemblance has been found between free Protozoa
and cells forming an integral part of an organism.

The ciliated Infusoria, in spite of their small size — the largest
hardly attain a length of more than a few tenths of a milli-
metre, present an interest of a different order ; their forms
already seem to obey the laws dominating the higher organisms.
The thin cuticle is pierced by two orifices functioning like those
found in the digestive tube of higher animals, one for the entry
of food, and the other for the expulsion of the residuum of
digestion. These orifices may be terminal, in which case the
form of the animal is disposed symmetrically to the axis uniting
them. The vibratile cilia form a continuous fleece (Holophrya)
or are arranged in a series of transverse rings (Didinium).
This is therefore essentially a swimming type, but most of the
Infusoria are able to move over the surface of Confervse,
minute Algae, or even directly over the ground. In this case
they have a flattened ventral aspect, to which the mouth has
been transferred. This latter is slightly eccentric. But for
this fact, the symmetrical currents, stimulated by the cilia,
would flow around it without directing any food to it. The
eccentric position of the mouth and the way in which the larger
lateral portion of that region of the body in front of it forces
the currents with the food particles they carry against it,
provides it with food. The vibratile cilia round about it are
at first similar to the others [Paramecium), but, as though
strengthened by the constant and intensive use the animal
makes of them, they grow larger than the others and form an
ado ral fringe that can twist itself in a spiral around the pseudo-

H4 PRIMITIVE FORMS OF LIFE

mouth (Spirostomum) , or be simply oblique (Bursaria). Finally,
when the Infusorian has become definitely ambulant, the cilia
of the dorsal side are atrophied as though through disuse,
and those of the ventral side take on special forms (hooks,
probes, cirri, paddles, etc.), adequate to the function they
fulfil. It is quite clear that we cannot assume for the Infusoria
anything comparable to volition, determining the use or disuse
of its organs, nor any sentiment of need. It is external
stimulation which incites to movement certain cilia rather
than others, and which determines the contraction or relaxing
of this or that part of the body. But use or disuse, although
determined by another cause, has had the same effect as in the
case of animals endowed with sensibility and volition. This
purely mechanical action is clearly exhibited in Sientor, a
large Infusorian provided with an adoral fringe analogous to
that of Spirostomum, and with a kind of posterior suction cup
that permits it to fix itself temporarily. When the animal
is free the cilia of the adoral fringe function like paddles
and propel it forward. When it is fixed behind by its sucker
they drag forward the body of the animal till it is stretched
and elongated into a kind of bell or trumpet, of which the adoral
fringe borders the base. This form becomes definitive in the
Vorticellids, which are almost permanently fixed.

There is a very interesting difference between the free and
the fixed Infusorians as regards multiplication. All the ciliated
Infusorians multiply by division, and bipartition is the
normal type of this mode of multiplication. In the free
Infusorians it is produced transversely, and in the Vorticellids
longitudinally, so that in the former case the two new
Infusorians are placed one behind the other, and in the
second case side by side. However, in certain species, this
separation into new individuals is either retarded or does not
occur at all. In the first instance we find a chain of individuals
resembling the body of an annelid worm, with its division
into rings (Anoplophrya, Hoplitophrya, Opalinopsis) ; in the
second a kind of little bush (Zoothamnium, Carchesium,
Epistylis). We shall find the same forms allied with the same
conditions of life in the higher animals.

Geometrically an egg floating in a homogeneous environ-
ment, such as water, ought to produce, after segmentation, a
hollow globe with walls formed of a single layer of blastomeres.

PRIMITIVE ANIMAL FORMS 115

Indeed, this is practically what happens when hereditary or
other influences do not disturb the phenomenon. There are
organisms that remain practically thus throughout their
lives (Volvox, Protospongia, Magosphczra, etc.) ; and a fairly
large number of embryonic forms in the higher animals
momentarily adopt this shape, to which the name blastula
has been applied. As a rule this stage is soon passed. The
blastulae are usually covered with vibratile cilia, and it would,
indeed, be remarkable if the strength and activity of these cilia
were to act with strictly equal force on every side of the
blastula. If this were really the case the blastula would be
continually whirling around its centre. As a matter of fact,
there is always one region in which the cilia are more active,
and these draw the embryo in their own direction. Therefore,
the blastula has an anterior and a posterior extremity. It
elongates along its axis of locomotion and becomes ovoid.
The active anterior end is the region devoted to the con-
sumption of reserves contained within the constituent cells
of the blastula, and these reserves are accumulated in the
inactive posterior area ; thus the constituent substances of the
ovoid blastula are constantly attracted forwards. Hence, a
current is established which induces the posterior half of the
blastula to become invaginated into the anterior half. This
explains one of the more common developments in embryogeny.
The blastula thus becomes a gastrula ; its anterior
hemisphere, formed of transparent cells, remains external and
becomes the ectoderm : the posterior hemisphere, formed of
granular cells on account of the reserve substances it contains,
now becomes the interior la37er and is known as the entoderm ;
the orifice, which is necessarily posterior owing to invagination,
is the blastopore. Various floating bodies, generally detached
from the entoderm, penetrate into the space separating the
ectoderm from the entoderm. These may fill the whole space,
or they may, in part, become attached to the inner, and in part
the outer side of the ectoderm, so as to leave a cavity between
them. This is the ccelom or general cavity, and the elements
between the ectoderm and the entoderm constitute the
mesoderm. The entoderm circumscribes the primitive digestive
cavity which, wherever a ccelom exists, is generally brought
into communication with the exterior by a second orifice
opposite the blastopore, which becomes the mouth.

n6 PRIMITIVE FORMS OF LIFE

Thus, we become acquainted with three simple organic
types, and to these we shall give the name merids. These
merids may remain fixed or become, in this condition,
free. In the first case they become the respective starting-
points for the three great types of ramiferous organisms :
the Sponges, with complete mesoderm, the Polyps, with
no mesoderm, and the Bryozoa, with a mesoderm hollowed
out by a ccelom.1 These three types must have been
simultaneously formed from the earliest times when life
existed on earth.

The modern Sponges have the property of forming in
their tissues small mineral concretions, of a sharply determined
form, known as their spicules. These spicules may be siliceous,
or calcareous, or they may be replaced by fibres of a substance
analogous to silk, and known as spongin. The earliest Sponges
seem to have been provided with siliceous spicules bearing six
rectangular branches. Our seas still contain them, and they
constitute the family of Hexactinellidae. The Polyps and the
Bryozoa can also deposit mineral substance in their tissues,
but this is always calcareous. It was they that built the
calcareous deposits of former ages. The Bryozoa have had
but a humble destiny, while the Polyps, on the contrary,
have at all times played an important part ; thus, it becomes
necessary to detail with precision the relations they bear to
one another.

One of the simplest forms in which they can be studied is
the freshwater Hydra, rendered so famous by the researches
of Trembley. It is, indeed, very difficult to imagine a more
primitive animal. It is a trumpet-shaped organism, six or
seven millimetres long, and attaches itself by its pointed end
to submerged leaves ; its orifice, serving at once as mouth and
anus, is surrounded by tentacles capable of seizing minute prey,
such as small crustaceans, worms, etc. After it has attained
a certain size the hydra ceases to grow along constant lines, but
produces laterally and in succession small protuberances
or buds, each of which develops in order to form a new hydra

1 We may designate these principal merids as spongomerids, hydromerids,
and bryomerids. These latter differ from the merids that have given rise to the
Artiozoa, or, at least, to the Annelid Worms and their derivatives, only in the
fact that they have become fixed. This is one reason why the Bryozoa,
Brachiopods, and a part of the Gephyreans have been united in an artificial
group of Vermes, containing at the same time primitive and degenerate forms.

PRIMITIVE ANIMAL FORMS 117

exactly like the parent. The new hydra detaches itself and leads
an independent life such as a slip taken from a plant would do.
At a mean temperature of some twenty degrees, a well-
nourished hydra buds with great activity ; the hydra born of
these buds detach themselves very slowly, and only after having
produced buds themselves. In this way Trembley obtained a
hydra wrhich bore nineteen others in three different generations.
What is exceptional in the case of the ordinary Hydra becomes
the normal condition in the majority of the innumerable marine
species which, together with this creature, form the main group
of Hydroids. Their bodies are generally supported by a thin
covering of horny consistency forming the polyp capsule.
One of these Hydroids, Cordylophora lacustris, has succeeded in
acclimatizing itself to freshwater, and can be obtained in the
Seine. The Hydroids, fixed like plants, develop like them by
budding laterally, and ramifying ; they take on the appearance
of small shrubs whose branches consist of single hydroid
Polyps, just as the primitive plant was formed of leaves. The
polyps, by remaining associated, have constituted a new
organism, which is to each of them what a rose-bush is to its
leaves, and what the polyp itself is to the plastids of which it is
composed. It is formed by the same mechanism — an association
of like parts, each capable of leading an independent existence,
but which lose part of this independence by reason of their
association.

Let us state at once that the mechanism we have seen at
work in the Vegetable Kingdom is also usual in the Animal
Kingdom. Thus, we ought to give a name to the organic forms
corresponding to the successive stages of this complication.
We have called plastids the simplest of these living elements,
which for a long time were called cells owing to incomplete
observations by the early histologists. We have described
as merids the organisms resulting from the association of
plastids. Hydras are consequently merids. An association of
merids we shall call zoids, and, as we shall also meet with
associations of zoids, we shall particularize them as denies.
These terms suffice to express all the stages of organic evolution.
Their brevity allows us to use them as suffixes in com-
pounds ; for example : spongomerid, hydromerid, bryomerid —
spongozoid, hydrozoid, bryozoid — spongodeme, hydrodeme, etc.
It sometimes happens that groups are formed within a deme

n8 PRIMITIVE FORMS OF LIFE

capable of liberating themselves and of leading an independent
life (Siphonophora) ; these we shall call denudes.

In these associations the component parts at first enjoy
almost complete independence, which has led to their having
been considered as constituting a special kind of body, to which
the name of colony has been given in order to distinguish it from
ordinary organisms. It is assumed — on a purely arbitrary
basis — that the merid of each zoid and the zoid of each deme
preserves its own individuality, although the zoid and the
deme are themselves deprived of it. However, as in the
associations of plastids, the diversification of form and function
in the merids brings about an increasing solidarity in the zoid,
which, through every possible transition has led us to transfer
to them the idea of indivisibility and unity that we have
produced from our own consciousness, and which we have
transferred to the higher animals and plants themselves.

In actual fact all the hydromerids forming a hydrozoid
preserve enough independence to invest them with the various
forms, each corresponding more or less to a particular function
(without that form, however, becoming indispensable) which
their position, the conditions of their nutrition, and the stimuli
to which they are exposed, determine. Contrary to the opinion
generally expressed in the meaningless phrase " the function
creates the organ ", which is often applied incorrectly and
misguidedly, just because it has no significance, the hydro-
merids among the Hydroids become modified quite inde-
pendently of any function. They then perform such actions
as their form and position allow, and this activity then becomes
a function of which each pseudo-individual is naturally the
organ. Thus, along with the normal merids, which preserve
their mouth, eat and digest, and which may be called
gastromerids, others are found which, since they are nourished
by the former, dispense altogether with a mouth. They are
able, however, to seize and palpate objects. These dactylomerids,
functioning like fishing-tentacles, take on a large variety of
forms. Others of the community, the acanthomerids , transform
themselves into defensive spikes, thanks to their horny
covering. Others, again, find themselves placed in such
conditions that the buds they produce rapidly develop germ
cells ; these are the gonomerids, the carriers of the gamomerids,
some of which are male and others female. A. de Ouatrefages

PRIMITIVE ANIMAL FORMS 119

was the first to describe the whole of the small and varied
world in Hydractinia that encrusts the shells inhabited by the
Hermit-crab. This variety of associated forms, which often
corresponds to that presented by the leaves of a plant, is
widely spread among the Hydroids, and has led to the same
results. When a gamomerid, or sexual merid, develops, at any
particular part of the hydrozoid, it brings about the trans-
formation of the neighbouring merids into dactylomerids.
All of these form a single whorl, which admits four merids,
for the simple reason that any circumference offers about
three times as much room as its diameter, and very little more.
These dactylomerids cannot coil about the gamomerid they
surround without drawing towards them the periphery of the
peduncle upon which they grow, and they thus necessarily
form a bell-shaped web membrane of which the gamomerid
constitutes the clapper. The walls contain muscles which
permit it to contract and instantly drive out the water which
fills it, and the recoil produced by this sudden expulsion of
water has the effect of tugging at the support which at its
summit unites it to the Hydrozoid. The peduncle finally breaks
and the bell is set free. It consists of a gamomerid provided
with a mouth and capable of digestion, an umbrella, which serves
as an organ for swimming, and four fishing-tentacles — all that
is necessary for maintaining an independent existence. It is
free henceforth to live in its own way. A new type of organism,
a veritable flower-animal, has come into being ; this flower-
animal is known as a medusa. The medusa? may remain
attached to the hydrozoid that produced them, which then
becomes a hydrodeme, since the creatures are themselves all
hydrozoids. Their formation is frequently influenced by
tachygenesis ; hence they sometimes remain incomplete.

Instead of attaching themselves to some solid body, certain
hydromerids, drawn by their lightness to the surface of the
water, find a way of imprisoning an air-bubble which thence-
forward buoys them up. The hydrodemes resulting from their
development remain floating and act together, like a fish
pursuing and capturing prey. Gastromerids, dactylomerids,
and medusae then take on the most diverse forms. A certain
number of contiguous medusae are employed like a crew of
oarsmen for locomotion, and by a phenomenon of tachygenesis
these medusae, which have an indispensable function, even

120 PRIMITIVE FORMS OF LIFE

develop before the gastromerids. Nothing equals the brilliant
coloration and the richness and variety of form manifested
by these swimming hydrodemes, constituting the order of
Siphonophora. They are real autonomous organisms, and
furnish definite proof that what used to be called a colony
is nothing but the first phase in the formation of higher
organisms.

The advance made by the medusas in the development of
Siphonophora can take place to an equal extent in the fixed
hydrodemes. By their help we can construct the stages right
up to that moment when the development of the egg ends, not
as in a hydrozoid which itself produces a hydrodeme, but
directly in a medusa. The gradual suppression of the
hydrodeme is here equivalent to the gradual suppression of the
prothallus in the Vascular Cryptogams. These medusae, in-
dependent of any hydrodeme, but whose formation was
prepared, and could not have been produced but for a
lengthy elaboration by a series of hydrodemes, themselves
undergo important modifications, becoming complicated in a
variety of ways till they finally attain many decimetres in
diameter. They form the class of Acalephae, comprising many
orders,1 the first culmination of the Hydroid series.

There is a second condition more important still, attained
by the Coral polyp via the Madreporaria, those very wonder-
ful reef -builders. Certain Hydroids akin to Hydractinia
had already been able to secrete lime. This property
is general among the hydrocorallines — so well studied by
Moseley in the course of the Challenger Expedition. In the case of
the hydrocorallines we can trace from the Echinopora, still closely
akin to Hydractinia, to Millepora, Allopora, Stylaster and
Cryptohelia, all the phases in the grouping of a certain number of
dactylomerids around a gastromerid, analogous to that which has
given rise to the medusae. But here the gastromerid, instead of
remaining independent in the centre of its ring of dactylomerids
attaches itself to them throughout its whole length and com-
municates with them by means of corresponding longitudinal
slits. It loses its tentacles, which are replaced by dactylomerids.
The whole forms a coralozooid achieved by a mechanism analogous
to that which produced the dialypetalous flowers with inferior
ovaries.

1 XLIII, 640.

PRIMITIVE ANIMAL FORMS 121

The Sea-anemones of our coasts are coralozooids that have
lost the faculty of producing lime, a property that permitted
the other coral-building organisms to play a tremendous part
during the Geological Periods, and which still makes them
important agents in modifying tropical coasts. In the present
state of almost all coralozoids, the dactylomerids associated
with the gastromerid number either six or a multiple of six.
This number may remain fixed or may augment during the
animal's life. The phenomena of embryogenetic acceleration
which I have discussed elsewhere,1 show how the Madrepore
corals constructed on the sextuple type were able to give rise to
the Coral and to animals which form with them the order
Alcyonaria. These animals appear at a first glance to be
Madrepora constructed on the eightfold type, but in reality
they are quite different.

From the point of view of the history of the development of
life on earth, we will draw from the foregoing these few con-
clusions only : alongside of the Sponges and the Bryozoa, which
appear to have but little plasticity, the Polyps were very
rapidly evolved ; obviously their primitive forms can only
have been Hydromedusae, but from these arose simultaneously
the parallel forms Acalephas and Corals. Although actually
free, the Acalephas must have appeared originally in sedentary
forms, which developed by branching. They acquired their
liberty secondarily, and only, as we have seen, through the
agency of tachygenesis.

While these organisms were evolving from the fixed merids
others were developing from the free merids. These last appear
to have belonged exclusively to the type provided with a general
cavity, which when they attached themselves to some
object, gave rise to the Bryozoa. There was no reason why
the preservation of their liberty should have deprived them of
their faculty of budding. Locomotion, however, is a factor
which has completely modified the conditions of evolution.
In fact, when the initial merid remained free and moved about,
its weight, locomotion, and the conditions of its search for food,
compelled it to abandon a form symmetrical upon one axis, such
as it could have retained if it had always swum suspended
in the water, and take on a form symmetrical to a single plane.

1 XLIII, 753.

122 PRIMITIVE FORMS OF LIFE

In order to succeed in remaining without too much effort between
two layers of water, it was obliged to possess the same weight as
the water it displaced ; and its constituent substances had to be
carefully distributed so as to give it this quality, as some of
them were heavier than water, and others, such as the fats, were
lighter. But this could only happen in exceptional cases. If
it were lighter than water, it would be drawn towards the
surface and exposed to all sorts of accidents. Hence the heavier
forms which were naturally drawn towards the bottom of the
sea had the richest potentialities for the future. Under these
conditions the merid continued to elongate in the direction of
its trajectory. The end which went first and which had to
explore the ground to which the rest of the body had to be com-
mitted, became differentiated from the posterior. Its constituent
parts acquired a greater and greater sensibility, and a fair
number were transformed into nervous elements, distributed
along the exploratory tentacles or grouped together to form
eyes. A little behind the latter came the mouth, naturally
preceded by the exploratory region. The animal, probably
by virtue of a tactile sense, without which it would have been
unable to live, forced this mouth toward the ground on which
it crawled in its search for food. Thus, the mouth became a
feature of the ventral side, which was, moreover, flattened
by its own pressure against the ground, light as this must have
been. As the ventral side and the whole periphery of the mouth
were thus constantly stimulated by contact with the earth, the
development of numerous sensitive cells within this area
finally produced around the latter a ring of nerve tissue, and
on the ventral side a similar strand. Little by little — in
certain embryos, indeed, all the stages of this phenomenon
can be followed — the nerve cells became isolated from the
epidermis of which they had at first formed part, and
eventually came to constitute in the adult creature, the
pharyngeal collar, and the nerve-chain, which is found in a more
or less modified form in all Arthropods, Annelid Worms,
Echinoderms, and Molluscs.

Locomotion has had even more influence on the final
evolution of the mobile protomerids than on their forms. The
same reason that determined the evolution of the fixed merids by
budding, holds good throughout for the free merids, except that
in the latter the buds would not be arranged in the same way.

PRIMITIVE ANIMAL FORMS 123

It is evident that a branched organism would be greatly ham-
pered in its attempts to move backwards, all its branches being
brushed back in front of its head. Forward movement would
result in bending back these branches against the body, and
thus prepare for their fusion. There is no reason why these
appendages pressed against the body should have been raised
from its surface, or spread out laterally, unless they could have
been used in locomotion, like the appendages of the Arthropods.
In this case they were only necessary because a rigid covering
of chitin around the animal's body prevents it from swimming
or crawling by means of undulatory movements. The budding
therefore is localized at the posterior part of the body,
relatively inactive and younger, and formed of non-specialized
cells. The new buds are arranged in a straight line behind the
old ones, all together forming a body made up in this way of
segments placed end to end. The posterior end of the body
of the embryo is always completely formed at an early stage
by a special segment, constituting a veritable rearguard of
sensitive tissue adapted to protect the young animal from
contacts to which it may be subjected.

This last segment or telson is always the second one to form ;
the others develop immediately in relation to it, so that the
youngest segment of the body is always the one before the
last. This short description suffices to give us the basis of the
embryogeny of all animals with segmented bodies : Arthropods,
Annelid Worms, and even Vertebrates. In the latter the body
segments, whose bounds are marked by the vertebrae, are also
formed one by one at the back of the body, progressing from
a terminal region corresponding to the telson.

The essential characters of the evolution of segmented
animals are thus outlined. At the beginning of their existence
they consisted of a single segment, which, from its constitution,
has been capable of budding at the posterior extremity, so that
the formation of segmented animals has been very precocious and
rapid. It is possible that the merids that gave rise to them were
originally similar, and that their integument was formed
externally of a layer of cells with vibratile cilia ; but this
initial type was soon resolved into two others. In one, the
superficial cells produced a solid coat,1 thick enough to glue the

1 Composed of a special substance of a horny consistency, called chitin,
derived from cellulose by the substitution, for one or more atoms of hydrogen,
of a nitrogen radical.

124 PRIMITIVE FORMS OF LIFE

vibratile cilia together, and cause them to disappear; in the
other, the vibratile cilia, arranged like fleece or in a ring, per-
sisted, and formed the primitive organs of locomotion. Failing
them, the merids of the first type were obliged to propel themselves
by means of lateral buds moved by muscles and provided with
rigid filaments, which developed into feet. From this type
arose the long series of Arthropod forms. The ciliated type
produced the series of Annelid Worms, which share with the
Arthropods all these characters of organization resulting from
their powers of locomotion ; Cuvier had already united the
two in order to form his group of Articulata. However, the
two series differ entirely in all those qualities entailed by the
absence of vibratile cilia ; they have evolved separately on
parallel lines, with no bond of relationship between them.

Embryogeny gives us some idea of what these primitive
merids may have been. All the Crustaceans of the large
sub-class Entomostraca, however complicated they may be,
are born in the form of small organisms, called nauplii, with
only three or even two pairs of appendages surrounding the
mouth. These serve, primarily, as swimming organs, but at the
same time they hold prey by means of hooks borne by their
proximal joint. These appendages, after having been employed
simultaneously as legs at their free end, and as jaws at their
base, develop into the two pairs of antennae and the mandibules
of the adult. Various species of higher Crustaceans have
continued to hatch out at the nauplius stage, notably the
large edible prawns1 found along the Mediterranean coast.
The embryogeny of certain fossil Trilobites of the Primary
Epoch has also been reconstructed. The species of Sao, for
instance, were born with only three segments, the others
being formed successively in front of the telson.

At birth the free marine Annelid Worms whose bodies are
not divided into distinct regions, and which have been called
Annelida Errantia, appear with a still simpler form, which,
strictly speaking, represents only the first segment of the adult
animal and the telson ; this is the trochosphere, an ovid body,
barred with two rings of vibratile cilia between which lies the
mouth.

Starting from these initial stages we can follow, in the two
series of Arthropods and Vermes, every step by which an

1 Penaeus scaramota.

PRIMITIVE ANIMAL FORMS 125

increasing embryogenetic acceleration, favoured by the
accumulation within the eggs of a larger and larger amount
of reserve nutritive material, leads to the higher forms that
develop entirely within the egg. These creatures hatch out
with all the segments they will ever have, and often in their per-
manent form. This is the necessary preliminary condition which
alone has permitted the realization of organisms capable of
living in fresh water, or on the earth, and hence of breathing air.
The two series of free and segmented animals have evolved
naturally at the same time as the Algae, the Sponges, the
Polyps and the Bryozoa. We may assume that from the
beginning the waters were peopled with the most diverse
forms, which could vary in many ways, according to circum-
stances, because they were not under the domination of
heredity and because, on the other hand, the struggle for
existence was not very intense and the mere ability to keep
alive sufficed to perpetuate their stock. All that was possible
was attained. It is due to this easy stage in the struggle
for existence that certain deformations, apparently dis-
advantageous, of primitive types have occurred and given rise
to forms which appear almost monstrous, but which, never-
theless, have managed to occupy a most important place in
nature. As from the point of view of locomotion, there are
only two kinds of existence, immobility, which means attach-
ment to some foreign body, and mobility we might suppose
that there should be only two types of structure for animals,
the branched type, linked with immobility, and the
segmented, linked with locomotion. There are, however, four
others : (1) the Echinoderms, radiate without being fixed ;
(2) the Molluscs, non-segmented, and often found in spiral or
helicoidal form ; (3) the Tunicates, fixed or swimming, but
unsegmented and non-radiate. This last is a regressive type, due
to degeneration following upon fixation to the earth of already
highly organized animals, and which were nothing less than
the precursors of the Vertebrates. Of these precursors
Amphioxus is the last representative ; (4) Finally we have the
Vertebrates, truly segmented, but with an internal structure
apparently quite different from the expected and theoretical
structure of segmented animals. Our task now is to find out
how such organisms were enabled to develop.

CHAPTER V

Attitudinal Changes and Structural Modifications

T X 7HEN in my book, Les Colonies animates et la formation
» » ^s organismes, I attempted to explain how the different
types of the Animal Kingdom had been evolved, it was not
difficult for me after having given a history of the branched and
segmented animals, to show, as other authors had pointed out
for each group in particular, that the Annelid Worms, in all
probability, were the progenitors of the Echinoderms, Molluscs,
Vertebrates, and, in consequence, of the degenerate derivatives
of the latter, the Tunicates. But although I had at that time
already pointed out the importance of tachygenesis, I had not
as yet realized the full consequences of this mode of hereditary
action, nor had I perceived one particularly powerful cause for
the modification of organisms, namely, the changes of posture
that have taken place in each species in the course of ages.

To convince ourselves of the reality of these changes, we
need but cast our eye over the existing series of living forms.
Among the Crustaceans, A pus and other Branchiopods swim
with their ventral side uppermost and their dorsal side down-
wards ; the same is true of Notonectes among the Insects, and
its name indicates this position ; among the Cirripedes, Lepas
and its allies suspend themselves from floating objects by their
head, which is drawn out into a long peduncle ; while forms like
Badanus, closely related to them, obliterate, so to speak, this
same extremity against the rocks to which they closely adhere.
In the subdivisions of the Tunicates we observe the same
contrast between Boltenia and the other Ascidiacea, while the
Tunicates that have reverted to swimming retain the
normal position. Among the Echinoderms the common
sea-urchin has its mouth below and the anus above,
so that the five radial areas, bearing their organs of
locomotion, are erected vertically like the petals of a flower,
all five arising from the mouth and capable of reaching the
orifice opposite. But there are some species which dig cease-

STRUCTURAL MODIFICATIONS

127

lessly in the sand, and in these the lower region of the body be-
comes flattened to form a ventral side, while the mouth advances
gradually towards the edge of this surface that the animal keeps
habitually in front. Above this, one of the ambulacral areas,
which has become the anterior one, moves up to the top
of the body, round which the other four ambulacral areas,
now become lateral, continue to converge ; the anus leaves
the top for a definitely posterior position, and finally reaches
the region of the edge of the flattened lower surface, which
thus forms a ventral side situated between the two lateral
ambulacral areas that are furthest away from the anterior one.
The Holothurians, or sea-cucumbers are Echinoderms closely
akin to the Sea-urchins, but the body is elongated like a
sausage instead of being globular. They often live in the crevices
of rocks ; they can only maintain themselves on the ground in
a recumbent posture, the openings of the digestive tube each
occupying one end of the body. A certain number of littoral
species, however, crawl on the sea-bottom ; they then acquire a
flattened ventral side always divided by one of the radial loco-
motor areas into two symmetrical halves and bounded by two
lateral ones. Exactly the reverse condition is found among the
Sea-urchins, where the ventral side has no median radial area
while the dorsal side has. The mechanism of the formation of
the ventral side, however, is quite different in both cases. The
Holothurians with ventral sides behave in two ways. Those
inhabiting great depths live on mud ; they direct the mouth
towards the earth by sharply bending the anterior extremity
of the body. At first temporary, this bending becomes later
permanent, and subsequently disappeared, the mouth finally
becoming definitely ventral. Those attached to rocks, on the
contrary, draw their nourishment from the surrounding water,
and their mouth becomes dorsal (Psoitis). Moreover, certain
Holothurians always live buried in sand ; some remain
elongated vertically,1 while others curve their body into a
U so as to bring their anus to the surface and evacuate their
excrement without soiling the sand. This attitude, at first
temporary,2 also becomes fixed,3 so that the two ends of the body

1 Molpadia, Ankyroderma, Synapta.

2 Certain Cucumarics.

3 Ypsiloth aria.

128 PRIMITIVE FORMS OF LIFE

approach one another more and more, and eventually fuse in a
single tube pierced above by two openings. The Holothurian
thus takes on the shape of a bottle, whose neck carries the
two digestive openings that have now become contiguous.1

The Mollusca are at least as accommodating so far as posture
is concerned. The molluscs with spiral or helicoidal shells
crawl on their ventral surface ; but all those capable of
swimming, even if only temporarily, swim upside down, the
abdomen uppermost and the back below. Some molluscs,
indeed, are exclusively swimmers ; 2 others exclusively crawlers,
and others swim or crawl, according to circumstances.

The molluscs with bivalve shells have aptitudes even more
varied. Mussels, and those molluscs akin to them, suspend
themselves by filaments which constitute the byssus ; the
Oysters, Pecten, Spondylus, etc., live resting on their sides ;
Tridacnae live on their backs on the polypary ; Venus,
Razor-shells, Pholades, and a host of others, bury them-
selves in the sand or penetrate into holes which they
hollow out even in rock, and live immobile, the head, or
what takes its place, being furthest in. A special form
of body corresponds to each of these attitudes, which is easily
accounted for by the continuous action of weight upon the
various internal parts of the immobile creatures. The body of
the mussel enlarges in the region turned downwards,
and becomes pointed in the neighbourhood of attachment of
the byssus ; the lower valve of oysters and other bivalves
that lie on their sides, originally symmetrical with the upper
valve, swells so as to form a sort of chamber, of which the
upper valve, flattened to concavity, is nothing more than a
cover ; the heavier organs of Tridacna sink below the
lighter, and reach almost to the hinge of the shell, so that the
mollusc appears doubled up inside it. In the species that
immobilize themselves in holes, the thick lime-secreting
mantle becomes elongated into two long siphons, one for
the entrance of the water which brings the animal air and food,
and the other for evacuation. These modifications, with the
exception of the last, have been brought about by the persistent
action of a most ordinary cause, namely weight pressure, which

1 Rhopalodina (LIV, 280).

2 Nautilus, Pteropods, Ianthina, and the larvae of all the marine Gasteropod
Molluscs.

STRUCTURAL MODIFICATIONS 129

is also responsible for forming the ventral surface of the
bilateral Echinoids and the deep-sea Holothurians.

Neither have the Vertebrates escaped attitudinal changes.
Amphioxits, the soles, turbots, dabs, and other flat-fish classed
as Pleuronectids, remain on their sides. They therefore become
d^s-symmetrical (much like the molluscs that live under the
same conditions) , and carry their two eyes on the same side of
their body. The Echeneididae attach themselves to sharks, press-
ing against the body of their hosts their dorsal surface, which
thus functions as the ventral surface of other animals with
respect to light and the soil. The dorsal surface becomes
discoloured and flattened, while the ventral side takes on the
characteristic of the ordinary dorsal surface. The influence of
external conditions on form and colour is thus clearly shown.

This influence is seen to operate unceasingly directly we make
any attempt to correlate animal characteristics with the con-
ditions in which they live, rather than considering them apart
from all the causes which, with any degree of plausibility, can
be invoked to explain their existence — as if they were the result
of some miracle. Let me give some examples. The links
which unite the main divisions of the Fishes x can be summed up
in this one. proposition : The branchial region, situated
between the head, to which the water offers resistance when
the fish swims, and the body, which is pushed forward by the
sudden propulsions of the tail, is progressively shortened
till it finally becomes atrophied in the Batrachians, their
descendants. Among the terrestrial vertebrates a neck,
which may be enormously elongated, takes the place of the
branchial region that has disappeared ; but when these
vertebrates again become aquatic and swim after the manner
of fishes, their neck, placed in the same mechanical conditions,
undergoes the same reduction, whether we take Reptiles like
Ichthyosaurus of the Secondary Epoch ; the Herbivora that
have become aquatic, like the Sea-cows and Dugongs ; Seals
that have become divers like the Zeuglodonts, or Cetaceans
which are probably descended from another stock. This
repetition of like phenomena, under like conditions, among
different Vertebrates, which, moreover, have preserved the
characteristic organization of their group, illustrates well how
these phenomena have been due to external actions modifying

1 XLIII, 2469.

K

130 PRIMITIVE FORMS OF LIFE

the parts of the body directly subjected to their influence and
not affecting other parts ; which is equivalent to saying that
these external actions are the causes of the modifications which
are correlated with them. This correlation is found in an
infinite number of cases. The legs of the swimming Arthropods,
for instance, which move them about only by thrusting
against the water, are flattened and acquire a fringe of
long hairs ; a web appears between the toes of the foot in all
walking Vertebrates, that return to the water, whatever the
type to which they belong : tailless batrachians, crocodiles,
pond and marsh tortoises, web-footed birds, Omithorhynchus,
desman, musk-rat, beaver, mink, otters, seals, etc. In all the
groups of climbing vertebrates which press their abdomen
against the trunks of trees, we likewise find species that
have lateral skin-folds running down on to their limbs in such
a way as to reach as far as the digits. This condition is
reproduced in Petaurus, among the Marsupials, in the lemur
Microcebes, in the insectivorous Galiopithicus, Pteromys
sibericus, and in the squirrel Anomaturus ; and in reptiles
that lead up to the flying dragons, such as Stychozoon and
Uroplatus. This condition prepared the way for the wings of
the Pterodactyles or Flying Reptiles of the Secondary Epoch,
and for mammals like the bats.

Certainly the kind of life led does not suffice to bring about
this transformation. Otherwise all climbing animals, for
example, would have acquired parachutes. Certain organic
conditions are also required which we as yet cannot define,
or perhaps a minimum degree of frequency in the repetition of
the same acts permiting the modifying forces to assert them-
selves with especial intensity, or the regular co-operation
maybe of many of these forces acting simultaneously. At all
events, the correlation is too frequent for us to believe that it
is independent of a causal factor.

An explanation of this correlation has been attempted by
appealing to what have been called pre-adaptations. New
characters make their appearance without our being able to
assign a reason ; they would be cryptogerous, as geologists
say of species that suddenly make their appearance in
certain geological layers, without it being possible to discover
for the moment whence the}r have come. Throw-backs due to
heredity, unknown modifications of the internal environment,

STRUCTURAL MODIFICATIONS 131

and various external actions whose influence it has not been
possible to determine — all of these may give rise to new
characters without their being of any immediate utility, but
once present, the animal, which at first had only to exercise
them, will make use of them as soon as it discovers how
to do so.

Thanks only to these new characters, which appear to have
resulted from the new conditions of its existence, the animal
was able to profit by the changed conditions. These pre-
adaptations are real, and it is due to them that natural selection,
which results from the struggle for existence, was so efficacious,
and it is they that have given Darwin's theory its whole value.
We must not conclude from this that the conditions of existence
or of development do not encourage the appearance of new
characters in harmony with them, either directly or through
their reactions on the animal. Often, on the contrary, pre-
adaptations and adaptations overlap. This is what has
happened to the Birds. Their feathers were not meant for
flying, but were at first merely tegumentary overlapping
excrescences, doubtless irregularly branched ; these branches
because of the deterioration resulting from the mode of super-
position, ended by developing laterally only ; thus those of
the wings and the tail were utilizable for support in the air.
The foot of the Bird, on the contrary, everywhere bears witness
to its will to stand erect on its hind limbs, which it straightens
by aid of its muscles to the point of using its toes only as
supports. The great toe ends by no longer touching the ground ;
it becomes atrophied, but is still represented by the spur of
cocks. Those muscles which extend from the pelvis to the
thigh and maintain the body erect, having extra work to
accomplish, increase in size, and cause considerable growth of
the pelvic bones, which invade more and more of the vertebral
region both behind and in front of the hip-joint socket. Here
we have an evident triumph of the Lamarckian principle of
the influence of use and disuse of organs, a principle alien to
the origin of the feathers, if not to the determination of their
final form. None of these characters were developed with a
view to flight ; it was simply a matter of co-ordination of bones
and muscles favourable to the biped posture and to hopping,
as is proved by the Iguanodons and other herbivorous bird-
legged Reptiles of the Secondary Period, or Compsognathus,

132 PRIMITIVE FORMS OF LIFE

another and carnivorous group of Reptiles of the same Period,
called Theropods. Many of these animals had bones which were
hollow or penetrated by the diverticula of the air-spaces
which are now peculiar to Birds, so that the respiratory
apparatus itself, so long considered as destined to obtain for the
bird the energy required for flight, is seen to have had no
original connexion with this special method of locomotion.
None of the characters that class an organism as a bird were
assembled for its present peculiar mode of life ; the feathers
arose from the multiplication of the cells of the epidermis
and their faculty of producing abundantly a horny substance ;
the conformation of their hind legs results from the advantage
the beast found in standing erect upon them and in hopping,
and the augmentation of activity it developed for this purpose
reacted upon the respiratory apparatus. Thus far, it might seem
that the animal was a kind of patchwork ; but once these
characters were all united, the Reptile, having become a
hopping creature making use of its feathered front limbs
as parachutes, was able to support itself in the air, as, by
different methods, the Insects and the Pterodactyls had
succeeded in doing, and as the Flying Fishes and the Bats
succeeded in doing later. Thus, from the fortuitous reunion
of a set of characters and organic arrangements, developed
without any end in view, or, at least, with an end other than
that of flight, the Bird subsequently perfected itself through
the exercise of these characters. We must, then, guard against
the belief that a single category of causal factors, a single
process, or a single method has sufficed to create the diverse
forms of living creatures, and that any one theory can account
for their evolution. All these living forms that surround us
are the result of a gargantuan conflict of forces and substances,
greater even than what we call the struggle for existence —
a conflict compared with which the history of peoples and races,
complex as it appears to us, is but a picture seen through a
diminishing glass. Nor must we forget that even in the case of
what are called pre-adaptations, the animal can only profit
by the new characters it has acquired by using its muscles and
its nervous system in a new way. It depends on itself whether
it makes the best use of these various features of its organization.
Adaptation to environment, initiated before its own volition
comes into play, is finally achieved only by this volition,

STRUCTURAL MODIFICATIONS 133

and obliges the organs to change their function. These changes
of function are frequent in the animal kingdom. Anton Dohrn,
the founder of the famous Aquarium at Naples, called attention
to these in an admirable series of memoirs.1 Flying fishes make
use in flight of anterior fins developed originally for
swimming ; the abdominal and anal fins of Gobins, Liparis
and Lepadogaster are transformed into suckers to facilitate
fixation ; the anterior part of the dorsal fin becomes a fixed
cephalic sucker among the Echeneididae ; Savigny has shown
how largely the buccal appendages of Insects can be modified,
according to the very varied food of these creatures ; the anal
terebra, serving as the ovipositor of Hymenoptera with
phytophagous or entomophagous larvae, becomes the defensive
sting of Bees, Wasps, and Ants ; the mouth of the Vertebrates
is a former branchial slit, etc. We might almost say that all
comparative anatomy is but an account of similar changes
of function — the very opposite of pre-adaptations. No more
than pre-adaptations can these explain everything, and with
them they merely furnish a basis, still too narrow, for a complete
theory of organic transformations. But if we bear these facts in
mind we shall be better able to recognize the determining causes
of those persistent characters which are found in all animals
of the same group, and lend to each group a special
physiognomy. To go back to their original cause, it will suffice
to call to our aid the fundamental principles of embryogeny
described in an earlier chapter. Let us first see how the
Echinoderm type was arrived at, whose larva} are free, or are
only fixed at a late stage, and which yet produce organisms
definitely radiate, i.e. ramifie, a phenomenon that at first
sight appears contrary to the laws that have determined the
two main types of animal structure.

Dominating the almost infinite variety that armogenesis
and tachygenesis together have imposed upon the embryonic
forms of Star-fishes, Sea-urchins, Holothurians, and Crinoids
forming the phylum of the Echinodermata, certain constant
characters appear that are essentially patrogonic, that is to
sa}', representing phases of the phylogenetic evolution of the
ancestors of the present Echinoderms. Whatever be the
external form taken by these embryos, they first present at
their birth a distinct bilateral symmetry. Their dorsal convex

1 LXVIII.

134 PRIMITIVE FORMS OF LIFE

surface is more developed than their ventral concave surface,
so that they might be regarded as curved like a C. Bands of
vibratile cilia, originally arranged round them in a girdle, as
in the larvae of the Synaptidae and the Crinoids, but deformed
by the excessive growth of certain parts of the embryo,
particularly the dorsal surface, divide the body into five
segments, whence the term pentatrochal applied to these larvae.
If the organism remained in this condition there would be no
hesitation about including it among the Annelid Worms.
Soon, however, calcareous spicules appear in its tissues, and at
the same time the internal organs become dissymmetrical ;
those of the side which develops most rapidly present the
characteristic feature of rolling up in a spiral. Shortly after
the appearance of calcareous spicules in the tissues, the young
organism, grown in weight, ceases to swim and falls to the sea-
bottom, and there its posture is steadily modified, the left and
right sides becoming respectively the ventral and dorsal
aspect of the adult animal. If we take these constant develop-
mental phases of the Echinoderms as patrogonic in origin —
and to do otherwise is to deprive embryogeny of all significance
■ — the phylogenetic history of these animals appears to be as
follows. Their ancestral form was that of a short Annelid Worm,
reduced to rive segments, whose body, merely because of its
muscular tonus, became curved into a C like the majority of
segmented animals in their fixed state.1 This worm originally
a swimmer, secreted lime, which was deposited in the form of
spicules in its tissues, thus gradually increasing its weight.
It finally fell to the bottom, and, having become rigid and
incapable of recovering its position, owing to this development
of spicules, so, because of its curvature, it remained lying on
its side. Thenceforward it became dissymmetrical, like the
larvae of Amphioxus and the Tunicates, and the Pleuronectoid
Fishes, which have changed similarly. But an animal lying on
its side is unfavourably situated for securing nourishment, for
it is particularly on the floor of the sea that the food it requires
must be sought. It is therefore forced to bring its mouth to the
floor, using for this purpose all the muscles at its disposal.
Guided by what Lamarck called the sentiment of need or of

1 Woodlice and other Isopod or Amphipod crustaceans ; the larvae of
Cockchafers among the Arthropods ; Aphrodite and other crawling Annelid
Worms with short bodies and ventral surfaces with strong muscles.

STRUCTURAL MODIFICATIONS 135

well-being, which to-day we tend to replace by what we call
tacticism, it disposes its anus as far as possible from its mouth ;
it will thus reach that stage of coiling into a helix, with whose
phases we are familiar in its embryogeny. Except that they are
fixed, certain Crinoids of the Primary Period, e.g. Agelacrinus,
seem to have been arrested at this stage of their development.
The causes limiting budding to the posterior region of the
body in mobile animals, and operative in the case of the Annelid
Worms, are here absent. Any segment of the body can produce
a series of buds that first share the linear arrangement of the
parent, but subsequently can also become ramified [Astrophyton
and other Ophiuroids that attach themselves to polyparies, also
Pentacrinoids and Comatulides) . It is in this manner that Starfish
originated, which go back to the most remote antiquity, and it is
easy to derive all the other Echinoderms from them by reference
to simple embryogenetic considerations. I have shown 1 that
among the Starfish, Brisinga still has its arms regularly
segmented ; that the new segments form directly in front of
the oldest segment, represented by the radial disc plate of the
embryo as in the case of Annelid Worms, and that all the
transitions between this type that therefore appears primitive
and the pentagonal Starfish, so far removed from it, such as
the Culcites and Pent agon aster, can be followed. After the
metamorphosis resulting from their pleuronectean attitude,
all the Echinoderms pass through a common embryonic phase.
What was formerly the right side, and has become the dorsal
surface, takes on a radiate structure characterized by the
presence of a central calcareous plate, surrounded by five
similar plates called basals, followed by five others alternating
with them, called radials. The former left side, now the ventral
surface, is rayed in the same way, but each ray is essentially
composed of a double series of plates, called ambulacra! plates,
connected with tentacles or tube-feet. According to the
special fashion in which the calcareous plates multiply,
starting from this common embryonic form, all the various
classes of the Echinodermata have been derived. This
multiplication is almost non-existent in the Blastoids which
have to-day disappeared. Among the Starfish and the
Ophiuroids new plates are formed between all the dorsal
plates, particularly between the basal and radial ones. They

1 XLI.

136 PRIMITIVE FORMS OF LIFE

are thus constantly being forced outwards, and five arms are
formed behind them, the ventral surface following step by
step the growth of the dorsal surface. Among the Sea-urchins
new plates are not formed between the dorsal ones, which
remain united around the anus, but the ventral surface under-
goes a rapid growth, so that the animal swells like a soap-
bubble suspended from the pipe by which it is blown. The
Holothurians are scarcely more than Sea-urchins whose
skeleton has become reduced to spicules. Among the Crinoids
the primitive plates remain united as in the case of the Sea-
urchins, but between the centro-dorsal and the basal plates
there is formed a layer of plates in the shape of a long peduncle,
by means of which the animal fixes itself. The ventral face
is not developed, but outside the radials, which remain united
to the basals, under the stimulus of the genital organs there
occurs an active budding which gives rise to five arms that
may remain simple (Hyocrinus, Rhizocrinus, Democrinus,
Eudiocrinus), may bifurcate (Antedon), or ramify in various
ways. Finally, the Cystids are fixed like Crinoids, and it appears
that, contrary to what occurs in Sea-urchins, only their dorsal
surface is developed. We may once again enunciate the
proposition : all that it is possible to achieve is achieved.

The phylum of the Mollusca has developed by analogous
changes of posture. All zoologists have been struck by their
resemblances to the Worms, either at birth, when they take on a
form very like the initial form of these last, or in various organic
characters of the adult state. One class only, the Amphineura
or Chitonidae, show actual segmentation of the bod}". Two
others, the Cephalopoda and the Gastropoda, are characterized
by the transformation of their dorsal surface into a large
cone, which must have grown in opposition to gravity if
the creature's posture had always been what it is to-day. This
cone does not exist among the Lamellibranchiata ; but, as we
shall soon see, it remains characteristic of the Molluscs. It was
straight, among most of the older Molluscs, Cephalopods
(Orthoceras) and Gasteropods (species of Tentaculites,
Conidaria, Hyolites, etc.) ; it has persisted in most of the
present Cephalopods (squids and octopuses) ; it is rolled up in a
plane spiral so as to retain the primitive symmetry in the
majority of the shelled Cephalopods (Nautilidse, Goniatitidae,

STRUCTURAL MODIFICATIONS 137

Clymenididae, Ammonitidae), and among some primitive
Gasteropods (Bellcrophon) ; among others it is wound not
in a flat spiral but in a helix, thus becoming dissymmetrical,
as has also happened in the case of some of the later
Ammonites (Turrilites). What relation is there between all
these facts ?

It cannot be supposed, as we said above, that the dorsal
cone of the Cephalopods and Gasteropods was able to grow
upright on the creature's back in spite of its weight, which must
then have flattened it. We may rather suppose that these
organisms originally either floated or swam on their backs
in the water, the ventral surface uppermost, and were able
to maintain this position by some means or other of
suspension and locomotion. In this case their dorsal surface
would inevitably have yielded to the pressure of the viscera
under the influence of gravitation and to the pull of the
calcareous protective shield, when there was one on this side.
A pendent dorsal cone must thus have been formed in the water,
and it is only thus that the posture of the Cephalopods and the
primitive straight-shelled Gasteropods can be conceived. On
the other hand, it is impossible not to notice that all the present
swimming Molluscs swim on their backs with their ventral
side uppermost (species of Nautihdae, Ianthinidae, Carinaridse,
Pterotracheidae, Pteropoda), and that all the marine larvae of the
Gasteropods provided with a shell swim in the same fashion.
If, as wre have explained, ancestral forms are recapitulated
embryogenetically, here is a definite indication that the
ancestors of the present Molluscs were swimming organisms,
and swam in the inverted position still maintained in larvae,
and re-adopted by adults when they revert to life in the ocean.

The causes that have produced the coiling of the shell are
not in the least mysterious ; they were in part suggested long
ago by Arnold Lang. The gills of the Cephalopods are situated
in a cavity, within which the anus also opens, and which there-
fore corresponds to the posterior region of the body. The
organism is able to respire freely only if the opening of this
cavity is uncovered by a forward inclination of the point of
the dorsal cone. This point is then pushed back and upward,
as a result of the resistance of the water to the mollusc's
weight, but the mollusc is propelled forward by suddenly
expelling the water contained in the branchial cavity ; the

138 PRIMITIVE FORMS OF LIFE

reaction of the water thus expelled pushes it forward, and the
resistance of the sea-water again intervenes to force backwards
the point of the cone, which is then pulled downwards by
gravity. All these co-ordinated actions, added to the phenomena
of growth, inevitably determine the coiling of the shell in a
spiral form, the opening being directed backward and the
coiled part forward, as is seen in Nautilus.

This is also the form of coiling found in the young shell of
the oldest Gastropods (species of Fissurella, Trochus, etc.), from
which we may conclude that their gills were primitively posterior.
These Gasteropods, like the Cephalopods (Bellerophon), were
originally swimming organisms, and were also obliged to coil
their shell forwards. The pressure of the water against the
shell carried thus forwards and spirally wound sufficed then to
keep the posterior branchial aperture open. Later, however, these
molluscs become crawlers (species of Pleurotomariidse, Fissurel-
lidae, Haliotidse, Trochidae, Turbo, etc.), and once more had to
apply the ventral aspect to the ground surface. The forward-
directed shell then became directed backwards, as a result of
crawling, and again masked the branchial aperture. Lang1 has
shown how the Gasteropods got out of the difficulty by con-
tracting one half of the body, so as to turn the branchial
cavity to the front, and Robert 2 has been able to trace the
phases of this rotation in the larvae of Trochus. The almost
permanent contraction of one half of the body has gradually
induced a shortening and then a partial abortion of this half ;
the spiral coiling of the cone thus became dissymmetrical, and
was replaced by a corkscrew formation. The torsion into a
figure 8 of the nerve cord, from which the visceral nerves are
derived, is at once a result and a proof of the displacement
of the branchial cavity.

How is it that the bivalve Mollusca, of which the Oysters are
typical, escaped both the dorsal cone and the coiling which
would be its natural sequel ? The method we have just followed
will provide the explanation. Being without any embarrassing
dorsal cone, those Molluscs, like the Oysters, which do not lie
on their sides, are strictly symmetrical, but it is not difficult
to discover the nature of their affinities with the other molluscs.
The primitive Gasteropods, in fact, present some peculiar
structural characters. The heart possesses two auricles, and
1 XLIV. 2 XL VI, 201.

STRUCTURAL MODIFICATIONS 139

its ventricle is traversed by the rectum, and they have two
bipectinate gills. These special characters are found again in
the Lamellibranchs, which ought, in consequence, to be
regarded as related to the older Gasteropods called Diotocardiac,
because of the two auricles with which their heart is provided.
As a matter of fact, all the present Diotocardiacs are dis-
symmetrical ; the most primitive of them all, the Pleuroto-
mariidce, the Fissurellidae, Haliotidae, and a few others have
retained as a common character the most manifest traces of
bilateral symmetry ; the anterior edge of the opening of their
shell is either deeply divided or curved inwards, at any rate, in
the young ; the slit may persist (species of Pleurotomaria,
Emarginula) and give rise to a series of holes arranged in a
helicoid line (Haliotis), or to an opening situated at the apex
of the shell, which is then in the form of an elliptical cone
(Fissurella). However, this slit, which indicates a division of
the mantle into two lobes, each connected with the two gills,
is also found, arranged according to the symmetrical plane of
the shell, in Bellerophon of the earliest Primary Period, now
extinct. There can be no doubt that these organisms were
diotocardiac Gasteropods, which, like the Cephalopods, all
swimmers, had preserved a perfect bilateral symmetry. But
for our purpose it is enough that organisms analogous to
Bellerophon, in the course of their pelagic life, gradually
re-absorbed their dorsal cone, and that the initial slit became
extended along the whole length of the plane of symmetry
in order that the shell should become bivalve. The play of the
muscles in closing the two valves of the shell compressed the
mollusc, which, having lost its dorsal cone, was able to crawl,
like the Solenmyidae, without any alteration of its bilateral
symmetry. The disappearance of the dorsal cone, moreover,
is a frequent phenomenon among the crawling Gasteropods,
and occurs in the most varied orders of this group ; it is, for
instance, complete in the Fissullidae, which are diotocardiac,
the Patellidae, which are heterocardiac, the Valvatidae, which
are monocardiac, the Limacidae and the Vaginulidae, which are
pulmonate, and among a large number of Opisthobranchs.
To suppose that it had disappeared among Molluscs analogous
to Bellerophon is therefore only to base our hypothesis on quite
a common phenomenon.

Thus the three main classes of Molluscs are easily explained.

140 PRIMITIVE FORMS OF LIFE

It remains to be seen how the molluscan type originated from
a transformation of a more easily explicable type. We have
already pointed out the transitional characters of the
Amphineura, of which the Chitons represent the common type,
and whose back is protected by eight calcified plates essentially
similar one to another, the shell-plates or "valves ", revealing a
segmentation of the body. It is the less possible to escape this
interpretation in that the valves are not a simple covering,
dead and calcareous like the shell, but are rather living
differentiations of the integument of which they form an
integral part, traversed by nerves, and the seat of sensitive
organs which may become eyes and which are repeated regularly
in the same place on all the valves. It is then quite clear that
the integument of the Chitons is segmented like that of the
Worms ; incomplete partitions even separate these segments
inside the body, where similar organs are encountered in all
segments thus divided. It must therefore be admitted that the
Oscabrians are closely akin to the Annelid Worms whose origin
we have already described. Their nervous system has been
studied in detail ; it is the nervous system of the Worm very
little modified, and this confirms our conclusion. The nervous
system of the Pleurotoma and the Fissurella has also
been carefully studied and described by Bouvier and Fischer.1
With the exception of those portions correlated with the dorsal
cone or superposed portion of the t jdy, their nervous system
is identical with that of the Chitons. Cuvier has said : at
bottom, the nervous system is the animal ; the close relationship
of the Chitons and the diotocardiac Gasteropods, which
their external form does not suggest, is here quite patent.
This, then, is the link showing how the Molluscs deviated from
the Annelid Worms. The nervous system of Nautilus, studied
by Gravier, brings further support to the assertion, for it is
manifestly formed of two rings united in front, instead of two
longitudinal cords. It could, however, hardly be otherwise,
seeing that the ventral surface of the Cephalopods, which
corresponds to the feet of the Gasteropods, is reduced to the
space between the mouth and the anus, that is to say, the
periphery of the mouth itself.

We come finally to the higher animals, to those in which

1 XL VIII, 117-272.

STRUCTURAL MODIFICATIONS 141

organization has attained the greatest development, namely
the Vertebrates, to which man himself belongs. The body
remains symmetrical. The structure of the vertebral column,
even the arrangement of the muscles in the body-walls —
especially among Fishes and Batrachians — of the nerves,
blood-vessels, and lateral sense-organs in the aquatic Verte-
brates, of the renal ducts in those Vertebrates provided with
gills at birth, and of the embryos of those where these organs
are vestigial and disappear before birth — all this leaves no
doubt about the relationship of the Vertebrates to segmented
animals, to which Etienne Geoffroy Saint-Hilaire,1 Semper,2
and Balfour 3 drew attention. Even in 1869, however,
de Lacaze Duthiers insisted that there was an unbridgeable
gulf between the Invertebrates and the Vertebrates. It is,
of course, true that the Vertebrates entirely lack the
characteristic arrangement of the nervous system found in all
Invertebrates in which a nervous system is differentiated,
— the ganglionic ring surrounding the beginning of the
oesophagus ; furthermore, while the nerve-chain which, in
Invertebrates, is usually a continuation of this ring, is ventral,
the spinal cord, which seems to correspond to it among
the Vertebrates, is dorsal. Conversely, the circulatory
centre is dorsal in the segmented Invertebrates, and ventral
in the Vertebrates. Etienne Geoffroy Saint-Hilaire had already
pointed out, in 1808, that this opposition was only apparent
and that in order to make it disappear it was only necessary
to place the segmented Invertebrates back downwards and
belly upwards — that is, to reverse their attitude. But why
this reversal ? Geoffroy Saint-Hilaire limited himself to
envisaging the matter from the point of view of unity of plan
in the composition of the Animal Kingdom, and though the
idea seemed to be ingenious and even drew an anonymous
letter from the physicist Ampere raising certain difficulties,
it was soon abandoned. Yet the realitv of the inverted attitude
suggested by Geoffroy can be both demonstrated and
explained. In origin, the oesophageal ring of the segmented
animals was simply the result of a sensitive differentiation of
the epithelial cells surrounding the mouth, brought about
by the stimulating action of the food seized and swallowed by
the organism. We can follow, as we have seen (p. 122) in the

1 L. - LI. 3 LII.

142 PRIMITIVE FORMS OF LIFE

case of the Annelid Worms, all the phases of this differentiation
and of the migration of the nerve cells out of the epidermis,
from which they only separate completely by slow degrees, in
order to form an independent ring. This differentiation and
separation, which early became independent of external
excitation, and operative only through heredity, gradually
became more and more precocious following the laws of tachy-
genesis, as the nervous system assumed greater importance.
What fundamentally characterizes the Vertebrates is precisely
the large volume of the nervous system in comparison with
the rest of the body. The nervous system must accordingly be
formed very early, and this is what we find, in fact, in Amphioxus
and in the Tunicates which are degenerate forms of the same
group. In these animal organisms — and the same is true of
all the lower Vertebrates — the nervous system is formed by
a modification followed by the invagination of one complete
embryonic surface, and these phenomena long precede the
formation of the mouth. At the time when the mouth can form,
the place it ought to occupy is taken by the already far
advanced general outline of the nervous system. But at this
particular moment there is formed in Amphioxus, on one side
of the body, the first branchial slit establishing communication
between the exterior and the cavity of the future digestive
tube. The young organism makes use of it as it would make
use of the mouth it does not yet possess, but it is obliged for
that reason to lie on its side, and, like the soles, to turn this
side into a ventral surface ; like them, also, it becomes dis-
symmetrical. This dissymmetry is revealed by the encroach-
ment by the muscle segments of one side of the body across on
to the other, so that each semi-segment of one side is in advance
of the other by one half of its length ; by the localization
on the side of the body that has become dorsal, of the olfactory
pit ; and also by the formation on the same free side of the
body, of two series of branchial slits arranged in a curve, and
thus betraying the torsion that the body has had to undergo
in order to bring over to its free side the branchial slits of the
other, which the impurities of the soil would have blocked up.
The young organism at this stage swims on its side like the
Pleuronectid Fishes. Later it burrows vertically into the sand,
and since everything around it is once more symmetrical, it
proceeds to repair its dissymmetry. The series of branchial slits,

STRUCTURAL MODIFICATIONS 143

displaced by the torsion of the body, regains its position on the
side abandoned. The first branchial slit, which remained in
its original place but enormously increased in size, is gradually
masked by a fold of the integument which comes down over
it like a shutter, and only leaves free a slit along the ventral
edge. The false lateral mouth, constituted by the first branchial
slit, becomes median, but is opposite to the nervous system
instead of being situated on the same side. In order to utilize
it, the organism is forced to turn itself towards the ground,
where it must, after all, find its food. It thus converts its old
dorsal surface into a ventral surface, and vice versa. The atti-
tudinal reversal pointed out by Geoffroy Saint-Hilaire is thus.
actually observed and explained in the most primitive of the
Vertebrates, and, as we have seen, it takes place twice over.

The Vertebrates that are descended from the primitive types,
of which Amphioxus is the last remaining example, have
necessarily preserved their type, because their nervous system
has merely gone on increasing in size, and because it is the
volume of the nervous system which determined it as a natural
consequence of tachygenetic processes that have come in in its.
method of development. Dohrn has since demonstrated that
in the Lampreys and Sharks also the mouth was only a
modified branchial slit, and these animals have retained
numerous traces of dissymmetry.

We must bear in mind from now on that the Vertebrates owe
their origin to the importance assumed by the nervous system.
It is by the subsequent development of this system that they
rise above the other animals, and arrive at last at Man, whose
evolution has thus been dominated by the rapid progress of
the organs in which intelligence resides. Here is a theme for
philosophers and above all for metaphysicians — a theme which
could provide a field for the adjustment of doctrines hitherto
regarded as irreconcilable. I have shown elsewhere how other
characteristics of Vertebrates, such as the formation at the
expense of the endoderm of a dorsal cord round which the
vertebral column develops, follow from these premisses.1

I will not here lay stress on the phenomena of degeneration

which produced the type of the Tunicates, nor the interest their

history presents, together with certain inferences to be drawn

from it. I have treated this important subject in another work 2

1 XXXVIII, 319. 2 XXVII, 358.

144 PRIMITIVE FORMS OF LIFE

in all possible detail. It is a subject 1 that has given rise to much
discussion, and has served as the basis of many and diverse
theories, having such general descriptive titles as alternating
generation, digenesis, gene agenesis , metagenesis, etc. It will be
sufficient for me to indicate that these facts are explained by-
considerations analogous to those which have here permitted
us to give the first scientific explanation ever attempted of
the formation of the great organic types which Cuvier regarded
as irreducible, and which he called " embranchements" .

To sum up, the causes that have determined the formation of
the four great branches of the Animal Kingdom, into which the
primitive organization of the Worms has been modified, can be
thus synthetized : — certain phenomena of a purely chemical
nature, such as the secretion of lime or of fat, by weighing down
or lightening the animal, or of a purely physiological order
giving to the development of the nervous system certain
advantages enabling it to advance more rapidly than the other
■organs, have determined a change of orientation in relation
to the ground. Either through some reflex action, or more or
less consciously, the animals that have undergone this change
in orientation have utilized such means as they possessed
within themselves, and especially their own muscles, to modify
their structure and bring about the greatest possible adaptation
of their organism such as it resulted from their former mode
of life, and the new conditions of existence imposed upon
them. In harmony with the general ideas of Lamarck's doctrine,
these animals have been the active agents of their own trans-
formation. For them this transformation was a period of crisis,
analogous to that which becomes so acute in insects which
undergo complete metamorphosis, and obliges them to shelter
themselves so carefully throughout its duration. They would
certainly have succumbed during this critical period if, at its
outset, their rivals had been very numerous and the struggle
for life very intense. It is therefore in an epoch when the com-
petition between them was not fierce, that is to say, very early
indeed, that these differentiations within the Animal Kingdom
must have begun. The struggle for existence which, as Darwin
showed in his celebrated books, played so important a role in
the choice of the secondary modifications characteristic of
the forms that have come down to us, and in the formation

1 XLIII, 231.

STRUCTURAL MODIFICATIONS 145

of the gaps which divide them into species thenceforth incapable
of intermingling, had nothing to do with it. On the contrary,
it would have rendered this differentiation impossible.

The causes which determined the formation of the four great
divisions resulting from these modifications, moreover, were in-
dependent of one another. Since all four sprang from theWorms,
their formation must have been simultaneous, and this enables
us to understand that, however far back we may go, these are
always to be found in association : except perhaps for a
slight delay in the appearance of the Vertebrates, which is
explained by the fact that they are the result, not of purely
chemical phenomena, but of the degree of perfection attained
by the nervous system.

These embranchements have persisted because the causes to
which they were due at first remained constant. Gradually, how-
ever, they became disengaged from these causes, and new causes,
essentially intrinsic and constituting what we call heredity,
were substituted for those that were primitively operative ;
and these hereditary determining factors are still sufficient to
perpetuate the fundamental forms they created. Later
modifying agencies have only been able to effect changes in
detail.

It was then, as we have seen, in the water, and certainly not
below the depth of four hundred metres reached by the really
useful solar rays, and particularly along the shores of seas where
all that is necessary for them in the way of food abounds, that
living forms became diversified. We must now inquire
how these forms descended to the depths of the sea and how
they came to enrich the solid earth.

.

CHAPTER VI

The Peopling of the Open Sea, the Ocean Depths, and

the Land Masses

|"F every living creature in the open sea, the ocean depths,
-*- and on the continents were to be destroyed, those
organisms still inhabiting the shore would suffice for us to
establish quite unmodified all these doctrines constituting
what is now called the zoological philosophy. It is true that
important culminating points would be missing ; Botany, reduced
to the history of the Algae and a few of the lower Fungi, would
have been greatly simplified. We should know nothing of
Arachnids, Myriapods, or Insects, and the wonderful blossoming
of lower forms into Reptiles, Birds, and Mammals would have
remained unknown. But the existing littoral forms would none
the less have furnished us with a continuous series in which each
form would have been explicable in terms of the others,
so that it would have been possible, through their comparative
study, to reconstruct the conditions essential to the evolution
of life. The fauna of the open sea and the ocean depths, and the
fauna of the solid earth, on the other hand, is full of gaps.
In the open sea, as well as along the coasts, there are, no doubt,
numerous microscopic swimming creatures which belong to
both kingdoms : the Diatoms and the minute Algae which draw
their nourishment from gases of the air and water combined
by the sunlight, and the Protozoa which live on these
microphytes. After these, however, comes a series of lacunae,
and whole classes are absent, or represented only by specially
adapted types, occasionally developed from forms normally
fixed to the ground. The Sponges are absent, and the order
of Polyps is represented only by the Medusae, in which tachy-
genesis has replaced the phase of fixation in the polyp type
by a direct development ; by Siphonophora which have
found a means of attaching themselves to an air-bubble
instead of to the ground ; and by the floating Actiniae, with

PEOPLING OF LAND AND SEA 147

their beautiful blue colour. Some of the Bryozoa also have
learnt to swim. In the Tunicates, tachygenesis has accelerated
the metamorphosis which must necessarily have followed
fixation, until the egg directly reproduces the permanent
form. A strange paradox thus appears. Three new independent
types of swimming Tunicates, Pyrosoma, Doliolum, and
Salpa, are created, in a sense, by their very immobility and
resulting degeneration. The Arthropods are represented
notably by small Copepods, which exist in countless shoals,
by Schizopods, and Squilla. Contrary to what might be
expected, the Annelid Worms, so agile when they squirm among
the Algae, furnish the pelagic fauna with few forms, which are
generally transparent and of small dimensions : Tomopteris,
Ophvyotrocha, Palolo, etc. There are also some strange open
sea Nemerteans. On the other hand, Sagitta, with its
exceedingly simple organization, entirely isolated among the
Worms, abounds at a distance from the coast. The heavy
Echinoderms are represented only by some floating
Holothurians. The Cephalopod Molluscs are essentially
creatures of the open seas, and very varied, but they are also
found along the coasts. Among the true Gasteropods on the
other hand we can cite only the Ianthinidae, the Atlantidae,
Carinariidse, and Pterotrachoididae, which have such special
characters that they form a group to themselves, the Heteropoda.
The true Gasteropods are replaced by the Pteropods, closely
related to the already aberrant Opisthobranchs among the
Gasteropods, but removed from them structurally by the
possession of swimming organs, which are very mobile and con-
sist of two flexible paddles, developed from the ' ' foot ' ' . Like the
Copepods and Sagitta, they live together in shoals. All the
pelagic Invertebrates have been more or less affected by a
curious mimetism. Their bodies, which look as though they
were inflated by water, are either transparent or coloured the
same shade as the apparently deep blue water of the open sea.
The fish naturally form a long series, but certain groups,
important from the geological view-point, are lacking. Among
these are the Lampreys, in fact the lowest of all ; and
absent also are the most primitive Bony Fishes, with pectoral
and abdominal fins far apart like those of the Sharks. Sardines,
Herrings, and Anchovies really belong to this order, but
they live too near the coasts to be considered truly pelagic.

148 PRIMITIVE FORMS OF LIFE

This fauna is completed by the turtles and the Cetaceans,
representing a special adaptation of Mammals to marine life.
It is obviously quite fragmentary, and the presence of turtles
and Cetaceans indicates an immigration from the coasts.

The fauna of the ocean depths is no less incomplete.1
When it was discovered, an idea became prevalent that
the depths of the ocean were particularly rich. Having
had the opportunity of studying the excellent collections of
Starfish gathered by Alexander Agassiz in the Caribbean Sea,
and those obtained in the Atlantic by the Travailleur and
Talisman expeditions, I had the curiosity to investigate how
often the dredge would have to be let down to bring up a single
organism of any kind, a species, or a genus, according as the
depth increased. The figures mounted progressively for the
three cases, which implies that the fauna of the depths
diminishes and becomes impoverished as regards the number of
species and genera as we go deeper.' It is therefore evident that
the depths of the sea are not, as was once believed, a reserve
of living forms. On the contrary, life reaches these depths
very slowly, and comes not from the surface, which, as we have
seen, was peopled in a special way and possesses only a
fragmentary fauna, but from the shore. In fact, all the species
of Starfish found at great depths are represented along the
shores by analogous species ; but the littoral species, which
can be regarded as the forbears of the deep sea species, are
scattered along the coasts in such a way that all the coasts may
claim to have supplied their contingent to the deep sea fauna.

These considerations almost dispense with the necessity of
having to examine the nature of this fauna in order to establish
its littoral origin. But it will furnish valuable evidence in
support of our point of view. We must make an important
preliminary distinction at the outset. Down to a depth of
fifteen hundred to two thousand metres we do find an increase
in species belonging to groups that flourished during the
Secondary Period and have since then become rarer or have
even completely disappeared along the coasts. Such, for
instance, among the "Phytozoa", are the glassy Hexact-
inellid Sponges, the hydrocoralines, the solitary corals

1 LIV, 336.

PEOPLING OF LAND AND SEA 149

(Flabettum and others) ; the Polychelidae, a kind of
flattened lobster akin to the Jurassic Eryon ; among the
Echinodenns the fixed Crinoids, flexible sea-urchins of
the type of Calveria, and Pourtalesia, related to the
Ananchytes of the Cretaceous Period, and among the Molluscs
the Pleurotoma and Pholadomya. The fish also belong
to types best represented in fresh water, which, as we know,
are the oldest ; they are akin to Salmon, Pike, Eels, or Cod,
types with which are likewise connected a certain number of
pelagic fish remarkable for the numerous eyes 1 they have on the
sides of their body, one pair on each segment, representing the
remains of modified lateral sense organs.

These archaic types disappear by degrees as we go gradually
deeper, and are replaced by organisms manifestly recent,
although specifically adapted to life in deep waters. Among
them the most remarkable are perhaps the Holothurians. They
abound along every coast. There nearly all of them are shaped
somewhat like a cucumber, and from this fact is derived the
name of one of the commonest genera, Cucumaria. Their body
is divided into five like parts by five rows of membranous
tubes ending in suckers and serving as feet. Ten more or less
spreading tentacles surround the mouth at one end of the
' cucumber ", while the anus is situated at the other. The
body thus possesses an absolutely perfect radial symmetry.
The organisms live among the pebbles, under stones, or in the
fissures of rocks, and under these conditions they utilize
indifferently any set of feet when they move. Some, however,
press constantly against the ground the same portion of their
body which comprises three sets of ambulacral tentacles,
one median and two lateral (Stichoptis, Colochirus). This body
area is distinctly flattened, and already constitutes the
beginnings of a ventral sole. This attains its maximum
differentiation in Psoitis, which lives attached to the surface of
rocks, and has a mouth, definitely dorsal, surrounded by long
ramified tentacles. These tentacles are covered with minute
vibratile cilia, whose incessant pulsations direct towards the
animal's mouth the microscopic particles constituting its
food. The ventral sole becomes the rule in the ocean depths,
and we have already pointed out (p. 127) how it is
formed, and for what cause. Here we can follow all the

1 Chauliodus.

150 PRIMITIVE FORMS OF LIFE

phases of a transformation whose point of departure is
manifestly the position imposed upon the animal by the
necessities of its search for food. The deep-water Holothurians
have nothing to get from the clear water around them, in which
none of the microscopic Alga sufficing for the nourishment of
Psolus are to be found. They feed on mud, and for this purpose
the tentacles that surround their mouths are reduced to simple
tubes spread out into the form of a button ; the contrast
between the dorsal and ventral surfaces is accentuated ; 1 the
suprabuccal bend of the Peniagone spreads out into a sort of
banneret, with the anterior border elegantly pinked ; the
unused dorsal tube-feet elongate into purely ornamental
cones in the case of the Deimatinae ; they are atrophied in
Psychropotes, and the body terminates in a broad pointed and
hollow tail ; the lateral tube-feet of the ventral surface
sufficing for locomotion, the median ones may disappear
altogether through disuse.

Even in mean depths of four hundred to two thousand metres,
where the light has ceased to penetrate, forms representative
of the fauna of Secondary times are scarce, and none are
related to those which characterized the Primary Epoch.
From this we must conclude that the fauna of the deep sea
is relatively recent, and since we have not discovered in the
depths those archaic forms with which Agassiz credited it, not
even a single one that might be considered the head of a series,
but only much modified organisms adapted to a special type
of life, we are forced to conclude that these forms have come
down from the shores, and as they descended into the deep
water, have gradually taken on special characters in harmony
with their mode of life. These adaptations are especially
remarkable in the Decapod Crustaceans. They are divided
into two groups : the swimming Decapods, of which Shrimps
are the common type, and those Decapods that walk on the
ground, represented by such familiar forms as the Lobster, the
Crayfish, the innumerable legion of Galatheidse, and the familiar
Crab. The first make but little use of the long, thin legs with
which their thorax is provided ; they swim either by means of
large flattened appendages which replace the legs on the segments
of the abdomen, commonly supposed to be the tail, or by sudden

1 Psychropotes, Oneirophanta, Deima, Peniagone, etc.

PEOPLING OF LAND AND SEA 151

flexing movements thereof. This last method of locomotion
is not unknown among the crawling Decapods, but they employ
it less often. Their abdominal appendages are not utilized in
swimming, and the creature progresses by the aid of ten
strong legs borne on its thorax. The swimming Decapods keep
below the surface most of the time, and move with great agility ;
the crawlers, on the contrary, hardly leave the bottom, with
which their feet are most generally in contact, and which they
are perpetually feeling, so to speak. The deep-sea adaptations
of these two types of Crustaceans takes place, consequently,
along two opposite lines. The antennae of the swimming
Crustacean become fine and exceedingly elongated, so as to
serve as tactile organs x to warn the creature of the least
obstacle, and their eyes become greatly enlarged. The
antennae of the walking Crustacean, on the contrary, remain
relatively short, and their powerful thoracic appendages dis-
appear, as also their eyes, now unnecessary owing to the
creature's extreme caution in moving.2 The increase in size of the
eyes of the swimming Crustaceans appears at first somewhat
paradoxical. But the darkness of the great depths is not absolute.
Many organisms become light-producing. Among these are the
Gorgonid Polyps, Crustaceans like Gnathophausia and Euphausia,
which bear luminous organs on their appendages, and numerous
swimming Decapods ; certain Squids are provided with
veritable light-projectors ; and many Fishes 3 have luminous
organs situated either on the head or in series on the sides of
the body, like the organs of the lateral line. We are unable to
say whether it was the darkness that caused the elongation of
the appendages and stimulated the development of the luminous
organs. Vire, however, has shown that the appendages of
certain Crustaceans kept in obscurity become very much
elongated ; and this happens likewise in the case of certain
Insects inhabiting dark caves. It is probable that the constant
use these animals make of their appendages for palpating
their surroundings has contributed to this elongation ; and it
is quite normal that where no stimulus occurs the eyes should
disappear. As to the frequency of luminous organs among
deep-sea organisms, one might say with the defenders of the

1 Nemalocarcinus gracilipes, Pandalus, Benthesicymns, etc.

2 Pentacheles, Nephropsis, Galathrodes, etc.

3 Chauliodus, Stomias, Malacosteus, etc.

152 PRIMITIVE FORMS OF LIFE

theory of preadaptations, that naturally the animals that
descended into the darkness of the ocean depths were those
that could illuminate it. As, however, the coastal species which
may be considered as ancestral are not luminous, we must
admit that the illuminating apparatus only developed after
their descent, and not dismiss too rashly the idea that the
absence of solar light favoured their appearance. Whatever
the reason may have been, this faculty of developing luminosity
is possessed only by a certain number of the types constituting
the deep-sea fauna.

The deep-sea forms are not directly related. We find
numerous vitreous Hexactinellid Sponges, and very few members
of the other groups ; Alcyoniaran Ccelenterates of the coral
type or the solitary Madreporaria (Flabellum) ; few Bryozoa,
but quite frequently doubtful forms assigned to them like
Rhdbdopleura and Halilophus dodecalophus . The Crustaceans also
abound, and orders that are generally of small size are some-
times represented here by gigantic forms, such as Bathynomus
giganteus, a large Isopod two decimetres long, or
Gnathophausia gigas and Goliath. Annelid Worms are seldom
encountered. Molluscs are rare and small, and it is their absence
that has led to the peculiar habits of the Hermit-crab, which
occurs fairly often. The Crustaceans of this group have large
soft abdomens, which they enclose, if they live along the coasts,
in hollow shells easy enough to find. As they grow they change
their shell in order always to have a house appropriate to their
size in which they can be completely sheltered. Quite often a
beautiful vivid red Sea-anemone, belonging to the genus Adamsia,
instals itself on this shell, and a kind of symbiosis is established
between the Crustacean and Ccelenterate. Certain hermit-
crabs can lodge in a fragment of bamboo.1 Some even make
out of earth their own mobile habitation, like a kind of
caravan.2 At great depths the Gasteropod shells are rare, and
small. The hermit-crabs can get into these shells perfectly
well when they are young, but as they grow larger they make
no effort to replace them ; then they keep them, merely from
habit, in order to satisfy their instinct, although the shells have
become useless, and we sometimes find splendid specimens of the
hermit-crabs 3 with abdomens the size of a large human thumb,

1 Xylopagunis.

2 Pylocheles.

3 Catapagurus.

PEOPLING OF LAND AND SEA 153

carrying at their extremity a shell hardly as large as a rose-
hip, and held by terminal appendages transformed into
hooks.

Certain species * have as allies epizoic Ccelenterates
which live upon their shell. When the Crustacean and
the Ccelenterate are young everything happens in the
same manner as in the case of the littoral hermit-crab ;
but the hermit does not change his shell as he grows,
whereas the polyp can produce, by the budding process,
other polyps similar to itself. The young family soon gets
too large for the shell, and spreads directly over the un-
sheltered portion of the hermit-crab's body, which thus
finds itself protected by a living cloak which always fits it.
This living cloak adapts itself so closely to the Crustacean that
it always retains the same shape, and it would be difficult
indeed to insist, in this case, that the form is not the direct
result of the conditions of development imposed upon the
relatively passive family of the polyp by the action of the
hermit-crab. Here we have a clear case of the influence of
external circumstances in the determination of organic forms.

The fact that the deep sea hermit-crabs can do without a pro-
tective shell Ostraconotus, or content themselves with an illusory
one, implies that they do not run any great dangers and that
consequently the struggle for existence is not, in this region,
very intense. Indeed, whatever be the group under con-
sideration, the number of individuals found is apparently
too small to lead to serious competition. This dissociation of
species is not due to natural selection. It is possible that
species of the same genus which are distinct in the abyssal
fauna are descended from species which were already distinct,
although belonging to the same genus in the littoral region.
It is also possible, even if we adopt the rarely applicable test
of their inability to unite among themselves, that their
formation may be a question of the chemical conditions
surrounding them, and that therefore the normal species may
be formed in this way by dissociation of the same type at
any particular depth. The chemical view-point is the best one
we can adopt if we wish to explain the perfectly useless colour
of animals living in complete obscurity.

1 Pagurus pilimanus.

154 PRIMITIVE FORMS OF LIFE

We have seen that the transparency and the blue colour of
pelagic organisms may be considered as protective characters
intended to render them invisible. Such colours are not
encountered in deep-sea specimens, which are generally
white (Polycheles, Deima), pink (Peniagone), red (Phormosoma
and many swimming Decapod Crustaceans), violet
(certain swimming Decapods and Echinoderms of the
genera Pourtalesia, Psychropotes) . The deep-sea fish are
generally black and their luminous organs green. Although
they belong to well-known groups — most commonly to the
type of " abdominal " or physostomous Fish — they, none the less,
present special characters. They are often provided with long
tactile appendages placed sometimes on the head, as in
Melanocetes johnsoni, sometimes under the jaw as in
Eustomias obscurns, in front of the fins as in Bathypterois
longipes, or in both these places (Echiostoma micripnus).
Here we find the same facts as among the Decapod
Crustaceans, which implies that they have been produced
by the same causes. Often, moreover, the mouth takes
on enormous proportions (Malacosteus niger, Eurypharynx
pelecanoides) . Only a few families are represented at
great depths ; the Scopelidae,1 also pelagic, the Clupeidse, of
which the Herring is the commonest type,2 and the Stomiadae,
which resemble the pike in the arrangement of their unpaired
fins. These all belong to the group of physostomous Fishes.
The physostomous Fish are represented almost entirely by
Malacopterygians, such as the Gadidce,3 typical forms of which
are Cod ; Macruridae, with the body terminating in a point, and
Ophididae, elongated like Eels.4 The Fish fauna, unrepresented
by Amphioxus, Lampreys, Sharks, and almost all fish with
spinous dorsal fins, i.e. the most agile swimmers, is therefore
essentially an incomplete fauna like the others, in other
words an immigrant fauna, and that of the freshwater Fish
will prove to be similarly incomplete.

But in this case the conditions of existence are absolutely
different from those of the deep sea. The pervading immobility
and the even temperature and consistency of the water gives
place here to agitation that is never ceasing in the streams,

1 Scopelus, Saiirns, Malacoceplialus, Alepocephalus, etc.

2 Halosanrus.

3 Mora, Balhygadus, Coryphcenoides.

4 Bathynectes crassus.

PEOPLING OF LAND AND SEA 155

and frequent even in stagnant waters. The temperature and
the composition of the water varies incessantly. The ' ' Phytozoa
are hardly adaptable to this mobility. They have only a few
freshwater types, such as siliceous Sponges with straight
spicules {Spongilla, Parmida, etc.), a very small number of
Hydroid polyps or medusae {Hydra, Cordylophora, Limnocodium,
Limnocnida) , an Asiatic fluviatile Actina, Phylactolcematous
Bryozoa with gelatinous investment, and some Gymnolcemata
(A rachnidinm, Victor ella) . All these organisms seem to be recent
immigrants. It is remarkable that the freshwater Sponges and
Bryozoa should possess another method of reproduction besides
the sexual ; during critical times fragments of their body-
substance are enclosed in a protective envelope, which
enables them to withstand all the destructive agencies that
might menace them, and to escape the vicissitudes, so frequent
in fresh water. These fragments subsequently free themselves
from the envelope and evolve into new organisms as soon as
circumstances are again favourable. Examples are to be found
in gemmae or amphidisc capsules of Spongilla and the
statoblasts of the Bryozoa.

The Crustaceans are represented only by Phyllopoda,1
which go back to a very remote antiquity ; by a small number
of Cladocera,2 Ostracoda,3 Copepoda,4 Isopoda,5 Amphipoda,6
Schizopoda,7 and Decapoda.8 These are very few in proportion
to the enormous number of Crustaceans extant. To them must
be added certain Arachnidas and Insects that have
become aquatic again after having led an aerial existence. With
certain rare exceptions, to which Charles Gravier has called
attention, the Annelid Worms present belong to the class
Oligochaeta, of which the Earthworm represents a giant
form, and to the class of the Leeches, which have only a
small number of marine forms, apparently imported by
migratory Fish. Among the Flat Worms only a small number
of Planarians and Nemerteans are encountered. The

1 Estheridae, Apuscancriformis, Branchippus.

2 Daphnidae, Polyphemidae.

3 Cypridae.

4 Cyclopes.

5 Asellidse.

6 Idothea.

7 Mysis relicta.

8 Caridina, Palcsmonetes, Alphceopsis, Niphargus, crayfish and other allied
genera, and some related crabs of the genus Telphusa.

156 PRIMITIVE FORMS OF LIFE

Echinoderms are entirely absent. The Molluscs deserve special
attention ; the Cephalopods are completely lacking, but many
successive migrations of marine Gastropods can be counted.
The Diotocardiacs are represented by the Neritinidae, the
herbivorous Monotocardiacs by forms like Ampulla, Paludina,
and Valvata. No carnivorous Monotocardiac, Opisthobranch, or
Pteropod occurs in fresh water. On the other hand, the
Pulmonata are fairly numerous, and we might well ask
whether they are not descended from terrestrial Pulmonata.
This fauna is thus very limited. The Lamellibranchs are
represented only by forms with a large open mantle,
therefore primitive forms, Unio, Anodonta, Cyclas, Iridina,
etc. ; and by a single siphoned form which merely
indicates the order, Dreyssensia polymorpha which pene-
trates into the rivers and carries with it Cordyhphora
lacustris and an annelid worm remarkable for its bristles of
complicated form, Psammoryctes imibellifer. This invasion
seems to have begun only since the beginning of the century,
starting in the Baltic, then reaching the Thames and finally
the Seine.

The group of freshwater Fish is among the most instructive.
The primitive Fish, fleeing from the struggle for existence
that was too intense along the coasts, sought refuge at some
distant period in the lakes and rivers, just as the sturgeons,
salmon, and shad still take refuge to spawn and place their
progeny in some place of shelter. The number of marine
creatures able to live in water containing no sea-salt is actually
quite small ; those which possessed this pre-adaptation to life
in fresh water, or have acquired it, could not be pursued by
those not possessing it, and this is why the rivers and marshes
which were at first deserted, were early invaded by fugitives
which preferred the calm of the inland solitudes to the dangers
lying in wait for them among the active and numerous
population of the coasts. Thus, the same desire for security
peopled the open sea, the abysses and the fresh waters.
If Amphioxus, the most primitive of Vertebrates, found a
hiding-place on sandy shores, the Lampreys, like Petromyzon
marinus, became the temporary guests of the fresh waters,
where they only penetrated to spawn, their young having to
pass the first part of their life in the fluviatile sand in the form
of Ammoccetes. Others like the Petromyzon fluviatilis are

PEOPLING OF LAND AND SEA 157

permanent inhabitants of rivers. Only one group of Sharks
has become lacustrine, Carcharias gangeticus ; but of the
three types of Ganoids still persisting, the Sturgeons,
Lepodisteus and Amia, only the first spawn in rivers, and the
other two do not leave their streams. In the same way
the Crossopterygians which, with the Ganoids, were the
most common fishes, and the most highly organized at the
time of the Carboniferous Formations, are represented to-day
only in the rivers of Africa by two closely related genera,
Polyptenis and Calamoichthys. The Dipnoian Fishes, which were
the first, nevertheless, to develop lungs, the organs of aerial
respiration, now exist only in three freshwater genera :
Proiopterus of Africa, Lepidosiren of Mexico, and Neoceratodus
of Australia. This geographical distribution indicates that the
first invasion of the fresh waters took place almost
simultaneously in various parts of the world during the Primary
Period. However, as in the case of the Molluscs, this was not
the only invasion that occurred. The Bony Fish, in their turn,
invaded the rivers shortly afterwards. One of the oldest families
of this group, the Siluridae, although rather poorly repre-
sented in Europe by two or three species, the gigantic Silurus
glanis of the Danube, and Silurus arisiotelis of Macedonia, is
yet possessed of an astonishing plasticity, and has invaded
almost all the rivers of the world in varied forms which have
subsequently been copied by all the other freshwater Fish, with
abdominally placed pelvic fins, retaining none the less the funda-
mental characters of the skeleton of its operculum. Like the
Rays, it produced a group of electric Fish, M alapterurus , of Africa.
Then followed the whole series of Fish with ventral fins far re-
moved from the pectoral, as in the primitive Fish, which Cuvier
called " les malacopterygiens abdominaux," in which the swim-
bladder opens into the oesophagus or stomach (the Physostomi
of J. Miiller) ; that is to say, Trout, Pike, the long series of
Cyprinidse, to which the majority of the Fish of our rivers and
swamps belong, Gudgeon, Barbel, Dart, Carp, Bream, Roach,
Tench, Loach, etc., which are represented elsewhere by the
Cyprinodontidse. The Herring, Sardine, and Anchovy, all
related to this type, have continued to live in the sea; but
the Shad, which belong to the same family, namely the Clupeidae,
come to the rivers to spawn, like the Salmon, relations of the
Trout. These are Fish of the same group that have furnished,

158 PRIMITIVE FORMS OF LIFE

as we have seen, the main forms of the pelagic and the ichthyo-
logical fauna of the deep sea. These two invasions of the fresh
waters were followed by a third. This time the newcomers
had soft dorsal fins, pelvic fins near the pectoral, and a closed
swim-bladder. This kind, however, is still scarce, and is
only represented in European fresh waters by the Lote, which
are related to the Cod. Certain others belong to the
pelagic forms that have a partially spinous dorsal fin and
include strong swimmers related to the Perch. Some
of these, like Coitus and the Red Gurnard, had reverted to
their littoral habitat, and were therefore predisposed to enter
fresh water. The Chubs of our rivers belong to this group.

Many marine Fish spawn an innumerable quantity of small
eggs and abandon them without bestowing the slightest care
upon them. As a rule, however, the species that penetrated
into fresh water and remained there belong to genera or
families which produce but a few large eggs, and attach them
to the under side of stones, to algae, or inside empty
shells, if they do not actually spawn in shelters prepared
in advance. These eggs are large because they are filled with
nutritive substances which save the embryo from seeking any
other nourishment until the supply is exhausted. Under these
conditions the embryo grows very rapidly, and when it leaves
the egg still often carries a part of the reserves in a receptacle
called the vitelline sac. Thus it acquires both the agility and
the resistance that will enable it to escape many of the dangers
besetting it. This enhancement in the size of the eggs can also
be observed in the case of the Prawns, which penetrate fresh
waters and are hatched in a form that is almost mature, while
their congeners still have profound transformations to undergo.
The same difference exists between the Sea Crayfish and the
Lobster. The former have small eggs giving rise to transparent
swimming embryos called Phyllosoma, which in no way
resemble the adults ; the others, on the contrary, spawn large
eggs from which the young are hatched out in their permanent
form except that they have still to grow, and it is probably
this that has permitted kindred forms to penetrate into the
fresh waters where they have engendered the diverse forms
of Crayfish.

The instability of the conditions of existence in fresh water
appears to have resulted among the invertebrates which sought

PEOPLING OF LAND AND SEA 159

security therein in a consequence at first sight most singular.
Many became hermaphrodite, for instance, the Oligochaetes,
the Leeches, ancestors of the flat worms (Trematodes, Cestoides,
Turbellarians) , and Pulmonate Gasteropods. Whatever may
be the general belief, hermaphroditism is not a primary condition .
The primitive genital elements, the spores, were simple asexual
cells and in the first place they multiplied directly without
fecundation. This is still the case with many cellular
Cryptogams and certain Protozoa, but even in these groups
sexual differentiation of the cells has already appeared as well
as fertilization in the ciliated Infusoria, for example, in the
Sporozoa and Foraminifera. When certain genital cells develop
without fertilization, as in Apus, Branchipus, Daphnia, the
Aphides, Cochineal-insect, the Cynipidae, Wasps, Bees, various
Lepidoptera of which Bombyx is an example, in certain free-living
Nematode worms, Rotifers, and Gasterotricha, the faculty has
been re-acquired.1 The male and female characteristics of the
sexual cells stand out clearly from their comparison in the Animal
and Plant Kingdoms. The male elements, as we have seen,
are produced by cells that multiply rapidly by division, and
are incapable of accumulating reserve material. Hence they
remain small, and their activity which is mainly of a mechanical
order, is spent in the rapid movements of vibratile cilia
or flagella. These are the antherozoids of the vegetable
Cryptogams and the spermatozoa of animals. The female
elements, on the contrary, are produced by cells in which
division is retarded, especially in the last stages of their
evolution, and of which the activity is essentially of a chemical
order directed chiefly towards the elaboration of the reserve
substances which accumulate in their protoplasm and increase
their volume, making the cell heavier and suppressing all
possibility of movement.

These characters, with which even unicellular beings
are invested in order to reproduce themselves, before becoming
a part of an organism, are retained by all living forms,
and in each animal species the same individuals are capable
generally of producing only one of the two types of sexual
cells. This is especially marked among species which stand at
the beginning of a series and therefore live in the sea. It would

1 We are not speaking here of artificial parthenogenesis, which is a
phenomenon requiring a special study.

160 PRIMITIVE FORMS OF LIFE

seem at first sight as though this rule did not apply to plants,
as each flower is hermaphrodite, but it must not be forgotten
that in plants the primordial individual element is the leaf,
so that a vascular plant is best considered as a collection of
leaves. In the flower, however, the fertile leaves are exclusively
male (stamens) or female (carpels), and consequently unisexual.
We should also remember that in the oldest flowering plants
the male flowers generally grow on different branches from the
female flowers. Both are made up of cones or catkins exclusively
male or female, and the sexuality frequently extends to the
whole plant, in which case it is said to be dioecious (p. 103).

Throughout the Animal Kingdom the males or females share
distinctly the characteristics of the sexual elements they
produce. The females of the species belonging to the same
genealogical stock generally resemble each other considerably,
and retain the forms and colours that are practically those of
the young individuals of the species, which indicates both that
they have a common origin and that they have evolved but
little. They are larger than the males, very often some-
what inactive, and usually accumulate more reserve substances
in their tissues. The males, on the contrary, use up the products
of their alimentation in activity. They are vividly coloured.
Ornaments of all kinds, horns, tusks, manes, plumes of
feathers, and aigrettes embellish the primitive form conserved
by the females. Sometimes they produce substances with special
odours. Through heredity, these acquired characters are often
passed on to the females. Thus the small blue butterflies of
our fields, called Argus, have generally brown females with
yellow spots ; but in some species the blue colour of the
male can extend to the female. Again, among the Kingfishers
the females of the Halcyon are grey, while the males
have those magnificent blue and tawny shades which in our
ordinary species are common to both sexes.

The incapacity of the males to provide themselves with
reserve nourishment has a fatal result for them in those groups
of the Animal Kingdom which do not endow the organism with
much power of resistance. Already among many Insects 1 their
span of life is short ; they do not concern themselves at
all to provide for the future of their young, and die as soon as
they have fulfilled their sole function of fertilization. Others

1 Bees, Wasps, Ants, and many Flies with four wings or Hymenoptera.

PEOPLING OF LAND AND SEA 161

are entirely incapable of nourishing themselves.1 Among the
marine Worms, such as Bonellia, the female is as large as a
nut, while the males are so small that they were once taken
for Infusorians living as parasites on the female organ, where
they are found to the number of seven or eight.

At first sight there seems to be a contrast between this
diminution in size and the splendour which the males attain in
other cases, and also a contradiction between this diminution
in size and the abortive forms so noticeable among certain
females. In the Glow-worm,2 many night-flying Lepi-
doptera,3 and Stylops, the females are without wings. In
the last case they are reduced to egg-sacs, and only
their almost formless heads protrude outside the body of
the wasp, in which they live as parasites. But all these
apparently paradoxical facts range themselves under one and
the same principle. It is the development and the nutrition
of the eggs, that is to say the accumulation of reserve sub-
stances in the cells still belonging to the mother, and perhaps
also the organism's disuse of its wings when it has become too
heavy for them, that has brought about the reduction and
disappearance of these organs in the Glow-worm and various
female Lepidoptera. The same causes have determined the
parasitism of the females of Stylops, a parasitism that has
brought with it, as usual, the complete decay of the locomotor
apparatus. Here we have a phenomenon analogous to that
which has been observed in the Chondracanthidae, which
are Copepod Crustaceans, and Bopyridae, which are Isopods.
The males, a hundred times smaller than the females,
which are almost formless and parasitic, remain attached like
minute lice to the abdomen of the latter. These female
Bopyridae are frequently found under the carapace of Shrimps,
which they raise into an irregular swelling on one side. In
another family of Copepods, the Lernaeidae, the males and
females, at first small and almost alike, are coupled together ;
the males then disappear and the females parasitically attach
themselves to the gills or other organs of some Fish, where they
become enormous, almost limbless, and so unrecognizable
that Cuvier classed them among the Worms.

From all this it follows that individuals of the male sex are

1 Mosquitoes.

2 Lampyris noctilnca.

3 Orgyia antiqua, Psyche helix, Cheimatobia brumata, etc.

M

162 PRIMITIVE FORMS OF LIFE

clearly affected either by a nutritive incapacity or by the
orientation of their organism towards a useless expenditure
of energy which destroys their alimentary reserves ; so that
they are, in short, impoverished organisms whose poverty affects
the reproductive elements themselves and imposes special
characters upon them. A predominance of males in an animal
population would therefore be a sign either of dearth or of
superactivity.

This last remark leads us to consider whether the explanation
of hermaphroditism is not to be sought in the conditions which
render alimentation precarious. Among these conditions one
is especially evident, namely the abandonment of a free life
for the sedentary one, and notably for attachment to the
ground, which places the animal at the mercy of all the
variations in its environment, from which freedom in move-
ment would permit it to withdraw. Outside the "Phytozoa",
in which fixation is primitive, this attachment to the ground
occurs as an accidental condition in the Cirripedes, which are
Crustaceans, and the Tunicates which are related to Amphioxus,
the most primitive of Vertebrates. In both cases it leads to a
complete change in the conditions of existence after the animal
has attained the form which should normally have been
permanent, and results in a complete deformation of the
body. The Cirripedes and the Tunicates are protandrous
hermaphrodites, that is to say, each individual commences
life as a male, becomes transitionally both female and male,
and finally passes definitely into the female condition. What
does this very general phenomenon signify ? The Cirripedes
give us the answer to the question. Most genera of Cirripedes
have no males at all. Where they exist they are not fixed,
remain very small, and have but a short life. As the other
individuals, in their quality of protandrous hermaphrodites,
are capable of reciprocally fertilizing each other, if not them-
selves, the exclusively male individuals are of no use at all.
They are not even what we sometimes call complementary or
supplementary males, but simply useless males, or, if we desire
to give them some designation, supernumerary males. Their
existence merely serves to qualify the other individuals ; it
demonstrates that among the Cirripedes, before fixation, the
sexes were distinct as among other Crustaceans ; that fixation,
with all its hazards, has been fatal for the males, which have

PEOPLING OF LAND AND SEA 163

become so rudimentary that they cannot even acquire organs of
fixation. The females, on the other hand, possessing reserve
substances and a special nutritive aptitude, have resisted these
dangers. Yet they have to pass through a very critical period
after the metamorphoses which follow in the train of fixation.
It is then that their reproductory cells evolve in the direction of
the male sex and regain their original sex when the physio-
logical equilibrium has been re-established. There are no super-
numerary males among the Tunicates, although their evolution
has gone much further, since tachygenesis has brought about
a regeneration of the free forms ; but their whole history
is so much of a pattern with that of the Cirripedes that there
can be no doubt as to the identical nature of their case.

The researches of Maupas l on free-living Nematodes
permitted him to report the existence of supernumerary males
among certain of these species. I myself 2 have given elsewhere
the reasons which lead me to classify the Nematodes not as
Worms, according to the usual procedure, but as Arthropods
degenerating through inherent inertia into parasitism, like
many of the sedentary larvae of Insects.3 So long as they are
parasites, these organisms live in superabundance. Their
passage to a free life, which is almost fatal in those
groups where the eggs are often hatched in the ground or in
the water, leads them back to these precarious food-conditions
just as surely as fixation, but by another road. Here, again,
there has been a great disturbance in nutrition, and we find
the same facts ; males becoming uncommon and inert, then
disappearing altogether ; females hermaphroditic, and finally
parthenogenetic, if the reproductory cells develop very early
through the operation of tachygenesis.

The organisms which passed from the sea to freshwater
streams, lakes, marshes, and damp localities were likewise
exposed to distressing uncertainties in the food supply ; and
these must have had the same results as in the preceding
instances. We have thus the explanation of hermaphroditism
in freshwater Annelid Worms,4 numerous species of Earth-

1 LV, 463.

2 LIV, 1345.

3 Larvae of Coleoptera living in fruit or digging into wood ; larvae of
Hymenoptera enveloped and provisioned, or nourished, by their parents ;
larvae of Diptera living in organic substances. These are all described in
popular language as Worms.

4 Dero, Nais, Stylaria, Tubifex, Enaxes.

164 PRIMITIVE FORMS OF LIFE

worms, and Leeches derived from them, contrasting with the
differentiation of the sexes so general in marine Annelid
Worms.

Exactly the same thing happened in the case of Gasteropod
Pulmonate Molluscs, of which the Snail is the common type,
and which are represented by countless species in the fresh
waters and in all damp land areas. All are hermaphrodite,
whereas the marine Gasteropods, with their helicoidal shells,
and gills protected in a special cavity situated in front of the
dorsal cone,1 are all unisexual.

The marine Lamellibranchs, which lead a sedentary life,
are often hermaphrodite, like fixed organisms ; hermaphroditism
is also definitely protandrous in the Oysters, which are fixed
like the Tunicates.2 We have very little information as to the
sexual conditions of the other Lamellibranchs.

Objections might be raised against the theory that
hermaphroditism is due to a precarious source of food supply,
particularly in fresh waters and on land, namely the existence
of hermaphroditism in true parasites, such as the liver flukes 3
of Sheep and similar animals 4 and in the Turbellarians, which
are free-living and form together with them the order of
Flat Worms, from which, however, the Nemerteans are to be
excluded ; and it may also be contended that every order of
marine Gasteropod Molluscs without an anterior branchial
cavity consists of hermaphrodites. However, a very few
words will suffice to deprive these objections of all validity.

In the first place, although the organization of the
hermaphrodite Flat Worms is so degraded that it has been
attempted on various occasions to describe them as primitive,
their double genital apparatus has preserved a complicated
structure of a very special, constant, and definite type ; this is
enough to show that we are here dealing with a group of
degenerate organisms, sprung from a higher group. The only
possible starting-point for this degeneration is the Leech,
whose class manifestly derives from the Earthworm, whose
organization is so similar that a man like Franz Vejdowsky,5

1 They are called Prosobranchatata.

2 LVI.

3 They form the two classes of Flat Worms, the Trematodes, and the
Cestodes, or Tapeworms.

4 They are called Opisthobranchiata.

5 LVII, 38.

PEOPLING OF LAND AND SEA 165

particularly competent in all that appertains to the history of
Worms, classed genuine Leeches, such as Branchiobdella
among the Naidids. The most salient leech characters appear
in certain Central African Worms, the Polytoreutidae,1 in which,
as in Leeches, the reproductive orifices are placed in a median
ventral line instead of according to the usual symmetrical
arrangement. In becoming carnivorous or parasitic, Leeches
have merely continued to inherit the hermaphroditism of their
oligochaete ancestors, who acquired it when they took to life
in marine or freshwater lakes. Subsequently they trans-
mitted the character to the Trematodes, which, when they
became free organisms, gave rise to the Turbellarians.

We have an even simpler explanation of the presence of
Opisthobranchs, which are all hermaphrodites, in the seas.
Like the Pulmonata, they have lost their primitive gills. This
loss suggests that the ancestral Opisthobranchs at one time left
the water and lived in the open, or at least in a low-lying littoral
zone washed by the tides, and thus often out of the water for
long periods. In this state they still remain, except for their
derivatives, the pelagic Pteropods. Had they remained aquatic
they would have preserved their branchial apparatus. There is
no reason why they should lose a respiratory system so
eminently advantageous after having once acquired it. It
must therefore have been during their change of habitat that
they became hermaphrodite like the Pulmonata, which aiso
lost their gills and present so many characters analogous to
the Opisthobranchs that we may justly ask whether some
phylogenetic relationship does not exist between these two
orders, and whether they are not linked up by certain still
existing non-aquatic forms.2 Having reverted to their earlier
environment the re-developed gills around the anus,3 on the
back,4 on one,5 or on both sides of the body.6

Access to dry land was not so easy as might be imagined.
In the first place there had to be preparation, and this, which
can be regarded if one so wishes as a pre-adaptation, had else-
where always consisted in the disappearance of the external

1 LXXII.

2 Oncidium.

3 Doridae.

* Nudibranchs.

5 Umbrellidae, Plcurobranchs, Aplysia.

6 Phyllidiae.

166 PRIMITIVE FORMS OF LIFE

apparatus of aquatic respiration, of which traces sometimes
persist, a disappearance that has often been produced in
immigrant marine organisms when they took up life in fresh
waters. For this aquatic respiratory apparatus was substituted
an internal one, which was thus protected against desiccation,
a danger to which air-breathing animals would be constantly
exposed, but which a marine animal need not fear as its
respiratory organs are always submerged and have only to be
protected against collision, or the predatory attacks of small
carnivorous creatures. Occasionally the branchiae, which
constitute the pre-eminent aquatic respiratory apparatus, were
not replaced, the surface of the body sufficing for aeration. This
is what happened in the case of the Earthworm, their close
kin the freshwater Annelid Worms, and the Leeches. Among
those organisms which live in fresh water or have returned to
the sea, the branchiae in certain conditions can be redeveloped,
as in the Opisthobranch Gasteropods. Thus, those beautiful
little Freshwater Worms, Dero (LVIII), have a sort of
outgrowth at the posterior extremity of the body, supporting
four retractile finger-like processes, the whole constituting a
respiratory mechanism over whose surface the water is
constantly renewed by the action of powerful waving cilia.
In the same way Ozobranchus, a Leech which lives in the mouth
of Crocodiles, marine Tortoises, and Pelicans, and the
marine Leeches of the genus Branchellion, living on the Electric
Eels, have recovered these branchiae, in the first case in the
form of tufts, and in the second in the form of trumpets.

The substitution of an internal for a branchial respiratory
apparatus naturally consisted merely in a process of
invagination of certain portions of the integument, or in
the adaptation to a respiratory function of internal organs
having communication with the exterior, as is the case with the
digestive apparatus. By means of a new application of the
principle " everything happens that can happen ", the two
types have been arrived at by methods sometimes a little
unexpected, and, moreover, independently of the conditions
of the habitat. The larvae of Dragonflies, though they remain
exclusively aquatic, have an internal respiratory apparatus
contrived at the expense of the rectal region of the digestive
tube. This same rectal region, provided with powerful
vibratile cilia, constitutes in Freshwater Worms a supple-

PEOPLING OF LAND AND SEA 167

mentary respiratory apparatus. Balanoglossus, a peculiar
marine Worm without locomotor bristles, has constructed a
respiratory apparatus at its other extremity at the expense of
the oesophagus. This consists of a series of symmetrical lateral
pockets, communicating both with the oesophagus and with the
exterior. This arrangement is found again among Fish such
as Bdellostoma and young Lampreys, and is slightly modified
in Myxine and the adult Lampreys. The pockets have
been replaced by simple slits in all the Sharks and Rays. The
separating walls of these slits are now only represented in
Sturgeon and Bony Fish by arches covered with a double row
of points, arranged like the teeth of a comb. These pockets in
Lampreys were also unquestionably preceded by simple slits,
since that is the form of the respiratory apparatus in
Amphioxus, from which is derived the enormous branchial
sac of the Tunicates, constituting a kind of oesophageal abyss.

In spite of their chitinous envelope, the internal respiratory
apparatus of the Arthropods originates from a simple
invagination of the integument. This is also the way in
which the integumentary glands of these organisms arise,
notably the highly important coxal glands, connected with the
base of the appendages, which, according to circumstances,
become either salivary glands, poison glands, annexes to the
proboscis in the Mosquito, the sting in the Bee, or else kidneys,
like the green gland of the Crayfish and the analogous gland
in Lobsters, Crabs, and their congeners, and which opens
at the base of their antennae. This similarity in origin,
entailing a certain similarity of organization, has led to the idea
that the tegumentary glands, at least in certain cases,
can be transformed into respiratory tubes. However this
may be, it would seem that four groups of Arthropods,
the Onychophora, Arachnida, Myriapoda, and Insecta, have
acquired independently an internal respiratory apparatus,
constructed in an analogous fashion, in its permanent form
at least.

The species of Pcripatus are peculiar organisms, living under
stones, in rotten wood, worm-eaten trees, and in vegetable
debris generally. They resemble Caterpillars with membranous
feet, and bodies terminating in front in antennae, but without
a distinct head. Thus in body type Peripatus also resembles
the Annelid Worms, but the body is protected by a chitinous

168 PRIMITIVE FORMS OF LIFE

envelope about as thick as that of the Arthropods. They are
very archaic organisms, belonging unquestionably to the first
land immigration of the segmented members of the animal
kingdom, for they are found at widely separated localities
which could only have been connected during the existence of
the former Gondwana continent, e.g. the Cape of Good Hope,
New Zealand, the Amazon Valley, etc. Their respiratory
apparatus consists of numerous invaginations of the thinner parts
of the integument arising indifferently from the dorsal or the
ventral surface of the body ; they are even seen on the surface
of the membranous feet, constituting as many internal tubes,
which, after being expanded into an umbrella, give rise to a
bunch of slender tubes spreading from the centre thereof
and terminating in a cul-de-sac without any rami-
fication. These structures are known as trachea, and this
same term tracheae is applied to all the internal respiratory
tubes of the Arthropods, whatever their form and origin.
No connexion is to be seen between these very numerous
respiratory tubes without any fixed morphological position,
and the so-called lungs of the Arachnida. MacLeod has
propounded an interesting hypothesis for the origin of these
last-named organs, which does not, however, destroy the
validity of Marie Pereyaslawzeva's x observations. For him,
in short, the lungs of Scorpions are nothing but a slight
modification of the branchial apparatus of Limuhis. The
abdomen of these creatures, the earliest known Arthropods,
since they are found in the Silurian deposits, possess
flattened feet in the form of large chitinous lamellae, in the
rear of which are sheltered a whole series of thin leaves, super-
posed like those of a book. If that portion of the integument
which supports these leaves were to be invaginated interiorly
to the body, drawing them with it, while the protective plate
constituted by the foot became shorter, a pocket would
necessarily be produced, having on its inner side a series of
leaves or lamellae and opening externally by a slit — that is to
say, a lung of the Scorpion type with its respiratory orifice.

1 These objections are founded on a lack of agreement between the actual
order of appearance of parts in the lungs of the embryo and the theoretical
order that ought to occur in the formation of these parts according to the
hypothesis of MacLeod. However, we know that such reversals are frequent
in embryogenetic development, and are the result of tachygenesis.
(LXXII, 247.)

PEOPLING OF LAND AND SEA 169

The lungs of Thelyphonidae, Phrynus, and Spiders, differ in
no way from those of the Scorpions, and MacLeod's L
explanation consequently extends to them also. Lamy,
moreover, has followed step by step in the case of the Spiders,
their metamorphosis into tracheal tubes.2 This metamorphosis-
is complete for the second pair of lungs of the Dysderidae and
Segestriinae, which are normal Spiders in all other respects.
Two tracheae co-exist with the lungs in all the other Spiders, but
are carried back towards the posterior extremity of the body,
and there is only a single median orifice placed in front of the
spinnerets. In the Galeodidae, Field Spiders and Pseudo-
Scorpions, the metamorphosis affects the whole pulmonary
apparatus, hence these Arachnida are known as trachean.
Mites or Acarina, generally small in size and often parasites,
likewise breathe through their tracheae, and thus seem to be
degenerate Arachnida. However, the position and the number
of the respiratory orifices which vary according to the genus
and which may disappear altogether, render the assimilation
of their tracheae to the respiratory organs of other Arachnida
rather uncertain so far as present knowledge goes. That does
not affect the fact that the Arachnida present a special mode of
forming their internal respiratory organs, different from that
met with in Peripatus, and that they represent a second group of
land immigrants, likewise archaic, and dating back to the
Silurian period. Scorpions, as a fact, have been found in Silurian
deposits, particularly in the island of Gothland. The Arachnida,
moreover, belong to a class of Arthropods in which the first
appendages of the body, anterior to or near the mouth, are
still at least partially utilized for functions other than the
retention or mastication of food, and which with creatures
like Pterygotus, Eurypterus, Limulus, and the Trilobites, con-
stitute the sub-class Merostomata.

With centipedes or Myriapods we come to a class manifestly
derived from the true Crustaceans, in which the first five pairs
of appendages are specialized for tactile or masticatory
functions. Here, however, the segments carrying these
appendages, more or less distinct in the Crustaceans — are
combined in a single mass, whose limits we are unable to
distinguish, and which we call the head. All the other segments

1 LIX. 2 LX, 836.

170 PRIMITIVE FORMS OF LIFE

are alike, and as they are variable in number we have no
alternative but to connect the Myriapods with the lower
Crustaceans or Entomostraca, a type which, though aquatic,
is quite distinct from that of the Merostomata, which came
later. In these, however, a tracheal apparatus develops, very
much like that of the Arachnida, in which the respiratory
orifices are also close to the limbs, one pair for each segment,
except in the Scutigeridae, in which there are only seven
orifices, placed on the median dorsal line of the body. The
Myriapods, in short, represent the third land invasion of the
Arthropods, and their respiratory apparatus, in spite of
resemblances to that of Peripatus and the tracheate Arachnida,
has been formed independently and quite contrary to the old
adage "Nature never repeats herself".

The Insects constituted a fourth wave of immigration,
undertaken not, however, by the Entomostraca with bodies
made up of a number of segments varying from type to type,
but by the Malacostraca or higher Crustaceans, which include
Wood-lice at one end of the scale and Crayfish at the other,
and mounts up through miniature freshwater Shrimps
and marine Shrimps to arrive finally at the Crabs. These
Crustaceans are innumerable, but all of them have twenty-one
body-segments. The Wood-lice and some related forms reached
the land without losing any of the characters of the Isopod
Crustaceans, and small tubes, elementary short tracheae,
develop on the respiratory feet borne on the abdomen. The
related Asellidae migrated to the fresh water without undergoing
any important modification, and there are in subterranean
waters certain other forms, manifestly marine in origin, since
species of the same genera still exist in the sea. In the same way
the freshwater Shrimps (Gammarus) belonging to the
Amphipod group, Palceomonetes, Palceomonella, and Caridina,
which are almost Shrimps, and Telphusa, which are Crabs,
all penetrated into fresh waters, and certain Crabs, of the genus
Birgus, and Gecarcinidae, which are Decapods, even became
terrestrial. But these are only individual immigrations, so to
speak, of relatively recent date, like the forms of the creatures
which accomplished them. Unquestionably such migrations
are still taking place. They have altered nothing in the general
economy of Nature.

PEOPLING OF LAND AND SEA 171

It was otherwise with the immigration responsible for the
Insects, whose role, in our days, is so important. For them a
new conquest was in store — the conquest of the air. Until their
appearance the only living organisms that had mounted up
into the air were the spores of Cryptogamous plants, the pollen
grains of Conifers, and perhaps the cysts of the Infusorians,
all borne along by the wind, and they were nothing but dust.
At first the only living organisms creeping about in the moss
were peculiar creatures like Acantherpestes, Palceocampa, and
Euphorberia. These creatures had some of the characters of
Peripatus, but were more varied in form and often carried dorsal
appendages, some of which have been interpreted as branchiae.
Doubtless they were the sole prey that the primitive Scorpions
could secure. The Myriapods themselves, although rapid in
their course, adhered strictly to the surfaces over which they
ran, and contributed a very slight modification to the
manifestations of life. With the appearance of the Insects a
great change takes place. All over the world creatures with
elongated limbs and very vivacious movements, begin to
multiply. New locomotor organs, their wings, carry them into
the air, and with a single flight they cover notable distances.
Before their coming, scarcely any sounds could have been
heard on earth but the whistling of the wind, the rustling of
branches stirred in its passage, the fall of the cones from the
trees, above which must often have arisen the roar of the
tempest, and of rivers in spate, the booming of the waves
whipped into fury, the crash of thunder, the explosions of
volcanoes, or the subterranean rumblings heralding earth-
quakes. Then came the first humming of rapidly beating
wings, and the strident voices of Cicadas, Grasshoppers, and
Crickets, great and small, singing, on the threshold of the dark
forests, the feast of the sun. The Insects in their countless
hordes carried everywhere a new animation. They swarmed
on the plants, devouring their leaves, boring into the bark,
draining the sap, sipping the nectar from the flowers, and
causing the appearance of bizarre swellings and galls on the
surface of stems and leaves where they had pierced them ;
but also fertilizing the flowers and manufacturing wax, honey,
and silk ; and, if they sometimes became troublesome pests,
like the Flies, or active propagators of disease, like all those
Insects which stab in order to draw blood, they became on

172 PRIMITIVE FORMS OF LIFE

account of their fecundity an inexhaustible source of food for
many other animals. The appearance of Insects therefore was
an event of first-rate importance in Nature, and deserves to be
closely studied.

There is no doubt whatever that these creatures are derived
from the higher Crustaceans, in which the number of segments
was fixed at twenty-one. In the insects themselves this number
is slightly reduced. At most it is nineteen in the larvae of the
primitive forms. It may diminish owing to the suppression or
transformation of the last segments of the body, but it is never
increased. Five pairs of appendages surround the mouth, as in
all Crustaceans,1 and this number remains constant. Further-
more, the mandibules and the maxillae are bifurcated like the
claws of the Crustaceans and exhibit on a base formed by two
articulations, an inner branch, the endo-podite, and an outer
branch, the exopodite, generally transformed into a tactile organ,
the palp. Beyond these appendages, in most Decapod Crust-
aceans, come three other pairs, more or less locomotor in function,
assisting also in the grasping of food, the maxillipeds. Finally
there are five pairs of walking legs and then the abdominal appen-
dages. The three pairs of maxillipeds have become the thoracic
legs of Insects ; all the others have disappeared, except at the
posterior extremity of the abdomen, where there are often
free appendages called cerci, and others utilized in the formation
of the external genital apparatus. The Machilidae, Lepismidae,
Campodea, Japyx, and some of the Staphylinidae,2 are the only
ones possessing true abdominal legs, which are repeated in the
Machilidae on almost all of the abdominal segments, whereas
among the Lepismidae they are confined to the last segments,
and in the other cases to the first. Everywhere else the abdomen
is devoid of appendages, but, on the other hand, bears as many
lateral respiratory orifices as it does segments. It is difficult
to say whether there is any connexion here between the two
facts, as in the case of Scorpions. In any case, the maxillipeds
have regained their locomotor functions and suffice for their
fulfilment. The three segments that bear them constitute the
thorax, and of these three segments the last two are provided
with wings. It is not very probable that these wings were

1 These are the antenna, the labrum, the mandibules, the maxillce, and the
infevior labium resulting from the fusion of two maxilla,

2 Spirachta eurymedusa.

PEOPLING OF LAND AND SEA 173

formed complete and unrelated to the parts already existing
in the original Crustaceans. There is general agreement that
they were primitively respiratory organs. This, therefore, is
the question we have to determine : is there any respiratory
organ among the Decapod Crustaceans that can possibly be
compared with the wings of the Insects ? Such an organ
actually exists. We saw that the second segment of the leg of
these creatures bears an articulated branch like the foot itself,
known as an exopodite. The first segment likewise carries an
appendage, the epipodite, but this appendage is not articulated
and has the form of a lanceolate plate. It rises from below the
carapace in an upward direction, and usually bears branchial
filaments. It is therefore a respiratory organ. Let us suppose
that the carapace, the protecting shutter of the branchiae,
disappears with the branchiae, and thus leaves the epipodite
exposed ; and let us assume that the segment of the leg that
bears the epipodite grows and becomes one with the wall of the
body ; then the epipodite, mobile, and to some extent already
directed backward, will be carried back against the dorsal
surface, just where wings are situated. It is exceedingly likely,
therefore, that these organs were originally respiratory
accessories of the feet — epipodites — which became wings by
a change of function when the carapace disappeared. The
' beating " of these accessories probably had no other object
in the first place than to renew the air around the Insect and
to assist its respiration, which, on account of the aerial tracheae,
had become very intense. Hence the wing is no new organ, but
a pre-existing one adapted to another function. Without this
organ, Insect-flight would never have been achieved ; it could
be regarded, therefore, as a preadaptation for flight, and this
simple deduction suffices to indicate how vague, inaccurate,
and elastic the word is, and how capable therefore of giving
rise to false interpretations.

We have thus seen how the creation of the Insect was evolved.
The earliest, Neuroptera and Hymenoptera, were represented in
the Devonian Period. Even in the Silurian deposits something
very like a wing of Hemiptera has been found. In any case
the Carboniferous Period witnessed the appearance of huge
Ephemeridae, of Libellulae seventy centimetres in span, of
gigantic Phasmidae, precursors of the Termites, the Cicada,
Fulgoridae, and the existing Hemiptera, in which the body

174 PRIMITIVE FORMS OF LIFE

possesses at birth practically every character of its permanent
form except the wings and remains active while these are
forming, instead of passing through that crisis of immobility
and renovation constituting the metamorphosis of the more
recent forms.

The prairies and forests also became full of life. But, at the
same time, another phenomenon of the greatest importance
occurred — the invasion of the land surface by the Vertebrates.
The starting-point in this great line of organic evolution,
naturally enough was the Fish ; two things were necessary
for its progress. Firstly, an important modification of the
respiratory apparatus, to protect it from the dangers that might
result from variations in the hygrometric condition of the air,
and secondly, the transformation of the fins into feet capable
of treading dry land. We cannot say which particular fossil
Fish manifest the first stages in the development of lungs,
though certain of the existing forms may perhaps give us some
idea of what took place. These are older types, such as
Polypterus and Protopterus of the African rivers, Lepidosiren
of America, and Neoceratodus of Australia, or relatively modern
forms like the Siluridse of the genera Heterobranchus, and
Saccobranchus inhabiting the Nile. All these freshwater Fish
live in large rivers subject to floods, which make the water
extremely muddy, and their respiration is greatly hindered
during the period when the water is polluted, so that they are
obliged to have a continual current of blood passing rapidly
through their branchiae in order to keep them active. The
branchiae are therefore more abundantly nourished. Their
epidermis develops more rapidly and ends by bearing
branching processes constituting supplementary branchiae.
These arborescent growths are highly developed in certain Fish
of the Siluridan order, the Heterobranchs and the Clarias,
and they are contained in a pouch-like expansion of the
branchial cavity. Unquestionably the external branchiae
observed in the early stages of Polypterus, and which, at all
events, are represented in the Ganoids, correspond to these
arborescent processes. They are very apparent in the young of
the Dipnoid order. Moreover, the expansion of the branchial
cavity of the Heterobranchs into the pouch-form in turn
corresponds in its vascular details to the pair of long pouches
attached to the branchial cavity in those other Siluridae, the

PEOPLING OF LAND AND SEA 175

Saccobranchs and Amphipiwits. The organs we call lungs in
the Dipnoid Fish differ in no way from these pouches in their
vascular qualities. They are themselves exactly equivalent to
the lungs of the Batrachian, which are provided in their early
stages, and sometimes throughout their whole life, with
external branchiae. There is certainly no genealogical relation-
ship between the Fish of the Silurid family and the Batrachians ;
it has not even been definitely established that the latter are
directly descended from the Dipnoi. If, however, we admit
a principle which has been so frequently demonstrated, namely
the same mechanisms acting on organisms of the same fundamental
constitution produce the same effects, then the arrangements we
have just compared permit us to assume that the Batrachians
owe their external branchiae and their lungs to the fact that their
ancestors had for a long time lived in waters frequently
polluted, i.e. in swamps or muddy rivers, as the Dipnoi
certainly did. The principle just invoked, moreover, is
the same that has brought about those resemblances, due to
causes other than heredity, which are found among different
animals, and which have recently been called phenomena of
convergence — a term far less exact than Isidore Geoffroy Saint-
Hilaire's expression parallelism.

Thenceforth the Vertebrates were provided with an apparatus
permitting them to brave the danger of desiccation, and to
breathe in the open air, but they could not move over the
ground by means of their fins ; they needed feet. How did
feet develop from fins, which they most certainly replaced ?
For can it be doubted that the amphibious Batrachians are
descended from Fish, and form the link uniting them with the
first definitely terrestrial Vertebrates, the Reptiles ? Here
we remain in the dark, but still we must know the reason why.
There are some Fish which walk with the aid of their fins,
but, unfortunately, these Fish are very different from the
primitive forms, and their comparatively recent attempts at
walking are far from perfect. Indeed, their fins are so little
adapted to walking that Anabas, which has special
arrangements in its branchial chamber permitting it
to live for a certain time in the open air, prefers, when climbing
trees, to use the spines of its operculum and the rays of its
caudal fin rather than its pectoral fins. However, the
Pteriophthalmidae, which live more out of water than in it, do

176 PRIMITIVE FORMS OF LIFE

walk by means of their pectoral fins, which present, so far as
this goes, no special modifications of the normal organ. The
Red Gurnet and Red Mullet walk on the sand by means of
three of the anterior rays of their pectoral fins, which have
become free and move like fingers. Frog-fish and analogous
fishes also make use of their pectoral fins for walking on sand, but
here we find a curious phenomenon of parallelism ; the portion
of the pectoral fins corresponding to the secondary rays is
attached as though it were a hand to a kind of arm supported
by two primary rays resembling the radius and the ulna, and
which themselves are mobile, and move on an unpaired element
resembling a humerus. There is, be it understood, no
genealogical connexion between the pseudo arm of the Frog-
fish and the anterior leg of the Batrachians, but the fact that
a similar development could have taken place so much later
at the expense of a fin already highly modified shows that it
might have taken place also at the expense of primitive fins
under the influence of the same mechanical conditions.

Unfortunately, the Dipnoan fishes, so closely related to the
Batrachians in many ways, have only left us representatives,
either in living or fossil form, in which the fin-skeleton is an
axis consisting of pieces placed end to end. They remain fairly
.simple in Protopterus and Lepidosiren, but in Ceratodus they
bear a double pennate series of multi-articulate rays. From
these facts we cannot draw any inferences as to the origin of
teet. We may feel fairly certain, however, that they are derived
from fins. Indeed, all the Fish and all the higher Vertebrates
are born with their limbs. Only the Batrachians are born
without them, and do not acquire them for a long time. Their
feet are formed slowly, in a very special way, and no longer as
accessories of the muscular segments or myotomes of the body
of the embryo, as in the case of all the other Vertebrates, but
as developments of small internal, isolated buds. The anterior
feet remain for a long time concealed under the skin in Frogs,
Toads, and other tailless Batrachians. This delay in the
appearance of the limbs can be explained if we assume that it
corresponds to a period in which the fins that the Batrachians
took from their ancestors, the Fish, are reabsorbed, after being
normally formed, in order to be replaced by feet. As required
by tachygenesis, to the normal period in which the fins
became gradually transformed into feet without ceasing to

PEOPLING OF LAND AND SEA 177

function there must have followed a period in which the
originally scattered elements which brought about this trans-
formation were placed in reserve, and began to develop into
feet only at the moment ripe for the reabsorption of the fin.
Subsequently the developmental stages of the fin destined to
disappear were still further economized by tachygenesis,
and the feet developed directly, but slowly, without first
passing through a fin stage. This would account for everything,
but we recognize without difficulty that the discovery of the
slightest intermediate link between a fin and a foot would be
infinitely preferable to our hypothesis, plausible as it may be.

Thus the development of feet is late and sudden. But
as the embryogenetic acceleration continues its task, their
formation by dormant buds in the manner of the Batrachians
is gradually abandoned ; they develop earlier and earlier
and finally revert to the primitive method of fin-development
by the formation of two buds on two consecutive muscular
segments of the embryo. This reversion, paradoxical as it may
seem, had already taken place in Reptiles. It doubtless results
from the fact that these muscular segments of the forming
embryo, which contributed in the course of their development to
the structure of the fins, each also furnished cells for the dormant
buds, at the expense of which the feet are destined to form
and replace the fins. Gradually these cells, instead of
detaching themselves from the muscular segments in order to
become one with the dormant bud, remain attached to the
embryonic muscular segments and are directly assembled in
order to form the foot. The time required for the formation of
the dormant bud is thus, in its turn, economized and nothing
remains to indicate the transformation that the fins have under-
gone in order to become feet.

Once formed in the manner proper to the Batrachians, the
feet preserve the same fundamental structure among all the
walking Vertebrates. They vary among themselves only in the
degree of proximity to the body of the distal extremities of
the humerus and femur again brought to move in vertical
planes, and in the reduction of the radius and fibula as well as
the number of digits.

With the acquisition of feet, the adult Batrachians possess
all that they need in order to live out of water, but it is other-
wise with the young, which are so frail that the parents are

178 PRIMITIVE FORMS OF LIFE

obliged to return to their earlier habitat, the water, in order
to spawn. Indeed, this is a general rule resulting from the
fundamental embryogenetic law, according to which the
young pass through the same stages of development as their
ancestors. As the latter were originally aquatic, they ought to
have offspring which begin with an aquatic stage, and then
progress more or less rapidly towards a terrestrial existence.
We may, indeed, consider it a law that when an animal has
changed its environment it returns for a long time after to its
original environment in order to reproduce itself. Thus the
Land-crabs return to the water in vast hordes to spawn there,
while the Seals leave the water to give birth to their young
on land. Such reversion, nevertheless, ceases in the end ;
the Whales, for instance, give birth to their young in the water.
The necessity for a periodical return to the water would
have inevitably retained the Batrachians, which are poor
walkers, close to the shores, and would have interfered with
the peopling of land. Fortunately, tachygenesis removed the
obstacle. Its action has been exercised in different ways. The
Ccecilians, Batrachians without tails or limbs, which live below
ground by burrowing in the earth like the worms they so closely
resemble, lay their eggs in their subterranean galleries without
returning to the water. None the less, in their embryonic
stage the young have enormous racquet-shaped or ramified
branchiae, completely enveloping them, which serve them
for respiration as well as for protection, and are finally
absorbed before birth. The young terrestrial Salamanders have
almost completed their metamorphosis when they are born in
the water, and the closely related black Salamanders of the
Southern European mountains no longer return to the water
to lay their eggs, but are now viviparous. Under favourable
conditions, viviparity can be induced in the land Salamanders
themselves. The young Pipa is likewise hatched at an advanced
stage of development, in the hollow pustules on the back of the
male, where the eggs have been lodged, the male remaining
in the water during the period of incubation. Certain Anura
(Leptodactylus ocellatus and L. mystacinus, Paludicola gracilis,
Pseudophryne australis and P. briboni) lay their eggs out of the
water, whither the young are brought by heavy rains after they
are hatched. The Chiromantis and Phyllomedusa attach their
eggs, enveloped in a glairy substance to the underside of the

PEOPLING OF LAND AND SEA 179

leaves of water-side trees on which they live. The young are
hatched within this sticky envelope, which the rains soak and
carry away into the stream below, together with the young
Batrachians inside. A Tree-frog of the Antilles, Hylodes
martinicensis, goes even further than this ; it also attaches its
eggs to the undersides of the leaves on the trees it inhabits, but
the young are born in their permanent form. The same is true
of Rana opistliodon and Hyla nebidosa. These are still but
tentative experiments, so to speak, in passing from an aquatic
or amphibian life to the life of the open air. Moreover, these
experiments, favoured by the large size of the eggs, very rich
in reserve substances, are relatively recent, since the tailless
Batrachians of the Frog type date back no farther than the
Tertiary Period, and there were Reptiles definitely terrestrial
in their habitat at the end of the Primary. In Tertiary times
the Batrachians renewed, this time without complete success,
the happy attempt of more remote times, to become dwellers
in the free air. However, the success of the earlier efforts had
been assured by a new phenomenon : nutritive material had
become accumulated within the egg, which finally became of
considerable size. Thus the embryo, finding within the egg all
the nutriment necessary, and not being compelled to expend
any of its energy in the search for food, employed it in
multiplying its structural cells. Hence its development was
considerably accelerated. The phases of development corre-
sponding to the aquatic life were gradually curtailed, finally be-
coming mere indications. Since the limbs remained unused they
were superseded in growth by the viscera and nervous system,
and the external form of the embryo was thus temporarily modi-
fied, the more so as it was obliged to expand temporarily above
the vitelline substance, which had become tremendously en-
larged, and to take on the appearance of a plate formed of three
superimposed layers, corresponding to the ectoderm, the meso-
derm, and the endoderm. Furthermore, those portions of the
embryo destined to disappear before birth have been constituted
by some of the cells born of the segmentation of the nucleus and
of the vital plasma of the egg, which have spread around the
spherical yoke mass and gradually enveloped it, producing the
blastoderm, which consists of cells that retain their primitive
aspects and merely fulfil a digestive function. This was
probably due to the fact that the first cells formed were early

180 PRIMITIVE FORMS OF LIFE

sufficient in number to become differentiated and to constitute
the essential parts of the embryo. As the nuclear substance and
the vital plasma of the egg were not yet exhausted, the cells
formed last remained outside the embryo, so to speak, and
merely served to help in nutrition. The egg itself was formed
in the same way ; the oldest elements within the ovary
or those best adapted for nourishing themselves alone
developed and nourished themselves at the expense of the
others.

The embryo naturally took its food from the region
immediately beneath it, the vitellus or yolk. It gradually
assimilated its substance, and consequently sank down into
it. Thereafter the extra embryonic blastoderm gradually spread
up and closed over the embryo, whilst it contracted below, thus
forming an envelope which is the less mysterious in origin in-
asmuch as it also forms for identical reasons and in the same way
around the embryos of insects. This is the amnion. The sac
becomes filled with liquid, and henceforth the embryo is
protected against all risk of desiccation. Respiration is accom-
plished in a fashion that is somewhat roundabout, but
therefore all the more interesting. Minute renal ducts early
appear in the mesoderm and empty the products of their
secretion into a pocket or receptacle which is nothing more
nor less than the embryonic bladder. This sac has no
external opening. Hence it retains the products of secretion
which it receives, and becomes so greatly distended as to
nearly line the amnion itself, while a close network of vessels
is formed in the thickness of its walls ; this is the allantois.1
As this membrane is extremely rich in vessels, is separated only
from the outer air by the thin containing membrane of the
amnion, and presents a large surface, it is admirably fitted to
assure respiration for the embryo all the time that the lungs are
not in communication with the outer air. Here we have a new
example of those changes of function resulting from the
accidental concurrence of circumstances to which Dohrn, as
we have already pointed out, so justly called attention.
Protected against desiccation, abundantly supplied with
nourishment, and breathing adequately, the embryo is now
developing under favourable conditions, and the process is

1 From a\\as sausage, so-called because at first it has the form of a
closed tube recalling that of a sausage.

PEOPLING OF LAND AND SEA 181

accelerated. It passes rapidly through the patrogenetic phases
of its evolution that had as their end the hereditary formation of
organs such as the branchiae, which it now has no need to
develop and can resorb as soon as they appear. Before leaving
its egg-shell the embryo can await the acquisition of sufficient
vigour to enable it to seek its own nourishment and to win
victory over those untoward chances to which existence in
the open air might expose it. The mother is no longer obliged
to return to the water in order to obey the hereditary instinct
of an aquatic organism which still exercises influence upon her
progeny. Independence of a humid environment, together with
an air-breathing mode of life, is finally acquired for the
Vertebrates. It is the life that will be led by Reptiles, Birds,
and Mammals, and which will make them masters of the world.
Since the respiratory system was at first feeble, and the
arrangement of the circulatory system a survival of the time when
breathing was done by gills, the internal combustion in the body
of the Vertebrate was not capable of producing a body-heat
that could defy the variations in the external temperature,
for the oxygen with which the blood plasma was only very
incompletely saturated did not suffice to supply the organs
with all they could have consumed. The creature lived in
a state of dependence on these conditions. Its internal
temperature, which regulated its activity, varied according to
that outside. When the latter fell below or rose above certain
limits the vital functions either decreased or ceased altogether.
The animal's vitality thus became intermittent. This is the
case with Reptiles. However, in their own way, and by different
methods, both Birds and Mammals succeeded in bringing their
lungs to a high degree of perfection, and in completely separating
in the heart and circulatory system the blood charged with car-
bon dioxide from the blood saturated with oxygen, thus assuring
a full supply of oxygen to the structural cells and organs, to
whose existence and functioning it is essential. This functioning,
if it consumes energy, develops a proportionate quantity of
heat, both the energy and the heat resulting from the com-
bustion of foodstuffs. Moreover, the heat developed is retained
within the organism once it has become warm, by the layers
of air imprisoned between the feathers of birds and in the fur
of Mammals. Certainly neither feathers nor hairs were
instituted for such a purpose ; these tegumentary growths

182 PRIMITIVE FORMS OF LIFE

were probably formed as a result of the stimulus which
perpetual contact with the air exercised upon the skin, and which
brought about, especially above the richly vascular papillae
of the skin, the rapid multiplication of the epidermic cells
which quickly dried up and accumulated outside the area
where they had multiplied. In this way there developed a
whole group of structures, with no particular object, but
accidentally adapted to protect the animal against loss of
heat. This protective apparatus, which has played the same
part among the Birds and the Mammals, owes its origin in
these two cases to entirely different circumstances. Birds, as
we shall see later, are only a specialized form of Reptile, itself
evolved from the Batrachians, whereas Mammals are directly
evolved from the Batrachians. Their evolution was parallel
with that of Reptiles, whereas the Bird, in a sense, was the
ultimate achievement of the evolution of the Reptile. The
Batrachians have a skin particularly rich in sensitive organs
and glands of all sorts. These glands have totally disappeared
in Reptiles, except in limited areas of the body, such as the edge
of the thigh in Lizards. The sensitive organs are equally few
and far between. Birds, like Reptiles, have a dry skin, and their
tactile organs are collected in definite regions of the body.
Their feathers develop like little thorns at the top of
dermal papillae that then become invaginated in the skin. In
the Mammals, on the contrary, the skin remains moist or
softened by numerous glands, the sudoriparous glands
producing sweat, and the sebaceous glands producing a liquid
which lubricates the hair and renders the skin oily. The hairs
themselves are modifications of a part of the sensitive organs of
the Batrachians. The bulb is often surrounded by a nervous
ring, turning them into tactile organs of great sensibility.
Instead of being formed like feathers, at the head of the
papillae, they arise from a deep epidermal bud which is buried
in the dermis or true skin and there, so to speak, indents
the pilary bulb. Certain skin-glands specialize in the
secretion of milk, and have given rise to the mammce which
furnish the young with their first food. The disappearance of
the skin-glands has made lactation impossible in Birds, whereas
it has become characteristic of Mammals.

Thus the nature of their skin might seem to accentuate the
differences which separate Reptiles and Birds from Mammals.

PEOPLING OF LAND AND SEA 183

On the contrary, it has brought them closer together, in that in
both it contributes to their protection against chilling, since it
preserves a constant internal temperature in spite of the
variations in the external air ; that is to say, it renders them
warm-blooded animals endowed with a new independence of
external environment, and capable of resisting its modifications,
thus enabling them to achieve the highest organic develop-
ment of all living creatures. This achievement was reached,
however, by two different paths, not directly, but by a
combination of circumstances nowise working towards
that end.

When the organisms of the warm-blooded Vertebrates
became accustomed to a constant temperature, this
temperature had to be artificially assured to the embryo,
which being inactive, could not itself produce it. This was
achieved passively in Mammals and actively in Birds, which
would thus seem in this respect to have made a definite
advance at some given moment. Those mammals which to-day
are least removed from the ancestral forms, the Monotremata,
represented by the two genera Omithorhynchus and Echidna,
lay their eggs in a sort of nest resembling a Bird's, and sit on
them in the same way. In the Marsupials, which come next in
the order of evolution, the eggs are no longer deposited. They
remain small and are retained in the womb of the mother,
where they develop without, as a rule, being in any way
linked with its walls. At birth the young are very small, and
their limbs are poorly developed. They are placed by the
mother in the ventral pouch, which most Marsupials possess,
and which contains the mammae, and here they develop. In
other Mammals the egg, detached early from the ovary, passes
into the uterus before it has exceeded in size the tenth of a
millimetre. It then contains only a very small amount of
reserve material. This, however, does not approximate it to
the small eggs of Fish, or even of Batrachians. It is not a
primitively small egg, but an egg which has reverted to a small
size, and which has hereditarily preserved the method of
development imposed upon large eggs by the enormous size
of their yolk. The reason for this mode of development, quite
obvious in the case of the large eggs, no longer obtains here,
and would be unintelligible and absurd if we did not know that
the primitive Mammals were oviparous and laid large eggs,

184 PRIMITIVE FORMS OF LIFE

like the Reptiles and Birds. The small eggs of the present
Mammals produce a yolk-sac, an amnion, and an allantois
like those of the Birds, and these organs, which under
Mammalian conditions cannot be accounted for without
recourse to heredity, are utilized in a new manner. It is at their
expense, and with the more or less active assistance of the
womb, that a placenta is formed, by means of which the young
Mammal can obtain from the blood of its mother the nutritive
substances not found in the egg. When the organism suddenly
abandons the womb, as a result of the mother's accouchement,
these substances go on accumulating in the parent's blood,
where they are no longer required. It is then that the glands of
the skin intervene and eliminate them. Those on the ventral
surface, stimulated by the incessant friction or the suction of the
young over which the mother is lying in order to keep them
warm, grow larger and finally become the w//&-producing
mammas that for a long period will furnish the only food of the
newly-born. Probably these glands were first differentiated
as a consequence of the twin acts of laying and brooding in
the oviparous Mammals, whose young simply licked the walls
of the ventral cavity in which the egg was still incubated.
Subsequently these differentiated glands became localized in
the ventral pocket where the Marsupials carry their young.
In the placental Mammals they were eventually multiplied
in two symmetrical lines. Both their number and the position
occupied were gradually brought into relation with the size of
the litter and the habitual posture of the mother, in conformity
with Lamarck's principle that use and disuse influences the
development of the organs independently of natural selection.
Dogs, Cats, and Pigs, in spite of the differences separating them,
have numerous mammas, because of the equally large size of
their litters ; the Horse family, Ruminants, and Monkeys,
which produce but one or two at a time, have only two or four
mammas. In fleet Mammals, these mammas are concealed between
the posterior limbs in such a manner that the young are hidden
and protected, while being suckled, by the body of the mother,
who stands erect while it suckles. Animals which use
their arms in climbing, like the Monkeys and Sloths, or to
hook themselves on to resting-places, like the Bats, or which
raise the anterior region of the body out of the water in order
to feed their young, like the Sirenians, have the mammas

PEOPLING OF LAND AND SEA 185.

placed on the breast. The position and number of the mammas
is thus seen to be independent of both diet and internal
organization, and simply depends on the degree of fecundity
and the posture. Heredity can intervene here as elsewhere
and seem to interfere with the conclusions that should follow
the application of these principles. But in reality it confirms
them when we discover that the supposed disharmony is
actually a concordance with primitive conditions of existence
now abandoned. The gait of the Ant-eaters, which progress
by supporting themselves on the edge of their feet or the back
of their toes, indicates clearly that these animals, though to-day
they burrow, were originally climbers, and for this reason
opposed the palms of their hands. On the other hand, the length
of their nails and their reproduction organization show that
in spite of the tremendous difference in the form of their heads,
they are related with the tree-Sloths ; they have preserved as
a fact their pectoral mammae. Elephants also have pectoral
mammae, and their past, once revealed, should explain the
reason for this arrangement characteristic of climbing
animals, which our knowledge of their present habits does not
suggest as a primitive condition, though the crossing of their
radius and ulna lends confirmation to it.

We may thus sum up all that has just been said about the
origin of the land Vertebrates : —

They are descended from the Batrachians, whose eggs-
became very large owing to the considerable accumulation of
this nutritive substance. The volume of these substances
caused the formation within the egg of a blastoderm over and
above the very limited portion of it destined to form the
embryo. The abundance of nutritive material permitted that
intensive embryogenetic acceleration which had already
suppressed the ancestral fins of the Batrachians to progress an
additional step, in consequence of which the imperfect
respiratory apparatus of the aquatic young gradually became
transitory, then simply suggested, to disappear completely
before the birth of the embryo. Thus, within the egg, the
embryo passed through its entire series of metamorphoses
under the protection of an amnion and an allantois — of purely
physiological origin, as we have seen. Henceforth the egg could
be deposited in the open air, protected as it was by a solid
shell. This stage of evolution, independently of the fate reserved

186 PRIMITIVE FORMS OF LIFE

for the skin, is common to Reptiles, Birds, and to the ancestral
Mammals represented to-day only by Monotremata.

While this evolutionary stage is maintained among the
dry-skinned Reptiles and their descendants the Birds, a
regression takes place in the viviparous Mammals. The egg
ceases to accumulate abundant nutritive substances, but
reverts to complete segmentation, which these substances
would hinder. Heredity, nevertheless, conserves in the embryo
the method of development it acquired by reason of their
former abundance although that method has lost its original
purpose. The enveloping membranes then change their
function, and, while continuing to act as a protecting organ for
the embryo, also form a placenta that serves as the link between
mother and embryo. New causes now intervene, however, in
the formation of this placenta ; first, the irritation which
two vital membranes of different nature produce upon each
other when they are perpetually in contact, and secondly, the
exchange of various substances that takes place between these
two membranes or through their walls, since it is impossible
that the embryo should draw certain substances from its mother
without giving others in return. Did the case actually present
itself, we might see here an explanation of the supposed
influence which the first male exerts on the later conceptions of
the mother, a process called tclegony. Thus it is no t the first male
but his first offspring, who would be responsible for influencing
the mother. Nor must it be forgotten, moreover, that immature
eggs confronted with spermatozoa frequently assimilate
them, so that strictly speaking the spermatozoa may thus be
added to those substances capable of influencing the egg's
final evolution.

Since the mammae arise as a result of the conservation of the
excretory functions of the skin, there are plenty of reasons to
account for a parallel evolution of the Mammals and Reptiles,
and for their having started to evolve at the same time ;
and to suggest that Mammals, at least the oviparous ones,
must be very early in origin. The case is otherwise with
Birds. They derive from a Reptilian type already highly
specialized, and also form a class whose homogeneity is in
marked contrast with the variety exhibited by Mammals.
Putting aside the development of feathers, a phenomenon of
a purely external order, the ancestor of the Bird must have

PEOPLING OF LAND AND SEA 187

first become a hopping creature, whose feathers, developed
quite independently, perhaps even before it acquired that
aptitude for hopping, later permitted flight. The only Reptiles
which have been preserved to us — we shall see why later
(p. 276) — are those whose method of progression was of the
humblest order. During the course of the Secondary Period,
however, certain Reptiles acquired dimensions of which even
Whales scarcely give us an idea, and nearly all had
developed modes of locomotion analogous to those of existing
Mammals. While many of them had bodies still sunken low
on the legs and trailed on the ground, like Crocodiles and
Lizards, others had straightened their limbs in such a way as
to permit the body to be carried high, dog-fashion, and a
number of others stood almost erect on their hind legs, like the
Kangaroo. It is among these last that we ought to look for
the ancestor of the Birds. This ancestor would have already to
possess the characters common to all : he must stand erect
with the sole of his foot straightened on his toes, five in number
at first, and his three median metatarsals, supporting the
upright sole of his foot, must unite in a single rod. The fibula
would be rudimentary, and united with the tibia at either
extremity. Now there exists to-day a Mammal whose hind
feet display most of these characteristics. This is the Jerboa,
or leaping Mammal par excellence. The union of the metatarsals
is seen also in Ruminants, the fleetest of the Mammals, whose
method of progression is nothing but a series of bounds. The
Bird, then, must be descended from a leaping and probably
arboreal Reptile. The a posteriori verification of this con-
clusion is provided by those Birds which have lost the faculty
of leaping, like Auks and Penguins, and which are essentially
swimmers and walkers, or the Parrots, which, instead of
hopping from branch to branch like Sparrows, hoist themselves
up using their hook-shaped beaks in the process. In both these
quite different cases, with nothing in common but the abandon-
ment of the leaping habit, the metatarsus is shortened and
broadened, and the three bones which united to form it are
tending to become isolated again.

From this vantage point we might be tempted to look for
the primitive Bird among those present-day birds unable to
fly : the African Ostriches, the South American Nandus, the
Indian Cassowaries, the Australian Emus, the New Zealand

188 PRIMITIVE FORMS OF LIFE

Apteryx. Their distribution seems to bear witness to their
antiquity, but a number of facts render this hypothesis doubtful.
We know from Archceopteryx, which has left fossil remains in
the Jurassic limestone of Solenhofen, that the ancestor of the
Birds preserved the long tail of the Reptiles ; that the jaws,
although invested with a horny plate, were not elongated into
a genuine beak, and that when this elongation took place it
did not at first cause the disappearance of the teeth with which
the jaws had been provided, since these occur also in the birds
of the Cretaceous Period, still inserted in separate alveolae,
in such forms as Archceopteryx, Ichthyornis, and Apatornis ;
or arranged in a common groove in Hesperomis, Enaliornis,
and Baptomis, which seems to presage their approaching
disappearance. It is scarcely probable that Archceopteryx
was capable of sustained flight. Its fore limbs were still
actually legs, whose four toes, provided with nails, were
definitely separated. The furcula was U-shaped, as in birds
of prey, but this form was not necessarily connected with flight.
In any case, the keel of the breast-bone was weak, and the long
tail, incapable of serving as a rudder, was rather in the nature
of a cumbersome ornament. Nevertheless, the feathers on
these anterior limbs and on the tail were already clearly
characteristic of the wing and tail feathers of flying birds,
so that they were actually prepared for flight.

This faculty was well developed in Ichthyornis of the Chalk for-
mations, whose tail was already reduced to a rump and the keel of
whose breast-bone was very prominent. But Hesperomis, al-
though more highly evolved, could no longer fly, which is enough
to render suspect the antiquity of the loss of this faculty, and leads
us to ask whether we were correct in including in one order,
i.e. the Ratitse, all those large Birds without a keeled breast-
bone and incapable of flight. It is quite likely that the Ostriches
are the only members of this order which represent a primitive
group, by reason of their large wings, their almost normal
digits, and their united pubes ; but they represent a much
modified form, since their feet have but two toes. The Nandus,
with their large wings and their united ischia, would be typical
of a second group coming nearer to existing Birds. TEpyomis,
Dinornis, the Cassowaries, and Apteryx with open pelvis and
small wings — indeed, wings in miniature, for they are so con-
structed as to deserve in every respect the name of wings —

PEOPLING OF LAND AND SEA 189

would be degenerate Birds which had lost the faculty of flight
as a result of long habitations of regions where no enemy was
to be encountered — like the Dodo, which is only a big pigeon,
the Penguin and the Auk, related to the Diver. Having
abundant food and living in complete security, they acquired
considerable proportions, and idly gave up all effort at flight,
since flight had become for the time being unnecessary. This
renunciation, resulting from the absence of any struggle for
existence, proved fatal to them when Man invaded their domain
and they could no longer flee from him.

The Ichthyosauridae were viviparous ; Seps, Slow-worms,
Hydrophis, Vipers, and other Reptiles have acquired this
character, and there is no a priori reason why certain Birds
should have developed it. Perhaps the size of their eggs made
a prolonged sojourn in the oviduct difficult, and their lime-
producing aptitude evidenced in the compact texture of their
osseous tissue, the thickness of the protecting shell of the egg,
and the precocity of its formation, were all obstacles to the
achievement of viviparity. Be that as it may, the Birds
remained oviparous, and all their energ)/ was directed to the
construction of nests in which they could lay and sit on their
eggs and shelter and warm their young. Their inaptitude for
viviparity must be very great, since it has reduced the Cuckoo
and the Cow-Bunting or Molobrus, a sort of American Starling, to
the expedient of confiding the incubation of their eggs and the
rearing of their young to other Birds, in consequence of the
disparity between the egg-laying season and the seasonal
migration.

We have now passed in review the conditions in which
the principal types, branches, and classes of the Animal
Kingdom arose. At the outset, and dominating even the
existing evolution of individuals, there is one property
fundamental to all living substance — the congregation
together in small masses which multiply by division and are
capable of association among themselves. The arrangement
of these masses or cells is at first regulated by purely
mechanical conditions : immobility and mobility determined
respectively two main structural types, the branched and the
segmented. One of the main divisions of the segmented
type, the Annelid Worms, with plastic body, thereupon

igo PRIMITIVE FORMS OF LIFE

lent itself to a series of modifications due to the immobility
which followed on a parasitic life or rendered necessary by
attitudinal alterations, themselves due to chemical phenomena
such as the secretion of lime or fatty substances, or to a
physiological phenomenon — the. great development of the
nervous system, followed by tachygenesis. Thus arose such
specializations as Flat Worms, Echinoderms, Molluscs, and
Vertebrates. The initial vertebrate forms, becoming degraded
as a result of their early fixation, constituted that peculiar
branch of the Animal Kingdom, the Tunicates. In all the varied
circumstances under which these animal modifications arose,
the organism, far from succumbing to unfavourable con-
ditions of existence, defended itself with success. It became the
artisan of its new organization, and, so to speak, created itself
anew by continuous efforts that could only be crowned with
success under conditions of absolute security. Natural selection
and the struggle for existence, as Darwin understood these
principles, had nothing to do with the creation of the great
organic types. Animals did, indeed, struggle for their existence,
but against the unfavourable conditions of their environment
and by reacting upon themselves, without having to fear
competition. They played an active part in their trans-
formations. How, indeed, could we suppose that animals
endowed with sense organs for receiving sensations, with nerve-
centres for their appreciation and reflexion to the periphery
in order to set the muscles and glands in motion, could remain
passive in the presence of incessant stimuli coming from
without ?

It was only later, when the chief differentiations into type
had already taken place, that competition made its appearance
on the over-populated sea-shores. Its first consequence was not
combat but flight — toward the open sea and the ocean depths,
the fresh waters, and terra firma. The urge toward the land was
especially productive of transformations. In so far as the animal
remained aquatic, the local multiplication of epidermal cells
were produced externally as easily as internally, and gave
rise to superficial prominent appendages utilized in respiration.
From the time the animal organism became terrestrial this
multiplication was able to give rise only to internal tegumentary
appendages — the tracheal sacs of the Arachnida and the
tracheae of the Myriapods and Insects. Lungs took the place

PEOPLING OF LAND AND SEA 191

of the gills in the Vertebrates. In order that these trans-
formations should produce their full effect, it was necessary
for the eggs to become transformed, for embryogenetic
acceleration to intervene, and for the organs resulting from a
reciprocal adaptation of mother and embryo to manifest
themselves. It is thus impossible to contain the history of
organic evolution in any one of those simple formulas so dear
to certain philosophers — creation by the word, astral in-
semination, preformation, use or disuse of parts, the
continuity of the germ plasm, natural selection, mutations,
and so forth. In reality all that goes to make up the energy,
motion, and substance of the world has taken part in its
turn in the evolution of life, and its organic forms are the
result of the unceasing action on them of these different
forces whose mobility only is translated by evolution.

Organisms themselves are capable of active intervention
in their own modification. When new organs appeared as a
result of the rapid multiplication or specialization of the
elements of a certain category, they might at first remain
unused, but favourable circumstances permitted the organism
to take advantage of them. The use to which it turned them
would then direct their subsequent modifications towards
some definite end. They would become more and more capable
of fulfilling the part that devolved upon them, and would
adapt themselves better and better to their function. In their
turn they might react on and modify the organs with which
they were connected. This is the histoty of the feathers of the
Bird and of the webbed feet of walking Vertebrates which once
more became aquatic. Feathers were at first merely an
epidermal investiture, consisting of long prominent papillae of
the skin, probably ramifying in all directions, as the down of
young birds would seem to indicate. The tegumentary papillae
then became imbricated, like the false scales of Serpents, and
consequently they tended to flatten, while at the same time
their mutual overlapping must have interfered with the
multiplication of the epidermal cells on the ventral and
dorsal surfaces. This multiplication then became confined to
the rim of the papillae, and brought about the quasi-symmetrical
arrangement of the branches hereditarily preserved after the
initial papilla was drawn back under the skin. Thus was
constituted the disc-shaped tegumentary appendage, made up

T92 PRIMITIVE FORMS OF LIFE

•of barbs sustained by a solid axis, which we call the feather.
There were feathers on the fore-limbs of those Reptiles which
stood erect on their hind legs built for leaping, and these only-
needed a certain amount of elongation to support the Reptile
in the air and transform it into a Bird. But once the faculty
of flight was acquired, the front limbs were modified in their
turn, no longer by accident, but by the actual use made of
them by the newly achieved bird. To give a greater solidity
to the wing during flight the two largest digits were closely
pressed against each other. These toes, still quite independent
in Archceopteryx, and almost so in the Ostrich, became united
and gave the anterior limb the definitive character of a wing.
In the same way, in order to assure the free movement of the
wing-elevating muscles attached to them, the dorsal vertebrae
were united, while the increasing volume of the muscles which
lowered the wings brought about the formation between them
of a prominent ridge attached to the sternum, called the
keel. A kind of epidermal accident has thus affected all
the rest of the organism, thanks to the animal's own activity,
and determined the direction of its evolution.

Analogous influences were exerted upon the organization of
the limbs by the web developed between the toes of walking
Vertebrates which had reverted to an aquatic habitat, but
the origin of this web was not accidental, as in the case of the
feather. No trace of it exists in any true terrestrial forms.
On the other hand, it is observed in all quadrupeds, no matter
to what group they belong, which inhabit marshes or water.
It is almost universal in the tetrapod Batrachians and occurs
again in Crocodiles and marsh or river Tortoises ; it is so
characteristic of water Birds that they are called web-footed
Birds ; it appears in Mammals, and, in an entirely independent
manner, in the Monotreme Ormthorynchus, the Desmans, which
-are insectivorous placental Mammals, in Myopotamus,Hydromys
and the Beavers, which are Rodents, and in the Martens, Otters,
and Seals, which are Carnivores. The fact that a similar con-
formation appears in animals so different, whose only common
condition of existence is their water habitat, and which is absent
in all those which do not share this habitat, clearly indicates
that identity in mode of life is the primary cause for the
development of the web. Indeed, we can readily understand
that contact with the wet ground would soften the skin of the

PEOPLING OF LAND AND SEA 193

toes, and that even the slight resistance of the ground on which
they press would make the skin stretch laterally so as to form
a web. Thus the web is no accidental product here ; it is
linked with a mode of life which the animal only accentuates
when it takes to swimming. The movements necessitated by
swimming have the same consequences everywhere. The better
to utilize its strength, the animal immobilizes the bones of its
limbs, and the pull on them of the muscles attached to the body
during the action of paddling, shortens the bones, while the
resistance of the water flattens them, and the web then
envelopes all the flat bones immobilized in relation to each
other and consequently brought closer together to form a
mutual support. Thus the entire foot is transformed into a
swimming paddle. This transformation, like the development
of the web itself, takes place in the most varied groups : first
in the Sauropterygians,1 the Ichthyopterygians,2 and certain
Mosasaurians — large Reptiles of the Secondary Period — then
in marine chelonians. Still later, after having been merely
rudimentary in the hind limbs of the Seals, it appears in
Halitherium, Zcuglodon, the Sirenians (Dugongs, Manatees),
and the Cetaceans. It is so clearly the mechanical conditions
of swimming that determine this foot-formation, that among
the Birds the Penguin's wing, also transformed into a
swimming organ, though it preserves all the essential characters
found in the skeleton of a bird's wing, is modified in the same
direction and transformed in the same fashion into a swimming
paddle. The same limb has thus been successively a foot, a
wing, and a swimming organ.

A parallel series of facts, similarly linked together, leads to
the development of flight in the climbing quadrupeds. When,
in climbing, they cling to the trunk or branches of a tree, the
skin becomes laterally flattened and thrust back on the base
of the limbs ; hence a kind of membranous parachute is formed,
which can be observed indifferently among Marsupials
such as Petaurus, Rodents like Pteromys and Anomalurus,
Insectivora like Galeopitheciis, Lemurs like Microcebes, and
culminates in the wing of the Bats. A striking instance of
this kind of arrangement is seen in certain specificalty
climbing Lizards of the Gecko family, which cling closely

1 Plesiosaurus and related genera.

2 Ichthyosaurus and related genera.

194 PRIMITIVE FORMS OF LIFE

to the trunk of the tree. In Urofilatus of Madagascar l the
skin runs back along the whole length of the head, trunk,
limbs, and tail, which is flattened into the shape of a trowel.
An analogous bordering of skin spreads out considerably in
Ptychozoon of the Malay Archipelago,2 and extends web-fashion
between the digits of the feet. This brings us to the remarkable
case of the Flying-Dragon of the Sunda Islands, in which the
skin at the sides forms a kind of a parachute supported by
bony rays attached to the ribs. It is probable that analogous
conditions gave rise to the wing of the Pterodactyls and
the other Pterosaurians of the Secondary Period. This wing
resembles that of the Bat in its mode of formation, but
instead of being supported by the four outer digits, the
pollex remaining free, as with the Bat, it is supported only
along the length of its anterior border by a single outer
digit which is greatly elongated.

Though it may be true that in certain cases we can explain
the intimate adaptation of animal organs to the functions they
carried out by supposing that these organs were formed with
no particular end in view, and that those animals, thus enabled
to lead a certain kind of life forbidden to others not thus
provided, profited by these organs to live an existence for which
they found themselves in some measure fire-adapted, the facts
we have just been enumerating show us clearly enough that
this hypothetical fire-adaptation can give us only an incomplete
view of the truth. Moreover, the word pre-adaptation itself
suggests the notion that animals have been formed in advance
to live in a predestined manner, and comes dangerously near
to reviving the old doctrine of determinism.

By the very fact that it is alive, an organism cannot be
considered to be passive. If it is subject to the influence of light,
heat, humidity, dryness, the regular return of day and night,
the periodicity of the seasons, in a word to everything that is
called external environment ; this influence must also react
profoundly on its internal environment, which thus becomes
a powerful agent of modification. Every living cell by the very
fact that it feeds, every muscular element that contracts, every
gland cell that secretes, and every neuron that undergoes
or elaborates a stimulus, pours into this interior environment
some substance capable of acting upon the cells with which it

1 LXI, 259. 2 LXII, 512.

PEOPLING OF LAND AND SEA 195

comes in contact, even though they may be separated
from it.

The wonderfully energetic action exercised by minute doses
of what are known as internal secretions, is only a particular
instance of this general phenomenon. The activity of an organ
does not modify that organ alone ; it may react on the whole
organism, as in the well-known instance of the maturation of the
ovum. It can determine modifications in other organs, and
become the cause of unexpected variations in characters, and
herein, perhaps, lies the secret of one part at least of those
sudden variations pointed out by Charles Naudin in 1865, upon
which was based a doctrine subsequently credited to De Vries.
It is the collaboration by means of their excretions of all these
structural elements in the formation of the internal environ-
ment, partly with the aid of the nervous system, and partly
in independence of it, which establishes the solidarity
characteristic of higher individualities. Every modification in
the chemical constituents of one of these elements may have
its echo in others, and, as Armand Gautier has shown, can
even modify the forms of living beings ; so much so that,
at some future date, morphology may be entirely bound up
with the chemistry, still so mysterious in many respects, of the
albuminoid compounds, diastases, and numerous other sub-
stances, to which, for lack of better knowledge, we now give
the vague names toxins, hormones, etc.

On the other hand, every time that two organisms
enter into permanent relations with each other they
gradually modify each other by reason of these very
relations ; this is what I described in 1881 x as the reciprocal
adaptation of organisms. A parasite is modified by its sojourn
inside its host ; but to an equal extent it modifies the body in
which it lives. Allmann in 1871 2 had already called attention
to the fact that the larvae of the Pycnogonida, which lodge as
parasites in Hydroids, give to the host merids that
nourish them the aspect of reproductory merids, and I
myself wrote in regard to this subject : " When the growing
reproductive organ attracts to itself the nutritive fluids, is it
not acting in the same way as a parasite which turns to its
own profit a part of the digestive activity of the polyp ? '\3
In fact the presence of the parasite often excludes all develop-

1 XXVII, 710. 2 LXXIII, 40. 3 XXVII, 234.

196 PRIMITIVE FORMS OF LIFE

ment of the genital organs, causing what Giard has called
parasitic castration. But this is not a matter of castration alone.
The appearance of the host may be modified to such an extent
that it appears to constitute a new species, as Jean Perez
showed in the case of the stylopized Andrena. These are all
specific instances of a general phenomenon which, when con-
sidered in its amplitude, ends by including within its own
circumference all the results of the struggle for existence and
natural selection. The present distribution and arrangement
of fauna and flora presupposes, in fact, a reciprocal adaptation
of organisms such that, without too much endangering each
other, they can live side by side. We shall have to apply this
principle in the course of our chapters on life during the various
geological periods.

Once these various organic types had been fully and securely
established, sea and land became rapidly populated. The
struggle for existence became more and more bitter, and if it
created nothing new, it did at least determine what could live
and what must die, assure the conservation and the
development of the most vital forms, and cause those gaps
among living organisms that mark off one species from the
other. This is what we shall find did actually happen when we
come to study the great geological periods.

PART III

TOWARDS THE HUMAN FORM

CHAPTER I

Life in the Primary Period

HPHE remains of plants and animals of former times, preserved
-*- in strata, deposited, abandoned, covered again, and under-
mined in turn by the sea or given over first to the eroding
action and then to the deposition of new layers of mud by
fresh water, form a series too incomplete for it to be possible
to reconstruct, from these resources alone, the world's primeval
aspect. Some of these remains — and it will appear strange that
they should be so few — have remained to some extent enig-
matical, or rather have left the palaeontologists uncertain as
to their true nature ; but the very rarity of such doubts clearly
demonstrates that the bounds set as the result of the study of
nature to-day have never been broken, that at all times the
same laws have presided over the evolution of life, and that the
considerations enabling us to relate existing forms retain their
full value for the past. They imply an order in the appearance
of organic types that determines for each series which forms
must have appeared the first ; they fix the position of those
that have disappeared, and even enable us to classify as
necessary evolutionary links certain forms that would be
perplexing if we had no such considerations before our minds.
It is interesting, therefore, to compare the indications of theory
with the evidence palaeontologists have hitherto obtained.

So far as plants are concerned, investigations from the
Silurian deposits onwards yield remarkable agreement between
theory and fact. The earlier strata also certainly contained
organisms. Theory indicates Algae as the first living earthly
organisms ; if we ever succeed in creating life artificially,
experiment will no doubt solve the problem ; but palaeonto-
logy provides no precise information as to the nature of the
earliest organisms. The oldest sedimentary deposits have
undergone in fact profound transformation. Certain layers

200 TOWARDS THE HUMAN FORM

may exceed 10,000 metres in thickness, but these have been
violently folded and eroded. All that remains to-day is that
portion of these colossal folds directed inwards into the
earth's surface where the heat generated lateral pressure at
the time of the folding, and the resistance of the still older
formations beneath to penetration by the edges of the folds,
was so intense that all the matter deposited by the
waters became dissolved or molten, and was regrouped
in crystalline mineral formation ; quartz, felspar, pyroxene,
mica, and amphiboles, whose association first produced
the mica-schists, then gneiss, and leptynites whose primitive
stratification is still discernible, and finally, the granites,
amphibolites, and unstratified porphyry, in which occur
isolated minerals such as garnets, tourmalines, emeralds,
and other hard stones. We could not expect to find in deposits
so completely metamorphosed, as the geologists say, the re-
mains of delicate primitive Algae. However, in Finland, the
oldest of these formations, the Archcean, contains carbonized
matter and specks of a special kind of lime called cipolin. We
may feel pretty sure that lime and organic matter found in
sedimentary deposits are all of organic origin. Hence there
must have been living organisms even at that remote epoch,
which was long known as the Azoic, because it was supposed to
correspond to an era in which the first consolidation of the
earth's crust took place, when life did not yet exist. A Scandi-
navian naturalist, J. J. Sederholm, has even found in it the
remains of organisms, but they are so ambiguous that some
have regarded them as plants, others as Echinoderms.

Furthermore, the existence of living organisms on the earth
during the Archaean Period is rendered highly probable by the
discovery of a variety of fossils in the Algonkian strata which
follow next, and are essentially formed of mica-schists, and
for a long time were also regarded as azoic. No plants have
been discovered here, nor yet in the Cambrian Deposits which
initiated the series belonging to the Primary Epoch, and which
at times attain a thickness of 3,000 metres. However, it should
be remembered that at Shunga, in the Government of Olonetz,
and at Snojarvi, in Finland, there are intercalated between the
layers of Algonkian schists beds of dense coal, presenting
here and there a metallic lustre, which are richer in carbon
than anthracite and often attain a depth of two metres.

LIFE IN PRIMARY PERIOD 201

Inostranzeff has given them the name of shungite. They may
result from vegetable fossils more highly altered than those
which formed coal measures.

During the Silurian Period Algae of the Siphoneae family
at last appear, and others that recall the large Laminaria of
to-day. With these are associated remains that would seem
already to be divided up into the three classes of vascular
Cryptogams : Horse-tails (Annularia) , Ferns (Sphenophyllum) ,
and Club-mosses (Sigillaria). The presence of Siphoneae is of
especial interest. These Algae, which still exist, may grow to
a large size, remain spheroidal (Codiaceae, such as Grivanella),
or branch out like the higher plants, the branches recalling
leaves and even forming whorls (Dasycladeacae, Palceoporella,
Rhabdoporella, Vermiporella). Despite this, they do not show
the cellular structure so general in organisms that are no longer
microscopic. The body, enclosed within a wall of cellulose,
supported by an irregular network of threads of the same
substance, consists only of an amorphous protoplasmic mass
within which are scattered numerous nuclei. In view of this
we may ask whether the cellular structure of almost all the
present animals and plants is not a secondary development,
resulting from an equal distribution of an originally continuous
protoplasmic mass between the nuclei which contain the sub-
stances regulating nutrition, such as chromatin. In the
cellular Algae we pass, by finely graduated transitions, from
organisms reduced to a minute sphere (Prutococcus) , or to a
single cell (Desmidiaceae, Diatomaceae) to filamentous Algae
(Confervae), Algae spread out in undivided lamellae (Ulva),
dentated or serrated (Fucus), and others in which we can
already discern a pediculate portion simulating a root, and a
free, more or less cylindrical part analogous to a leaf-bearing
stem (Cystocira, Macrocystis, etc.). Rudimentary leaves
already begin to be characteristic of cellular terrestrial plants
of the class Muscineae, in which gradual differentiations can
be traced from Hepaticae, such as Riccia or Marchantia up to
Mosses. Thus, leaves which in the higher plants are so indi-
vidualized that we can say that such plants are really an
assemblage of leaves arising one from the other, whose con-
crescent parts have formed the branches and the stem (p. 100),
have only acquired this individuality, like the cells, as a
secondary development. Just as the intimate structure of

202 TOWARDS THE HUMAN FORM

plants results from the multiplication of a single initial cell,
the ovum, so their general form is actually achieved by the
successive multiplications of leaves, beginning with two, or
even one.

Bernard Renaud discovered the presence in coal-seams of
monocellular Micrococci, already attacking the cellulose, as the
Bacillus amylobacter does to-day. On account of their fragility
the Algae, Hepaticae, and Mosses have rarely been preserved
in a fossil state, so that the forms by which vascular Cryptogams
(Horse-tails, Club-mosses, Ferns), the first plants with roots,
detached themselves from the Algae or the Mosses, is still
hidden from our knowledge. From that point, however, all is
clear — everything happened in conformity with the conditions
indicated by the law of tachygenesis. Grand'Eury has estab-
lished the formation of veritable ovules evolving into seeds in
plants — Pteridosperms, which are Gymnosperms in this
respect, though still Ferns so far as their leaves are concerned.
The Gymnosperms (Cordaiteae, Conifers, Gnetaceae, Cycads)
associated with the vascular Cryptogams are the only
terrestrial vegetable forms of the Primary and the
Triassic Periods. In the Jurassic certain questionable Angio-
sperm forms alone are known, and it is not until well into
the Cretaceous that we see such plants definitely flourishing.
While the Conifers among the Gymnosperms were multi-
plying vigorously, Dicotyledons were abundant, but they were
chiefly represented by small-flowered plants, generally uni-
sexual and with the flower arranged in catkins something after
the style of the cones of the Conifers. These were Poplars,
Willows, Birches, Myrica with male flowers often reduced to
one or two stamens, Beeches, Oaks, Walnuts, Figs, Bread-fruit,
Credneria, Plane-trees, Liquid-ambars, and Maples, to which
were added a few flowering plants : Ivy, Dogberry-tree,
Laurel, Saxifrage, etc. To these small-flowering Dicotyledons
were already added a few Gamopetalous plants, such as the
Viburnum and Oleander.

Next to the Dicotyledons with small unisexual flowers, the
oldest plants must be those in which the flower-parts, still very
numerous, have retained the helicoidal arrangement of the
Conifers and in which the sepals are often transformed gradually
into petals and the petals into stamens. These are the Magno-
liaceae, the Nympheaceae, Cacti, Ranuculaceae, Rosaceae,

LIFE IN PRIMARY PERIOD 203

Papaveracese, Berberidaceae, etc. It is rather astonishing that
there are not more of these plants among the fossils of the
Secondary Period, but we shall find other lacunae in the Animal
Kingdom that indicate quite clearly the paucity of the available
evidence. From the beginning of Tertiary times, all the
present-day plant-types can be traced. Their distribution,
however, is different, and we have seen how important is the
study of their geographical distribution to our knowledge of
climate in different parts of the earth. We need not go over
this again.

In the preceding pages (p. 109) we have given our reasons for
considering the Monocotyledons as being derived from Dicotyle-
dons living in marshy soil, and which owe to their ordinary
habitat in regions of this nature, their thick parallel-veined
leaves, their long underground stems, or their bulbs, and the
peculiar structure of their aerial stem, which resembles that
of the vascular Cryptogams, whose stem is likewise often
developed on the underground stems or rhizomes. Van
Tieghem has established, moreover, that the Graminaceae at
least, which appeared rather late, are Dicotyledons in which
one of the cotyledons has been suppressed. They must have
appeared after the Dicotyledons ; but it is impossible to
establish the exact date of the appearance of either. In any
case they became sharply differentiated only at the time when
the Dicotyledons were already numerous in the Cretaceous
deposits, and since the Dicotyledons probably go back as
far as the Jurassic, the appearance of the Monocotyledons
in the course of the Cretaceous is in no way astonishing.

Theory and fact are, therefore, in perfect agreement. More-
over, as the laws of tachygenesis apply equally well to the
Animal as to the Vegetable Kingdom, we may have confidence
in the inductions we are going to draw from it as regards the
first of these kingdoms.

Theory demands for animals as logical an order of evolution
as for plants, but their variety is much greater. The unicellular
animal organisms called Protozoa, which constitute the first
step in animal organization, ought to have appeared first.
But we can hardly expect to find any traces of these delicate
organisms, as e.g. Rhizopods, with their diffluent protoplasm
incessantly changing form, either by sending out delicate
ramifications that often anastomose their network into still

204 TOWARDS THE HUMAN FORM

finer divisions, or by contracting in such a manner as to fray
out from their surface lobes of varying depths, as in the case
of the Amoebae ; Infusoria of definite form, motile on account
of their one, two, or more long, fine flagella, or, thanks to the
waving of vibr utile cilia, arranged either as a uniform fleece or
along regular belts ; or Sporozoa, living a parasitic life in the
bodies of other organisms. Of all these generally microscopic
organisms only the Rhizopods, the most delicate, have left
behind any traces. Amongst them are trie Foraminifera, which
secrete a sort of calcareous covering that is often exceedingly
elegant ; and the Radiolaria, which secrete silica that is
distributed throughout their substance in delicate disjointed
bodies of varied form constant for each species, or is united
in a kind of skeleton which often has the appearance of
a ball of lace stuck all over with needles. Cayeux has
found spicules of Radiolarians in the phtanites of the
Algonkian strata of Lamballe (C6tes-du-Nord) . As beds of
lime are already found in these layers, one might imagine
that skeletons of Foraminifera had been incorporated in
them. But the earliest Foraminifera definitely identified
date back only to the Cambrian Period, and it is worthy
of note, as confirming the stability of the simplest living
forms, that these are Orbulince and Globigerince , whose ana-
logues still float on the surface of our seas to-day in consider-
able numbers, and when they sink to the bottom form a
Globigerina ooze very much like that which resulted in our
white chalk.

Ramified animals, as we have seen, are divided into three
distinct series parallelly evolved, whose starting-point was
from certain initial forms that can be described schematically
as ovoid vase-shaped organisms fixed at the base and differing
among themselves in the make-up of their walls,1 and which we
propose to call Spongomerids, Hydromerids, and Bryomerids.

Embryogeny alone could have told us how a Spongemerid
becomes transformed into a Sponge ; but unfortunately the
Hexactinellidae, the sponges that go furthest back into remote
times, are not sufficiently well known from this point of
view, though their life-history would be particularly instructive.
The most beautiful of the Sponges, they have continued through

1 Cf. p. 115.

LIFE IN PRIMARY PERIOD 205

all the geological periods and are still plentiful in the depths
of the Atlantic and in the less profound regions of the Philli-
pine and Japanese waters where they attain a considerable
size. The exactly rectangular arrangement of the six branches
of the large spicules, constituting the essential part of the
skeleton, gives it the appearance of elegant opaline lace. They
are generally vase-shaped, with the upper opening protected by
a kind of operculum formed of siliceous tissue with delicate
meshes. Within the fugitive living tissue enveloping the
skeleton are regularly arranged delicate thimble-shaped sacs
whose walls are covered with large cells each bearing a vibratile
flagellum arising from the bottom of a funnel. These are the
active elements, the choanocytes found in all Sponges, and which
so exactly reproduce the form of the remarkable Infusoria
of the Choanofl agellate order that James Clarke classed Sponges
as simple associations or colonies of these Infusoria.1 It is not
impossible that the earliest Sponges were gradually formed by
an association of this kind, in which diverse elements were
afterwards differentiated. As a matter of fact, the Choano-
rlagellates frequently form both ramified and compact colonies,2
and one of the last has even been called Protospongia.

The ovoid sacs of the Hexactinellidae are found also in
the Hexaceratinae, which also have six-branched spicules
made of spongin, the elastic and flexible substance seen in
the fibres of toilet Sponges. These sacs were the origin of
the flagellate chambers of other Sponges. They are always
connected with a system of tubes which bring to them the
water that has been attracted by their flagella, and which
then passes into the efferent cavities opening on the outside
by means of large orifices, the oscula. To the Hexactinellidae
must be added, somewhat later, Sponges with calcareous
spicules, belonging to the Pharetronid family,3 and then the
Stony Sponges with spicules united by a siliceous glaze, the
Lithistidae,4 and finally the sponges with fundamentally four-
branched spicules (Tetractinellidae) or with spicules in the
form of a pin (Monactinellidae). From the last are derived
fibrous sponges without spicules, employed for domestic
purposes. But the organization of Sponges has remained

1 LXIV.

2 Salpingceca, Codosiga, Codonocladium, etc.

3 From the Trias onward. 4 In the Jurassic.

206 TOWARDS THE HUMAN FORM

fundamentally the same from the very beginning ; it has been
modified only in the details of its canalization.

At this point we are confronted with problematical
organisms, Oldhamia, not found later than the Cambrian ; the
Graptolites, innumerable in the Silurian Period, but extinguished
in the Devonian in the ramified forms called Dictyonema ;
Pleurodictyum, confined to the Devonian, and many others
that have been attributed somewhat hazardously to the
Hydromedusae, to Corals, or to Bryozoa.

The fossil Oldhamia are fine ramified imprints radiating
from a centre {Oldhamia radiata), or diverging from the top
of a broken line {Oldhamia antiqua). They have been classed
both as Algae and as Hydroids, and it has even been thought
that they simply represent the trail of Worms. The fossil known
as Oldhamia radiata, according to this notion, came from a
tubicolous Worm living in the mud, which must have placed
the anterior part of its body in turn all round its hole. And
Oldhamia antiqua marked the track of the Worm which, as
it crawled over the mud, must have frequently changed its
direction, hesitating at each change and inclining the anterior
part of its body at different angles before deciding on its new
path. These changes of route would occur at such regular
intervals on this hypothesis as to be quite astonishing. We
know, too, the tracks of Annelids, in the Cambrian, at first
taken for Algae, and called Eophyton ; they were broad
and strictly rectilinear. Apart from their radiated form, not
a single character justifies us in interpreting Oldhamia as
Hydroids, and it is difficult to see in them merely ripples
on the surface of the Cambrian mud — another explanation
proposed. In short, there is no really plausible hypothesis
which we can adopt.

The Graptolites lasted much longer ; they lived through
two geologic periods and in such great numbers that they have
ornamented the entire surface of certain slates. They consist
of minute chambers with narrow openings* arranged in close
formation in a single plane extending the whole length of
a hollow stem. These chambers may appear on one side of
the stem only (Monograpfiis), or on both (Diplograptus,
Pkyllograptus, Climacogr aphis) ; the stem may be rectilinear
as in the preceding genera, curved in the forms of hooks
{Rastrites), double and branched in the form of a printer's

LIFE IN PRIMARY PERIOD 207

" bracket " (Didymograptus), in three (Cyrtograptus), or four
(Tetragraptus), or in a large number of radiating branches
(Dichograptus), curved in the shape of an " S " and bearing
branches along its whole length (Ccenogr aphis), twisted in the
form of a helix (Monograptus turriciilatus), or, finally, arranged
in the form of a net (Dictyonema). The general view is that
these are all ttydroid polyps. Allmann, however, pointed
out that the opening of the chambers was too small to allow
a polyp with tentacles to pass through, and he also called
attention to the fact that in the Plumularice there are two
kinds of chambers, one large, inhabited by polyps, the other
smaller, sheltering only fishing filaments, the dactylomerids,
which can emit protoplasmic filaments from their surface,
capable of capturing prey and digesting them, and con-
sequently of feeding themselves. He noticed also that at
first the colonies of the Plumularias were formed exclusively of
these small chambers with their fishing filaments, and he was
therefore fully justified in considering the Graptolites as
Hydroids which had persisted in this state although adult. An
important discovery made by R. Ruedemann, however, has
altered the whole question. It was formerly believed that the
stems so abundantly found in the Silurian schists were free,
and they were classified in as many different species as forms
discovered. In reality stems presenting very different
characters were attached to a soft body formed generally of
a kind of central globe surrounded by a crown of smaller
globes between or under which the stems with their chambers
were attached. This body has been regarded as a mere floating
organ, but this would greatly diminish the importance of so
large an organ, which would seem moreover to have been
provided with a mouth. It seems more likely that this was
the real organism comparable in structure to a Medusa or
Cydippe, which both have long tentacles, and that the stems
with their chambers are really, as Allmann thought, fishing
filaments, nematophores or dactyomerids invested with a rigid
coating instead of being free and flexible. How were the
helicoidal Graptolites, whose axes are connected by an inter-
mediary network, attached to the central organism ? That
question has not been answered.

The study of existing hydroid polyps is very instructive. We
have already seen how they gave rise to the large bell-shaped

208 TOWARDS THE HUMAN FORM

Medusae, which were bordered at their opening by a mem-
branous ring or velum, and how by embryogenetic acceleration
they gave rise to the large Medusae, umbrella-shaped, without
this velum— Pelagiae, Rhizostomata, etc. All these Medusae have
four planes of symmetry, and we can connect with them certain
internal impressions with the same kind of symmetry, called
Medusites and Laotira, found in the Cambrian. The relation-
ship of Brooksella with the Medusae is less evident.

However, the hydroid polyps possess another interest
for us.

It was formerly believed that all calcareous poly paries
were made by organisms similar to those that build up the
coral branches. Only two groups were recognized. The poly-
paries, formed of tubes divided into storeys by horizontal
plates — the tabulate polyparies — and the drugose polyparies,
so called because of their coarser appearance. During the
famous voyage of the Challenger, a member of the expedition
named Moseley showed that among the smooth group there were
polvparies whose bases were constructed by organisms called
Alcyonarians,1 akin to the coral-builders, but that the others, as
Dana and Louis Agassiz had recognized, were the work of Polyps
of the Hydroid group. I myself have shown2 how the series of
Hydroids with smooth, calcareous tabulate branches, which
Moseley classed together as Hydrocorallia, and which comprises
Spinipora, Millepora, Allopora, Stylaster, Cryptohelia, etc.,
leads directly through special groups analogous to those that
have produced the Medusae, to the present-day Polyps which
build reefs, and to the ordinary Sea-anemones, thus forming
together the order of Hexacorallia ; and I have pointed out
how the embryogenetical researches of Lacaze Duthiers on
these Polyps, and those of Marion on the Alcyonarians, force
us to the conclusion that, in spite of their eight tentacles, the
Alcyonarians were only Hexacorallia modified by embryo-
genetic acceleration. Now the Hexacorallia did not make
their appearance before the Triassic of the Secondary Period,
so that it is not very likely that Heliolites and Plasmopora of
the Silurian, and Cladochonus and Syringopora of the
Carboniferous, could have been Alcyonarians. They are far
more likely to have represented special types of hydrocorallines,

1 Heliopora. 2 XXVII, 298.

LIFE IN PRIMARY PERIOD 209

and the same can be said of the other forms included by
various writers among the Tabulata.1 On the other hand,
the Hexacorallia are noted for the defmiteness of the
chambers of their polypary and the regular arrangement
into radiate systems of the septa dividing them, and all these
characters can be logically deduced from the theory classing
them with Hydrocorallia.

Nothing like this is found among the Tetracorallia of the
Primary Period which have septa and chambers of a very
rudimentary character. Some fixed Medusae exist, e.g. the
Lucernarians and others, and the large Medusae constituting
the Acelephae class, also begin here in the form of fixed
Scyphistoma. Since certain Hydractinias, and all the Hydro-
corallia, which are real hydroid polyps, secrete lime abundantly,
there is nothing improbable in the assumption that organisms
comparable with Lucernaria and the Scyphistoma were able to
do the same, and we should therefore regard as kindred animals
the Tetracorallia which constructed around the continents
of the Devonian and Carboniferous ages the vast coral reefs
which afterwards became marble. Theoretically, these Tetra-
corallia should have appeared before the Hexacorallia.

Pleurodictyum problematicum of the Devonian Epoch, which
looks like a deep funnel, with walls formed of elliptical particles
united by transverse twigs, at the bottom of which is
found a kind of a Serpula bent back upon itself, more nearly
resembles a Bryozoan like the Adeona of the present day, which
is likewise funnel-shaped, than a hydroid. It would, however,
be imprudent to go too fast when certain forms intermediate
between the Hydrocorallia and the Bryozoa are under dis-
cussion. The latter are easily recognized from the Silurian
onwards. They have persisted in large numbers up to the
present day without ever playing an important part, or showing
the least tendency towards a higher evolution. We shall
therefore pass them over like the Sponges.

We now come to the Artiozoa, which began simultaneously
in two kinds of segmented animal organisms, the Arthropods,
which have preserved their primitive structure almost intact,
and have not attained a high development, and the Worms,
which are also segmented but display great plasticity. We

1 Favosites, Alveolites, Trachypora, Aulopora of the Devonian: Chcstetes,
Michelinia of the Carboniferous.

210 TOWARDS THE HUMAN FORM

have previously enumerated their various metamorphoses, and
presaged their great future.

The evolution of the Arthropods can be outlined very
simply. We have already called attention to Peripatus,
that ambiguous creature tossed from Worms back to
Arthropods, which even to-day still appears to be
distributed along the edge of the old Gondwana continent.
All the segments of its body are alike, except three : the
first, bearing the tactile appendages comparable to antennae ;
the second, bearing the mouth ; and the third a pair of
appendages directed towards the mouth, and provided with claws
that serve as mandibles, incorporated with the cephalic region
through the formation of a kind of lip rising behind them
and united to the corners of the mouth, thus enclosing them in
a kind of buccal cavity. Similarly among the Arthropods,
the locomotor appendages are successively put to the use of
mastication in varying numbers and different ways. The first
stages in this adaptation are still unknown, but the Algonkian,
which has already revealed so many traces of the Arthropods,
may perhaps some day give us the desired information.

In the Cambrian Period we find ourselves in the presence
of fairly advanced adaptations. In one group the five
(Eurypteridae) or six first feet (Limulus) differ but little from
the locomotor appendages, or, at times, even preserve this
character, but they surround the mouth and from the base arises
a laminated process which assists in mastication. The first
pair in Pterygotus resembled pincers, and this creature during
the Devonian Period acquired a length of two and a half metres.1
This first pair resembled the appendages of Eurypterus, and in
both these genera the fifth pair, very large and flattened, have
become a swimming organ. In Limulus, which already existed
in Silurian times, and to-day are to be found in Mouccan
and Japanese waters and along the two sides of the Isthmus
of Panama, the first five pairs of legs terminate as pincers, the
first being smaller than the others, and the extremity of the
last pair is furnished with complicated appendages that, how-
ever, hardly modify their appearance. All the segments
provided with appendages are united in a large cuirass bearing
the eyes, which, strictly speaking, might be considered as a kind

1 Pterygotus anglicus.

LIFE IN PRIMARY PERIOD 211

of head. These organisms are grouped together under the
name Merostomata, signifying that the limbs encircle the mouth.
It is worthy of note that in this group, so homogeneous in
appearance, Euryptcrns and Pterygotus lasted but a short
while, whereas Limitlus has persisted almost unchanged through-
out twenty million years.

Side by side with these organisms lived the Trilobites, in
which the first pair of appendages had already been trans-
formed into antenme, while the five other pairs preserved
the regular structure of the Merostomata, from which there is
no reason to separate them. Arising from the abdominal
articulations were very small feet surmounted by branchiae,
so fragile and delicate that for a long time they remained
unobserved. It is puzzling to see how such heavy organisms
could make use of them. They lived on the sand and could
no doubt descend to great depths, for some species are blind.
Others, on the contrary (JEglina), had enormous eyes. Two
longitudinal grooves running along the carapace, demarcated
a median area, the glabella, which they separated from the
genes, or cheeks, on either side of which were placed the eyes,
and these grooves extended the whole length of the abdomen,
whose terminal articulations were sometimes united in a
pygidium appendant to the carapace (Bronteus, Agnostus). The
body was thus divided into three longitudinal belts, hence the
name of Trilobite. Embryos of Trilobites have been recovered,
those of the Cambrian genus Sao in particular, and it has been
established that after the carapace and the last segment had
been formed, the others were formed one by one in front of
the terminal segment, so that the method of segment formation
nowadays common to Arthropods, Annelid Worms, and
Vertebrates dates back at least twenty million years. That is
equivalent to saying that it has never varied, any more than
the mechanical conditions which determined it.

In Primary Times the Trilobites were distributed through-
out all the seas. They were especially numerous during the
Silurian and Devonian Periods, but in the Carboniferous
were represented only by Prcetidse, themselves reduced to
two genera, P rectus and Phillipsia, somewhat resembling the
Cambrian Paradoxides, the oldest Trilobites known. Trilobites
present a large variety of forms. Not only can we distinguish
littoral and deep sea species, but also, as one might say, local

212 TOWARDS THE HUMAN FORM

species and genera, permitting the delimitation of zoological
provinces even in the Cambrian Period. At that time the
species and even the genera of the Northern sea inlets were
distinct from those of the Tethys ; and the Circum-pacific
Ocean also had its own species. Sao, Conicephalus heberti and
C. levyi, and Paradoxides mediter ramus were unknown along the
coasts of the North Atlantic Continent, where Olenus was
common. During the Acadian Period the first Asaphidae
appeared in the Pacific. Thence they spread towards the
waters of the future Europe, which they did not actually reach
until the Ordovician Epoch. Dicellocephalus was characteristic
of the region of the Circum-pacific Ocean, which extended from
the western shores of America to Australia, but Olenus was
absent. During the Silurian Period certain Trilobites acquired
the faculty of rolling themselves up into a ball, as the Wood-
louse and Glomeris do to-day. Their genera and species
multiplied, but remained characteristic of distinct zones.
The existence of such zones, however, does not imply a
difference of climate, for the calcareous deposits did not change
in character. The floating Graptolites remained cosmopolitan,
and coral banks continued to form in the northern as in the
equatorial regions ; therefore, the temperature must have
remained high everywhere. Nevertheless after the Ordovician
Period the Trilobites enable us to distinguish clearly the
Northern European, American, and Bohemian regions. The two
first tend to become merged during the Gothlandian Period,
on account of exchanges taking place between these regions,
particularly between America and Europe, by way of the
Arctic Ocean. In the Devonian Epoch this communication
disappeared, and the American and European fauna once
more became distinct. The American fauna extended from
the United States to South America and the southern parts of
Africa, while the European extended over the rest of the world.
The Trilobites lose all importance in the Carboniferous
Period. These strange organisms approximated to Crustaceans
in the possession of antenna? ; but Crustaceans have two
pairs and their buccal appendages have definitely become
mandibles, jaws, and maxillae. As in the Trilobites, five pairs
of appendages, or six as in Limulus, if we count the peduncle
of the eyes in the higher Crustaceans, are employed either as
tactile organs, or for prehension and the trituration of food.

LIFE IN PRIMARY PERIOD 213

The constant number of these appendages leads us to believe
that the Crustaceans may very well be descended from the
Trilobites. They must have diverged very early, however,
for in the Cambrian Epoch true Crustacea exist already, with
large membranous appendages serving both for swimming and
breathing, like those of our present Apas, which still resembles
the. Trilobite in some respects, or our Branchipus, Artemia, and
the Estheridse.1 There are also Crustaceans related to Cypris,
commonly known as Water Lice, and frequently used in
pisciculture to feed the fry. These have received the name of
Ostracods,2 because of their bivalve carapace resembling the
shell of the Lamellibranch Molluscs. These two orders were
thenceforth reinforced by the appearance of new genera, which
in some cases displaced the older genera and in others lived
alongside them. From the Silurian Period onwards the
Ostracods were replaced by the Cirripedes, represented to-day
by Balanidae or acorn-shells, shaped like sharp-edged
truncated pyramids, with which the rocks bristle at low-tide,
and Barnacles which suspend themselves by long peduncles to
floating wood or to the keels of ships. For a long time there
Mas considerable hesitation as to the place these organisms
should occupy; they are born in naupliiis form (p. 124),
a character common to all lower Crustaceans, and are later
transformed by the acquisition of a bivalve shell and six
pairs of bifurcated abdominal legs, into little organisms so
closely resembling Ostracods that they have been called
cypridian larvae. This stage implies a relationship not with
the present Ostracods, but with some still unknown pre-
Cambrian Ostracod. The cypridian larva attaches itself, by
means of a sucker in its antennae, to some solid submerged
body, and it is only then, while undergoing an important
change in attitude, that it finally acquires the characters of
a Cirripede.

Myriapods 3 and Insects have also been discovered in the
Silurian strata. This is important. We have seen that
Myriapods are derived from the early entomostracan
Crustaceans, and Insects from the higher Crustaceans, or
Malacostraca. Hence the existence of Myriapods and Insects

1 Hymnenocaris, Protocaris.

2 Isoxys, Leperditia, Primitia.

3 Archidesmus.

214 TOWARDS THE HUMAN FORM

in the Silurian presupposes the existence at some earlier epoch,
either the Tower Silurian or the Cambrian, of Crustaceans
belonging to these two orders. They have not been found.
Yet such gaps occur in all groups ; indeed, a group sometimes
appears to nourish in one epoch and then to vanish, only to
reappear later on in very much the same forms, and occasionally
to persist even till the present day. It is evident that these
disappearances and reappearances are only apparent. When
they are not merely the result of our own imperfect investiga-
tions they simply hide from us migrations that have taken
place owing to some alteration either in the composition of
the water, its depth, the nature of the deposits at the bottom,
or the direction of the currents, and so forth. Such phenomena
are neither uncommon nor in any way mysterious. Only a few
years ago a series of hard winters in the bay of Saint-Vaast-
la-Hougue, rendered famous by the researches of Henri
Milne-Edwards, de Quatrefages, Claparede, Grube, and many
others, caused the disappearance of the Comatulids and Asterina,
which lived there in great numbers, and brought in exchange
various northern species, hitherto unknown in these latitudes.
The old fauna has not even yet been restored. This represents
on a small scale what often happened during the great geological
periods.

Why did the Trilobites disappear ? We saw that the
existence of Myriapods and Insects at the close of the Primary
implied the presence in the seas of that epoch of higher
Crustaceans whose fossil remains do not become numerous
till we get into the Secondary. With their very complete
buccal armature, their stout appendages, adapted in some cases
to walking and in others to swimming, these creatures should
have been able to supplant the Trilobites easily, either by
preying upon them or simply by competing with them for
food. In Victor Hugo's words, " Ceci devait tuer cela." x
Thus the mere demonstration of the existence of a group of
animals at some definite epoch can be extraordinarily
suggestive.

Significant facts of this kind are not lacking. Two genera
of Scorpions have been found in the Silurian (p. 169). This
is not at all surprising, since Scorpions are very closely related

1 The second had to kill the first.

LIFE IN PRIMARY PERIOD 215

to the primitive Merostomata and especially to Limulus.
But Scorpions are essentially carnivorous and confine their
depredations to other terrestrial Arthropods. It is certain,
therefore, that other terrestrial Arthropods existed during the
Silurian Epoch, and this is confirmed by the discovery of the
wing of a bug,1 in these same layers. Bugs are Insects
already far removed from primitive forms. Though their
metamorphoses are still reduced to the appearance of wings,
the mouth-parts are highly modified ; the mandibles
and maxillae have been elongated into pointed probes and
the inferior labium has become a case in which these stylets
are enclosed. A very long time must have elapsed for these
primitive parts that still retained notable features of their
early condition as legs, to be modified to this extent, and
during this period Insects with powerful mandibles — Neuroptera
and Orthoptera, at least — must have multiplied greatly.
We know but few examples of them, and this is due to the
fact that very little of the continental formations of the Silurian
period has come down to us.

It is not absolutely impossible that Insects should have
existed already in Cambrian times ; nevertheless, their class
seems to have made little progress during the Devonian, for
we still find only Neuroptera and Hemiptera. It is not until
the Carboniferous that we see a real blossoming of this class.
A luxuriant vegetation of Club -mosses, Horse-tails, Ferns,
Conifers, Cycads, and Cordaites then clothed the land. Some
Club-mosses and Horse-tails attained the dignity of trees,
possibly equal in size to our most beautiful Conifers. The
atmosphere was hot without the heat being excessive ; the
temperature was high but uniform, and the sunlight filtered
through a humid and misty atmosphere — a phase through
which the planet Venus is probably passing at present. These
are conditions thoroughly favourable for Insects, which were
then represented chiefly by Neuroptera such as the Ephemeridse,
Dragon-flies, and Perlidse, or by Orthoptera such as Phasmidae,
Cockroaches, Locusts even, or again by Hemiptera2 related to
our large Fulgoridse, Cicadas, and Bugs. The clear differentia-
tion of orders with which we recognize to-day had not yet
been achieved. Transitional forms, notably between the

1 Protocimex siluricus.

2 Dictyocicada, Eugereon, Fulgorina, Mecynostoma, Phtanocoris.

216 TOWARDS THE HUMAN FORM

Neuroptera and Orthoptera, existed; for instance, Protophasma
dumasi had the body of Phasma and the four large flat
wings of the Neuroptera, whereas Phasmas to-day are wingless
or have very small anterior wings and posterior wings folded
fan-wise. This last character, which is nowadays common to
all Orthoptera, was lacking in their ancestors, whose posterior
wings, scarcely larger than the anterior, remained flat when
at rest. Finally, in certain forms traces have been recognized,
or claimed as recognizable, of a pair of wings on the prothorax,
which is innocent of wings in present-day forms. This confirms
the opinion previously expressed that the wings were at first
epipodites, or dependences of the legs, since each of the
segments provided with legs could also be provided with wings.
But the most astonishing thing about the Insects of the
Carboniferous Period, which have been studied so carefully
by Charles Brongniart, is the size to which they attained.
Titanophasma fayoli achieved a length of twenty-eight centi-
metres ; certain Dragon-flies had a wing-span of seventy
centimetres, and the wings of a species of Ephemeridae of the
genus Meganeura measure no less than thirty-three centi-
metres in length. This great size was a characteristic no
doubt of certain species only, though very large Phasmids,
Cyphocrana, for instance, and very large Scarabs, Dynastes
and Goliath, still live in hot countries. But the fact merits
no less attention on that account. To-day the life of Insects
is short ; it hardly exceeds a year except for those larvae which
live sheltered under the ground like those of the Cockchafer
or Cicada, or in tree-trunks like those of the Stag-beetle and
large Capricorn-beetle, or in waters that do not freeze, like
those of our large Dragon-flies. These larvae live three
or four years. There is an instance of a Cicada in the United
States x which will live underground for as many as seventeen
years. It is so largely a question of shelter that longevity
increases considerably in adult Insects living in social groups,
and having arrived at the building of common homes, such
as Termites, social Wasps, Bees, and Ants. This leads us to
conclude that brevity of life in Insects has been caused by the
annual variations of temperature, which brought periodically
excessive cold in winter or excessive rains in summer. These

1 Cicada septemdecim.

LIFE IN PRIMARY PERIOD 217

variations did not exist in the Primary times. They only
began to be clearly marked, and even then in moderate
fashion, in the Polar regions, towards the close of the Secondary ;
hence there is no reason why the longevity of the larvae and
adult Insects of that time should not have been much greater
than it is to-day and have permitted them to attain a
greater size.

Insects to-day grow only during their larval stage during
which they shed their skins three or four times, corresponding
to as many epochs of sudden growth. At the end of this
stage they shed their skins yet once more. Immediately
after this last sloughing, short, oval sheaths, the rudiments of
the wings, are seen attached to their meso- and metathorax.
After this sloughing they either preserve their activity, as in
the case of the Neuroptera, Orthoptera, and Hemiptera,
the only orders represented in Primary times, or lose the power
of moving their cephalic and thoracic appendages, as in the
case of the more recent Coleoptera, Hymenoptera, Lepidoptera,
and Diptera. The first group undergoes an incomplete
metamorphosis, and the form of the body is fixed from birth ;
the second has a complete metamorphosis, and the larvae
vary according to the mode of life. They may be agile and
slender, plump,1 and provided with thoracic legs only,2 or
provided with thoracic legs and false abdominal ones 3 ; with-
out legs,4 or without legs and without a differentiated head.5
The different phases of their existence are not always so
clearly distinguished as this would indicate. In the aquatic
larvae of the Ephemeridae, which carry on the back of each
abdominal articulation a pair of scales singularly like rudi-
mentary wings, the first signs of wings appear after the first
or second, and grow larger with each successive moult. It
is the same with the Termites, which are, morphologically,
inferior Insects. Hence we may conclude not only that
primitive Insects had no sudden metamorphoses, but that the
growth of their wings was distributed through the various
phases of their life, and that their evolution was continuous
like that of other animal organisms. The winged Insects of
the present day do not grow any further, but lay their eggs

1 Campodeiform larvae. 2 Melolonthoid larvae.

3 Eruciform larvae or Caterpillars. * Helminthoid larvae.

6 Acephalate larvae.

218 TOWARDS THE HUMAN FORM

and die ; but our Ephemeridae, which inherited the earliest
forms achieved, after having attained their permanent form,
do not fly away until they have freed themselves of a light
envelope, which actually constitutes a final moult. We
may therefore ask whether the primitive Insects, arrived at
their adult form, were not still capable of growth and moulting.
In that case we must grant either that the wings were still
formed of living cells — whereas there is no living substance in
the wings of our present insects except in the muscles attached
to the base in order to move them — or else that the wings fell
off spontaneously, as is the case with Termites, where their
falling is prepared in advance by the formation of a rupture-
line at their base, but that they could be subsequently reformed
at each reproductive period. This would bring the Insects
thoroughly into line with the general rule. Is it not singular
that they should have only a few weeks to live after they have
attained maturity ? Many other animal organisms — the
lowly Worms,1 Fishes,2 and many Birds — display brilliant
colours or splendid ornaments during the mating season.
Sometimes the eyes enlarge, the organs of locomotion are
perfected, the creature becomes more agile, and all the dis-
tinguishing marks of this season constitute their bridal apparel.
It is just in characters of this kind that the adult Insects
differ from their larvae. Is not the definitive stage just the
mating apparel that the insect of to-day only puts on once,
but which their ancestors displayed at each period of repro-
duction ? We are justified in asking this question since the
larger Crustaceans can reproduce themselves several times.
The duration of life in an adult Insect can be prolonged,
moreover, if certain precautions be taken. Labitte has kept
the beetle, Blaps, alive for more than eight years.

We need say little of the Worms which have left evident
traces (Nereites, Arenicolites, Scolithus, etc.) in the tracks of
their bodies imprinted on sand, or mud, in the holes where
the}'' lived, or else material remains such as mandibles.
Among these there are still Eunicidae and Amphinomae,
which attain a great size, as much as two metres in length
and four centimetres in width. It is also possible that the

1 Syllids (Autolytus, Myrianis, etc.), Nereids (Nereis cullrifera),
Phyllodocids, Cirratulids.

2 Macropods of China, Sticklebacks, Minnows.

LIFE IN PRIMARY PERIOD 219

passage of large Worms may be responsible for tracks such
as those that have been grouped as Biiobites, and that have
been attributed occasionally to Trilobites. To the Worms must
be linked other animal organisms, the Brachiopods, which
were long taken for Molluscs, but are still isolated. Morse
has given a very interesting explanation of these organisms,
which has inspired his theory of cefihalization. He draws
attention to the fact that in the majority of segmented
organisms the part nearest the mouth undergoes greater
development proportionately than the posterior region, which
tends to diminish and disappear. Among the Merostomata
and Trilobites, the body ends in a point ; that of the Scorpions
has shrunk to a post-abdomen bearing the poison-sting. In
the majority of the Batrachians, Reptiles, and Mammals, the
viscera are so much concentrated in the anterior or at least
medial region that the posterior part of the body becomes
a tail behind the anus, which tail is sometimes used for pre-
hension, but may disappear altogether when not used. This
phenomenon is easily explained on Lamarck's principle. In
the anterior region of the body are assembled together not
only the mouth but the sense organs. This portion initiates
the movements which drag the rest of the body, and the
posterior region can but follow. The anterior region therefore
is generally the active region par excellence, and the one which,
according to the principle we have just invoked, ought to
attain the maximum development, while the inactive part is
atrophied. That is the reason why the number of body
segments in the Arthropods and the higher Worms tends to
be reduced to a fixed, indispensable minimum. If, however,
the posterior region of the body does become active, after
this reduction has taken place, the segments will not increase
in number, but they will be very large. The higher Crustaceans
which swim, like Squilla or the Crayfish, by striking the
water with a suddenly flexed abdomen, have this part power-
fully developed, while in the Crabs, essentially walking
creatures, the abdomen is atrophied. In the same way Fishes,
Cetaceans and Sirenians, which swim by striking the water
laterally with their tail, possess broad tails. The marine
tubicolous Worms, which bury themselves in the mud, live
under conditions which favour the marked development of
the anterior part of their body at the expense of the posterior

220 TOWARDS THE HUMAN FORM

region, which is deprived of all contact with the exterior
environment. Hence their heads developed those voluminous
plumes covered with vibratile cilia which by their movements
draw towards the organisms both food particles and water
charged with oxygenated air. On account of these plumes,
Lamarck called all these worms Cephalobranchs.

Brachiopods enclosed between the two valves of their shell
obtain food in exactly the same way. Their mouth lies between
two respiratory plumes that are either twisted spirally 1 or
like a screw,2 or variously convoluted before being rolled. It is
to these plumes that the Brachiopods, now under consideration,
owe their name. In studying the embryogeny of the Lingular,
which existed already in the Cambrian Epoch, and have
scarcely been modified since that distant period, Morse was
struck by the resemblance between these young organisms and
Serp-ula. The two valves of the shell develop in a region of
the organism's body corresponding to the collar of Serpula. He
was thus led to consider the Brachiopods as cephalized Annelids.
Embryogeny, moreover, leaves no doubt but that these
organisms are derived from Annelid Worms with a reduced
number of segments. Their resemblance to bivalve Molluscs
is entirely superficial. The valves of their shell are dorsal and
ventral, instead of left and right, like those of the Molluscs,
and their texture is totally different. Their internal structure
has nothing in common with that of Molluscs. On the other
hand, the Brachiopod clearly approximates in internal structure
to one or two segments (Rhynchonella) of the Annelid Worm
that have become individualized.

This said, we can distinguish two main types of Brachiopods :
Firstly, the Inarticulata, in which the valves of the shell,
with their somewhat horny consistency, are independent of
each other; secondly, the Articidata, in which the two strongly
calcified valves are united with each other by a real hinge.
It is muscles that open the shell, and not a mere ligament
which springs back as in the bivalvular Molluscs or Lamelli-
branchs. Furthermore, the shell of a dead Brachiopod is
obstinately closed, whereas that of a Lamellibranch gapes.
The Lingular live in the sand, where they bury their long,
mobile peduncle, which represents, according to Morse, the

1 Terebratulidae. 2 Rhynchcnellidae such as Spiri/er, etc.

LIFE IN PRIMARY PERIOD 221

body of the primitive Annelid. Articulate Brachiopods
attach themselves permanently to the rocks by the extremity
of this peduncle, and indeed a very large number of both non-
articulate and articulate species glue themselves to the rocks
by means of one of their valves. The Inarticulate
Brachiopods have a complete digestive tube open at both ends.
In the Rhynchonellidae, of which there are living specimens
as of Lingulidae, the body is apparently composed of two
body-segments, and ends in a ccecum. Among other
articulated Brachiopods, the digestive apparatus is reduced
to a sac which is prolonged as a thin filament directed toward
the hinge. According to the theory of cephalization, these
arrangements would clearly indicate an organism undergoing
reduction.

It may be asked how creatures so simply organized, and
destined for a life of immobility, were able to multiply as they
did during the Primary Period, and become so abundant and
varied that they furnish geologists with precise stratigraphic
evidence. The non-articulated group is dominant in the
Cambrian, and is there associated with the Strophomenidae and
the Pentameridae, but after the Silurian numerous families,
including the Rhynchonellidae, are added to the former group,
and the latter undoubtedly also existed in the Cambrian.
Among the new forms we must cite Productus, with a much
rounded lower valve, which during the Carboniferous Period
attained one decimetre in diameter. The families, genera and
species, continue to multiply during the Devonian Period, and
it is then that the Terebratulidae, which still inhabit our present
waters, make their appearance. The Carboniferous, in turn,
is even richer, and it is only during the course of the Secondary
Period that the decline begins and continues to become more
pronounced down to the present day, when the Brachiopods
play an insignificant part. They could not have prospered
so well during the Primary Period unless the plankton, their
only possible source of food, had then offered abundant supplies
for which there was little competition. The Primary, there-
fore, must have been the epoch of microscopic floating Algae,
Protozoa, and minute embryos.

This abundance of the plankton in the seas was equally
necessary for the evolution of the Crinoids, all of which are
fixed Echinoderms, living entirely on the small particles directed

222 TOWARDS THE HUMAN FORM

to their mouths by the currents set up by the vibratile
cilia on their branchial groove. Theory indicates that
this branch must have begun with more or less spheroidal
forms, derived from some short worm rolled up in such
a manner as to describe a complete corkscrew turn. The
Cystids, limited to Primary times, seem to correspond
to this earliest phase in the evolution of the Echinoderms.
We have seen how embryogeny thereafter yields an initial
radiate form, originally without arms, from which it is easy
to derive all the other classes. The Cystids antedate the
embryonic form in question ; they seem to have been
affected by all manner of external influences, from which
they were unable to escape, owing to their fixed position. This
fixation has brought with it changes in form that were calculated
to render the initial type unrecognizable. These varied both
according to the age at which the embryo became fixed and
to the conditions of fixation. An average embryo is generally
fixed by means of its anterior extremity ; but these
particular embryos were weighed down by the lime in their
tissues and sank upon the ground, to which, therefore, they
could attach any part of their body whatsoever. Once this
fixation was accomplished, the embryo must have effected
a rotational metamorphosis, like all fixed embryos, with the
object of placing mouth and anus as far as possible from the
point of fixation. This metamorphosis was achieved by the
Cirripedes among Arthropods and by the Crinoids among existing
Echinoderms, as well as by the Tunicates, and it completely
altered the shape of their bodies. The Cystids evidently
underwent this rotation, since mouth, anus, and genital
orifice are usually grouped together at the opposite pole to
the point of fixation. Such a change could not have occurred
without profoundly altering the initial type, and this, no
doubt, is the reason why these organisms appear to be so
aberrant. How they obtained their food, fixed as they were
with scarcely any mechanism for directing alimentary or
respiratory currents to their mouths, remains a problem, in
spite of the richness of the surrounding waters in plankton.
It may be that their digestive tubes were highly ciliated or
that they fell back on a symbiosis with green Algae.

From the Silurian onwards other classes of Echinoderms
are already characterized, and represented by numerous

LIFE IN PRIMARY PERIOD 223

individuals ; these primary forms, however, were very
unlike those of the present day and sometimes not so clearly
differentiated. For instance, there were Star-fish with the
madreporic plate situated on the ventral side of the body,
as in the Ophiuroids. In the Sea-urchins, the ambulacral
areas were very narrow and furnished with enormous spines,
as they still are in our present Sea-urchins known as Cidaris ;
these areas were sometimes almost linear and sinuous. The
inter-ambulacral plates were numerous and arranged in mosaic,1
instead of merely forming two alternate rows in each radial
area. Nevertheless true Cidaris appear in the Carboniferous
and even Diademse with their long spikes, hollow and fragile,
similar to those of the Mediterranean species, which have
their ambulacral areas already broadened, and bearing
ambulacral pores arranged in groups of three pairs. The
Crinoids have comparatively short arms ; their calyx comprises
three rings of plates ; five radial, bearing the arms ; five
basal, placed below and alternating with the latter ; and
sab-basal plates, occasionally but three in number, con-
necting the ring of basals with the stem. The last of these
rings of plates and often the penultimate ring are absent in
existing Crinoids. Such are the salient characters of the early
Echinoiderm fauna.

We sketched on page 135 the probable descent of the
Molluscs. The Gasteropods and the Cephalopods may have
evolved simultaneously. The first preserved a broad ventral
sole, probably provided with lateral lobes utilized for swimming ;
in the second the ventral sole diminished until it was reduced
to the region around the mouth. Both must originally have
had straight shells, which later on developed a spiral form
in the swimming species and a corkscrew form among the
Gasteropods which had reverted to the crawling habit.
Palaeontology confirms these deductions, which in turn throw
light on certain palaeontological problems. If the Gasteropods
were really descended from the Chitons, and if their shell
was derived from the dorsal plates of the latter, the shell of
the oldest forms should be formed of triangular plates
juxtaposed from top to bottom. The shell of the Comdaria
fulfils this condition. That of the subsequent forms ought

1 Melonites, Lepidocentrus, Cystocidaris, Bolhriocidaris.

224 TOWARDS THE HUMAN FORM

to be continuous but straight. This decides the place that
Hyolites and Tentaculites should occupy, which, if this
deduction is not followed, are sometimes classified among the
Annelid Worms. The phase of spiral formation is represented by
Bellerophon. All these forms are Cambrian, and with them we
must include the helicoidal forms of the Diotocardi ac Gastropods,
whose primitive characters we have already described, as well
as Euomphalns, and the Pleurotomarice. These last persist
to the present day in the deep-sea fauna. From the Silurian
onwards may be added such forms as Trochus, also diotocardiac,
Patella, transitional forms representing the first Monocardiacs
with shells entirely open,1 the carnivorous Purple-Fish,
whose shell is channelled at the opening in order to permit
the passage of a siphon destined to bring the water into the
branchial cavity. The Turbos, differing from Trochus in
the thickness of its calcareous operculum, and Capulus with
its small, hood-shaped, scarcely pointed shell, appear in the
Devonian. The Carboniferous witnesses the arrival of the
" Worm-shell ", which attaches its shell to foreign bodies, and
the first true Snails and other pulmonata Gasteropod, such
as the Pupae. Seeing that the lake deposits and river drift
of the Carboniferous are so incomparably better known than
those of the preceding periods, it is conceivable that the
pulmonate type had been achieved much earlier.

The straight-shelled Cephalopods are represented by the
Orthoceratidae. The Cephalopods retained their swimming
habits, and when their shell became rolled it simply formed
a spiral and remained symmetrical. Both types, at the latest,
existed in the Silurian. It was not until the Cretaceous that
certain Ammonites, which probably became crawling organisms
for reasons we have already given (p. 137), acquired the
helicoidal form, and thus constituted the Turrilite family.
The straight-shelled and related forms enable us, moreover,
to divine the causes that determined the special characters
of Cephalopod shells. These shells are divided internally into
successive chambers by calcareous septa, concave near the
shell orifice, and either attached to its walls in a gradual
manner so as to preserve their curvature — a characteristic of
the most ancient forms, constituting the group of Nautilidas

1 Littorinidae, Scalarid?e, Pyramidellidse.

LIFE IN PRIMARY PERIOD 225

or else folded in such a way that the line of junction of the
septum and the shell forms a line broken only at its
point of origin,1 or a wavy line whose curves increase in
number and consequently decrease in size — the lines traced
thus becoming more and more complicated as the Jurassic
period advances ; these complicated lines of junction are
characteristic of Ammonites. The septa are traversed through-
out by a tube, the siphuncle, which among the still existing
Nautilidae, congregating in large numbers below the surface
of our warm seas, becomes attached to the top of the shell
which is perforated there by a slit ; whereas in the inner shell of
the Spirulidae, partitioned like that of the Ammonites but with
smooth walls like those of the Nautilidae, the siphuncle goes
through the last partition and terminates in a small ovoid
sac, the ovisac, which is attached to the top of the shell by
a ligament, the prosiphon.

From the head of the Nautilus spread a number of discs,
bearing very mobile vermiform tentacles that give these
organisms a most characteristic appearance ; they have four
branchiae. The head of Spirula, on the contrary, is formed
like that of the Calamary and the Cuttle fish ; and has only
two branchiae. Munier-Chalmas, who discovered these
differences between the terminations of the siphons among
these creatures, has shown that Spirula resembles the
Ammonites in this respect. From this he concluded that the
latter, like the Spirulae, were dibranchiate Molluscs with ten
tentacles to their heads, whereas the large Cephalopods
with smooth septa should be grouped with the Nautilus.

The Cephalopods, with straight and partitioned shells,
of Primary times have, however, a much larger siphuncle than
the true Nautilidae (Orthoceras). It is sometimes lateral
(Cyrtoceras), sometimes central, and the septa themselves
may be lateral (A scoceras) . We must conclude, therefore,
that the siphuncle was at first an integral part of the body, and
that in Orthoceres, whose straight shell can exceed two
metres in length, it is nothing but the integument of the
upper portion of the body, originally fixed to the shell but de-
tached on account of the weight of the latter, since the animal,
as has been said, swims with its ventral side uppermost.

1 Goniatites, with siphon near the convex wall of the shell. Clymenia
with siphon on the opposite wall.

Q

226 TOWARDS THE HUMAN FORM

It must have been a sort of a tail whose formation would be
mechanically conditioned by the weight of the shell hanging
in the water. Once formed, this siphuncle would be hereditarily
preserved in the later spiral forms. This implies that the part
of the Mollusc's body containing the viscera mounts up within
the shell step by step as it grows, and secretes behind it,
at each stage, a partition isolating it from the empty part of
the shell. The siphuncle remains pressed against the outer wall
of the shell in the Goniatites ; it is internal in the Clymenise,
a group which lasted but a short time. The same theory that
accounts for the origin of the Cephalopod Molluscs finds a
natural extension here. We shall probably never know
exactly how Orthoceras was formed, but it is impossible to
doubt its genealogical relationship with the other shelled
Cephalopods.

From the Silurian Period the septa begin to become
sinuous in Goniatites of the genera Anarcestes and A goniatites.
These continue to grow more complicated, each series
being characterized by the relative proportions of height,
width, and length of the chambers, particularly of the last,
which is necessarily moulded upon the body of the mollusc.
Von Mosjisowicz, En. Kayser, Fr. Frich, Emile Haug, etc.,
have been able to follow the gradual evolution of the diverse
series of Ammonites, thus contributing important evidence to
demonstrate the theory of evolution.

From the general point of view, at this stage, there is little
to be said about the Lamellibranch Molluscs. They began
in the Lower Cambrian, which indicates that the symmetrical
Diotocardiac Gasteropods, which evolved into Bellerophon, must
have already existed during the Pre-Cambrian Period. Not
until the Silurian, however, do their species become sufficiently
numerous to enable us to follow the successive stages of their
evolution. As theory indicates, the oldest forms have a long
hinge with a very simple articulation ; these form the group
of " Pakeochonchae ".1 Then come the genera in which the
very long hinge has numerous small close-set teeth, Cucullella,
Leda, etc. ; and, following them, species which suspend
themselves by a byssus, and whose shell becomes broadened
near the base on account of its own weight, of which the muscles

1 Cardiola, Conocardium, Dualina, Lunulocardium, Prcecardium, Slava,
Vlasta, etc.

LIFE IN PRIMARY PERIOD 227

are consequently unequal : these are the Aviculida from which
the Monomyaria are derived, forms with a single valve-
retractor muscle, represented in the Devonian by the Pectens.
By the side of these are found Lamellibranchs of the normal
type : Anodontopsis, Paracyclas, Amita, etc., reminiscent,
to a certain extent, of the forms found in our fresh waters.

Vertebrates have not yet been encountered in the Cambrian ;
but they are represented in the Silurian and the Devonian
by Fishes, and also in the Carboniferous by Batrachians,
and finally by true Reptiles. This succession would seem to
indicate that we have arrived at the point when the evolution
of the Vertebrates begins. We know that they must have
started in a form analogous to Amphioxus. The nature of
the tissues of Amphioxus does not readily lend itself to
fossilization, but we have found fossilized Medusae, whose
tissues are even softer, and we must not give up all hope of
also discovering fossil ancestors of the Vertebrates. After
Amphioxus, the simplest Fishes — simplest because the
vertebral column consists only of the embryonic dorsal chord —
are the Marsipobranchii, of which the Lampreys are typical.
Mounting up from these, the evolution of fishes follows a logical
order. In my Traite de Zoologie, 1003, I began their history
by calling attention to the modelling they had undergone
by the pressure of the surrounding water, occasioned chiefly
by the sudden movements of their tails in swimming, and to
the fact that the number as well as the position of their dorsal
fins was due to the tearing of an originally continuous dorsal
fin by the currents that were thus formed on the creature's
sides.1 Frederic Houssay has been able to demonstrate
this by interesting experiments. He showed that the first
stage in the development of a fish's shape is that taken by
a cylindrical linen sack filled with a soft paste, when it is drawn
horizontally through water or held horizontally in a vase full
of v/ater and opposite an aperture through which the water
flows out. This form is that described as "la veine inversee ",
because it results from the pressure exercised by runnels of
water flowing swiftly into the place of the water running out.
But if we can thus account for the normal shape of Fish, the
explanation does not stand for the special forms they some-

1 XLIII, 2364 ff.

228 TOWARDS THE HUMAN FORM

times take. These, too, however, result from the reactions
of a liquid on an organism in the act of swimming, reactions
which modify the branchial region in particular. From this
point of view three types of Fishes can be distinguished :
Marsipobranchs, Elasmobranchs, and Ctenobranchs. The
Marsipobranchs are represented to-day by three genera
only : the Bdellostomas, Myxines, and the Lampreys. The
Elasmobranchs include numerous genera belonging to the
Sharks, Rays, and Chimaeroids ; the Ctenobranchs comprise all
the rest. In the Marsipobranchs the branchial system consists
of two almost symmetrical series of sacs placed behind the head,
independent of one another, and each communicating directly
or indirectly, by means of afferent and efferent ducts, with
the oesophagus and the exterior respectively. A kind of
cartilaginous grille supports each sac. In the Elasmobranchs
these gill-sacs become flattened, unite with one another,
and become indistinguishable from the ducts in such a way
that each sac communicates with the oesophagus by one
slit and with the exterior by another. Cartilaginous arches,
from which numerous rays branch out, support the thick
partitions resulting from the union of the walls of the gill-
sacs. In the Ctenobranchs the partitions are reduced to the
supporting and now osseous arches, to the dependent rays,
and to the highly vascular tissues which clothe the arch and
the rays it supports, while leaving these rays completely
independent. The Bdellostomas have as many as fourteen
branchial sacs, and their embryos show indications of many
more ; the Lampreys have seven on each side and Myxine
has only six, opening to the outside by a single duct. Seven
branchial slits are observed also in Sharks of the genus
Heptanchus ; Hexanchns and Chalmydoselackus have but
six, while five is the number characteristic of all the others,
as well as of Rays and the Chimaeroids. Finally in the Cteno-
branchs there are generally four branchial arches, rarely less,
and the rudiments of a fifth. This simple enumeration will
suffice to show that the branchial region constantly diminishes
as the type of Fish becomes more advanced.

We have pointed out (p. 130) that the cause of this shortening
was the resistance offered by the water to the progression
of the animal propelled forward by the movements of its
tail. As is always the case, some Fishes have resisted this

LIFE IN PRIMARY PERIOD 229

transformative action and have come down to us unchanged,
whereas others have been obedient to it and have become
modified. This action, moreover, has been exercised equally
on the trunk, properly so called ; gradually the purely
muscular and impulsive part of the body constituting the tail
increased at its expense, whilst at the same time the currents
it produced forced forward the pelvic fins, which were
primitively situated at a distance from the pectoral, until
they were placed underneath and in front of the pectoral fins
and articulated with the branchial skeleton itself. This,
as we have seen, is the characteristic of the swimming
Fishes par excellence, the fishes of the open sea.

The Marsipobranchs must therefore be considered the
oldest of all Fishes. They show no tendency to secrete lime
and their skin is absolutely denuded of any solid product.
However, in the buccal cavity, where it is naturally subjected
to incessant friction, the epidermis of its papillae, in Lampreys,
takes on a horny consistency, and produces short pointed spines,
broad-based and conical in shape, which play the part of teeth,
but which are only the antecedents of teeth and are known
as odontoids. The epidermis of the Elasmobranchs, on the
contrary, becomes calcified all over, but in such a way that
it becomes a sort of a mosaic of small thick scales, circumscribed
by linear intervals where the epidermis remains flexible.
This epidermal structure extends to the mouth as well, and
is identical with that of the dental enamel of all the other
vertebrates. In certain parts this calcification continues
below the epidermis to the superficial portion of the dermis,
to which the living cells that have produced it send fine
prolongations without themselves penetrating it. Solid plates
are thus formed, more or less covered by enamel, and sometimes
with sockets carrying spurs, as, for example, in the armature
of the Rays. These plates and sockets, formed of calcareous
incrustations and traversed by fine vessels, have the same
structure as dental ivory, and, as they are covered with enamel,
the teeth of the terrestrial vertebrates must be regarded
as the last remnants of the defensive armour of the Elasmo-
branch Fishes, finally localized on the jaw.

The Elasmobranchs have no bones. Their vertebrae, it is
true, may become calcified, but this calcification, which
takes place in various ways, does not modify their internal

230 TOWARDS THE HUMAN FORM

structure. The vertebras are still cartilage impregnated
with lime. This is also the case with the earlier Ctenobranch
Fishes, whose direct descendants are the present-day Sturgeons.
With them, however, calcification is, so to speak, more
deep-seated. Abandoning the epidermis, so as to reach
the dermis, the process of calcification invades the region
of the star-shaped dermal cells, which then constitute the
osseous corpuscles. The superficial parts of the dermis,
richer in lime and more compact in texture, form at first
over each osseous plate a brilliant glaze, to which the name
ganoin has been given. Fishes having such scales were called
by Louis Agassiz Ganoids. At first they preserved a
cartilaginous skeleton, and resembled the Elasmobranchs
in the peculiar shape of the tail, the extremity of which
curves up. Underneath this erect part the caudal fin
develops into a triangular blade, which gives the tail the
appearance of being divided into two unequal lobes. On
account of this dissymmetry in their tails, Sharks and Ganoids
are called heterocercal. Franz Eilhard Schulze, Professor at
the University of Berlin, has shown that this arrangement
aided the Elasmobranchs, which have no swim-bladder, to
rise in the water. It persists as a simple inherited
character among such of the Ganoids as possess it, and
tends to disappear in Amia of the North American rivers,
which are Ganoids in all other respects. In the other
Fish described as homocercal, the caudal fin terminates either
in a regular convex curve or is emarginated into a fork having
two equal branches.

Ossification of the skeleton has already begun in the higher
Ganoids, and it is definitely osseous in the homocercal Fish
or Teleostei. Here the tegumentary skeleton goes deeper
even than in the Ganoids, and the fish is protected by plates of
bony tissue pure and simple, contained in the dermis itself.
These are the true scales. They unite in the region of the
head, and form more or less extensive plates which closely
fit the cartilaginous cranium, but are still easily detachable
in the Salmon and the Pike, for example, but in later forms
become incrusted in the cartilage, uniting with the
bones of the cranial basis, and constituting, in the higher
Vertebrates, the bones of the cranial vault known as the
membrane-bones. Their frontal and parietal bones, and their

LIFE IN PRIMARY PERIOD 231

temporal and occipital scales, like their teeth, are a heritage
from the Fishes.

The preceding considerations retrace in a general way
the genealogy of Fishes, and indicate the order of their
appearance. Not a single species is known in the Cambrian,
and what we know of the Silurian is evidently incomplete.
In the Devonian, however, there is a singular form, Palceo-
spondylus gunnii, which, if it does not belong to the Marsipo-
branchs, belongs to a still more primitive type. Analogous
forms must have existed in Silurian times, but they are
unknown. On the other hand, in the Upper Silurian of
England, the Island of Axel, Podolia, Galicia, Ludlow, and
various other places, there are strange creatures which we can
only consider as Fishes, but which do not seem to fit into
any existing series. Their shape was flat, and they bore
a superficial resemblance to the Trilobites, especially on
account of the shield-like form of their head. Their large
ventral mouth, elongated into a transverse slit, had no jaws,
but their cephalic cuirass was protected by real bones, containing
bone-cells. They initiated the series of Ostracodermous
Fishes devoid of lateral fins. Among them were Cephalaspis
and Aiichenaspis, associated with Pteraspis, whose trunk
and tail were covered with lozenge-shaped scales, and with
various other genera.1 To these are to be added similar
fishes which, however, were provided with a pair of paddle-
shaped fins, also covered with polygonal bony plates,2 and
of these certain forms may have existed from Silurian times
on the east coast of the Baltic. At the same time other forms
appeared, with occasionally globular heads,3 strongly armour-
plated with polygonal bony articulated plates, which gave
them a very distinctive appearance.4

The fins of Pterichthys are already highly specialized organs.
Since many of the Selachians, even during the Carboniferous
period,5 and of which there are representations to-day,6 have
very primitive fins conforming almost to the genealogical
indications furnished by embryogeny, it must be assumed

1 Ateleaspis, Birhenia, Cyathaspis, Lanarkia, Thelodus, etc.

2 Asterolepis, Bothriolepis, Pteriichthys.

3 Coccosteus.

4 Dinichthys, Heterosteus, Homosteus, Titanichthys.

5 The Pleuracanthidae especially.

6 Chlamydoselachus of the Japanese waters.

232 TOWARDS THE HUMAN FORM

that these armoured fishes are more recent than the Elasmo-
branchs, and that we shall have to look in the older strata
for connecting links between the two groups.

It has been considered surprising that these primitive Fishes
had heads so heavily armoured, and that they should have
resembled Trilobites ; it has even been suggested that they
are descended from them. They were found, however, in
the Old Red Sandstone, which in some places attains a thickness
of six thousand metres, and which was deposited as mere
sand. In this sand there lived, together with numerous
Trilobites, Pterygotus, Eurypterus, and other large Merostomata
which they hunted, probably by digging in the sand. This
common way of life would naturally produce resemblances
in external form between the preying fishes and their victims,
and would lead to a considerable development of the solid
plates on the head of the former in accordance with what
we have said before about the action of friction and shocks
upon the development of the skeletal parts.

Ctenobranch Fishes also appear in the Devonian ; they are
heterocercal Ganoids, naturally : * Crossopterygians,2 still
represented in the rivers of Africa by the two closely related
genera Polyplenis and Calamoichthys, whose pectoral and
pelvic fins, distant from one another, have the form of big
scaly stumps fringed with a membrane supported by rays
and Dipnoi whose fins are supported by an axis with numerous
articulations, bearing rays arranged almost symmetrically
on each side, as in the present Ceratodus of Australia.

The armoured Fishes disappeared at the same time as the
majority of the Merostomata and Trilobites, during the
Anthracolithic or Carboniferous Period, when the coal beds
were formed. The Elasmobranchs of this period, however,
have left numerous remains, especially the Pleuracanthidae,
whose cartilaginous skeleton was packed with calcareous cor-
puscles and therefore fossilized perfectly. They have furnished
us with exact information on the organization of primitive
Elasmobranchs, and I myself have pointed out 3 how easy it was
to derive from the structure of their fins those of the Dipnoi, such
as Ceratodus, whose rays are arranged like the barbs of a feather

1 Chirolepis.

2 Glyptopomus, Holoptychus, Ostcolepis.

3 XLIII, 2432.

LIFE IN PRIMARY PERIOD 233

on each side of an axial ray. This arrangement distantly
resembles that of the rays in a branchial arch, and led the
celebrated anatomist Gegenbaur to the audacious supposition
that one of the arches of the fish's gills had become modified
both in form and function until it developed into a fin.
Unquestionably an organ can change both its function and its
form, but there must be some reason for this change. We
might perhaps admit the possibility of such a change in the
anterior fins close to the branchial cavity, but how could it
happen in connexion with the posterior fins, which are far
removed from this cavity ? and what should we say of
the unpaired fins, whose structure so closely resembles that
of the paired fins that Tristichopterus appears to carry on its
back a third fin similar to the pectoral fins ? The embryogeny
of the Elasmobranchs agrees with comparative anatomy in
showing that the fins were at first represented by four
longitudinal folds of the body wall extending along its whole
length, one dorsal, one ventral, and two lateral, the last
two forming what is called the patagium, and the two former
the diphycercal fin, which only exists in Marsipobranchs.
Each segment of the body still furnished these fins, in the
course of their development, with the same number of rays,
muscles, nerves, and blood vessels. At first continuous,
the folds were subsequently broken (p. 227) at the places that
bore the force of the backwash set up by the quick flexions
of the tail to the right and left in swimming. It has been
suggested that the apparent absence of the lateral fins in
certain Ostracoderms is due to the fact that these flattened
Fishes have preserved their patagium or developed it again,
as the Rays and the Torpedo-fish, which live the same kind
of life, have done to a certain extent — more in appearance
than reality.

We now come to the beginning of the Carboniferous Era.
The gradual perfecting of their organism has made the Fishes
the dreaded enemies of the Gigantostraca and the Trilobites,
on whom their relatively greater size has destined them to
prey— and whom they have probably caused to disappear
on that account. So the Fishes now prepare to invade the
land. Many of them had already penetrated into fresh
waters, and, apparently, taken to their new surroundings,

234 TOWARDS THE HUMAN FORM

for, apart from the Sturgeon, which goes thither only to lay
its eggs, it is here that the last representatives of the oldest
orders of Ctenobranchs are to be found : the Ganoids repre-
sented by the Lepidosteus and Amia in North America ;
the Crossopterygians localized in the rivers of Africa ; the
Dipnoi represented by Protopterus in Africa, Lepidosiren
in America, Ceratodus in Australia. These last, as we
have seen, are by now very well adapted for leaving
the fresh water and venturing on land. We have already
explained the mechanism by which they acquired the organs
that were to prepare them to live outside the water (p. 173).
The pioneers of the conquest of the land were very modest
indeed. Their skin was covered with delicate scales ; their
cartilaginous cranium was protected by a bony covering
like that of the Fishes ; between the parietals was an
open space which, if we may judge by the existing conditions
in Lampreys and certain Lizards, must have been occupied
by a single dorsal eye whose nerve was connected with the
epiphysis of the brain or pineal gland, and which has become
an eye for gauging temperature, a sort of a thermal eye, rather
than an optic one : a circle of bony pieces fixed to the sclerotic
surrounded the pupil. There were only four digits to all the
limbs : these creatures resembled Salamanders. In the
Carboniferous of Bohemia, Ireland, and Ohio we already
find Keraterpeton, whose ventral surface was covered with
scales and whose head bore two small horns. The European
species, Kereterpeton crassum, attained a length of thirty
centimetres, of which the tail occupied twenty. Urocordylus
came near it. In the Permian lakes of the district of
Autun the larvae of Branchiosaurus developed with external
brancheae, and Albert Gaudry has described them under
the name Protriton petrolei. We have been able to study
their growth from the time when the}7 were sixteen millimetres
long to the adult stage, when they never exceeded sixty-four
millimetres. They were small Salamanders, with minute
scales covering their entire bodies. The vertebrae of these
creatures consisted only of a notochord surrounded by a bony
pellicle. It was the same with the Dolichosomaatidae, which,
although they preserved their external gills, had already lost
their limbs and elongated their body until they had one
hundred and fifty vertebrae to the length of one metre.

LIFE IN PRIMARY PERIOD 235

Whenever the limbs of an animal are missing or are not used for
locomotion, the body elongates thus and the segments multiply.
This proposition is as true of Arthropods and Worms as of
Vertebrates in which the number of body segments is indicated
by that of the intercalated vertebras. Like other biological
propositions, it is capable of being interpreted in two contra-
dictory ways, both of which may be correct under different
circumstances : Firstly, the body if it elongates sufficiently for
undulatory movements to satisfy all the needs of locomotion, ren-
ders the limbs useless, and they become atrophied through lack
of use ; secondly, if the limbs become too short to lean on the
ground, or give the body sufficient speed, the body itself will
take an active part in locomotion. The increase in its
activity means a greater intensity in the phenomena of
nutrition, which by tachygenesis may already manifest itself
during the period of multiplication of the body segments.
The number of these segments then increases, and the body
itself becomes more and more capable of providing for the
animal's peregrinations. The first interpretation would seem
to fit the case of primitive animal organisms, in which an
indefinite multiplication of the body parts is a sign of their
reciprocal independence and a mark of inferiority. That can
be admitted for the Myriapods, such as Geophilus, with
their elongated bodies, and for errant Annelids such as
Myrianidae, Phyllodocidae, Nereidae, Eunicidae or even Nais, etc.
The second interpretation, on the other hand, especially
fits the Vertebrates, in whom the number of body segments
early became limited and in whom locomotion was accomplished
very early by the aid of limbs whose original insufficiency
we cannot admit. The aquatic Vertebrates, in which the
undulatory movements of the body clearly play a pre-
ponderating part in locomotion, have especially good reasons
for neglecting to use their limbs when moving, and it has been
proved precisely in the case of existing species which live
under special conditions that this atrophy of the limbs
coincides with a multiplication of the body segments. This is
clear in the case of the Proteidae of the Adelsberg cave,
in Carniola, in which the fore-limbs have only three digits
and the hind-legs two. They preserve their gills all
their life and, by tachygenesis, are born with the four legs of
the adult.1 This is shown even better in the lacertine

1 Marie de Chauvin, Zeitschrift /. wissenschaftliche Zoologie, Bd. xxxviii,
1883, p. 671, and Nature, vol. be, p. 389.

236 TOWARDS THE HUMAN FORM

Sirenidae, which also preserve their three pair of branchiae,
and have only two short front legs with three or four toes.
These are unquestionably former terrestrial Salamanders,
in other words quadrupeds that have again become aquatic.
In fact they indicate the normal metamorphosis of the forms
destined to become terrestrial by losing the branchiae which
they possessed at birth. These gills are subsequently
regenerated. The atrophy of the hind-legs can be attri-
buted to the lengthening of the tail, which in an animal
of seventy centimetres has a length of about twenty-five
centimetres. The Amphiumae, whose body is elongated, but
whose tail, on the contrary, is short, preserve their hind-
legs as well as the others.

An analogous phenomenon, even more striking, is produced
in other Batrachians which have no legs and live underground
like worms. They constitute the group of Caeciliidae. About
forty species are known, distributed over India, Malaysia,
tropical Africa, the Seychelles, South America, and Panama,
that is to say, in regions which were all part of the continent
of Gondwana in Carboniferous times. These animals were
originally aquatic, because their embryos, while still in the egg,
acquire magnificent branchiae. Their general characters
resemble those of the Stegocephala of that epoch. Certain
species have even preserved the scales concealed in the seg-
mented folds of their skin.1 We may therefore ask whether
these vermiform Batrachians are not genealogically related
with the Dolichosoma.

The other stegocephalous Batrachians belong to higher
types. Their vertebral centra are at first formed of four pairs
of elements, the upper ones bearing the arches which surround
the spinal cord. They are therefore called temnospondyious.
The four pairs are already reduced to three in the vertebrae
of the trunk in Archegosaurus, Actinodon, and Euchirosaurus,
where only the caudal vertebrae preserve the primitive com-
position. The Batrachians become stereospondylous when all
the parts are united in one single bone in the form of an hour-
glass, with concave bases. They generally have scales only on
the ventral surface of the body, thus betraying the influence of
friction on the development of the solid parts of the integument.

1 Ickthyophis, Hypogeophis, Dermophis, C&cilia, Rhinairema, Geotrypetes,
Crytopsophis, Gymnophis, Herpele.

LIFE IN PRIMARY PERIOD 237

Many genera of Stegocephala are known, all belonging to
the Permian epoch. They were not very large, the largest,
Sphenosaurus, being about two metres in length, Archegosaurus
de Decken of the Permian of Germany measuring a metre and a
half, Chelydosanrus of the Permian of Bohemia about one metre,
and Actinodon of the Permian of Autun, which has been so
completely reconstructed by Albert Gaudry, a little less.
Euchirosaurus of the same region was a related form. All
these organisms had the general appearance of small Crocodiles
or large Lizards, but it has been established that the young
of Archegosaurus had branchial arches. The scales on the belly
of Chelygosaurus formed about forty bands " enchevron ", very
regularly and elegantly arranged, while the belly of Actinodon
was equally well protected. Some species such as Dinorophns
multicinctus of Texas had a carapace like that of the Chelonians
united to the vertebral skeleton, and for that reason Cope
called them Batrachian-armadillos. The Stereospondyles are
represented by analogous forms, Loxomma of the upper
Carboniferous of England and the Permian of Bohemia. They
really constitute an outpost which continued into the Trias,
when the structure of their teeth, characterized by sinuous
folds, has earned for them the name of Labyrinthodonta. The
Stegocephala, Temno- and Stereospondyles seem to have
belonged to the fauna of the North Atlantic continents.

Even at this epoch, however, the true Reptiles had already
appeared, whose embryos no longer had anything but useless
rudiments of gills, and alone were born with a special
apparatus for aerial respiration. This advance seems to have
been made during the lower Permian period ; it seems to have
been first achieved in America by Eryops, whose skull
alone was six decimetres long and four decimetres wide, and
by Cricotus, which was almost four metres long. The bodies
of the vertebrae were still made up of three pairs of separate
parts in Eryops, while in Cricotus the neural arches were
united with posterior elements called interventrals, and the
basiventrals were united to each other, a condition which also
occurred in the former genus. This last character marks
the line of separation between the first Reptiles and the last
Batrachian Stegocephala. The transition between the two
groups is thus practically imperceptible.1

1 In the early Batrachians and in the embryos of the present forms during
the early phas s of their development, the vertebras are composed of two

238 TOWARDS THE HUMAN FORM

The Microsaurians were Stereospondyles ; they had dermal
scales, dorsal as well as ventral, arranged on the belly like
those of Stegocephala ; their pelvis, largely cartilaginous,
had only two osseous discs widely separated from each other.
They have also been classed among the Batrachian
Stegocephala, but they have feet with five digits and mobile
chevron-bones on their caudal vertebrae, and iliac bones which
are articulated to two vertebrae instead of one. These
characteristics are common to the Reptiles, and in the absence
of embryogenetic data we can only make purely conventional
distinctions between these primitive groups. The Hylonomes of
the Carboniferous of Nova Scotia, their near relative Hyloplesion
of the Upper Permian of Bohemia, which was only a decimetre
in length, Seeleyia, only four centimetres long, and Melaner-
■peton and Orthocosta were all kindred forms. In Petrobates the
ventral armour showed a striking resemblance to the abdominal
ribs which we shall find in the Rhynchocephala, and which
also exist in Crocodiles.

The Rhynchocephala, sprung from the Microsaurians, are
probably the stock whence all the other Reptiles diverged.
Their biconcave, stereospondylous vertebrae are separated by
spaces, and bear caudal chevron-bones ; the quadrate bone is
fixed ; they have abdominal ribs formed of disjointed parts
arranged in chevrons as though, by a process analogous to that
already encountered in fishes, the ventral dermal bones were
only embedded in the wall of the abdomen, and did not show
any superficial dermal ossification. Their teeth are planted in
the sharp edge of the jaws and have no alveoli. A pelvis
similar to that of the Microsaurians still persists in Palczohatteria
of the Permian sandstones of Saxony, and the Protorosaurians
of the magnesian limestone of Thuringia. These were lizards
of about one and a half metres long, and they lead up to the
true Rhynchocephala with their completely ossified pelvis ;
among which are to be included Callibrachion, reconstructed
by Boule and Glangeaud, and Sauravus costei, described

anterior dorsal parts, the basi-dorsals ; two ventral anterior parts, the basi-
ventrals ; two dorsal posterior parts, the inter-dorsals ; two ventral posterior
parts, the inter -ventrals. Those animals are by general agreement regarded as
Batrachians in which these parts have remained distinct, at least in the caudal
region, and those in which the inter-ventrals are missing, since the half of
each vertebra is simply tripartite. Those forms in which the half-vertebras
are likewise tripartite and the inter-dorsal is missing are classed as Reptiles.
This is the case with Eryops and Cricotus.

LIFE IN PRIMARY PERIOD 239

later by Thevenin ; the last-named comes from the Upper
Carboniferous of Blanzy. A Rhynchocephala, protected by
special laws, still lives in New Zealand, the Sphenodon punctatum
or H attend punctata.

Up to this point all this world of the early Reptiles is a
modest one, even in comparison with living forms. But the
struggle for life during the Primary Period did not stop here.
The way was being prepared for the appearances of monster
Reptiles of unknown origin, forming a new order — the
Theriodonts. Pareirasaurus appears suddenly and simul-
taneously in the neighbourhood of the Dwina in Russia and
at the Cape of Good Hope. By what unknown route did
such heavy and massive beings make their way from one of
these regions to the other, the first being a part of the North-
Atlantic Continent and the second of the Gondwana continent,
separated, at least since the Devonian Period, by an un-
interrupted tropical sea ? Must we put still further back, to
the Silurian, in fact, the origin of Reptiles ? To this problem
no solution has yet been found.

Life was already prodigiously developed on the earth when
the Primary Epoch closed. But throughout its manifestations
there was but a faint foreshadowing of what would follow ;
monotony prevailed in the sea as on the land, where, through
the warm northern mists, the already much-softened profiles
of the eroded Huronian and Caledonian mountains stood
out against the sky, whilst in more southern latitudes the
young Hercynian chain showed, under an equatorial sun,
jagged summits at an even greater altitude than the peaks of
our Pyrenees and Alps.

Everywhere the sea waves buffeted the reefs built by polyps,
whose indeterminate shapes could not compare with the
brilliant garland of living gems encircling our Polynesian
islands and tropical continents. Sponges, which scatter with
splashes of gold, lapis, malachite, and scarlet the rocks of our
seas to-day, transforming them into palettes of glowing colours,
were then elegant but without colour. On the reefs, in the
sand and in the mud huge Pterygotus, Eurypterus, Limula, and
Trilobites went where they would without fear almost un-
disturbed, but from Silurian times onwards were less bold
and learned to roll themselves into balls at the slightest
alarm. Worms of all kinds, forms, and colours undulated

^4o TOWARDS THE HUMAN FORM

among the reefs and under the smallest rocks. The fairest
•ornaments of the sea, they were also the habitual food of all
those creatures such as Merostomata and Trilobites, which
contented themselves with small game.

The Echinoderms and the Molluscs had not yet attained
their final form, for they had scarcely yet recovered from their
efforts to save their lives under the hazardous conditions
through which they had had to pass. Endowed with only
feeble powers of locomotion, the Echinoderms multiplied in situ,
the Cystids and Blastoids growing like buds of stone where-
•ever they could attach themselves. A few Encrinites out-
spread vigorous blossoms on the rocks, and Starfish lived on
them when Molluscs were not sufficiently plentiful ; Melonites
heaped their purple globes one upon the other in great banks
along the sea shores. The Turbos and Avicube, the Nautili,
the Pleurotomarias, and the Trochi, had shells almost entirely
of shining mother-of-pearl, which was to change later into
porcelain, but they had not yet acquired those glowing hues
nor those shapes so capricious in appearance — though in
reality strictly and wonderfully geometrical — nor yet that
ornamentation of such fantastic design, which, under the form
of cones, pyramids, sailing barks with twisted and horned
prows, delights our eyes to-day. Feeding entirely on such
small fry as Diatoms, Radiolaria, Infusoria, and the larvae
which were flung as the small change of life into each wave,
the early gasteropod Molluscs still floated under water, where
they were -easily captured by Sharks, against which their
only weapon of defence in the struggle for existence was their
prodigious fecundity. Although strange fishes were decimating
the swarming worlds of Trilobites at the bottom of the sea,
none of those species were in existence which infest it to-day
in swift-moving, unnumbered shoals.

On the land a mantle of green had spread wherever
the soil was sufficiently moist, but there was no turf, for our
green grass is composed of Grammar, which it required
many centuries to elaborate. The soil belonged entirely to
Hepaticse, Mosses, the humblest of the creeping Lycopods,
and herbaceous ferns, among which the horse-tails uplifted
their ringed stems, on which, at regular intervals, grew circlets
of slender branches. Above these sorry prairies arose
serried ranks of straight-branched fragile trees — Calamites and

LIFE IN PRIMARY PERIOD 241

Lepidodendrons — a vegetation typical of damp soils.
Abundant water, in fact, was essential to the fecundation of
these plants, as their antherozoids could move only in drops
of rain or dew. The place they occupied in relation to the
higher plants might be compared with that of the Batrachians
in relation to the land Vertebrates. They were ill adapted
to grow on mountain slopes. However, tachygenesis gradually
suppressed their complicated method of reproduction ; the
microspores became pollen grains l and acquired the power of
fertilization ; thus the wind sufficed to carry them to the
ovules. Thenceforward the Cordates were enabled to cover
the ground with a forest of reeds, and Conifers were enabled
to climb the mountain-sides, whilst Cycads spread out their great
plumes in the sheltered valleys to be borne away on the wings of
the tempests. Wherever roots could penetrate the soil became
clothed with a vegetation that was extraordinarily luxuriant
in Carboniferous times, but so fragile that the wind often
stripped its branches, broke its stems, and tore the plants
up by the roots. The remains of such as grew in marshy
regions or along the borders of lakes have accumulated in situ.
Protected by drift brought down by floods, or by the mud
spread over them by the waters, these beds of fallen vegetation
have been preserved to us. Plants that grew on the valley-
slopes, far from the sea, as in the Central Plateau, were carried
along by torrents to the freshwater lakes, which they gradually
choked up. We can still identify the successive layers thus
formed by floods at the height of each inundation. Still others
were carried as debris by the great rivers down to the sea, as the
Mississippi still carries it at the present day. And as this
went on through century after century, in the course of
which the configuration of the earth scarcely changed and the
rivers kept to their old beds, vast accumulations of trunks,
branches, leaves, and even herbs formed, thus creating the
coal seams which feed our modern industries.

But while all this preparation for the mad activity that
devours us to-day was slowly taking place, nature itself was
silent and stern. Not a single flower lightened with the fresh
colours of its petals the sombre green monotony, scarcely even
varied in shade, of the vegetation, for, as there were no seasons,

1 p. 101.

242 TOWARDS THE HUMAN FORM

it was the same all the year round. This vegetation grew in
rank profusion, without pause or pity, with undiminished
vigour throughout the year. Under a warmer sun in a moist
atmosphere, with an almost constant temperature, the pro-
duction of vegetable matter, at any given time, must have been
much greater than in our own da}', when regular cold and dry
intervals interrupt its growth. This is one reason why the
coal beds remained so extensive and so intact, although, as
Bernard Renaud has shown, cellulose-destroying microbes had
already begun their work of disintegration upon the cellulose
of which the solid plant tissues are composed in the manner of
our existing Bacillus amylobacter. But it was not only its
green uniformity that made this luxuriant vegetation seem
so mournful. No living creatures were to be seen crawling
among the mosses and on the trees but millipeds hunted by
scorpions, indeterminate-looking spiders, spiritless Insects, such
as white Ants, Cockroaches, and Phasmids scurrying to shelter.
In such a world slow-moving armoured Salamanders must
have looked like giants. The air was practically uninhabited.
The swiftest of its denizens were May-flies, Ant-lions, and
Dragon-flies. There were neither Bees, Butterflies, nor Birds.
No voice sang of the joy of living, or sent its love-calls or even
its cries of terror into the moisture-laden air. There was no
intelligence present to be scared by volcanic eruptions, by
the flash of lightning, or the rumbling of earthquakes. Life
was manifestly experimenting. It was not to blossom till
the period which we shall now enter.

CHAPTER II
Life in Secondary Times

FN Secondary Times life blossomed in every direction.
-*- During the Carboniferous Period the whole of Europe
had been slowly but profoundly transformed by the hercynian
folding along two main lines of direction : one running north-
west to south-east, the other south-west to north-east, crossing
each other at a sharp angle in the Central Plateau. Analogous
movements took place in the north of Africa, the Altai
region, the north of China, the Rocky Mountains, Bolivia, and
the basin of the Amazon. In all these areas the once deep
valleys where deposits accumulated up to the Dinantian
Period were heaved up, and the mountains thus formed
have been called the Hercynian Chain.

At the beginning of Secondary Times, during the
Triassic, volcanic eruptions caused by these uprisings were
still taking place in the Tyrol, the Pyrenees, Spain, Portugal,
Morocco, all around the Pacific, especially in British Columbia,
where the debris of volcanic eruption is found over a vast
area, the strata often being four thousand metres thick, and
in New Caledonia, New Zealand, etc. But in time everything
became calm once more and until the beginning of the up-
heaval of the Pyrenees — that is to say, for at least four
million years — tranquillity reigned almost undisturbed on
the earth. No doubt the surface did not remain absolutely
stationary. As it has always done and is still doing to-day,
even on our coasts, it rose or sank slowly in different places,
so that the sea invaded a certain number of coasts in the north
and east of Africa, for instance, and formed gulfs in the region
of the Jura and the Alps, penetrating even to the heart of the
low-lying portions of the continents, which it inundated with
shallow expanses of water, temporarily isolating Scandinavia
and Finland from the rest of Russia during the Jurassic. These

244 TOWARDS THE HUMAN FORM

oscillatory movements of land surface levels were accentuated
to such a degree during the Cretaceous Period that a deep
fold, invaded by the sea, was produced right across Europe,
then consisting of a series of archipelagoes, from east to west,
and across the North American continent from north to south,
cutting it in two, and also across Africa, whose western portion,
now projecting into the Atlantic Ocean, was thus cut off from
the rest of the continent. It was then that the shifting and
derangement of strata took place known as the dislocation of
the chalk. Elsewhere, however, the sea retreated, leaving
behind it lagoons which dried up and left evidence of their
presence in deposits of salt, while the summits emerging from
the water formed islands and temporary archipelagoes. New
communication was thus established between the different seas
and former communication was cut off. The faunas hitherto
separated became mixed in some districts and in others
was isolated in groups and thus forced to follow individual
lines of evolution. Hence a greater variety of marine species
resulted, and many southern species were carried north by
currents passing through the new straits, whereas northern
species penetrated to the south, so that we cannot arbitrarily
assume persistent variations of the mean temperature from
the presence of such species in given waters. Such changes,
however, were of minor importance and in no way disturbed
the universal calm.

In every respect the transition from the Primary to the
dawn of the new era was effected gradually. Throughout the
Triassic Period the vegetation did not differ, except in details
of genera and species, from that of the Primary ; nor would
it seem at a first glance, at least, judging by our information
at present, to have been greatly modified during the subsequent
Jurassic Period. It is probable, however, that it was during
this era that the fertile female leaves, which remained open
in the Gymnosperms, in certain instances coiled up and closed
around their ovules in order to protect them : a decisive step
forward was thus taken in the Vegetable Kingdom — Angio-
sperms had been evolved. At all events, they were abundant
and varied from the beginning of the Cretaceous, and the
families that made their appearance first were precisely those that
we should expect to do so according to the theory enunciated
on p. 106. Dicotyledons were greatly in the majority, and

LIFE IN SECONDARY TIMES 245

among them the first to appear, as we should expect, were those
having catkins : Poplar, Willow, Birch, Beach, Oak, Walnut,
Myrica, and their near relatives the Plane-trees and Liquid-
ambers ; then the Maple, Eucalyptus, and Laurel, with
numerous stamens having traces of ramifications, and Myrtaceae
with ramified stamens. With them there were certain plants
with isomeric flowers and even inferior ovaries, such as Ivy
and Dogberry-tree, and gamopetalous plants like Viburnum
and Oleander. The Monocotyledons were already represented
by several families having large flowers : Liliaceae, Alismaceae,
Pandanus, Palms, and even Aroideoe. It must not be forgotten
that, once they had become differentiated from the isomeric
Dicotyledons, the Monocotyledons must have developed
parallel with them and even rapidly, for they could no longer
modify themselves except in details.

Everything indicates a very mild climate during this period.
Seasons did alternate in the regions around the Poles (p. 51),
but everywhere else the temperature remained practically
uniform. There were no annual periods of frost capable
of holding up vital processes, no seasons of torpor or death,
and even in the polar regions, although Palms were absent,
the Bread-fruit tree, nowadays confined to the tropics, was
growing in Greenland. On the western coast there was a
succession of three distinct and very rich floras, testifying to
a gradual cooling, for the tropical Cycads gradually disappeared,
and Dicotyledonous plants became more and more important.
The Tethys — the great Mesogean Sea of Douville and the
Central Mediterranean of Neumayer — warmed by a two-fold
inflow of waters from the torrid zone, kept its two coasts at an
almost constant temperature considerably higher than that
of the Cote d'Azur. The two arms of this sea which enclosed
the North Atlantic continent ensured it a mild climate, and
the other continents were equally well endowed — all were
enveloped in a sort of Gulf Stream. The Madrepores built up
coral reefs all along the coasts right up to Scottish latitudes.
The Madrepores of this epoch were very like those of our own
day, and were Hexacorallia closely related to the builders
of the fringing reefs of the Red Sea and of New Caledonia,
the barrier-reefs of the north-west of Australia and the
Fijian archipelago, and the atolls, those remarkable ring-
shaped islands of the Pacific. Now we know that the

246 TOWARDS THE HUMAN FORM

polyps cease building in waters whose temperature falls
below 25" C. So abundant are their remains that they
constitute huge calcareous formations, providing the name
for the Coralline division of the Jurassic.

The Oolitic limestone, which plays so large a part in the strata
of this epoch, is simply a precipitate of the calcareous granular
dust, formed from broken-off pieces of polyparies after
they have been battered about in the waves, which collects
round debris of one sort or another. In its fossilized form
it has given the name to one of the two main subdivisions of
the Jurassic.

In the seas encircled by these coral-builders a whole world
of new invertebrates found a home. Elegant Radiolaria 1
floated in the water, and the rocks blossomed with every sort
of siliceous and calcareous Sponge,2 with Polyps, and with
Crinoids so closely resembling plants that they are called
Sea-Lilies when they attach themselves by a stalk to the sea-
bottom and look like living flowers, and marine Palms when
they spread out at the summit of their fifty-foot stems great
plumes that looked exactly like the leaves of date-palms, as
the Pentacrinoids do that still exist as green meadows in the
waters off Rochefort.

It was at this time that some of these Sea-Palms detached
themselves from their stems, and gave rise to new free forms
like our modern five-armed Eudiocrinus, which lives in the
depths of the Pacific and the Atlantic ; to Comatida, which
has ten tentacles like rose-coloured feathers and swims in
a leisurely fashion by undulating them alternately ; and to
Actinometra, an inhabitant of the warm seas, whose ten
primitive arms have an indefinite number of ramified branches.
Over these reefs, gay and glowing as those of whose incompar-
able beauty Saville Kent has written, countless Molluscs
dragged shells which displayed an infinite variety of new
forms. For, in addition to the surbased forms and those
with rounded openings there were Scalaria and Turitellidae with
long shells and corkscrew turns, Natica? and others with rounded
and polished shells, large Strombidae with long scooped-out
orifices, many forms of carnivorous Gasteropods with shells
either notched or drawn out into a tube, Cerithium, Fusella, etc.

1 Spumellaria and Nassularia.

2 Hexactinellidae, Tetractinellidae, Lithistidese, Monactinellidae, Phare-
tronids and other calcareous Sponges.

LIFE IN SECONDARY TIMES 247

It was at this time, too, that the hermaphrodite Gasteropods
greatly increased— and terrestrial Snails and Slugs, the future
freshwater Limneae and Physse, the Bullae, first of the series of
marine Molluscs in whom we can follow the gradual loss of the
shell, and Acteons, the least modified of the Opisthobranchs,
themselves probably the forebears of the open-sea Pteropods,
which fly in water by the aid of two large wings dependent
from their feet as butterflies fly in the air.

The bivalve Molluscs were not behind the Gasteropods
in progress. During the Jurassic period the majority of the
varieties existing to-day were added to those we have already
come to know. But there were others as well. We have
nothing in our seas that can be compared to Diceras, whose
two cow-horned valves, joined at their base, faced each other ;
to Requienia, in which only one of the horns persisted, the
other being reduced to a simple operculum, closing the orifice
of the first ; to the Rudistae, whose large valve exhibits a form
and texture so disconcerting that it has suggested the possibility
that they are really operculated polyparies like Calceola sandalina
of the Devonian strata. They are considered to-day to be
related to simple existing bivalves like the Chamidae, which
has one of its thick valves attached to rocks, as in the case
of Oysters, and the other one free. The powerful hinge
uniting the two valves in fact resembles that which unites
the two valves of the Rudistae. Among living Lamelli-
branchs, the only variety having a valve by which the
creature attaches itself, developed in a way recalling the
Rudistae, are the ^Etheriidae, found only in the rapids of Central
African rivers. Dr. Anthony believes that the exaggerated
development of this valve is due to the continuous action
of the violent currents to which it has been subjected. He
surmises that the Rudistae lived in waters in which they were
violently buffeted by the waves. Like the coral reefs they
replaced in many localities, they formed a defensive bulwark
for the continental masses.

Throughout the Cretaceous Period the Madrepores were
gradually retreating southwards as though the temperature
were progressively falling. The polar regions then enjoyed
a relatively temperate climate, but the south of
France and southern Europe still retained their tropical

248 TOWARDS THE HUMAN FORM

climate, as we can tell by the presence at certain points of
lateritic minerals, which can be formed only under the
action of intense solar radiation. Douville has discovered
Orbitolites — large circular Foraminifera — which only inhabit
warm seas abounding in lime, wherever there are reefs of
Rudistse. They presage the imminent arrival of the
Nummulites which will play so great a part in the seas of
the Eogene period.

We cannot help being struck by the modifications produced
in the habits of animals during Jurassic times. In the
preceding period almost all the Gasteropods had shells with
entire openings ; these organisms lived exclusively upon
vegetable food, and the pulmonate Molluscs which also have
shells with entire openings, and which had invaded both
land and fresh water, are likewise almost exclusively
vegetarian. The carnivorous Gasteropods, the opening of
whose shell is either notched or drawn out into a tube, did
not make their appearance until the Secondary Period. This
correspondence between the diet and the shell aperture is
not due simply to chance. The carnivorous Molluscs are led
to their prey by the sense of smell. As soon as a dead body
falls into the water it is surrounded on all sides by Nassse. Now
the olfactory organ of the Gasteropods, the osphradium or false
gill, is situated in the branchial cavity near the true gill. A
tube or siphon, formed by a prolongation of the fleshy top of
the branchial chamber, conducts the water into this chamber,
and on to both the osphradium and the branchiae, whose
functions are thus regulated. This siphon fits either into the
notch or the canal of the opening of the shell, and we can
see that its gradual elongation was due to the efforts of the
mollusc to induct the maximum quantity of odoriferous
effluvia within its reach.

Was it the great number of these preying molluscs that drove
certain of the Lamellibranchs to adopt the life of the recluse ?
Their senses are so rudimentary that they can hardly be credited
with sufficient intelligence to carry out a deliberate intention.
It is, however, undeniable that during the Primary Period those
Lamellibranchs living on the surface of the ground and
crawling by means of a foot, somewhat similar to that of the
Gasteropods, or suspended by a byssus, were in the majority.
Whereas, in the course of the Secondary those Lamelli-

LIFE IN SECONDARY TIMES 249

branchs increased that buried themselves in sand, mud, or
even limestone, and that remained in communication with the
exterior only by means of two long tubes, the siphons, situated
in the posterior part of the body, of which one distributed the
water on to the branchiae, which then passed it on to the
mouth, while the other ejected the water from which the
oxygen and food particles had been assimilated, and which
carried with it the excreta.

This change of habit, which, indeed, furnishes us with food
for reflection, is not limited to the Lamellibranchs, for it also
occurs in the Sea-urchins. The Sea-urchins of Primary times,
without any predilection in choosing their direction, crawled
among the Algae or on rocks. The shell of the more recent
species was divided into ten areas and bore numerous spines.
These characteristics have been preserved, but there were
others as well — burrowing species, covered all over with fine
spikes, which dug their way in the sand in a definite direction.
In these species, continually pressed against the covering earth,
the shell is flattened around the mouth and forms a true
ventral surface ; the ambulacra on this side have taken on an
entirely different appearance from those of the dorsal side,
and henceforth their tube-feet alone play a part in locomotion.
As the excreta are now no longer easily evacuated through the
top of the shell, buried as it is in the earth, the anus changes
its position from the top to the neighbourhood of the ventral
face, thus characterizing a posterior region of the body opposed
to that which the sea-urchin carries in front when it is
burrowing. Thus a very definite bilateral symmetry (pp. 127
and 149) is superposed on the primitive radial symmetry. The
mouth at first remained situated in the middle of the creature's
ventral aspect and conserved the jaws of the primitive Sea-
urchin, though somewhat diminished in size — an example of
which is provided by the Clypeastridae. Later the mouth
moved almost to the anterior edge of the ventral surface ;
the posterior lip advanced, spoon-fashion, in such wise as to be
capable of being dug into the muddy sand, and of shovelling
it into the sea-urchin's mouth. The useless jaws disappeared.
An example is seen in the Spatangidae. During the Secondary
era we find all the stages of transition between the ordinary
Sea-urchin and this type, and they are so numerous in
certain geological layers that they have served to characterize

250 TOWARDS THE HUMAN FORM

them. The burrowing Sea-urchins actually swallow the mud,
and this mode of nourishing themselves is a factor in their choice
of habitat. But, we may ask, is not this in itself a result of their
search for security ?

Among the Lamellibranchs Cardium digs up the soil as if
seeking food in it, and may serve as a starting-point which
will explain the formation of siphons in organisms such as Solen,
the Razor-shell, which only moves upward and downward in a
vertical burrow and feeds on floating particles carried thither
by the water without any search on the part of the Razor-
shell . It is impossible to see anything in its underground habitat
beyond the desire for security. This is quite evident in the case
of the Pholadidae, which perforate the limestone they cannot
possibly eat, and in that of Teredo, which lives in wood. If these
animals were thus led to live in seclusion, we may suppose that
those among the congeners of their ancestors which did not adopt
this way of life were destroyed. This would be a consequence
of that struggle for existence, in which only those organisms
survived that were able to avoid it, either involuntarily or of
set purpose.

This motley crowd of Invertebrates was dominated by
innumerable swimming Molluscs, first among whom we see
the Ammonites riding the waves and seated as one might say
in their shells, spirally twisted like the horns of Jupiter Ammon,
and divided into chambers, whose origin and increasing com-
plexity during the entire Jurassic Period we have already
described. What purpose can have been served by this com-
plexity, which was never produced in the Nautili ? If we
admit the assimilation, postulated by Munier-Chalmas, of the
straight-partitioned Cephalopoda with the Nautili, and of
those having folded partitions with the Spirulae, certain
observations become unavoidable. The first of these must have
had at least two pairs of branchiae and the second only one,
possibly because of a shortening of the body, which was in
communication with the outside world only by its anterior
extremity, and which thus underwent a kind of cephalization.1
Under these conditions the mantle, increasing its surface
by folding, was able to take the place of the second pair
of absent branchiae. The folds would become more complicated
as the Cephalopod became more active and its potential size

1 Cf. pp. 219-20.

LIFE IN SECONDARY TIMES 251

greater — certain Ammonites approached a metre in diameter.
They evidently kept either close to the surface or at moderate
depths, and we thus understand how it was possible for the
transformations to come about that they underwent during the
Cretaceous Period. The last convolution of the shell is at first
detached from the others as if it hung in the water below the
remainder of the shell and served as a ludion ; then it described
an upward C-shaped curve, as though the creature's mouth,
at first directed downwards, were subsequently upturned.
This change in the orientation of the mouth is perhaps only
apparent ; we may, in fact, admit that the shell, having
originally opened upwards as in other Ammonites, was now
oriented in such a way as to keep the mouth as far as possible
in the same direction, whenever there occurred any displacement
of the centre of gravity, due to the growth of the Mollusc and
of the air-filled chambers of the shell, such as would upset the
balance struck between the animal and its shell. Having
once begun, this uncoiling continues, and ends in the complete
unwinding of the shell from its point of formation. Thus we
pass from the type of Scaphiles and Crioceras to that of Pictetia.
The shell of the last is C-shaped, and the upper hook is coiled
spirally. In Hamites the convolutions are no longer spiral, but
formed of parts bent at right angles one over the other. Finally,
in B acuities the straight portion is so long in proportion to
the coiled part that we might think it a reversion to the
Orthoceratidae. The actual organization of the Ammonite,
moreover, undergoes a kind of degeneration. The folds of the
mantle, which follow the sinuosities of the lines of suture,
become so simplified as to resemble Ceratites of the Trias,
or even Goniatites of the Primary. It was thus, no doubt,
that the transition was gradually effected to the form of the
little Spirulae of the present epoch, with its interior unwound
shell and simple septa.

The Turrilites, which are twisted corkscrew fashion instead
of being coiled in a flat spiral, and which are consequently dis-
symmetrical, could not have been produced if the organism
had remained either floating or swimming in some homogeneous
environment like water. The torsion the shells have undergone
must be due to the same causes as those which affected the
Gasteropoda, and indicates the existence of a group of crawling
Ammonites.

252 TOWARDS THE HUMAN FORM

Why did these splendid creatures disappear ? For long ages
they had ruled the sea. Their shells have been preserved in such
great numbers that all their variations can be followed, and
their genealogical tree be worked out so completely that the
history of this group may be considered as an irrefutable
demonstration of the modification of living forms. Yet puissant
and plastic as they were, they became extinct. Are we to
think that the Ammonites needed such specialized food that
at some given moment it was not forthcoming ? Had this been
so Palaeontology would have given us at least some indication
of the facts, and we have none. Is it conceivable that some new
carnivorous marine animal of greater activity multiplied and
caused such a carnage among the Ammonites that they were
annihilated ? We shall see later that this was not impossible.
Side by side with this solution, however, the manifest
simplification of form and the profound alterations in certain
of them suggest some modifications in the environment in
which these beautiful molluscs prospered and elaborated their
structure until it proved insufficiently plastic to survive the
new conditions. As they were sea-animals, this change can
only have consisted in a lowering of the temperature, for the
sudden extinction of an organic type in unvarying surroundings
is thoroughly improbable.

The only Molluscs which disappeared together with the
Ammonites were the Belemnites, which were also dibranchiate
Cephalopods and very numerous. Their conical shell, short,
straight, and partitioned, terminated in front in a kind of a
large spoon-shaped shield, concave towards the base, and
behind in a calcareous point with the form and dimensions of
a cigar. Such perfect imprints have been found that all the
soft parts of the body are easily recognizable. The ink-sac
has been so well preserved that if its contents are crushed and
mixed with water it can still be utilized to make a wash-
drawing. These organisms were close kin of our Squid.
They must have been more active swimmers than the
Ammonites enclosed within their shells, and they could thus
easily prey on them. However, the most important part in the
wiping out of both was probably played by the Fishes.

This was the period when bony Fishes had been evolved,
and were added to those whose skeleton was still cartilaginous.
These newcomers undoubtedly sprung from the ganoid Fishes

LIFE IN SECONDARY TIMES 253

which multiplied so rapidly during the Jurassic Period, were
limited during that period to the Leptolepididae, but afterwards
became very varied. The majority at first, as we should expect,
had pectoral and pelvic fins far apart like those of the Sharks
and Ganoids, and fifteen families can be enumerated, many of
them specialized. Among them were families which still
thrive, such as the Scopelidae, now pelagic and resembling the
Salmon ; Clupeidae, closely related to our Sardines and
Herrings ; 1 the deep-water Halosauridse ; Osteoglossidae, and
even Murenidse, which have lost their fins.2 Fishes with pelvic
fins close to the pectoral also made their appearance in the
form of the Berycidae, representatives of which still exist.

It is thus an already quite important fauna, consisting of
agile Fishes, whose very moderate size enabled them to find
their way everywhere ; hence they must have made life
very difficult for the Ammonites ; not only pursuing them,
but competing with them for food. This must be taken into
consideration if an explanation of the disappearance of the
great swimming molluscs is sought. Those that lived under
special conditions — for instance, the Cretaceous C-shaped
Ammonites, which lived suspended in mid-water far from the
surface, persisted much longer than the others, because the
zone they inhabited was relatively poor in large-sized prey and
little frequented by Fishes.

Let us now turn our eyes to the land. The sombre and
monotonous vegetation of the Primary Period still persisted,
for the most part, during the Triassic and Jurassic, but in the
Cretaceous the virgin countryside was brightened by many a
different shade of young foliage and brilliant flowers. The
trees we know to-day uplifted their capriciously branched
trunks somewhat shyly at first among the severely regular
stems and arms of the primitive conifers ; but they ended by
driving them out of the plains, and Poplars, Willows, Birches,
Beaches, Oaks, Walnuts, Plane-trees, and Maples, the first
branches of the theoretical genealogical tree we set up a few
pages earlier, crowded into their place. The surface of the earth
became covered with vast forests in which there grew also
F"igs, Bread-fruit trees, and other unisexual flowering Urticeae.
Holly, Ivy, and different members of the Cornaceas family
sprang up in their shelter, and even some gamopetalous

1 Diplomistus, Scombroclupea. 2 Urenchelys.

254 TOWARDS THE HUMAN FORM

forms such as Viburnum and Oleander. And if we cannot
add to this list a long series of brilliant flowers, it is because
beautiful flowers hardly ever grow on big trees, and because the
delicate stalks of shrubs and herbaceous plants which do bear
them are ill-adapted to fossilization.

All this new vegetation naturally had its echo in the graceful
and active world of Insects living in its midst. Apart from
certain Hemiptera, which stuck a sharp probe into the young
branches and sucked their juices, the Primary Period had
scarcely known any Insects but those which lived on solid
food crushed by their powerful buccal armament. But the
new prairies, with their blossoms, and the woodlands with their
tender foliage, offered the restless Insects a thousand new
occasions for the exercise of their activity. Honeyed drops
collected on the leaves, nectar formed within the depths of the
corolla of the blossoms. This was dainty and almost ambrosial
food for aerial denizens. Cutting mandibles and jaws armed
with powerful pincers were of no use for imbibing such exquisite
fare, and they had to be elongated, softened, refined, and
partially atrophied, transformed into the lamina which support
the bee's flexible tongue, the proboscis of the butterfly, or
the suction tube of flies. Thus to the clumsy insects of
Primary times was added a host of delicate, swift-flying
creatures often eclipsing in brilliance the very flowers they
plundered. The earth is at last decked in such fairy colours as
we admire in the tropics. The time has come when its surface
at least teems with living things, and the air is peopled. The
conditions of Primary times so eminently favourable for this
world of tiny creatures to-day so fragile, continued into
Secondary times. Nowhere did the temperature drop
sufficiently to destroy at one fell blow all the Insects of any
particular region. Like the higher organisms they died one
by one, and the duration of their lives was cut short only by
accidents. This full span of life permitted them to observe, to
acquire experience, and to profit by what they had learned.
One generation overlapped another. Parents lived to see and
know their progeny, could live among them, care for them, and
feed them as long as they were unable to feed themselves ;
or, at least, place them in such conditions as would provide
them with the means of subsistence close at hand until they
were old enough to go farther afield and seek it for themselves.

LIFE IN SECONDARY TIMES 255

The older generations, moreover, had time to educate their
young, and these being perpetually in contact with their
parents, imitated their actions, and thus were initiated into
life, profiting from the acquired experience which in this way
became transmitted from generation to generation.

Their activity was limited at first to a few simple actions,
partly in the nature of those constituting what botanists have
long called tactism, and therefore unconscious acts. As the
organism perfected itself, these acts were replaced by others,
more or less conscious ; but the repetition of the same acts,
stimulated by the same circumstances, caused them to become
automatic, like those associated with habit or performed uncon-
sciously in sleep, those which are simply the result of tactism,
and those which Claude Bernard has called reflex actions,
and which we ourselves perform without the intervention of
our will and unregistered by our consciousness. Thus we blink
our eyes when a ray of light suddenly strikes them, make a
defensive movement if our face is menaced by a blow, and
contract our muscles in walking and swimming. In these
conditions the minute brain of the Insects, constantly
stimulated by the same influences, and set working by the
performance of the same actions, gradually acquired an
appropriate organization which was transmitted by heredity,
so that the slightest external stimulus thereafter sufficed to
set going a whole series of actions marvellously linked together,
succeeding each other in a given order, even when the specific
purpose they were intended to serve had been suppressed.
This was the elaboration of what is called instinct.1

Certainly the theory put forward above supposes an initial
intelligence analogous to that to be observed at the present
day at work side by side with automatism in Birds, which
live with their young in conditions not unlike those which
prevailed in the Cretaceous Period when Insects lived with
their larvae ; and it may come as a surprise that such fragile
creatures should be credited with similar intelligence. Such

1 I developed this theory of instincts in 1881 in a textbook called Anatomie
el physiologie animates, written for the Philosophical Course of the Lyc6es.
Almost at the same time, although somewhat later, the same theory was
elaborated in England by G. J. Romanes in his volume on Animal
Intelligence, for the French translation of which I wrote a preface (1883).
Then we were both brought to a standstill by the difficulty of explaining the
transmission of instincts from one generation of Insects to the other, since two
generations are not contemporaneous.

256 TOWARDS THE HUMAN FORM

intelligence, however, exists and functions to-day in the very
manner we have just indicated in all the social Insects — White
Ants, Wasps, Humble-bees, Bees, and Ants, and we must
necessarily bow to the facts. Darwin made a masterly study
of what we call instinct in birds, where the word designates an
assemblage of unconscious and more or less conscious faculties.
He demonstrated that in the same group of Birds, Molo-
brns, for instance, a kind of American Starling, we can
follow all the stages in the development of an instinct identical
with that of the Cuckoo which deposits its eggs in the nests of
other birds. It is the same with the social insect, and especially
in Ants, where we can see the social instinct, the constructive
instinct, and the instinct prompting a provision for both larvae
and adult, as well as many another, occurring in different
species and genera under forms which are easily graded from the
most primitive to the most complex manifestations of in-
stinctive behaviour. From this we must conclude that in Insects,
as in Birds, instincts are not innate, and were not bestowed upon
the creature once for all, without possibility of variation, but
were gradually perfected in just so much as the insect modified
itself, and that this apparent innateness is nothing but heredity.
The same gradation of instinct can be observed in Insects which
live solitarily. We know that all insects are not equally
endowed in this respect. Those which have preserved the
primitive forms and mode of development (Archineuroptera,
Orthoptera, Hemiptera) have generally remained at the very
bottom of the scale so far as instincts are concerned. Insects
with crushing mandibles and a complete metamorphosis
(Euneuroptera, Coleoptera) are somewhat better endowed
without there being any connexion between this fact and their
method of evolution, for the Lepidoptera and Diptera are as
poorly endowed as the Archineuroptera, whereas the White
Ants of the Neuroptera group are almost equal to the most
remarkable Hymenoptera. Their social species, it is true,
appeared only during the Secondary Epoch.

In the order of Hymenoptera, both in the solitary and the
social forms, the instincts exhibited can be arranged in a
definite series and their progressive evolution followed from
species to species, be it in connexion with the building of nests,
the provisioning of the young, or the manner of killing the prey,
right up to the manifestation of those other instincts that have

LIFE IN SECONDARY TIMES 257

been so beautifully observed and have inspired such eloquent
writing on the part of that great naturalist, the recluse of
Serignan, J. H. Fabre.1 In those species which feed on sweet
liquids, whereas they nourish their young on animal prey, we
can even trace the transformation from a carnivorous diet, at
first common to larvae and adults, to a sugar diet, originally
limited to the adults as in various Wasps, and then extended
to the larvae as well, as in the case of Bees and Ants. It is
obvious then that instincts have been evolved, though any
explanation of such evolution is brought up against a difficulty
which seemed insurmountable to Darwin, Romanes, and
myself, which set Fabre against the doctrine of evolution, and
whose solution I myself only guessed at much later.2 This
explanation lies simply in the fact that the Hymenoptera,
among all insects able to live on liquid food, are those in whom
the mouth-parts have the most varied aptitude, so much so
that we find among them all the transitional stages between a
mouth adapted almost entirely for crushing and one essen-
tially constructed for licking, so to speak, like that of the Bee.
Hence they were able to profit more greatly than the Lepidop-
tera and Diptera by the particularly favourable conditions
prevailing in the calm, warm Secondary Period. The advent
of winter seasons caused the disappearance of all those insects
wliose individual evolution took longer than a year, and which
had not learned to shelter their larvae or themselves against
the rigours of the periodic cold season. Among those indi-
viduals whose evolution took less than a year, only those
survived whose development happened to take place during
the summer. In this way the seasonal rhythm of Insect
reproduction became established. This rhythm had as a
result the isolation of one generation from another. While
the brevity of life cut out experience, the seasonal rhythm did
away with education. The insect brain, however, was already
sufficiently organized to make most of the reproductive acts
automatic. Heredity preserved what has been acquired in this
way, but the winters prevented all possibility of modifications,
and in this way the instincts that had become fixed took on
that guise of mystery that deterred for so long any attempt at
explanation. As soon as the veil of mystery is withdrawn, we
arrive at the apparent paradox that the very fixity of Insect

1 LXXVII. 2 LXXVIII.

258 TOWARDS THE HUMAN FORM

instincts is in itself an unexpected argument in favour of the
theory of evolution, and of the mutability of living forms.

Contemporary with this development of Insects, such small
creatures, the evolution of the terrestrial Vertebrates took a
sudden step forward. During the Triassic Period the Stego-
cephalan Batrachians were still represented by temnospondylous1
and stereospondylous 2 forms. Among the latter, the Mastodon-
saurus of the Trias of Germany and England attained a gigantic
size ; the skull alone was one metre long. The last representa-
tives of this group, which did not survive the Trias, appears
to have been Labyrinthodon of the county of Warwick and
its vSouth African counterpart Rhytidosteus. Thenceforward,
the forms which were to persist came closer to those of to-day.
A small Batrachian something like a salamander, Hyolceo-
batrachus, is found in the Wealden clay. The anurous Batra-
chians began to appear in the Jurassic with Palceobatrachus,
but the large Batrachians, such as the more or less armoured
species, had had their day. The world was to belong to the true
Reptiles whose skin was so dry as to become scaly and in
whom the skull was articulated with the vertebral column by
a single condyle, whose branchial arches were atrophied before
birth without ever being used, so that the animal could breathe
only in the open air.

At the time of their appearance the world was empty of large
animals. Vast horizons were opened to their activity. We
can hardly admit that the struggle for existence or natural
selection played any considerable part in the evolution of
those that did exist. This evolution was in two directions.
The first large Reptilian fauna that appeared on earth is known
to-day chiefly by the fossils found at Elgin in Scotland, in the
Permian of Bohemia, Thuringia, and Autun, in the Karroo
formations of South Africa belonging to the early part of the
Triassic Period, and in the North American deposits of the
same age. These Reptiles seem to have disappeared toward
the middle of this period. We have no precise indication of
their origin, but they appear, however, to approximate to the
Stegocephalan Batrachians. Pareiasaurus, which appeared,
as we have seen, towards the close of the Carboniferous Period,

1 Eupelor, Brachiops, and in India, Gondwanasaurus.

2 Trematosaurus, Capitosaurus, Metopias in the Trias of Germany ;
Diadetognathus, Pachygonia, Gonioglyptus.

LIFE IN SECONDARY TIMES 259

bad the aspect of a Frog as large as an Ox, and had a short
tail. These Reptiles attained a length of two and half metres.
Their membranous skull was entirely covered with bony
dermal plates, leaving a hole for the parietal eye. These plates
were rugose as if they had been hewn, and in Elginia, a related
form, had peculiar spiny processes. The teeth were small and
uniform, with several serrated points, arranged in series, and
arose from both jaws and the palate. The limbs, short and
squat, each terminated in five digits, whereas the Stegocephala
never have more than four. The skull articulated with the
vertebral column by a single condyle, as in the case of the
Reptiles, whereas Batrachians have two. The lower jaw,
made up of several parts, was attached to the skull by
a quadrate bone united to it. The shoulder girdle com-
prised a scapula, a united coracoid and precoracoid, and a
cleithrnm. These characters are clearly Reptilian, but in the
shoulder we already observe some features which appear later
in Mammals. The coracoid bones are united with the
scapula in the manner of the coracoid process of the Mammals
and the scapula is provided with a spine characteristic of these
animals. These characters are accentuated in the pelvic girdle,
constructed on exactly the same plan as in Mammals, and
which articulates with two or three vertebrae constituting a
sacrum. Pareiasaurus and Elginia form the first group of
Theromorpha, the Pareiasaurians.

In a second group, the Theriodonta or animals with
mammalian teeth, the bony envelope of the skull remains in-
complete as among the other Theromorpha. In these animals
however, some very remarkable modifications are produced
in the dentition. The teeth no longer serve merely to hold the
prey ; they also grind the food — the Reptile uses them, as later
on the Mammals used theirs ; nor is the number very different.
We can already classify them as incisors, canines, and molars.
The dental formula of Lycosaurus, for example (i| c} m£),
might be applied to the mammalian Marsupials. That of
Gomphognathus (if c^ m|.|) differs only in having more molars.

The molars, however, retain their reptilian character.
They have but one tubercle and one root, except perhaps
those of Tritylodon, which have two, and consist merely in
one broadened tooth, whereas the molars of the Mammals are
formed by the union of several teeth. Also, side by side with

260 TOWARDS THE HUMAN FORM

resemblances that are sometimes more remarkable still,
we find certain differences that are no less striking. Tritylodon
had long incisors deeply imbedded in the jaws and of perennial
growth, no canines, but in their place a gap, as in Rodents.
The molars of Trirachiodon were multituberculate. There were
likewise no canines in the continuous tooth-series of Stereorachis
of the Permian of France, nor in Empcdias molaris of Texas,
which had palatal and vomerine teeth. Clepsy drops, Dime-
trodon, and N anosaurus of Texas, on the other hand, some-
times had more than two canines in each jaw, which never
happens in Mammals. Thus for these reptiles we have no
typical dental formula fixed by heredity, as for the placental
Mammals, from which it would be possible to deduce all
later formulas by simple reductions. The dental matrix was
altered in shape under the pressure of the teeth according to
the use to which the teeth were put. Naturally, the muscles
of the lower jaw were also modified according to the use the
animal made of it, and this entailed a corresponding modifica-
tion of the facial region to which the muscles were attached.
A zygomatic arch was constituted, recalling that of Mammals,
but somewhat differently composed. The chewing habit
adopted by the Theromorpha suffices to explain the resem-
blances the skull presents to that of the Mammals. A certain
identity in gait likewise explains the form of their scapula and
the construction of their pelvis. There is nothing to prove that
we are here in the presence of the ancestors of Mammals.

In the Triassic, indeed, there were already small Mammals,
Marsupials like Dromatherium of the Carolinas, and Micro-
conodon.

Certain Theromorpha, particularly Cynognathas, had all
the ways of our Carnivora, but were much larger. Their skull
was sixty centimetres long. They captured their prey and
carried it away in their jaws like our Tiger. The head in conse-
quence had to be firmly fixed. We also see the single condyle
of Pareiasaurns becoming broadened and kidney-shaped,1
and finally assuming the two-fold shape seen in Mammals.2
At the same time the cervical region was shortened. It had
only six vertebrae, whereas the dorsal region had twenty-nine.
The existence of such carnivores also supposes the contem-

1 Cynognatus platyceps.

2 Cynognatus berryi.

LIFE IN SECONDARY TIMES 261

poraneous existence of herbivorous reptiles, or at least
reptiles which fed on insects, molluscs, and other small prey.
We are thus far from having any knowledge of the food habits of
the terrestrial vertebrate fauna of the Trias.

Perhaps we should see herbivorous vertebrates in Anomo-
dontia, represented by several genera distributed from Elgin
in Scotland to the Cape. The dentition of these animals is
reduced to two tusks in Dicynodon, recalling those of the
Walrus ; these canines are short and conical in Gordonia and
Geikia of Elgin, and can be present or absent in individual cases
in CistecepJialus, suggesting that they are characteristic of the
male sex. This would lead us to assume that Oudenodon, which
had no tusks at all, was merely the female of Dicynodon. The
jaws of this animal, whose skull can attain a length of two
decimetres, elongate beyond the tusks and were probably
covered by a beak analogous to that of the Chelonians, which,
as a matter of fact, were already represented in the Triassic
Epoch by several genera.1

The Rhynchocephala were represented by Telerpeton.

Finally, the series of Theromorpha terminates in the Placo-
donts, terrestrial animals which had again become marine and
lived on molluscs whose shells they crushed with the aid of two
or three scissor-like teeth on the intermaxilliary, and three to
five rounded upper molars and some flattened teeth borne by
the palate and the posterior part of the mandible, arranged
like paving-stones. A number of varieties of Crocodiles
completed the Triassic reptilian fauna.

Rhynchocephala, Crocodilians, and Chelonians all became
more and more diversified in detail throughout the Jurassic and
Cretaceous — two periods most clearly marked with the impress
of new ages. The heavy Theromorpha disappeared, but whilst
vegetation of marvellous variety flourished, the development of
Reptiles positively luxuriated. They had no competitors on
land; the earth was theirs, and the constancy of the temperature
was particularly favourable to them. No danger menaced
the more powerful ; they grew slowly like the Crocodiles of
our times, but the length of their peaceful lives was such that
some of them were forty metres long. Given that their
rate of growth approximated to that of Crocodiles, this would

1 Chelzytion, Arctosanrus, Psammochelys.

262 TOWARDS THE HUMAN FORM

imply that they had a longevity of five or six centuries.
If some retained the squat form, others were slim and
elongated. Gradually many of them abandoned the recumbent
posture of their ancestors, to which present-day Reptiles are
condemned— we shall see why later.

Using the muscles coupling the limbs to the trunk in a new
fashion, the extremities of the humerus and tibia were brought
back towards it in such a manner that the arms and thighs,
instead of moving in horizontal planes like those of the Lizards,
moved in vertical planes like those of the running Mammals.
Hence the abdomen no longer trailed on the ground. The same
muscular effort exerted on the limbs — now become elongated
lever arms — forced the extremity much further forward ; thus
the Reptile no longer crawled, but walked, ran, and even jumped.

Then, assuming an even prouder attitude, the animal raised
itself up on its hind legs, which grew very large, whereas the fore
limbs, being scarcely used, either shortened or became trans-
formed. This was the preparation for the bird form — the form
that would very soon venture into and take possession of the air.
A certain remarkable anatomical arrangement that was to be
retained in the future is to be observed already. Cavities
filled with air, no doubt in communication with the lungs, made
their appearance either in the vertebrae of the large Dinosaurian
Reptiles,1 or in the long bones, while at the same time the
structure and method of using the limbs were already approxi-
mating to that of Birds. That it was merely necessary for these
Reptiles to make a demand on their muscles for those muscles
to bring about such modifications is in no way surprising.
A large Australian Lizard of our present day fauna, King's
Chlamydosanrus, is still capable of assuming this erect attitude,
which is its posture for defence.

A first attempt at the conquest of the air is thus fore-
shadowed, but it was only partially successful. Not until
their prey became scarce and the ground a dangerous place
for them were Reptiles obliged to hunt in the air, and then
only after having been put to tree-climbing in their efforts to
find food in security. A further indication of such insecurity
on the ground surface lies in the fact that other Reptiles,
whose ancestors had taken great pains to leave the water and
invade the land, returned to the seas, and, while retaining their

1 Brontosaiirus, Ccelums, Anchisanrus, Compsognathits.

LIFE IN SECONDARY TIMES 263

reptilian organization, resumed the life of Fishes in order to
hunt them and dispute with them the easy prey presented by
the indolent Ammonites found in every sea.

In the course of passing through the different stages just
enumerated, Reptiles naturally developed new characters,
used by naturalists to distinguish each group leading the same
kind of life. At first the pelvis remained very similar to that
of the Crocodiles. Below the iliac bones the two pubes formed
a V with the apex directed forward, and the two ischia a V
with the apex directed backward. The Reptile could only
stand erect under exceptional circumstances, but it could be
either plantigrade or digitigrade, that is to say, it could walk
on the entire sole of its feet or only on the toes, the sole being
raised up off the ground. The Sauropoda exemplify the first,
and the Theropoda, with extremely elongated bodies, and the
Ceratopsidae with the ponderous form of our Rhinoceros,
exemplify the second condition.

In another series the hind-quarters gradually assume a
greater development than the fore-quarters, and it is likely
that the animal was able to stand erect. The thigh muscles
consequently become larger, and the pubic bones to which
they were attached acquire a greater surface, and, above all,
present, as in birds, both an anterior and a long posterior
branch (post-pubis) for the insertion of the muscles that erect
the body ; the pelvis remains open in front as with Birds.
These features characterize the Orthopods. Those orthopod
Reptiles which continued to walk on all four feet and remained
plantigrade form the sub-group of Stegosaurians ; those whose
fore limbs are so small that the animal could no longer have
supported itself upon them, and must have held itself erect
on its hind legs in the manner of a Kangaroo, form the sub-
order Ornithopods. All these animals together form the sub-
class of Dinosaurs or giant Saurians comprising the biggest
and strangest terrestrial creatures that ever lived.

Sauropods had the aspect of huge Serpents with an elephant's
body stuck midway of their length. At the end of a long neck
they carried a remarkably small head, which in Brontosaurus
excelsus,1 an animal thirty metres in length, was no bigger than
the fourth cervical vertebra of a neck made up of thirteen. Con-
temporaneous with it in the Wyoming strata was Atlantosanrus

1 Of the Upper Jurassic.

264 TOWARDS THE HUMAN FORM

immanis, which was nearly sixty metres in length. Morocaurus
grandis, on the contrary, was half the size of Bronto-
saurus, and had only four sacral vertebrae instead of five.
Another of their contemporaries in Colorado, the celebrated
Dipiodocus longus, completely reconstructed by Professor
Holland, and a magnificent cast of which was given by Carnegie
to the Museum d'Histoire Naturelle in Paris, measured 26metres
in length. Its head, not so small as that of Brontosaurus , had
somewhat the aspect of a horse ; its lower jaws were provided,
in the front only, with long incisor-like teeth, each accompanied
inside by a row of replacing teeth.

The form of the teeth in all these large Reptiles shows them
to have been herbivorous. If the connexion, previously pointed
out, between the multiplication of the vertebrae and the part
taken by the trunk in locomotion be recalled : if to this we add
that the caudal vertebrae of Dipiodocus was provided with
bones arranged chevron fashion, and each having two sym-
metrical horizontal rafter-like supports, indicating that this
tail must have been planted on the ground and used for
propulsion — then we are led to the conclusion that the Sauro-
podians lived in dense jungle, through which they had to thread
their way by separating the growth with movements of their
long necks and then pushing into and through it by the leverage
of their tails, their limbs permitting them to raise themselves off
the ground where the tangle of branches was thickest. The
shape and small size of their feet excludes the notion, sometimes
advanced, that they were marsh animals, and the position of the
nostrils, on and not at the extremity of the muzzle, a character
common to Sauropodians and aquatic animals, is even better
explained by the use they made of their heads in forcing the
branches apart. This action alone would mechanically push
the nostrils back, the more so because if they had been situated
at the end of the snout they would have been constantly torn
and blocked by thorns.

All the large Reptiles above mentioned belong to the Upper
Jurassic, but analogous animals must have been living much
earlier, from the Lower Trias, in fact. In the sandstones of
Fozieres near Lodeve, which date back to that period, and in
those of Connecticut, imprints of pentadactyl feet with a
separated pollex actuallyhave been observed. These cannot have
been made by Stegocephala, in whom four digits is a constant

LIFE IN SECONDARY TIMES 265

feature of the feet. Again, a tridactyl foot has left tracks so
much like those of a Bird that Hitchcock, when he discovered the
first of them in Connecticut, called them Ornithichnites, i.e. bird
imprints. There were certainly no Birds at the beginning of
the Secondary Period. It is therefore impossible to attribute
these foot-prints, some of which are four decimetres long, to
other than the Theropods, at least provisionally. Pentadactyl
four-footed imprints, of which the fore tracks were distinctly
smaller than the hind, have also been found. They were made
by animals of various sizes, but manifestly of the same species —
as if the young had lived with their parents. The steps taken
by these larger beasts sometimes equalled a span of two metres.
The persistence of these tracks up to the time when new
strata were deposited over them, seems to confirm the
assumption that these animals were not very numerous, and
that the struggle for life was consequently not very active in
those regions where their footprints have been discovered.
To this unknown animal, which has thus imprinted its foot-
steps in the sand, the name of Brontozoum giganteum x has been
given. Brontozoum has left in the sand imprints of its tail, as
well as of its feet.

The Theropods had pointed, hooked teeth ; they were
carnivorous Reptiles moving in the same manner as Kangaroos.
The elevation of the body to an erect position on the hind legs
was evidently the result of a habit that had gradually modified
the size of the muscles and their points of attachment,
modifications which reacted on the bones and on the size of the
limbs. This habit is easily explained in the case of carnivora
living in thick low bush, and which are obliged to raise their
heads above it in order to reconnoitre, watch their prey, and
retreat to a place of safety at need. Such a habit had already
no doubt begun to be imposed on the Sauropodians, whose
hindquarters were better developed than the fore-limbs ; later
it was associated with the further habit of leaping. The
posterior limbs, still almost plantigrade in Anchisaurus of
Connecticut, become gradually digitigrade. Thereafter the
smallest toes, which cease to touch the ground, become
rudimentary. Zanclodon of the Upper Trias of Wurtemburg,
which was three metres in length, and analogous forms in

1 Brontozoum means " thunder-animal ". We have already met with
Brontosaurtis or " thunder-lizard ".

266 TOWARDS THE HUMAN FORM

France, England, South Africa, and India have five digits to
each limb. The Megalosauria which flourished from the Trias
to the Upper Cretaceous in France, England, Colorado, and
India are slightly larger and have only four toes on their
hind feet. Hallopus victor of Colorado did not exceed one metre
in length ; its extremely short front limbs had only four digits,
its hind limbs three, the first being absent and the fifth repre-
sented by a short metatarsal. Ceratosaurus of the same region,
which exceeded five metres in length and bore a horn on its
nose, also had but three toes on its hind legs, but all three
metatarsals were united — a condition we shall see produced later
on in leaping and swift-footed animals. The Allosaurians of
North America possessed but three digits on all their feet. Finally
the hind legs of the small Compsognathus longipes of the Jurassic
of Bavaria were veritable bird legs whose three existing
metatarsals were united not only to each other, but also to
the distal series of the bones of the tarsus ; the proximal
series being likewise adherent, without being united to the
tibia, to which was joined a rudimentary fibula. In spite of
this the pelvis remained typically reptilian, and had behind it
a long tail. Sharply pointed teeth extended the whole length
of the jaws. Many Theropods (Ccehtrus, Hallopus, etc.) had
hollow bones presenting holes in their surfaces into which air
sacs dependent from the lungs were inserted, as with the birds,
from which these creatures were still far removed by the form
of their pelvis.

The pelvis of the Orthopods, on the contrary, approximated
sufficiently closely to that of the Birds for Huxley to propose
for them the name of Ornithoscelidse. This form of pelvis does
not necessarily correspond to a permanently erect attitude ;
it implies no more than a great development of the posterior
members relatively to the fore-limbs, and the possibility of
erecting the body on them. The Reptiles grouped together in
the sub-order of Stegosaurians were still almost plantigrade.
Those of the genus Scelidosaurus, however, have only four digits
on each foot, while in Stegosaurians there remain but three
on the posterior feet. The Scelidosaurians slightly exceeded
four metres in length ; they lived at the time of the Lower
Jurassic (Lias) of Lyme Regis. Analogous forms are also found
in the English Wealden (Hylceosaurus poly acanthus). The
Stegosaurians of the Upper Jurassic of Wyoming and Colorado

LIFE IN SECONDARY TIMES 267

approach ten metres in length. These Stegosaurians were
strange beasts. The disproportion between their anterior and
posterior limbs caused considerable convexity in the back
when they went on all four feet, and along the line of this curve
in Scelidosaurus was arranged a double row of projecting
bony plates, which became unique on the greatly elongated tail.
The dorsal plates of the Stegosaurians formed but a single
row, but they were of great size, triangular, and erected
vertically, with the apices in the air, the largest of them being
almost a metre in height. This row of plates divided into a
double series on the tail, which thus carried two rows of spines
sixty centimetres in length.

The digitigrade type became highly accentuated and con-
stant in the Ornithopods, which habitually held themselves
erect on their hind-quarters. Their long bones were hollow
and in communication with the air sacs like those of Birds.
We have already met with this character in the Theropods,
which had also adopted the biped attitude. This attitude
implies a greater expenditure of muscular effort in the posterior
body-region than the quadruped attitude. On the other
hand, the development of the air sacs adds considerably to the
respiratory power of the lungs. In the case of both Theropods
and Orthopods it is not impossible that the possibility of
acquiring their new method of locomotion, endowing them
particularly with an aptitude for running and leaping, was
due to this increase of respiratory activity. We find in
Ornithopods a series of forms analogous to those of the
Theropods. Camptosaurus of the Lower Jurassic and of the
lowest layers of the English Cretaceous (Wealden) had five
fingers and four toes. Hypsilophodon from the same localities
had only four fingers and four toes. The northern Ignanodon,
of the Neocomian of Belgium and Germany, had only four
digits on its fore-legs and three on its hinder, the pollex having
been transformed into a formidable spur. Hadrosaurns and
Trachodon of the same regions closely resembled them, except
that the mouth was prolonged into a sort of edentate duck-bill.
At the back of this bill were several rows of small teeth, forming
one functional row, followed interiorally by numerous rows
of replacing teeth, the total number being two thousand.

The best known of all these Reptiles are the Iguanodons,
so named because their herbivorous teeth resembled those of

268 TOWARDS THE HUMAN FORM

the large American Lizards called Iguanas. They nourished in
the time of the Upper Cretaceous of England, Belgium, and
Germany. An early species, Iguanodon mantelli, was found in
England, and measured only five or six metres in length. The
complete skeletons of thirty individuals of another species,
Iguanodon bernissarti, were found together at Bernissart
between Mons and Tournay in Belgium, close to the French
frontier, at the bottom of a mine-shaft two hundred metres
below the present sea-level. They were discovered in an
excavation in the Carboniferous earths filled in by Wealden
clay, on the surface of which were still to be seen the imprints
of their feet, indicating that the hind-legs only were placed on
the ground. As no tracks made by the tail have ever been found,
it is to be assumed that it was held far above the ground and
was used to balance the Reptile. The Iguanodons were certainly
herbivorous ; they had no teeth in the fore-part of the mouth,
the lips probably being covered with a horny envelope. Their
attitude indicates, moreover, that they did not browse on grass,
but ate the leaves of trees, whose trunks they seized between
their powerful hands, as did Megatherium at a later date.

The last representative of this group was Ornithomimns
of the Upper Cretaceous of Colorado, all four of whose limbs
were tridactyl, and in whom the proximal end of the third
metatarsal, set deep between the second and the fourth, was
partially united with them, as it is in young Birds. They were
very large animals, but unfortunately all we know of them is
their limbs.

All the Dinosaurs that we have briefly passed in review were
marked by a family resemblance. They had a long neck, a
long tail, and a trunk generally not exceeding the neck in length.
The head was nearly always small, or even diminutive — so
much so that the brain was sometimes less in volume than the
lumbar portion of the spinal cord. They must have formed two
parallel series, the one carnivorous and the other herbivorous,
each beginning as a plantigrade species with a closed pelvis
and no post-pubis, and closing with an erect species having a
post-pubis. Having regard to the latest discoveries, this is
probably the order in which we shall have to set up their
genealogical classification. For if it be easy to understand that
animals feeding on the same kind of food should gradually
assume the series of attitudes just described,, it is hard to see

LIFE IN SECONDARY TIMES 269

why a different form of pelvis should correspond with two
different dietaries. Unfortunately the series of carnivores is
still very incomplete, and is represented only by digitigrade
Theropods in which a post-pubis is absent.

The monstrous Ceratopsidae, of which we have still to speak,
present a complete contrast with the Reptiles we have described.
Their neck and tail were of medium size. The trunk was powerful,
and the four limbs almost equal, each with five digits, all of which
were planted on the ground. It had the massive appearance of a
Rhinoceros, but of a rhinoceros whose gigantic dimensions
exceeded six metres in length and two or three metres in height
in the rear. Its head was perhaps one of the strangest things in
the whole animal kingdom. It terminated in front in a sort of
beak like that of a Bird of prey, which did not prevent the jaws
from being provided with two-rooted teeth implanted in alveoli,
and dilated in the rear into a great thick, osseous funnel-
shaped mantle, which covered the neck and reached almost to
the shoulders. This formidable head, two x or three 2 metres in
length, carried three powerful horns, one on the nose and two
others above the eyes. Other members of the Ceratopsid group,
Nodosaurus, for instance, were still further protected by a
bony, dermal armour-plating. These monsters lived during the
Cretaceous Period in North America, notably in Wyoming.
Only a single genus is known in Europe, CratcBomus, whose
presence Deperet discovered in Herault. They were herbivorous
like the Titanosaurians, Iguanodons, and Trachosaurians, which
may have been their contemporaries and were even more colossal.
All these herbivora must have lived in comparative peace.
Their great enemies were the Megalosaurians and Lczlaps, huge
carnivorous leaping Theropods of swift movements, against
whom they confidently opposed those terrible weapons, their
beaks and horns, and their impenetrable cephalic shield.

Whence did these extraordinary and gigantic beings come
which peopled the land in Secondary times ? Doubtless the
land Vertebrates had already tentatively appeared by the close
of the Primary Period. Reptiles of the Trias, with varied
dentition, although still earth-crawlers, had attained large
dimensions, and some of them are distantly linked to the large
Stegocephalous Batrachians, to which also belong the Rhyn-
chocephalic Reptiles. These creatures, though still of moderate

1 Triceratops flabellatus. 2 Triceralops prorsus.

270 TOWARDS THE HUMAN FORM

dimensions, seem to have been the ancestors of the Dinosaurs,
to which they passed on various peculiarities of skull-formation,
and particularly the construction of the palatal vault. But if
the physiological mechanism is clearly apparent that has
turned crawling Reptiles into Reptiles that walk and leap,
and if it has been possible to reconstruct at great intervals
some of the steps in this evolution, the series of stages covered
is broken nevertheless by enormous gaps. We can see that
any such reconstruction will be difficult. Many of these
cryptogenous beasts appear almost simultaneously at parts of
the globe so widely separated from one another that we find
some difficulty in admitting that an}^ means of communication
existed easy enough to allow such heavy animals, probably
sedentary in their habits, to cover such great distances. Forms
that vary but slightly from the Triassic genera, Zanclodon and
the Megalosaurians, for example, are found in Europe and the
United States, which both formed part of the North Atlantic
continent, and also in the southern parts of Africa and in India,
which at that time formed part of the Gondwana continent.
Morosaurus, Ccelurus, Stegosaurus, Camptosaurus, Triceratops,
and Hadrosaurus are represented sometimes by different species
in Europe and the United States, that is to say, at the
two extremities of the North Atlantic Continent, during the
Jurassic and Cretaceous Periods. Although these periods lasted
long enough to admit of the lengthiest journeys into the interior
of a single continent, this wide distribution remains remark-
able, and it is incredible, in any case, that such migrations took
place between Gondwana and the North Atlantic Continent.
We must admit, therefore, that similar forms may have arisen
separately, which confirms the view that constant natural
forces acting upon organisms which at first differed but little
from one another, as the early Batrachians must have done,
have independently produced analogous organic series in
widely separated regions of the globe. That is equivalent to
saying that the same causes acting in similar conditions always
produce the same effects. This is an elementary truth well worth
remembering in the domain of natural science, where the idea
of capricious and independent creations reigned for so long.
The parallel evolution of the herbivorous and carnivorous
Dinosaurs shows, moreover, how weak was the principle of the
correlation of forms and the subordination of characters upon

LIFE IN SECONDARY TIMES 271

which Cuvier based his essentially finalistic comparative
anatomy.

We have now studied the wonderful evolution of the land
Reptiles. But they did not limit their activity to the invasion
of the land. They also acquired wings, probably as a result
of the folds of skin similar to those we have already mentioned
(p. 130), which formed upon the flanks of tree-climbing varieties
in the Secondary Epoch. Unfortunately the transitional forms
are unknown. The wing of the Pterosaurians was always con-
structed on the same plan. At the back a large membrane ran
along the whole length of the sides as far as the end of the tail,
and in front spread to the exterior edge of the digits of the fore-
limbs, which had become three times as long as the body.
Contrary to all that took place in the preceding cases, the
enormous head was sometimes one-third as long as the body
(Pterodactylas crassirostris) . It was perpendicularly articulated
with the neck and its bones united as in Birds, an arrangement
which seems to indicate a relation between this condition and
rapid aerial locomotion. The jaws carried sharply pointed
teeth (Pteranodon) , and were sometimes replaced by a sort of
horned beak, of which the termination of the jaws in a point
in Ramphorhyncus may be considered an indication. The oldest
known remains of a Pterosaurian go back to the Lias of Lyme
Regis. This forerunner (Dimorphodon macronyx) of the Pterosaur-
ians had a slender tail six decimetres in length, and the body was
almost the same length. Omithocheirus of the English Wealden
also had a long tail terminating in a kind of membranous rudder ;
the teeth were pointed, widely spaced, and inclined forward.
On the other hand, their contemporaries, the Pterodactyls,
had short tails ; their size fluctuated between that of a Crow
and that of a Sparrow. The giant among Pterosaurians was
Pteranodon, which spanned six metres and whose dimensions
far exceeded those of our largest Condors. It flourished in
Kansas during the middle Cretaceous Epoch. They were
Insect-eaters ; their long pointed beak did not permit them to
tear their prey. Like Bats, they could not rest on the ground
in order to capture small animals, or they would have been
unable to take flight again. This also applies to all Pterosaurians,
which in order to rest were obliged to suspend themselves
from the branches of trees by means either of the normal four
fingers of the hand, or by the feet. They had then merely to

272 TOWARDS THE HUMAN FORM

open out their wings as they fell, in order to start flying again.
The size of Pteranodon indicates that insects must have in-
creased greatly during the Cretaceous Period. The existence of
Dimorphodon in the Lias proves that numerous flying Insects
must have already existed. But we have still to discover what
use Ramphorhyncus and the Pterodactyls made of their
teeth, which were too long for such minute prey. This seems to
imply that Birds already existed, and that Archceopteryx
was perhaps not the most perfect of them.

We come at last to those Reptiles which invaded the water
during the Secondary Period. This return to a former environ-
ment need not unduly astonish us, since Crocodiles have never
abandoned the neighbourhood of rivers. Since the time of the
Trias there had been marine Reptiles whose legs, by a contrary
process from that which took place in Dinosaurians, were
shortened and broadened. The digital phalanges were often
multiplied and the feet finally transformed into paddles which
could only have been used for swimming. They belonged to two
types : in one, the Plesiosaurians, also called Hydrosaurians or
Sauropterygians, the head was small and the neck elongated,
as in the Dinosaurs, but the tail was very short ; in the other,
that of the Ichthyosaurians or Ichthyopterygians, the head,
on the contrary, was large, the neck very short, the tail long but
flattened, which, like a fish's tail, gave the animal the greatest
possible impetus in swimming. To these differences in aspect
two quite different modes of life must have corresponded.
The Plesiosaurians, swimming only by means of their lateral
paddles, helped perhaps by the undulations of their long,
swan-like necks, probably lived on the surface, and must
have been able to dive quite easily, but confined themselves
to shallow waters, where they probed and dug the mud in
the manner of geese and swans. The Ichthyosaurians, on the
contrary, lived like real Fishes, and only came to the surface
in order to breathe, as our Porpoises do. Swimming not
only with their paddles but also by the aid of their tails, the}'
would be met with the same resistance by the water as are
Fishes. Hence their neck would be shortened and they would
acquire the same shape as the Fishes. In the fine
palaeontological gallery of the Paris Museum, there may be
seen an example, acquired by the Societe des Amis du Museum,
preserved with its integument held together by small scales.

LIFE IN SECONDARY TIMES 273

Apart from the paired fins, it had a median fin on its back,
and its tail terminated in a fin divided into two unequal
lobes. That part of the vertebral column corresponding with
this fin described a sharp downward curve in the opposite
direction to that of heterocercal fishes. We saw (p. 230) that this
tail was an organ of levitation to bring them to the surface ;
that of the Ichthyosaurians, on the contrary, was a diving
organ. Lightened by the air in its lungs, the Ichthyosaurian
was naturally borne to the surface, and had to exert effort in
order to descend.

Up to the present no transition of form has been found
between the Ichthyopterygians and terrestrial Reptiles, unless it
be Mixosaurus of the Trias, in which the radius and ulna are still
elongated and separated by a slight longitudinal interval. The
teeth, very numerous in Ichthyosaurians, became very small in
the Ophthalmosaurian of the English Jurassic and Cretaceous.
They have quite disappeared in Baptanodon of the Upper
Jurassic of Wyoming, as they have done in our Baleen-Whales.

The Plesiosaurians are less isolated. They are linked with
Reptiles which, like themselves, had biconcave vertebrae,
and present an upper temporal fossa and ventral ribs, while
their limbs, still differing little from those of land Reptiles,
are, however, already adapted for swimming. These are the
Nothosaurians, primitive forms in which the notochord is pre-
served in the centum of the vertebrae. Mesosaurus, the initial
type of this group, is found in the Triassic sandstones of the
Karroo in the south of Africa and in those of Sao Paulo in
Brazil. They had only nine cervical vertebrae, and did not
exceed three decimetres in length. Lariosanrus attained a
length of one metre, and preserved its palatal teeth. Its neck
consisted of twenty vertebrae and its tail of forty, although these
were very short. Nothosaurus grew to a length of three metres
and had sixteen cervical vertebrae. Other forms have been found
in the Muschelkalk, near Magdeburg. In the Plesiosaurians,
properly so-called, which lived between the Lower Triassic
and the Jurassic, the neck was still more elongated, and
possessed as many as from twenty-eight to forty vertebrae.
The neck was longer yet in the Elasmosaurians, in which the
number of the vertebrae varied between thirty-five and seventy-
two. On the other hand, the tail was extremely short. The
Elasmosaurians differed especially from the Plesiosaurians in the

274 TOWARDS THE HUMAN FORM

details of their shoulder-girdle, whose scapulas were joined
ventrally instead of remaining separate as in Plesiosaurians.
Elasmosaiirus of the Upper Cretaceous of Kansas had a neck
about seven metres long, to a total length of fifteen metres.
Pliosaurus, which was ten metres long and whose bones are
found in the Kimmeridge clay, probably swam under water
more habitually than the other species. Its cervical vertebrae,
twenty in number, were, in fact, flattened as if they had been
compressed by the resistance of the water. They were
creatures of terrible aspect, armed with formidable teeth, some
of which were three decimetres in length, and would not have
found on the coasts prey worthy of such a powerful maxillary
apparatus. The limbs of all these Plesiosaurians wyere less
modified than those of the Ichthyosaurians. They never had
more than five digits, whereas the Ichthyosaurians sometimes
had six owing to the division of one of them. The number of
phalanges only was notably augmented. The humerus, radius,
and ulna, as well as the corresponding bones of the hind-
limb, remained considerably more elongated than the
carpus, tarsus, and digits.

While the Ichthyosaurians and Plesiosaurians, which had
sprung from the lower forms of Reptiles, disappeared from the
seas of the Upper Cretaceous, other Saurians became aquatic
and even marine ; but they were quite differently characterized.
They seem at first to have appeared in the southern seas. Their
dentition clearly indicates their relationship with the Lacer-
tilians. The Plesiosaurians had each tooth implanted in an
alveolus, while those of the Ichthyosauri an were aligned in
grooves, not divided into alveoli. Those of the new aquatic
Reptiles, the Pythonomorphs, were simply welded to the
maxillaries as in numerous Lacertilians. But the form of these
teeth was varied, and this gave the palaeontologist Dollo some
indications as to the nature of their food. The powerful dentition
of Mosasauras indicates that they doubtless attacked either
less well-armed Mosasaurians or marine Chelonians. The thin
curved teeth and weak jaws of Plioplatecarpiis would hardly
have allowed it to attack any but medium-sized molluscs
such as the Belemnitellae. Globidens with its rounded teeth
and weak jaws probably fed on sea-urchins. This is no
mere hypothesis ; their prey has sometimes been found
fossilized along with them.1 These animals already existed

1 XCIV.

LIFE IN SECONDARY TIMES 275

in the Lower Cretaceous. When they became aquatic their
body elongated, like that of the Snake, the limbs, however,
retaining the essential characters of land Reptiles, except that
they had shrunk. Their bones became shorter and natter, and
the whole limb thus became a swimming blade. The oldest of
these was Doliclwsaurus of the English Lower Cretaceous,
which was only one metre in length. The rami of their
mandibles were united. They had supplementary articulating
apophyses on their vertebrae, like Snakes. Acteosaurus of
Istria was similarly endowed, whereas in Plioplatecarpus of the
Upper Cretaceous of Holland these apophyses were absent.
In the Mosasaurians the resemblance to Snakes was accentuated
by the substitution for the mandibular symphysis of a
ligament permitting the separation of the two rami of the
lower jaw. The Mosasaurians, whose name means the Lizard of
the Meuse, were able to attain a length of six or seven metres,
the average length of a Boa or Python. In the Museum at
Brussels, there are beautiful complete specimens of Clidastes,
which was still longer and more slender. They have been found
in Europe and in North America, that is to say on the coasts of
the former North Atlantic Continent. Platecarpus and Liodon,
however, have an even larger area of distribution. Their
bones have been collected from North America and
Europe to New Zealand. Liodon haumuriensis of this region
attained a length of thirty-five metres. On account of the
distensibility of its lower jaw and the specially articulated
apophyses of their vertebrae, the Mosasaurians have been
regarded as the ancestors of Snakes. Yet though the presence
of two posterior rudimentary feet in pythons may prove that
the Ophidians are descended from animals with feet and that
these feet gradually disappeared in the Scincoidians, from the
Skinks to the Slow-worms through the intermediate form
Seps, we are still unable to tell how the order of Ophidians
arose.

The Chelonia date back to the Triassic, where they are repre-
sented by the genera Chelyzoon, Arctosaurus, Psammochelys,
and Progomochelys, which seem to bear some relation to the
Rhynchocephala and Crocodilians. Possibly they had a
common ancestor with the Theropoda in Primary Times.
Hans Gadow has attempted to reconstruct the first Chelonian
by attributing to it the more general and apparently primitive

276 TOWARDS THE HUMAN FORM

characters known in fossil and living forms. He supposes that
in this imaginary animal each of the body segments except
those of the anterior half of the neck and posterior half of the
tail, carried a transverse series of dermal bones, covered by
horny shields whose relative position and dimensions were
subsequently modified by the manner of growth of the trunk,
which took place by a rapid diminution of the parts nearest
the neck and tail.

The order of Chelonians attained its maximum development
toward the end of the Secondary Epoch. The extant types are
but a remnant of those existing in Secondary times. It is
probable that the normally web-footed varieties inhabiting the
marshes were the ancestors of terrestrial forms whose mode of
progression is still reminiscent of a kind of swimming action
on resistant ground, and that marine Turtles, with their
feet transformed into paddles, were likewise derived from them,
the feet having gone through a modification analogous to
that which we have already noticed in Plesiosaurs and Ich-
thyosaurs, and on whose significance we have already insisted.1

At the close of the Secondar}^ Period, those prodigious
Reptiles whose history we have just narrated disappeared as
completely as the Ammonites had disappeared from the sea.
To what are we to attribute the world-wide extinction of such
puissant animals, whose vitality was manifested by their
extraordinary longevity ? We can scarcely believe that organic
types, like individuals, grow old and die. This oft-repeated
proposition has no other value than as a figure of speech. So
long as a given species has representatives capable of repro-
ducing their kind, and sufficiently numerous to carry on the
process, that species is no more likely to disappear spontaneously
than the type to which it belongs. Of course it is within the
bounds of possibility that some extraordinary modification
in environment may induce sterility in all the individuals of
the same organic group, but for this to come about the modifica-
tion must be so general that no species escapes it, and so sudden
as to make any adaptation out of the question. Both suppositions
are equally unlikely, and hence we are led to conclude that
things came to pass in those days very much as they do to-day,
when species do not disappear unless wiped out by their enemies

1 Cf. pp. 193, 272.

LIFE IN SECONDARY TIMES 277

or by some scourge operating in the regions in which they live.
Thus we must seek to discover what agency was capable of
destroying the most gigantic animals that ever dwelt on this
earth.

From the beginning of the Secondary era two types of
Vertebrates had slowly and sparsely multiplied — Birds and
Mammals — which we have hardly had occasion to mention.
The oldest of the Birds, Archceopteryx lithographica, is known
by two forms only, discovered in the lithographic limestone of
Solenhofen of the Oolitic Period. Birds do not reappear
till four genera are found in the Chalk — Enaliornis of England,
Hesperornis, Ichthyomis, and Apatomis of Kansas, in North
America. All these Birds are still very strange. Archceop-
teryx had short jaws rounded at the end instead of being
pointed and elongated like those of the majority of present
Birds, and furnished with teeth. The anterior limbs had
wing-feathers, but the four toes terminating them were free
and provided with almost normal claws ; the tail was long and
reptilian and composed of twenty-two vertebra?, each bearing
a pair of long tail feathers — a most encumbering appendage
for flight, and had it not been for its feathers Archceopteryx
would undoubtedly have been classed among the Reptiles.
Thus is the reptilian origin of Birds clearty indicated.

The Cretaceous forms had more distinct birdlike characters.
The beak was clearly characterized and the body ended in a
rump of normal form instead of in a long tail. Enaliornis and
Hesperornis had rudimentary wings, or none at all, and no keel
on the breast-bone. The vertebrae of Enaliornis were mostly
biconcave like those of the primitive Reptiles ; while those of
Hesperornis were concave on the terminal aspect, convex on the
other. In both these genera the teeth were situated in a simple
groove and not enclosed in alveoli, a fact that has led to their
classification together under the name Odontolcae. In Ichthyomis
and Apatomis the teeth were implanted in alveoli and accom-
panied by replacing teeth (Odontormae). The wings and the
keel on the breast-bone were well developed. It is evident that
these Birds, despite their alveolar teeth, were more primitive
than Hesperornis, whose wings had disappeared and whose
teeth, placed in a simple maxillary groove, were on the road to
disappearance. This fact alone would indicate that rumped
Birds were already old in the Cretaceous Period, seeing that

278 TOWARDS THE HUMAN FORM

they had had time to modify themselves ; and, since we find
practically all the types of the present day at the beginning
of the Tertiary, it is extremely probable that they had already
been achieved in the Cretaceous, and that owing to one of
those peculiar chances so frequent in palaeontology, we are
acquainted only with the abnormal types of this epoch.

The Mammals had evolved side by side with the Birds. In
the Trias they were already represented by the genera Droma-
therium and Microconodon. To these were added during the
Jurassic, many Marsupials with special dentition,1 and during
the Cretaceous further new genera of the same type, together
with Plagiaulax, provided with teeth of a new type. None of
these appear to be of great importance in the fauna of the time
at the outset, nor is it till the seasons become marked that they
become more considerable. By the end of the Cretaceous
Period, however, the seasonal cycle is accentuated. Birds
and Mammals were not affected by this modification in the
climate which, as we saw, reacted so profoundly on the Insects.
Their blood was at a constant temperature, and they main-
tained the same activity all through the year. And since
Birds sit on their eggs and Mammals are viviparous, the young
of both were able to avoid, like the full grown creatures, the
vicissitudes inseparable from variations in the temperature.
With Reptiles, however, it is quite otherwise.

All existing Reptiles have a body-heat which changes accord-
ing to external variations in temperature. An excess of heat
or cold benumbs and can kill them, and they take no care of
their progeny, which are more exposed than themselves to
extremes of heat and cold. There is no reason for believing
that it was otherwise with the great Reptiles of the past.
The minute size of their brains indicates that they were
extremely unintelligent creatures, and their organization was
no higher than that, for instance, of their contemporary the
Crocodile. As in the Crocodile, the arterial and venous blood
was probably mingled. But even if they had been more perfect
in this respect they would have been little better off. Inner
heat is a function of activity, and the unintelligent Reptiles

1 The Triconodonts : Amphilistes, Phascolotherium, Triconodon ; and the
Trituberculates : Amblotherium, Dryolesles, Amphitherium of the Jurassic ;
and Pedromdys, Dielphops, and Crinolestes of the Cretaceous.

LIFE IN SECONDARY TIMES 279

of the Secondary Period could only move their huge bodies
with some difficulty. Moreover, in the higher organisms, the
body-heat is preserved by the layer of air which feathers or
fur keep at a constant temperature. A shorn rabbit soon dies.
The large Reptiles of the Secondary Period had no such pro-
tection, and the heat produced in their bodies by respiratory
processes would be dissipated, not only by the surface of the
trunk, but also by the long neck and enormous tail. So long
as the external temperature remained warm and fairly constant
they did not suffer from these imperfections, and the Birds and
Mammals had no advantage over them. It was otherwise when
extremes in temperature became greater. Their lives would
be punctuated by more or less lengthy periods of torpor,
during which they would be at the mercy of animals having
a constant body temperature, such as Mammals and Birds,
which could maintain the same activity at all times. Thus the
Reptiles became an easy prey. Indeed, it was inevitable that
they should disappear before the increasing number of their
rivals. The composition of present day reptilian fauna
furnishes a powerful argument in favour of this explanation.
The flower of the reptilian class has disappeared ; none but
a few species of Crocodiles have survived — species that hide in
water and are further protected by solid armour ; or Chelonians
that, enclosed in a carapace, are almost impossible to extract ;
together with Lizards set low on their legs, and Snakes with
none at all, which are therefore able to hide themselves in holes
and the interstices of rocks inaccessible to the majority of
preying animals ; or those endowed with special means of pro-
tection, such as the green colour of Dendrophis, the Tree-snake,
the faculty the Chameleon possesses for changing its colour,
or weapons as treacherous as they are formidable, such as the
venom of Helodermes among Lizards, and, above all, the
poison of snakes. All those Reptiles which were not able to
dissimulate their presence or to defend themselves by treachery,
have disappeared : the existing class consists only of those
which escaped in the struggle for existence.

Apart from a few Scincoid Lizards such as the Slow-worm,
and several Snakes like Vipers and the marine Snake or
Hydrophis, the Reptiles of the present epoch lay eggs. The
Ichthyosaurians, and perhaps Compsognathus, were viviparous,
but there is no evidence that this method of reproduction,

280 TOWARDS THE HUMAN FORM

consisting simply in the hatching of ordinary eggs inside the
oviducts, and depending often on more or less temporary
external conditions — was more widespread among Reptiles in
the past than it is to-day. It is true that we have not up to the
present discovered fossilized eggs of these large animals which,
however, like Crocodiles' eggs, must have been protected by
a very strong shell. Be this as it may, the young, like the
eggs, were equally exposed to the teeth of Mammals small
enough and alert enough to escape all pursuit with ease, or
to the beaks of Birds whose wings would carry them out of
danger by capture.

With regard to cerebral development, Mammals and Birds
were already gifted in a very different degree from the colossal
brutes of the reptilian class. They were clever enough to save
themselves in time from the least menace on the part of these
creatures. Just as their nervous system, taken as a whole,
has given to Vertebrates supremac}' over the other animals,
so the improvement in the brain was to give the warm-blooded
Vertebrates supremacy over the Vertebrates whose blood
had a variable temperature. With Tertiary times, intelligence,
which had already built up instinct in insects, though it has
subsequently become frozen in their tiny brains, was to re-
appear on the scene and gradually expand till, by its possession,
Man should become master of the world.

CHAPTER III

Life in Tertiary Times

rT^HE rising up of the Pyrenean, Alpine, and Himalayan
^ mountain chains gradually gave to the world its present
contours. The seasons became more marked. The torrid,
temperate, and frigid zones were on their way to their present
limits, though the polar regions were throughout favoured
with a temperate climate. Plants took on the forms in which
they still appear to-day. New Protozoa, the Nummulites
with lenticular shells, round like coins, invaded the seas in
such quantities that the first half of the Tertiary has been
called the " nummulitic period ". They make their first
appearance in the Pyrenees, Istria, and Egypt, in
layers where we still find a few survivors of the large
Mosasaurian and Dinosaurian Reptiles, whereas in these
same layers in Patagonia we see the oldest known placental
Mammals appearing for the first time and in considerable
numbers.

At the opening of the Eogene, which corresponds to the
first half of the Tertiary, western Europe and North America
were joined by a strip of land which probably comprised
Scotland, Ireland, Cornwall, Brittany, the Central Plateau,
the Iberian Meseta, and the eastern coasts of North America,
and which was here and there broken up into archipelagoes.
From time to time communication between Europe and
America was sundered, notably in the middle of the Neogene,
and was again established for a time toward the end of the
same period, after which it was completely broken, and the
North-Atlantic continent was formed.

The Sino-Siberian continent remained isolated. It was
probably the home of the even-toed Mammals which, on
several occasions, suddenly appeared in Europe during the
Lutetian and Ludian Periods, for Anoplotheriam already
existed in Asia at that time. The Afro-Brazilian continent

282 TOWARDS THE HUMAN FORM

still persisted : Tree-coneys, and Orycteropus which is
to-day localized in the south of Africa, also lived in
that part of Patagonia where the Carolozittelidse and
Pythrotherium are perhaps somewhat analogous to the
precursors of Elephants discovered in the Fayum deposits
in Egypt. This continent included Madagascar, whose
fauna presents curious affinities with that of South America,
and its northern edge was then prolonged as far as the Antilles,
as is indicated by the resemblances between the fauna of
this island and the Mediterranean fauna of that epoch.

The Australo-Indo-Madagascan continent was then splitting
up. But while Australia became definitely isolated so that
its fauna is still one of Marsupials, India and Madagascar
remained united, which explains the existence of Lemurs
in both these regions. The Tethys Sea still extended between
the North Atlantic and Sino-Siberian continents on the one
hand, and the Afro-Brazilian, Indo-Madagascan, and Australian
on the other. It cut the American continent in two at the
Isthmus of Panama. From the region now occupied by that
part of the Atlantic Ocean extending from the Caribbean
Sea to the Franco-Spanish coasts, it thrust a narrow, fluctuating
channel into the sea which lay between Europe and the North-
Atlantic continent, and so outlined the North Atlantic coast.

The physical relation then existing between Europe and
North America and between South America and the African
continent suffices to explain the simultaneous invasion of the
two Americas by the placental Mammals, and makes it
unnecessary to assume a problematic Pacific continent.

A shallow expanse of water covered the Paris basin, the
basin of Mayence, and its southern prolongation, the valley
of the Rhine, and the region of eastern Europe between the
North Sea and the Caspian, and skirting the eastern foot
of the Urals it separated Europe from Asia. It abandoned
these countries after the beginning of the Neogene Epoch,
but continued to submerge Aquitania and the coasts of
Portugal. The region once occupied by the Tethys, for the
most part, was now above water. There were still, however,
some low-lying areas which the sea alternately invaded and
abandoned and which corresponded to the south of Spain
and to that portion of the Mediterranean which washes its
coasts as far as Provence. The water extended over the

LIFE IN TERTIARY TIMES 283

site of the Alps and reached the basin of Vienna, the Baltic
area, etc., and sometimes leaving only a few narrow channels,
until the time when the Mediterranean was to take its present
form.

During the Neogene Period, the European and the Sino-
Siberian continents united, never again to separate, so that
the Mammals of Asia easily passed over to Europe, and it
was moreover through Asia that African animals migrated
into Europe. North America and Asia were still in communica-
tion by way of Spitzbergen and Greenland, but an arm of
the sea separated Europe from the Arctic continent. North
and South America were separated ; the latter ceased thence-
forth to be united to Africa, and Madagascar became isolated
from India and Australia. The hypothetical Pacific continent
seems to have disappeared under the water. Summing up
these data we find that there was now an Arctic Ocean
separated from the Atlantic by the continent which included
North America, Spitzbergen, and Greenland, and which
was connected to Asia ; and that the present Atlantic, Pacific,
and Indian oceans were now definitely constituted.

During the Eogene Period, the alternate rising and sinking
of the land surface allowed the passage of ocean currents,
flowing sometimes from the Arctic and sometimes from tropical
seas, and this brought about a more or less durable fall or
rise of temperature along the coasts, although the mean
remained relatively high. The oldest known flora of this
Period, the Gelinden,1 contains Willows, Cupuliferae,2
Ranunculaceae,3 Laurinaceae, Celastrinacese, Menispermaceae,
etc., which still recall the Cretaceous flora. A little later 4
the petrifying spring of Sezanne encrusted the flowers, leaves
and fruits of plants which are found to-day, some in temperate
and others in tropical regions, and still later a definitely
tropical flora flourished in the Isle of Wight.5 The climate
must therefore have become hot again. The tropical flora
was maintained still later 6 in the sandstone formations at
Sabalites in the region of Maine and in the south of England.7
At the end of the Tertiary Era 8 the mean temperature of

1 Lower Thanetian. 2 Dryophyllum.

3 Dewalquea. * Upper Thanetian.

5 Lutetian. 6 Auversian.

7 Lattorfian. 8 Neogene.

284 TOWARDS THE HUMAN FORM

the Arctic region was still about 120 C, according to
Oswald Heer. At Spitzbergen there grew side by side with
Osmundas, Horsetails and Taxodiums — Poplars, Plane-trees,
Walnuts, Elms, Hazels, Hamamelidacere, Alders,. Magnolias,
Lime-trees, Viburnum, Catalpas, etc., and to these were
added in Greenland, Willows, Birches, Myrica, Beeches,
Maples, Holly, Ash, Hawthorns, Plum-trees, Black Alder,
Rhubarb, Ivy, Cornaceae, and even the Grape-vine. The
relative lowering of the temperature during the Cretaceous
Period, however, is sharply indicated by the absence of Palms
from these regions. Fewer species appeared even in Europe.

Although these questions have been discussed before
(pp. 28, 51), from another point of view, it was necessary to
recall the facts here in greater detail to render intelligible
the relation they bear to the various fauna that succeed one
another. The Nummulites appear to be a transformation of
an older genus of Foraminifera, the still extant Operculina,
to which should be related the Assilinas with their less
complete spirals. The Nummulites are so numerous in
that it has been possible to use them to determine the
lines of the sea-coast, and on account of their widespread
distribution they have furnished us with the best method of
studying the deposits of this age and their development.
The different types of our present Invertebrates were already
determined, and though their species, dating like coins the
age of the various strata, have a great interest for geologists ;
though it is often possible to follow their transformations
through a series of layers (as in the case of certain Cerithidse)
and to bring thereby supplementary, but not indispensable
support to the doctrine of evolution ; yet they are only
of secondary importance from the point of view that we
are considering here. What we seek are the causes which
lead to the formation of the principle organic types, and
the laws that have determined their evolution. We
cannot enter here into a discussion of the infinitely varied
accidents — often, indeed, quite beyond our ken — that have
determined the characteristics of species.

Among the Vertebrates we saw different types of Fishes,
Batrachians, and Reptiles appear, evolve, and very often
disappear. From the Cretaceous up to the time when they
appear to be almost as varied as they are at the present day,

LIFE IN TERTIARY TIMES 285

the evolution of Birds is wrapped in impenetrable mystery.
This evolution must have been rapid, because although Birds
are descended from a highly specialized branch of the Reptiles,
they differ among themselves only in characters that are really
secondary. Already at the end of the Cretaceous era some
had lost their wings and the keel of their breast-bone, and being
more completely affected by this retrograde evolution than
those of our present-day birds unable to fly, cannot be con-
sidered as their ancestors. This alone suffices to render
suspect the natural character of the order of Ratites. Since,
however, it is characterized by this inability to fly, it is the
only order which has raised hopes of providing some indication
of the ancestral form of Birds. Unfortunately, the faculty
of flying can be lost as well as acquired ; and it is often
difficult to distinguish retrogressive from initial forms. The
earliest known Tertiary Birds are Gastornis, Diatryma,
Dasornis, and Remiornis, all Eocene. There is no reason for
placing the one that lived in France during the Tertiary
Period — Gastornis — at the head of their geneaological tree.
Some naturalists make it a Goose, some a Bustard of the size
of an Ostrich and unable to fly. The others : Diatryma
of New Mexico, Dasornis of the London clay, and Remiornis
of the neighbourhood of Rheims, are all incompletely known.
Only a metatarsal of the first, skull fragments of the second,
and some fragmentary bones of the third have been discovered.
It is too little to warrant us in drawing inferences as to the
structure of primitive Birds.

In the Miocene strata at Santa Cruz in Patagonia,
Dr. Ameghino dug up a whole series of Birds, which have been
grouped by Morenco and Mercerat under the denomination
of Stereornithes. But this grouping would seem to be entirely
artificial. Of its constituent genera, Mesembriornis seems
to be akin to the Nandus which still abound in South America ;
Dryomis was a bird of prey related to the Condor; Dicholophus
resembled the Cariama ; Phororhachos, with its enormous
skull, its upper mandible terminating in a strong hook and
the lower bent up over it, remains enigmatic.

The Ostriches may perhaps be nearer to the initial type
than any of these fossil Birds. The digits of their wings
approximate more closely to the ordinary digital type than
those of all other Birds ; and they present a pubic symphysis, in

286 TOWARDS THE HUMAN FORM

which they are more backward than the Orthopod Dinosauridse.
They have, however, lost three of the toes of their feet, showing
that the type had already experienced important modifications.
They are present in the Miocene of Samos.

The Nandus also lived in the Miocene, but in South America.
As in the ostriches, the pelvis was closed, though in their
case by union of the ischia, whereas it was the pubic bones
that were united in the ostrich : the foot terminated in three
toes, the wing digits had already the conformation found in
flying birds, and they were still further removed from the
ostriches by the structure and position of the vocal organ
or syrinx. It is probable that they did not even belong
to the same series.

The Cassowary group is represented in the Pliocene by
the genus Hypselornis. These birds have scarcely any wings,
but the skeleton of this minute wing with its two united
digits is that of degenerate Birds which have lost the ability
tony.

After the Ratites, the present-day birds presenting the most
primitive characters are the Tinamous of tropical America.
They are characterized by the union of the vomer with the
palatine bone, a condition already indicated in the Emu and
Apteryx, by the articulation of the quadrate with the skull
by a single condyle, the absence of union in the ilium and
ischium, and the independence of all the caudal vertebrae.
But they are not known in the fossil state. In the Miocene
we find every type of Bird already represented, as the fine
work of Alphonse Milne Edwards on the fauna of Saint-Gerand-
le-Puy in the department of the Allier have shown. Nothing
enlightens us as to their past, so that interest becomes con-
centrated on Mammals, whose wonderful and gradual expansion
during the Tertiary Period constitutes one of the most brilliant
chapters of Natural History.

Mammals had lived side by side with Reptiles from Triassic
times, but during four million years they occupied a modest
position, effaced by their small size. As with Birds, they only
became important when the day of the Reptiles was over,
but their progress, instead of being made in regard to detail,
fundamentally modified their organization and was slower
than that of the Birds. Accordingly, we can follow it step
by step. We must not imagine, however, that this evolution

LIFE IN TERTIARY TIMES 287

took place in such a manner that we can pass consecutively
from primitive to modern forms, each fossil genus furnishing
us with a link in the chain binding them together. A great
many series remain outside this chain. They are like the
branches of independent genealogical trees, forming a veritable
forest when seen from above, but in which it is extremely
difficult to recognize the trees, and, on these trees, the branches
to which present-day forms should be attached.

The small Mammalian forms that appeared in the Trias
(Tritylodon) are encountered again with their multituberculate
molars and complete coracoid in the form of Neoplagiaulax,
Polymastodon, Ptilodon, and Chirox, in the Nummulitic
deposits of New Mexico.1 The Ornithorhynchus and the
Echidna are their present representatives. The horny tooth
of Ornithorhyncus is, in fact, preceded by a rudimentary
indication of a multituberculate tooth. These Mammals,
confined to New Guinea, Australia,2 and New Zealand, even
in some cases to Australia alone,3 are still oviparous, and it
is probable that the multituberculate forms also were oviparous.
These Mammals, which form the sub-class Monotremata or
Prototheria, are removed only from Reptiles by their hairy
skin richly provided with glands, some of which are already
lactigenous ; their mode of reproduction, the structure of the
shoulder-girdle comprising two clavicles united into a sort of
fork, with a coracoid and a precoracoid bone on each side, like
that of the Lizards, and their marsupial bones, the last remnants
of abdominal ribs, are distinctly reptilian.

With the exception of the Theriodontia, the Reptiles were
chiefly modified in the direction of locomotion, for they retained
their simple teeth, with a cutting edge in plant-eaters and
sharp points in flesh-eaters. The Mammals, on the contrary,
evolved in three directions — gestation, dentition, and locomo-
tion. Further, their flexible skin, permanently moist, and
rich in glands, but also in the sensitive cells to which even
hairs are only, as it were, annexed, constituted a source of
multiple excitation, which explains in some measure the rapid
development made by their cerebral apparatus.

From the point of view of gestation the present viviparous

1 In the San Juan Valley (Puerco and Torrejon beds).

2 Proechidna and Echidna.

3 Ornithorhynchus.

288 TOWARDS THE HUMAN FORM

Mammals exhibit two stages, of which one is certainly primitive
and has led to the other. In the first the young develop
within the body of the mother in a special pocket, the womb,
formed at the expense of the oviducts and which simply served
to shelter them. They are born in an early stage of develop-
ment, and at once deposited in an external sub-ventral pocket
called the marsupium, containing mammae to which the }7oung
immediately attach themselves. These Mammals form the
sub-class Marsupialia, Didelphia, or Metatheria. They have
retained the epi-pubic bones of the Monotremes, but the
shoulder-girdle is singularly simplified. It is reduced to
clavicles and to scapulas, with which are united in the form of
an apophysis all that remains of the atrophied coracoids.
The two clavicles are never united into a furcula. The
posterior angle of the mandible is turned inward.

The other Mammals form the sub-class Placentalia, Mono-
delphia, or Eutheria. The embryonic envelope of the young
and the maternal womb here enter into intimate union,
through the medium of highly vascular villi produced by
the embryo, which penetrate the uterine wall, to form, in
conjunction with it, the placenta, thus permitting the easy
filtration of the nutritive elements in the mother's blood into
the blood of the foetus. In the Eutherians the marsupial
bones have vanished, and the angle of the mandible is never
inflected. The placenta can be discoid (shaped like a cake),
zonary (shaped like a muff), bell-shaped, diffuse, or cotyledonary .
The same form of placenta characterizes an entire order.

If, however, we attempt classification according to placenta
form, the Primates find themselves somewhat singularly
grouped with the Insectivora and the Rodent ; Elephants,
and the herbivorous Hyrax with the Carnivora, and Lemurs
with the Pachydermata, while the order of Edentata would
be broken up, for Orycteropus and the Armadillos have a zonary
placenta like Hyrax, the Ant-eater's is bell-shaped, and the
Pangolin's diffuse. The contact area of the allantois and
the chorion that furnishes the placental villi, is small in the
Insectivora and employed in its entirety in their formation.
It is extensive in the Primates where the villi are restricted
to a part of its surface only. There is here a considerable
difference, though it is not impossible that the one arrangement
may have developed from the other. In the other zoological

LIFE IN TERTIARY TIMES 289

series it is highly probable that the placenta was at first discoidal,
then became zonary, and finally diffuse or cotyledonary.
To the Insectivora with discoidal placentas succeeded the
Carnivora with zonary placentas, and here the evolution
was arrested. The Rodents correspond to the initial condition
in the herbivorous animals, Elephants and Hyrax to the
second stage ; Pachydermata and Ruminants to the last.
In support of this way of looking at it, it may be pointed out
that the young of animals with a discoidal or zonary placenta
are born incapable of feeding themselves or of walking, and
that the Herbivora which have a diffuse or cotyledonary
placenta are born in a fairly advanced state of development,
and are capable of walking and running. It is in these animals,
moreover, that the limbs are most highly differentiated.
The Metatheria are confined to-day to South America and
Australia, land-areas which were united only during the
existence of the Gondwana continent, and we must con-
sequently put their origin back to that period. At one time,
however, they were cosmopolitan. The Eutheria appeared
later, probably outside the regions to which the Metatheria
have been driven back to-day — at any rate, outside Australia —
where the Metatherians constituted the entire Mammalian
fauna prior to the European occupation.

In common with Reptiles the primitive Mammals had
uniform teeth, and four limbs constructed on the same plan
each ending in five digits. Living under the same conditions
they would necessarily have evolved in analogous fashion
if these conditions actually counted in their evolution. Like the
Theropod Reptiles of the Triassic Period, all Mammals
masticated their food, and their teeth were appropriated
in the same way to the various functions that this habit
requires ; they were divided into cutting teeth or incisors,
tearing teeth or canines, grinding teeth or molars. Except
that the molars, instead of remaining simple and being modi-
fied only by a broadening of the crown, as in nearly all the
Theropods, were made up like those of the Ceratopsidse,
by the union of several teeth, whose roots generally remained
separate but whose crowns became one. Efforts have been
made to determine the number of the teeth thus united from
the number of tubercles possessed by the crown, and the
following adage has even been formulated : tot numeramus

u

2go TOWARDS THE HUMAN FORM

denies quot tuberculia.1 But if in that stage of their develop-
ment, when they consist entirely of enamel, teeth can become
united by their crowns, in the later stages it is the number
of dental bulbs, and hence the roots that have remained free,
that will indicate the number of teeth united. This union
often occurs in an accidental manner in the simple teeth of
the Cetacea, and is also evident in the molars of certain
Marsupials, such as the Thylacine. It may happen, however,
that a compound tooth appears to have but one root, as in
the outer incisor, always marked by a notch, of the Giraffes
and the Okapi. This incisor results from the union, throughout
their extent, of two teeth, one of which is reduced almost to
its crown. Considerable prudence must therefore be exercised
in enumerating the teeth that have entered into the composition
of a molar, but the fact that they have been thus produced
by union cannot be contested, and establishes an important
distinction between the Theropod Reptiles and Mammals.

The molars of living Marsupials do not all appear simul-
taneously. After the first dentition is established, the last
cheek-tooth falls out and is replaced by another behind which
new molars are formed. In the placental Mammals all the
teeth of the first dentition are replaced by others, followed
by the eruption of new molars. These are the molars properly
so-called. The cheek-teeth replaced are called pre-molars.
As teeth are modified with the change of diet, the mar-
supials can be divided, according to the form of their teeth,
into orders corresponding exactly to those adopted for the
placental animals, as follow : the Creophagi corresponding
to the Carnivora, the Entomophagi to the Insectivora, the
Rhizophagi to the Rodents, the Poephagi or Grass-eaters
to the Herbivora. This correspondence does not imply,
however, that the form and the number of the teeth correspond
for each group with what may be observed in placental
animals. In the Creophagi there are four or five pairs of
incisors in the upper jaw, whereas in ordinary Mammals
there are never more than three at the most ; hence
Richard Owen called the first Polyprotodontia. On the other
hand, the Carpophagi and the Poephagi have but a single
pair of incisors in the lower jaw and generally three pairs
in the upper, and these Owen grouped as Diprotodontia.

1 There are as many teeth as there are tubercles.

LIFE IN TERTIARY TIMES 291

An identity of diet has occasionally produced in Marsupials
and Placental Mammals some astonishing resemblances in
detail over and above the general resemblances just enumer-
ated. Diprotodon, for example, which lived in Australia at
the beginning of the present era, was about as large as a
Rhinoceros and had a dentition almost identical with that of
the Rodents. Its upper jaw, having no canines, became
elongated into a snout bearing two enormous incisors separated
from the molars by a wide space, and concealed immediately
behind these large incisors wrere smaller ones similar to those
of a Rabbit, except that instead of one there were two, one
behind the other.

The limbs underwent slight modifications only, and in
a particular direction. The anterior limbs, being frequently
used for prehension, retained their five digits ; but the hind
legs, in species belonging to numerous genera living on insects
or fruits, have the second and third toes united and are
relatively slender. This arrangement recalls that to be
observed in the Kingfisher, Hornbill, and other syndactylous
Birds, and is due to the same cause. These Marsupials live
on trees whose branches they are obliged to seize, and there-
fore the longest digit plays the principal role ; the others press
against it, unite with it, and partially atrophy. This arrange-
ment is preserved and exaggerated in the jumping Kangaroos,
whose median digit is very large, the hallux absent, and the
other digits astonishingly slender and joined together by skin.
Nothing in the Kangaroo's present mode of life demands such an
arrangement. But it is at once explained if we regard these
animals as descendants of climbing Marsupials, a supposition con-
firmed by the existence of arboreal Kangaroos, the Dendrolagi.
The Marsupials are, moreover, far removed from the Placentals
with regard to their place in the scheme of Nature.
From the beginning of the Tertiary Epoch, the Placental
Mammals, being endowed with a method of reproduction
far superior to that of the Marsupials, have everywhere had the
advantage of them, have multiplied very rapidly, and adapted
themselves to the most varied conditions of life ; and, living
in security and amid plenty, they have frequently been able to
increase their size from one generation to another. They
thus played the same part that the Reptiles filled in the
Secondary Epoch, without attaining to their dimensions,

292 TOWARDS THE HUMAN FORM

except in the water, but surpassing them greatly in both
agility and intelligence. Like the Reptiles, some are
carnivorous, others herbivorous. The carnivores are planti-
grade or digitigrade, without presenting any great modifica-
tions in limb ; the herbivorous types not only raised them-
selves upon their digits, but succeeded in achieving what
the Reptiles never did, a stance on the end of the distal phalange,
around which a nail developed so as to form a hoof ; they now
became " unguligrade " and constituted the order of Ungulata.
As the Reptiles had done before them, they took possession
of the air and of the water. We saw before (p. 193) how climbing
Mammals of many orders acquired a parachute, and how they
led up to the Bat, which has wings constructed on the type
of the Pterosaurs of the Secondary era, but more highly
perfected, since four of its digits instead of one are employed
in supporting the flying-membrane. Indeed, this seems to
have been achieved twice, that is to say, by two distinct
types of Mammals, for the large fruit-eating tailless Pteropus
of warm countries is very different from the ordinary Bat,
which is insectivorous and has a long tail incorporated in the
wing membrane.

Twice, also, have placental Mammals managed to acquire
the freedom of the ocean, as did the Ichthyosaurians, which
they resemble but surpass in the perfection of their adaptations.
Thus we find Herbivorous Mammals constituting the order
of Sirenidia, which preserved the mobility of their elbow,
and Carnivorous Mammals the order of Cetacea, which preserved
only the mobility of the shoulder. In both cases the
hind limbs disappeared, and the tail became a very powerful
motor organ. The Sirenidians have pectoral mammae and rise
half out of the water to suckle their young ; the Cetaceans, by
a sudden muscular contraction, ejaculate their milk into
the mouths of their young, which do not suck : their mammae
are inguinal. Possibly a third type presents this same
adaptation to an aquatic life. Seals are Carnivora of an
advanced type which have preserved their four limbs in a form
less removed from the ordinary foot than the natatory paddles
of the Sirendia and the Cetacea, modelled on those of the
Ichthyosaurians. However, in the Eogene Period there
lived in Alabama and New Zealand a huge aquatic Mammal,
the Zeuglodon, which sometimes attained a length of thirty

LIFE IN TERTIARY TIMES 293

metres, like our Baleen Whales and Cachalots. It had no hind
limbs and its tail was probably pointed, not flat like that of the
Cetacea, and it had molar teeth with two roots, singularly
recalling those of Seals, whereas in Cetacea all the teeth
are alike and have but one root.

We have now to see how these diverse forms were grouped
during the successive periods of the Tertiary Epoch.

The laws determining modification of limbs are simple
and precise. Confining our attention to the exterior aspects,
we may say that, whatever diet was adopted, every series
began by forms in which the feet rested entirely on the ground,
consequently known as plantigrade. Then the foot gradually
became raised so that the toes alone were on the ground ;
in these conditions the shortest toes soon ceased to touch
the ground ; being unused, they tended to disappear : but
this disappearance occurred much earlier in a hind- than in
a fore-limb. The anterior limb was often put to various
uses, whereas the hind-limb was always more specialized
for the locomotor function : it was the main instrument of
propulsion in other types besides Mammals. So much so that
the following rule may be formulated : The hind-legs of land
quadrupeds, more especially utilized for propulsion, are both
more highly developed and more modified than the fore-legs.
In general the contrary is true for aquatic Vertebrates, for
as the tail plays a considerable part in propulsion, the unused
posterior limbs are either reduced (sub-brachian Fishes,
Ichthyosaurians) or disappear (Sirenia, Cetacea, Siren among
the Batrachians, Sirens, Eels, etc.).

The limbs of the Carnivora undergo no important modifica-
tions. The plantigrade forms are numerous and preserve
the digits on all four legs. In the digitigrade forms, the Dog and
Cat have only four digits on their hind and five on their fore
feet. Hyenas have only four digits on all four feet. In the
Herbivora, modification extends much further. The digits
of the Carnivora, utilized more or less for seizing and holding
prey, terminate in claws. It is the same with Insectivora,
whose feet remain pentadactyl. In the Rodents, on the
contrary, the number of toes is often reduced to four or even
three, and the structure of the tridactyl hind foot of the
Jerboa, with its united metatarsals, recalls the foot of a Bird.

Certain Rodents (Cavy or Cabiai) have the extremities

294 TOWARDS THE HUMAN FORM

of the toes provided with nails resembling a hoof. They
would thus appear to have led up to the Ungulates, which
arrived eventually at walking only on the extremities of their
toes, and in whose limbs the highest degree of reduction of the
digits is attained. The arrangement of the carpal and tarsal
bones is subjected to the most remarkable modifications. These
bones are disposed in two rows. In the carpus the first row
comprises three bones : one of them, the scaphoid, articulating
with the radius, is also called the radiate, and another, the
cuneiform or pyramidal, articulating with the ulna, is there-
fore sometimes called the ulnare. Between the two there is
intercalated the intermedium or semilunar bone. The bones of
the second row are placed exactly in front of them : the radial
supports the trapezium and the trapezoid ; the intermedium the
os magnum, and the pyramidal the uncinatum or unciform
bone, which itself results from the union of the fourth and fifth
bone of this row. Each of these bones supports one digit only,
with the exception of the unciform bone, which is double and
supports two. Thus the bones of the digits and those of the
carpus are disposed as far as the bones of the forearm in
longitudinal series, in which each bone unites only with the
one preceding and the one following, and is free laterally. This
serial arrangement in the carpus is not particularly inconvenient
and has perhaps some advantages for animals with a heavy
tread, in whom the foot plants the whole extent of its inferior
aspect on the ground and is thus unembarrassed by
irregularities. On the other hand, it exposes fleet-footed animals
to the risk of dislocations, since at each bound the}' land
suddenly upon the end of the toe, which is the only part of the
foot to touch the ground. This arrangement is already modified
in the hind foot in the oldest plantigrade forms. There the
tibiale and intermedium are united to form the astragalus, which
articulates with the tibia ; the fibular e or peroneal, which
follows the fibula, develops particularly in the rear, and forms
the calcaneum or heel-bone ; a special bone, the navicular,
represents the os centrale of the Batrachians, and a free bone,
the pisiform, is perhaps the remnant of a sixth digit that has
always remained rudimentary. In front of the bones of the first
row are arranged the five bones of the second, of which three,
the cuneiform bones, remain free and two are united to form
the cuboid. The serial arrangement appears only after these

LIFE IN TERTIARY TIMES 295

last, each cuneiform supporting one toe and the cuboid two.
This serial arrangement is characteristic of a group of mammals
which did not survive the Eocene Period, and to which Cope
gave the name of Condylarthra. Their principal representa-
tives are mainly, if not exclusively, American : Periptychns,
still plantigrade, and Phenacodus, semi-digitigrade, about the
size of a large sheep. Among the large Ungulates, all of them
Eocene, this seriation had already become modified ; they were
still semi-plantigrade, and consequently provided with all
five toes. Cope grouped them together as Amblypoda. In their
feet, the bones of the second row of the carpus slightly over-
ride the first, and the metacarpals alternate with them
regularly in such a way as to support themselves between two of
them and thus maintain their union.

Representatives of this order particularly well distributed
in North America are Pantolambda, Coryphodon, Loxohphodon
with a skull more than a metre in length, and Dinoceras,
about the size of a Hippopotamus, powerfully armed, like the
others, with horns and canines, of which we shall speak later.
The short feet still have four to five toes, all of which rest on
the ground in Mceritherium and Palceomastodon, in various
precursors of the Elephants, and in the Elephants themselves.
These have all been grouped together in the order of Barypoda,
in which the dentition undergoes considerable reduction.
We see, finally, a gradual diminution in the number of toes,
coinciding with important modifications in dentition in the
heavy animals, with serially arranged tarsus or carpus, as in
those Condylarthra that Burmeister has included in the order
of Toxodontia. Homalodontherium and Prototypotherium are
still pentadactyle, but there are only four digits in the hind
feet of Typotherium, and this reduction has also taken place
in the fore feet of Toxodon. Finally, in Hyrax, an animal of
the size of a Rabbit, our present-day representative of the
whole order, there are only three digits in the hind and four in
the front foot. This brings us to those orders in which the
straightening of the foot having reached the maximum, the
animal only rests the extremity of its longest digit upon the
ground.

If the third digit is sufficiently longer than the others, it
supports the whole weight of the body. Ungulates with feet
so constructed are called Perissodactyla. If the third and

296 TOWARDS THE HUMAN FORM

fourth digits are almost equal they share the task of supporting
the body and become almost exactly alike. The foot then
assumes the cleft form characteristic of the Artiodactyla.
In both cases the lateral toes tend to disappear thiough lack
of use and all the stages in this retrogression can be followed.
In the order of Perissodactyla, where the foot is reduced to a
single toe, as in Horses, this reduction and disappearance
takes place onlv after the bones of the carpus and the tarsus
have gone on for some time being displaced in order to afford
mutual support, piling up over one another and articulating
one on the other. They may unite, but do not disappear. It
is otherwise with the Artiodactyla. Here the reduction was
produced in a first series of forms, while the carpus and
tarsus were still seriated. The bones of the carpus and the
corresponding bones of the tarsus are either reduced or dis-
appear,, and both hind and fore feet have preserved their
frailty. This is what Woldemar Kowalevsky, brother of the
famous embryogenist, called non-adaptive reduction. The
Artiodactyla that underwent it all disappear from Miocene
times onwards : they were Dichobune and Hyopotamus, provided
with four digits ; Anoplotherium , an aquatic animal which had
only two to the fore limbs, with a third much reduced
digit to each hind limb ; and Xiphodon, more graceful than our
gazelle, which had only two toes on all four feet, and whose
molars were the first to show the Ruminant tendency, although
Xiphodon must not be considered as their ancestor. To
these must be added Anthracotherium, Cheer opotamus, and
Hyothcrium, related both to the Wild Boar and the Peccary,
and particularly Entelodon, large as a Rhinoceros. In the
persisting forms which have led in one direction to the Pig
and in another to the Ruminants, the heads of the third and
fourth metacarpals have been broadened as though crushed
under the animal's weight. They have encroached upon the
carpals supporting the lateral toes, and thus assured the
preservation of these last. When the reduction in the number of
toes begins only after this modification has taken place,
W. Kowalevsky describes it as adaptive reduction. This is
the condition in the Hippopotamus, Wild Boar, Peccary, and
the other existing Pigs. The metacarpals and metatarsals
in these animals are never united, nor were they united in
primitive Ruminants. The latter series begins with Oreodon,

LIFE IN TERTIARY TIMES 297

a form probably originating in the Condylarthra, related to
Pantolesies, and which still possesses, besides a complete
dentition, five digits on the fore feet and four on the hind feet ;
the pollex is already very small and the four persisting digits
are all equal in size. Oreodon was closely related to the
ancestors of the Camel, whose first representatives are
Leptotragidus of the Eocene of North America, which still
had four digits on its fore limbs, and lateral meta-
tarsals without toes on the hind. The Pabrotherium of
the Oligocene of America had only two toes and two
rudimentary metacarpals in the fore limbs. The meta-
carpals and the metatarsals are united into a single
cannon-hone in Protolabis and Procamelus of the Miocene.
This same union has come about in another and quite
independent series of Ruminants. In these initial forms there
are four complete digits on each foot, only two of which touch
the ground ; in Dorcatherium and Hypertragidus, both of which
are Miocene, there is no union between the metacarpals.
Union is present, however, in Gelocus, also Miocene, so far as
the metatarsals are concerned, and also in Hycemoschus, still
living in Western Africa. There is union in both in Tragidus
of the Pliocene. In all other Ruminants the metacarpals
and metatarsals are respectively united to form a cannon-bone.
In Cervidae and Bovidae there are still two lateral toes, but
the metacarpals and metatarsals are more or less incomplete
and reduced often to a simple splint. In the Ovidae there is
no longer any trace of lateral toes, and they are absent also in
Giraffes, Sivatherium, Samotherium of the Miocene in Samos,
Helladotherium and the Okapis, although these forms are
less highly evolved than the Cervidae so far as the horns are
concerned. Here the feet are completely consolidated and no
longer comprise any useless parts. If the animal had not in
the beginning immobilized its metacarpals and metatarsals —
or practically done so — by a deliberate act which became
habitual, their union, itself a proof of such immobilization,
could not have taken place. The part played by the animal
in the modification of its own organism is thus clearly
apparent.

The Perissodactyla present digital reductions parallel to
those of the Artiodactyla. They had a common ancestor in
the five-toed Phcnacodus, with seriated carpals and tarsals.

298 TOWARDS THE HUMAN FORM

This seriation is preserved in the Titanotheridse of North
America (Lambdotherium, Palceosyops, and Diplacodon of the
Eocene), which, with Titanotherium, attained in the Miocene
to the size of an Elephant. These animals had four digits on the
front and three on the hind feet, and bore on their noses a
pair of large protuberances, which doubtless supported horns
analogous to those of the Rhinoceros. The Macranchenia
and the Proterotheridae had only three digits to each foot.
They lived in South America and constituted a series which
immediately followed on to the Condylarthra. In another
series the carpal and tarsal bones had ceased to be seriated.
This series begins in the Eocene with Hyracotherium, an animal
about the size of a Fox, which appeared in America, and
there evolved into Pachynolophus and Propalceotherium,
represented in America by Orohippus, Eohippns of Wasatsch,
and Epiphippus of Uriste, which had four digits on the fore
and three on the hind limbs. The Lophiodontidse of Europe
and of the American Eocene (Lophiodon, Heptodon, Helaletes),
the Tapirida?, which differ from them in the character of their
molars (Systemodon, Hyrachyus, Tapiravus, of America, and
Protapiriis and Tapirus of Europe), all had four digits in front
and three behind. But in Palceotherium and Paloplotherium
of the Eocene of Europe, many species of which have left their
remains in the gypsum of Montmartre, the number of digits on
all four feet had already decreased to three, all of which rested
on the ground. These animals had the gait of Llamas ; their
radius and their fibula were complete, and they had a rudi-
mentary fifth metatarsal. Similarly the Rhinoceros, which has
survived to our own times, appears first in the Eocene of
Wyoming and the Uinta formations as the genus Amynodon,
with few exceptions (Acerotherium, Dicer atherium) as a tridactyle
animal.

The reduction of the toes was continued in the series of
Equidae, whose molars are marked by a median longitudinal
crest. The three toes in this series are still almost equal and
touch the ground in Mesohippus of the American Oligocene,
whose fibula has begun to be reduced. The median toe becomes
prominent in the American Miohippus, which migrated into
Europe in the Miocene, where it constituted the genus
Anchitherium in the Middle Miocene of France and Germany.
This predominance is accentuated, and the lateral toes cease

LIFE IN TERTIARY TIMES 299

to touch the ground in the American MerycJrippus and
Hi-ppotherium, as also in the European Hipparion of the Upper
Miocene. Finally, in Protohippns and the Pliohippus, only one
functional toe remains. These last reached South America,
and then produced Hippidium and the true Horses, which
gradually spread over both hemispheres, but died out in
South America.

In all these animals, when the foot could no longer make
any rotatory movement in relation to the leg, the muscles
attached to the fibula, which determine these rotatory
movements, were no longer used, but atrophied, as the
doctrine of Lamarck prognosticates, and brought about
the gradual atrophy of the fibula to which they were
attached. For the same reason the radius of the fore leg which
corresponds to the fibula became completely united with
the ulna.

To sum up, the same tendencies are at work in the evolution
of the limbs both of Mammals and Reptiles. In both classes
the terrestrial animal succeeded in penetrating into other
environments open to its activity — the water, from which its
ancestors formerly came, and the air, from which its weight
would seem to exclude it, and it arrived at progression in both
these media by analogous procedures. On land its evolution,
apart from a few special adaptations, such as that permitting
underground or arboreal life, for instance, was dominated by
two needs — to see as far and to run as fast as possible — which
induced them to erect themselves on their limbs. In both cases
the intervention of the animal's own volition, with a view to
attaining a desired end, is evident. The resulting modifications
were not linked with any particular diet ; therefore the modi-
fication of the teeth do not strictly follow those of the limbs.

The oldest placental Mammals possessed what is called a
complete dentition, that is to say, forty-four teeth — eleven to
each half of the jaw (three incisors, one canine, four premolars
and three molars). This dentition is seen at the beginning of the
series in the herbivores, the insectivores, and the carnivores. It is
occasionally reduced, but never increased, except where
elements of the molars become dissociated, as in Cetacea. It
must therefore be considered as the primitive dentition of
the placental Mammals, and its generality leads us to think
that all these animals descend from the same initial type, one

300 TOWARDS THE HUMAN FORM

that probably existed during the Cretaceous Period, but which
has not as yet been found.

Both cutting-edged incisors and sharply-pointed canines
had only one root and are but little removed from Reptilian
teeth. They are teeth that cut or tear, and by these actions
stimulate the dental germ that produced them and maintains
them in activity. Hence their growth was continuous, especially
in the case of animals which attack hard substances like wood.
This phenomenon had been already produced once before in
the case of the Marsupial Diprotodon (p. 291) . It occurred again
in Eocene times in Tillondontia, in whom the first and
second incisor (Psittacotherium) or the second only (Estonyx)
Tillotherium, or even the third (Stylinodon) , underwent great
development ; the others became smaller again or disappeared
(Tillotherium). In Rodents the second incisor is highly
developed, while the first and third attenuate or disappear.
In Hares, Rabbits, and analogous forms the upper jaw
of each side has two incisors, one large and the other small,
situated one behind the other. In other Rodents the small
incisor disappears. Toxodontia also had incisors very
unequally developed (Nesodon) or even reduced to two pairs
(Toxodon). The same phenomenon is produced in the series
leading up to the Proboscidea, which, in addition to a trunk,
possess enormous incisors constituting tusks.

Thanks to the discoveries made in the Fayum, in Egypt,
twenty years ago, we can here follow this transformation step
by step, and determine the exact causes which have
produced these tusks and have led by way of repercussion to
the development of the trunk. In this region there lived about
the middle of the Eocene period Mceritherium, of the
dimensions of a Tapir, wdiose second pair of incisors had taken
a considerable development in each jaw. The large incisors of
one jaw came into contact at the extremity with those of the
other, and this reciprocal pressure tended to bring them into the
position of a prolongation of the jaws. The other incisors
and the upper canines were rudimentary ; they had already
disappeared from the lower jaw. The Mceritherium must have
possessed either a long mobile upper lip, like that of the
Rhinoceros, or a short trunk like that of the Tapir. A little
later on there lived in the same region the Palceomastodon,
which had only two enormous incisors in each jaw and no

LIFE IN TERTIARY TIMES 301

canines at all. Its lower incisors, having become almost
horizontal, were no longer worn away at the edge with use,
and consequently became greatly elongated. The upper
incisors clearly tended to become parallel with them —
one step more and we arrive at the condition in Tetrabelodon
and the Mastodons, which had four large horizontal incisors,
two upper and two lower. All these animals had trunks ;
that of the Mastodon rested on its tusks and consequently could
not be curled around an object like the trunk of an Elephant,
and could only seize things by the terminal lobe. We can
therefore see the mechanism at work in the production of
this singular appendage. It was at first a simple, mobile,
and prehensile lip like that of the Rhinoceros. As fast as the
incisors grew, the efforts of the animal to continue to seize
with his upper lip the food that lay beyond their extremities
was bound to lead to the gradual elongation of the lip, which
was constantly being extended beyond the incisors, trans-
formed into tusks, and thus grew to a great size, constituting
the trunk — prehensile only at its extremity — of the
Mastodons. From these animals, by the disappearance of the
upper incisors, was derived the huge Dinotherium, and by the
disappearance of the lower incisors the Elephants. In the
Dinotherium the lower tusks, at first bent downwards by
the upper ones, eventually grew vertically, the animal using
them in the manner of picks. In the Elephants, the upper
incisors are widely separated, leaving an empty space between.
In both cases the trunk, having become free, can be either
raised or lowered at the animal's will, and serves him for the
most varied purposes.

The animals above described balanced the great develop-
ment of the incisors by losing their canines. In the Dinoceratidce,
on the other hand, it was the canines of the upper jaw that
became large. They are very long, and flattened like
sword blades, in Dinoceras, and curved back in a semi-circle in
Loxolophodon. This pronounced development of the upper
canines was balanced by the disappearance of the incisors of
the same jaw. This may be compared with the disappearance
of the upper incisors in the Chevrotains, where the male is
provided with a pair of enormous canines, whereas the incisors
disappear, so that this disappearance of incisors in the upper
jaw would seem to be covered by a general law. This

302 TOWARDS THE HUMAN FORM

disappearance once achieved in the Chevrotains, it would be
preserved by heredity in other ruminants, such as the Cervidae,
where the males still have a canine.

The molars, being employed in the trituration of food,
naturally become modified according to the use that the animal
makes of them, and end by being more specially adapted to the
consistency of the food than either the incisors or the canines.
The primitive number of seven — four premolars and three molars
— may be reduced, but they never disappear in animals which
masticate their food. Arising from the union of several teeth,
such as the purely prehensile teeth of the Reptile, in the first
place they naturally had a crown with a broad and
mamillated surface, especially as this crown might already
present, in Reptiles, certain surface complications, such as we
noticed in Theriodontia. These surface bosses or tubercles
may be joined in such a way as to form ridges transversal to
the direction of the jaw (Mastodonts, Tapirs, etc.), or
longitudinal crests (Carnivora). On the basis of these data,
a first approximation of the essential facts may be condensed
into some such formula as this :—

As generation succeeds generation, the modifications in the teeth
occur as though the adults transmitted to their descendants the
forms that have been acquired in the course of their lifetime
through use and attrition.

According to the degree in which a Mammal adopts an
increasingly carnivorous diet, the molars of the lower jaw meet
those of the upper jaw scissor-fashion, and become sharpened
by the shearing away of the upper edge of their crown. Thus
we see the transition from the tuberculate molars of the Bear
to the exclusively scissor-edged molars of the Cat. On the other
hand, when Mammals live on vegetable food, generally hard,
the crowns of the opposing molars in the two jaws become
planed down and present a large grinding surface striped with
bands of enamel. It is in this fashion that the molars of
Mastodons, with their protruding transverse ridges, became the
flat-crowned teeth of the Elephants, in which the enamel is
arranged in lozenge-form (Loxodon or African Elephant), or
in flattened ellipses (Elephas or the Asiatic Elephant). In the
same way the tuberculate bossed teeth of Palceotherium and
Anchitherium are replaced by the flat-surfaced teeth of Horses
in which the enamel bands with an apparently capricious

LIFE IN TERTIARY TIMES 303

contour outline the base of the primitive tubercles. The
tuberculate teeth of the Rhinoceros have a flattened crown
but an elongated body, and thus evolved, as Boule has pointed
out, into the smooth, elongated teeth of Elasmotherium. In
Rodents we can follow all the transitions between the bossed
teeth of the Marmot and the rasp-like teeth of the Cabiai,
Beavers, Dormice, etc. The omnivorous cleft-footed
Mammals, of which our Wild Boar is typical, have retained
the mamillated teeth of Anthyacotherium, and Waldemar
Kowalevsky has created for them the sub-order Bunodontia.
These teeth are replaced in the herbivorous forms, which he
called Selenodontia, by teeth with a flat crown, formed by
juxtaposed crescents which represent the bases of the worn-down
tubercles of the Bunodontia. But as attrition always causes
the disappearance of the enamel on the surface of the teeth,
and as enamel is produced here in the ordinary way, it is
evident that there is no question here of inherited attrition.
In reality the dental germ takes the form determined by the
pressure transmitted to it, according to the use the animal
makes of its teeth while they are growing. Constant pressure
of upper and lower teeth one against the other must bring
about a flattening of the surface of the dental germ, and, as a
result, must cause it to produce a flat tooth which looks like
a worn tooth, with its tubercles reduced down to their bases,
these also looking like worn tubercles. The same obtains for
the lateral compressions in the teeth of Carnivora.

The influence of the increasing development of certain teeth
on neighbouring teeth, already pointed out in connexion with
incisors and canines, is again encountered in the molars of the
Carnivora. Here the molars that do the most work are those
situated in the neighbourhood of the attachment of the
masticatory muscles to the jaw. They grow and develop that
cutting edge which has earned them the distinctive name
of camassials. They are already clearly characterized
in Dogs, some of which still have forty-four teeth. In the
Carnivorous group the other molars decrease in the front as
well as at the back of the carnassial teeth, and finally dis-
appear one by one in measure as we pass from the Dog to the
Civet, Marten, and Cat families. Thus their number decreases
from seven to two (Machcerodus).

The reduction of the number of teeth is due, however,

304 TOWARDS THE HUMAN FORM

to other causes besides the disproportionate growth of
certain individuals. Among the herbivorous animals the
Ruminants are the first examples of this. These animals, as
we have seen, appear to be derived from Oreodon of
Oliogocene times, which already had the molars of Ruminants
but five digits, of which one was very small on the front feet
and was absent in the hind ones. They appear to be descended
from the Condylarthra (Pantolestes) , and were followed by
Ccenotherium, which still had a complete dentition, though a
wide space known as the gap or diastema, in which the canine
occupied a variable position, had been produced between the
incisors and the molars. In their successors the lower jaw
preserved the complete dentition, in spite of this gap, except
that the canine was placed against the incisors, whose form it
took, and the first premolar, with a greatly reduced root,
united with it, so that it appeared to be hollowed out on its
cutting edge in the Giraffidae (Giraffe, Okapi). Thus apparently
there were only six molars in all, and that is the number that
persists in the other Ruminants. Things were far more com-
plicated in the upper jaw. There the dentition was still
probably complete in Leptotragulus and Proebrotherium of the
North American Eocene ; but in the Camels the middle
incisors disappeared, and the laterals, canines, and first
premolars, set very wide apart, took the form of sharp, curved-
back hooks. There are only two premolars in the upper jaw
and one in the lower, and in Halomeniscus and Eschatius
there is actually only one in each. As for the other Ruminants,
those forms with hollow horns have neither incisors nor canines
in the upper jaw. It may indeed be asked why the incisors
of Ruminants have disappeared while they remained in
Horses, which also browse on grass. Aristotle had already
pointed out, and after him Cuvier, that Ruminants with horns
had no canines, but both made use of this coincidence as an
argument in favour of finalism, on the grounds that animals
which could defend themselves with their teeth had no need
for horns, and vice versa. The correlation pointed out by
Aristotle is not, however, strictly accurate, nor is it an explana-
tion. Is it possible that the calcium employed in the formation
of the bony portion of the horns has been used up at the expense
of the teeth ? Triceratops, the only Reptile with real horns,
had no teeth in the anterior portion of its jaws, which were

LIFE IN TERTIARY TIMES 305

transformed into a kind of beak. Dinoceras, lacking upper
incisors, was armed with three pairs of horns analogous
to those of the Rhinoceros, whose upper incisors have also
disappeared. These teeth were also very small or altogether
missing in Titanotherium, the most pronouncedly horned
form of Perissodactyl ; but the reduction of the number of
teeth begins in their series with the appearance of horns.
The canines are already weak in Hyracodon of the White
River Oligocene, and disappear from the upper jaw of the
first Rhinoceroses, which have no horns (Aceratherium), and
retain only two pair of incisors in the upper and one pair in
the lower jaw. They migrated to the former continent and
arrived in India during the Upper Miocene, and disappeared
in the Pliocene. During this Period the American Rhinoceros
(Diceratherium) acquired symmetrical horns ; the true
Rhinoceros has only one median horn or two placed one behind
the other. These already existed in Europe during the Middle
Miocene (Sansans), where their most highly modified repre-
sentatives presented neither incisors nor canines. This is also
the case in the African Rhinoceros (A telodus) , in the Rhinoceros of
Pikermi (AteloduspacJiygnathus) , and the Rhinoceros Tichorhinus
(Calodonta), the contemporary of man. The molars themselves
were reduced to five, and had bands of enamel extraordinarily
folded in the gigantic El as mother ium of Siberia, which had
a head a metre long, and an enormous horn on its forehead.

From what we have seen above it follows that it is no more
possible to affirm in the lineage of the Rhinoceros than in that
of the Ruminants that the reduction in the number and dimen-
sions of the teeth present, particularly in the upper jaw,
can be due to the development of horns. Nevertheless, we are
dealing with such a remarkable coincidence that we have
the right to ask whether some fundamental relationship does
not exist between these two phenomena, connected with
some competition for the valuable lime salts to which both
teeth and horns must have recourse in their development.

The oldest horned Ruminants date back to the Oligocene
Period, and from that time forward were liberally provided in
that respect. These were species of Protoceras of the White River
in America. They had then four well-developed digits in front,
but two only and a lateral splint behind, large canines, and
ten pairs of horns in the male, reduced to two in the female.

306 TOWARDS THE HUMAN FORM

The upper incisors were absent. Following them, in the
Miocene, is Procervulus, in which the horns were not shed and
as a rule were simply bifurcated. During the same period,
however, they acquired a circle of "pearls" separating the
deciduous part from a long persistent peduncle in Dicroceras
of the Miocene. In the Upper Miocene the peduncle
became shortened and almost the whole of the horn became
deciduous in Cervulus, still extant in India. Thus we come
to the Roebuck, which dates from the Upper Miocene. The
Giramdse (Helladotherium, Sivatherium) appear at the same
time. At this time also the Antelope, in which a horny casing
covers a bony axis, with hollow spaces in it, becomes distinct
from the Deer, and thus opened the series of Ruminants
with hollow horns, in whom canines have disappeared. Hence
the Aristotelian idea of a " balance ", as G. Saint-Hilaire
would say, between the defensive organs. Arsincetherium of
Fayum, which will be discussed later, supplies the gravest
objection to such a conception.

It is not easy to explain how the teeth could become simplified
and disappear in those animals which are grouped together
in the class Edentata. This is, however, no isolated instance.
The Ornithorhynchus and the Echidna replaced the multi-
tuberculated teeth of their ancestors in the Secondary period
by horny ones, except where they lost them altogether. The
teeth of the Sirenia and Cetacea, like those of the Edentata,
are simplified, multiple, and at last completely atrophied.
A general problem thus arises. In the Eocene of Patagonia
Ameghino discovered fossil Mammals whose molars were
simplified and had become cylindrical, but which still possessed
their complete canine and incisor sets. Lestodon and
Megalonyx of the same period still retained one canine. They
may be considered the ancestors of the living Sloths, which
live in trees and feed exclusively on such leaves as they can
pull off with a minimum of effort and which they then only need
to masticate. We may here invoke the consequences of disuse.
The gigantic Megatherium likewise, in spite of its great size, which
sometimes equalled that of the Rhinoceros, had numerous
affinities with the Sloth. Instead of climbing trees to get their
leaves, they pulled them down ; but they walked only on the
outer sides of their feet, as the Sloths are compelled to do when
on the ground because of the length of their nails. If they are

LIFE IN TERTIARY TIMES 307

descended from Megatherium, to whose diet they have remained
faithful, there is no reason why their dentition should have
been modified. Ant-eaters have the same way of walking,
and their pectoral mammae indicate that they are descended
from tree-climbing animals, and the structure of the repro-
ductive apparatus makes it clear that these tree-climbers
were Sloths. But they have changed their diet : they live on
Insects, and their extraordinarily long vermiform tongues are
all they need to take hold of their food, which does not have
to be masticated. Lack of usage can explain the total dis-
appearance of the teeth, the form of the tongue, and the
elongation of the head and jaws.

In the skin of Mylodon, related to Megatherium, and
which has not long disappeared from South America, there
were numerous ossicles. These ossicles formed a complete
carapace in Glyptodon, whose back was hemispherical and
nearly two metres in diameter. The head still resembled
that of the Megatherium, but the feet rested flat on the ground.
It is quite likely that the Armadillos of to-day, which can be
traced back to the Tertiary (Eutatus, with a carapace formed
entirely of mobile strips, and Dasypus), are related to them
in some degree ; but in their case the jaws are elongated, and
this coincides with a multiplication of teeth, which in the
great Armadillos are twenty-six in the upper half-jaw and
twenty-four in the lower, a total of one hundred in all.

Orcteropius and the Pangolins of the Old World seem to
form a special group in which we observe the same abortion of
the teeth. They date back to the Miocene.

And here we encounter a new difficulty. Among the
fossils of the Eocene beds of Montmartre, Cuvier found a bifid
phalange with a nail which he attributed to a very large
Pangolin, the only animal except the Mole that possessed
a similar character. This hypothetical Edentate received from
Lartet the name of Macrotherium, and some time after a head
attributed to a kind of Horse was named Chalicotherium. Sub-
sequently, however, an unexpected discovery in the beds of
Sansans proved conclusively to Filhol that Macrotherium and
Chalicotherium were one and the same animal. Related forms
were dug up in the Eocene deposits of North America, and
completely reconstructed by Professor Holland (Moropus,
Eomoropus, and Pematherium). They had the general

308 TOWARDS THE HUMAN FORM

appearance of a horse walking on its fetlock- joints, and were,
indeed, almost plantigrade. They had only three toes on their
feet, terminating in enormous nails. How, we may now ask,
did they lose their lateral toes ? Were they descended from
climbing or burrowing animals ? We do not know.

All Edentata are characterized by the remarkable develop-
ment of the skeletal system, which presents a curious contrast
to the abortion of the teeth. The same contrast is manifested
in Ornithorhyncus and the Echidna. Can we, therefore,
suppose that this enrichment of the skeleton by the lime salts
was accomplished at the expense of the dental system, thus
rendered comparatively inert ?

This massivity of the skeleton coincides in the Sirenians
with an analogous reduction of the teeth. The Eocene
Prorastomus, indeed, had almost too many, since in addition
to the normal number of incisors and canines it had eight
molars instead of seven in each half -jaw. Halitherium,
likewise Eocene, which had preserved the rudimentary femur
of its hind limb, had already lost two incisors and the supple-
mentary molar. Only the male Dugong has functional
incisors, and four of its six molars are rudimentary, while in
the Sea-Cow the two incisors remain concealed under a horny
plate, but the number of molars of each half -jaw increases, as
in the armadillos, and reaches eleven altogether, of which six
only are functional. Finally, in the adult Rhytina, the teeth
have been replaced by horny plates, as in Ornithorhyncus,
These great animals had already been exterminated by 1768,
twenty-five years after their discovery.

The dentition of the Cetacea has undergone similar
vicissitudes. No fossil forms are known that present a
dentition like that of the primitive placental Mammals.
Zeuglodon seems to approximate rather to the Seals. From
the very beginning, as the jaws elongated, the molars seem
to have become dissociated and to have returned to the
conical form seen in Reptiles. Only the Miocene Squalodon
shows a differentiation of the teeth into incisors, canines, and
molars. At that time, however, there already existed Dolphins
whose teeth were all of the same pattern ; Cachalots which
had none except in the lower jaw, and species of Hyperoodon
which had only one pair of teeth at the free end of the mandible ;
as well as a large number of Bakenoptera, or even of Whales

LIFE IN TERTIARY TIMES 309

like the Greenland whale, which no longer had teeth but
horny baleen plates. We know that while Porpoises and the
Grampus live on fish, Dolphins, Sperm-whales, and Hyperoodon
live chiefly on soft cuttle-fish, and Baleen-whales on all kinds
of small creatures. Such diet, giving the teeth no work,
would account for their disappearance, since there would be
no stimulation of the formative bulb.

A number of works, pre-eminent among which are those
of the American palaeontologist, H. F. Osborn (xc, xci, and
xcii), have made us remarkably well acquainted with the fauna
whose remains were carried down by large rivers during the
Eocene Period and deposited in the valleys of the Rocky
Mountains. The deposits thus formed are of different ages,
and Osborn divides them into four successive groups ; in the
first, comprising the deposits of Puerco and Torrejon in the basin
of the San Juan of New Mexico,1 were found Neoplagiaulax and
Polytnastodon, inherited from the Triassic period, Insectivora,2
Creodonta, Taeniodontia, Condylarthra, and Amblypoda.
Some of the animals of this first phase have also been found
in France,3 others in Patagonia.4 From the second phase
onward, at Wasatch, there are added to these primitive groups
Rodents, genuine Perissodactyla, and already — interesting
to observe — Primates.

During this second phase there are no longer any forms
common to both North and South America, which were at that
time probably separated, but numerous species appear in
Europe. They become rare during the third phase, which
corresponds to the whole of the Meso-Nummulitic,5 a period
that witnessed the disappearance of the Condylarthra and the
appearance of families indigenous to the New World, to which
they are restricted, such as the Oreodontidae, herbivorous
animals with an even number of digits, which lasted until the
end of the Tertiary, and the Titanotheridae, represented by
the gigantic Titanotherium or Brontotherium. Huge monsters
were also produced among the Amblypoda.

1 These deposits are of the Eonummulitic Epoch (Montian, Thanetian,
Londinian).

2 Miochlosnus, Oxyacodus, Wortmannia, Onyckodecles, Triiosodon,
Oxyclcenus, Loxolophus.

3 They belong to the fauna of Torrejon : Neoplagiaulax, Proviverridae,
Arctocyonidae, Mesonychidae, Phenacodus.

* Trigonolestes, Helohyus, Parahyus.
8 Fauna of Puerco.

310 TOWARDS THE HUMAN FORM

Among the Perissodactyla, which were more numerous than
the Artiodactyla, Hyrachyns began the line which led to the
Rhinoceros, and Orohippus that which led to the Horse.

In the fourth phase, corresponding to the Neo-Nummulitic,1
numerous types, notably marsupials,2 became common to
North America and Europe, but the two Americas remain
completely separated. Side by side with the Marsupials,
Peratherium, the Creodonts are still represented by Hycenodon.
The true Carnivores likewise made their appearance with
Cynodictis, which appears also in France, and to which
Filhol has related all the other Carnivora. Perissodactyla,
Protapirus, presaged the coming of the Tapirs, and Meso-
hippus formed a new link in the genealogy of the Horses ; later
on they were associated with Miohippus? Finally, among
the Artiodactyla, common to the old and new Worlds, we
find Elotherium, Anthracotherium, and Hyopotanvus.

The basin of Paris and of the south of England was not, at
this epoch, equally rich in Mammals. Nevertheless, after the
Thanetian, we find the following : in the tufa of la Fere,
Arctocyon, a large plantigrade Creodont whose name signifies
bear-dog ; in the sandy beds of Cernay discovered by Victor
Lemoine, and belonging to the Upper Thanetian and the
Sparnacian, in the conglomerate of Meudon and Vaugirard :
Neoplagiaulax, Hycenodictis, and Arctocyon, Lemurs of the
genus Plesiadapis, and lying above other Creodonts,4
Coryphodun, as in America, and Lophiodon, the precursors
of the Tapirs. At this same level of the Sparnacian, more-
over, the sands of Ay and the London clay have yielded
Hycenodictis and Pachynoluphus, the latter constituting an
advance in the direction of the Tapirs. To these genera must
be added, among others, in the Lutetian or the coarse lime-
stone of Gentilly, Passy, and Nanterre, the first Palceotherium,
and Pigs of the genera Dichobune and Cebochcerus. Then come
the famous Ludian gypsum formations of Montmartre, where
Cuvier made the discoveries that laid the foundations of
palaeontology. Here were discovered Peratherium, also known

1 Lutetian, Auversian, Bartonian, Ludian (in the order of their age).
* The Oligocene or Tongrian comprises, in the order of their antiquity, the
Lattorfian, the Rupelian, and the Chattian.

3 Besides Ronzotherium, which belongs to the Rhinocerotidae, there are
Entolodon, Protapirus, Paratapirus, Cadurcotherium, Titanomys.

4 Pachyhycsna, Palcsonictis.

LIFE IN TERTIARY TIMES 311

in America, Cynohy&nodon, Crcodonta with teeth similar
to those of the Cynhyaenas, Cynodictis, P alee other ium,
Anoplotherium, Xiphodon, and among Lemurs Adapts, all of
which since Cuvier's time have been quoted in the most
elementary textbooks. The earliest Bat, the true Vespertilio,
also made its appearance. This fauna is almost exactly reproduced
in the Lattorfian limestone of Brie, and in the Rupelian sands of
la Ferte-Aleps appears the first European representative of
the Rhinoceros group, Acerotherium, still without a nasal
horn. An analogous fauna is found at Ronzon in Velay, but
here we must also draw attention, along with the Ccenotherium,
intermediate between Anoplotherium and the Ruminants,
to the first true Ruminant, Gelocus.

Analogous animals lived in the Quercy district, where the
waters have hollowed out in the limestone plateaux extensive
caverns, whose walls have been covered with a layer of
phosphorite, and into which all sorts of bone fragments have
been carried. These bones, studied by Filhol, belong to the
second half of the Meso-nummulitic and the commencement of
the Neo-nummulitic. Finally, during the Chattian period, are
seen the precursors of the Shrew-mice (Amphisorex, Sorex),
the Moles (Myogale), Otters (Potamotherium) , Cats (Eusmilus),
Beavers (Stenofiber) , and hornless Ruminants (Dremotherinm,
A mph itragulus) .

While Mammals were thus evolving in the different portions
of what had been the North Atlantic continent, evolution was
proceeding along entirely different lines in those parts of
America and South Africa, which resulted from the dismember-
ment of the old Gondwana continent. In the Montian
Epoch Dinosaurs still survived in these regions. There were
also numerous Allotheria,1 Marsupials already analogous to
our Opossum, Edentata foreshadowing Megatherium,
Orycteropodidae which still live in South Africa, Sloths and
Armadillos which have remained exclusively South American,
Insectivora,2 Typotheria, Amblypoda, many of them allied
to Lophiodon,3 the precursors of the Proboscidea nowadays
localized in Asia and Africa, Phenacodon already existing in
North America, the Hyracoidea analogous to the Hyracidae,
whose representatives are now confined to Asia and Africa,

1 Plagiaulacidae, Polydolopyda?, Promyzopidac, Odontomysopidae.

2 Spalacotheridae.

3 Carolozittelia, Paulogervaisia.

312 TOWARDS THE HUMAN FORM

Palaeotheridae and other Perissodactyla as well as Lemurs
now no longer seen except in India, South Africa, and
Madagascar. This fauna, known as the Notostylops fauna, is
followed by two others preserved in the clays mixed with
volcanic ash which are found in the neighbourhood of the
gulf of Saint-Georges. To the preceding Mammalian groups
we must add other later precursors of the Proboscidians,
such as Promcerytherium and Pyrotherium, large animals
studied by Albert Gaudry, whose molars with transverse ridges
recall those of Rodents and Elephants, and whose lower jaw
carries two long almost horizontal incisors. In this collection
there is no trace of the Bats, Creodonta, Carnivora, and
Artiodactyla, all of which already existed in North America,
but, on the other hand, it includes Sparassodontia, Edentata,
Typotherium, and Toxodontia which specifically belong to it,
while its Perissodactyla are of a particular type. They were
represented by Macrauchenia, so named because of its
long neck, and by forms which approximated to the Equidse,
but were quite different from those of North America.

This curious South American fauna is less astonishing than
that discovered twenty years ago in the Fayum of Egypt, and
belonging to the Middle Eocene. The oldest zone, that of
Birket-el-Querun, is still marine, but it already contains
Zenglodon, found also in Alabama and New Zealand, and some
related forms,1 which supposes a long anterior existence for
the aquatic Carnivora like the Seals. The Middle Zone, that of
Kasr-el-Sagha, contains, in addition to Crocodiles, Turtles,
Snakes, and Cetacea, one of the oldest Sirenidans known,2 a
mammal whose position is doubtful, Baryiherium graui and
Mceritkerium lyonsi. In the 300 metres depth of strata com-
prising the third zone, to whose formation the sea and a large
river have contributed, there are entombed innumerable
fragments of Mammalian bones.

Three things have rendered the Fayum fauna especially
remarkable : first the existence of the monstrous
Arsinoetherium, second that of Mceritherium, Palceomastodon,
and Tetrabelodon, ancestors of the Elephants (p. 300), and third
the existence of a group of Monkeys, some of which to-day are
exclusively American, while others belong to the Old World.
The simultaneous presence of these groups of monkeys

1 Isis, Prozeuglodon, Eocetus. 2 Eosiren.

LIFE IN TERTIARY TIMES

313

causes the antiquity of these fundamental groups to recede
far back into the past (p. 321).

The colossal Arsinoetheriwn, larger than a rhinoceros, had
the complete dentition of the herbivores. On its nose there
rose two enormous bony horns, no doubt clothed in a sheath
like those of Oxen, and behind which two smaller horns
appeared.

In the Neogene Epoch the fauna of Europe, Africa, and Asia
tended to acquire sufficient homogeneity to permit the whole
of the regions in which it is distributed to be called Arctogean.
In France the oldest specimens of this fauna are found at
Saint-Gerand-le-Puy, in the department of the Allier, and it is
also seen at Ulm in Germany, where it belongs to the
Aquitanian. Anthracotherium, so frequent during the
preceding period, now persisted only in India. It was
replaced by Brachyodus, associated with a species of Tapir,1
two genera related to the Rhinoceros,2 a genus of Pig,3
two genera of Ruminants,4 and above all with numerous
Ccenotheria. All these types appear to have evolved in the
locality in which they were found. The fauna of the sands of the
Orleanais,5 which is a little older, was enriched by a genus of
Chevrotain, Hycemoschiis, which still survives. But as these
animals are less advanced than the Ruminants with complete
cannon-bones, which existed already, they must date back still
further. Palceomeryx and Dicrocerus have taken the place of
Dremotherium and Amphitraguhis. To these autochthonous
types we may add the Mastodonts and Dinotherium , which no
doubt came from Africa, since their ancestors have been
discovered in the Fayum ; two new types of Rhinoceros,6
two genera of Pigs,7 a new Cervulus,8 and finally an Anthropoid
Ape, sprung, undoubtedly, from the anthropoid genus of
the Fayum, Pliopithecus. America, where the Horse type was
rapidly evolving, contributed Anchitherium.

At Sansans in Gers, at Grive-Saint-Alban and Saint-Gaudens
in France, at Erbiswalden and respectively at Simorre and
Montebambili,9 the first Felidas now appear, as well as the
Porcupines which came from South America by way of Africa

1 Paratapirus.

3 Pal<xochoerus.

5 Burdigalian.

7 Choerotherium, Listriodon.

9 Vindobonian.

2 Aceratherium, Diceratherium.
4 Dremotherium, Amphitragulus.
8 Teleoceras, Ceratorhinus.
8 Micromeryx.

314 TOWARDS THE HUMAN FORM

(the Afro-Brazilian continent), while Asia and Africa furnished
a whole series of Bears,1 a new anthropoid, Dryopithecus, a
tailed Monkey of the Afro-Asiatic type, Oreopithecus, and
Chalicotheriiim, which had already existed in the Orleanais
sands. The Pontian fauna of Pikermi near Athens and that of
Mount Leberon near Avignon are celebrated by the researches of
Albert Gaudry. It was in connexion with the first of these that
this eminent scientist, before Darwin and relying entirely
upon his own observations, had the courage to reinstate the
theory of evolution abandoned since the days of Lamarck.
The Pontian fauna is particularly rich, and Gaudry's poetic
mind lent realit}' to the Lion of Nemea, the Boar of
Erymanthus, and the Goat of Amalthea,2 whose generic names
suffice to indicate how nearly this fauna approached to that of
to-day. The Felidae even surpassed in their evolution the
point arrived at by the Lion in a form now extinct, but which
must have been redoubtable. This was Machcerodus. Its
long upper canines, flattened and curved like the blade of a
scimitre, pointed, sharp, and notched on the inner surface,
must have been terrible weapons. Their development was
such that the animal could not bite with its incisors, but tore
strips of flesh from its prey with the powerful canines in order
to drink the blood of its victims. This costly diet must have
led to the creature's rapid disappearance as Antelopes became
thinned out. It had only two molars in the upper jaw and three,
including one which was rudimentary, in the lower. The
Antelopes, preyed upon by Hyaena,3 were already divided into
numerous genera, probably of African origin : Gazelles,
Palceoryx, Palceorcas and Protragelaphus — and they were
accompanied by the first Roedeer,4 which initiated the series
of Ruminants with ramified antlers, and the earliest Sheep
{Criotherium). The Giraffe family was represented by many
genera. One of these, Helladotherium, which Albert Gaudry
dedicated to Greece, was remarkable for the relative shortness
of its neck and the absence of horns, and was almost exactly
like the Okapi, which differs from it only in the presence of

1 Pseudarctos, Hycenarctos, Ursavus.

2 Tragoceras.

3 Lychycena, Hycenictis, Hy&na.

4 The African origin of the Roedeer is perhaps a little doubtful ; the lateral
metatarsals of these deer are, in fact, atrophied in the same fashion as those of
the American Cervidse, of which only one, the Canadian deer, shows the same
kind of atrophy of the lateral metatarsals as the European Cervidae.

LIFE IN TERTIARY TIMES 315

small horns in the male. Orycteropus, the Hyracidse, and a
Rhinoceros (Atelodus) had also come from Africa, but we have
seen that the Orycteropidas already existed in South America
throughout the preceding period. The African migration
was completed by the arrival of the tailed Monkey,
Mesopithecus, which added two genera to the anthropomorphs,
Dryopithecus and the Anthropodus. At the same time
Hipparion and the Hare crossed from North America to
Europe by way of Asia.

The series of Neogene fauna came to an end in France with
that of the Pliocene of Montpelier and Perpignan. It was not
quite so rich in precedent forms as some that had gone before,
but it had been reinforced by an African Pig, Potamochcerus,
a Macacus, and a new type of Mammal, Ruscinomys. A
Hippopotamus 1 had come from Asia, as also some of the
present Cervidas, Axis, and the Fallow Deer, accompanied by
another of the genus Polycladus. From Asia, too, came the
Raccoons, although they were emigrants from North America
and made their way over an isthmus at the site of the
present Behring Straits, and no longer by way of the North
Atlantic continent already described. Among the Rodents
we also observe the Vole.

At the same time a fauna analogous to that of Pikermi
existed in Persia. The richest fauna of Asia, however, was that
whose elements had been brought to the foot of the Himalayan
chain by streams that descended its slopes, and which
formed the Siwalik Hills. Machoerodus, in company with
smaller Felidae, JEluropsis and JElurogale, still hunted
Strepsiceros , Deer properly so-called, as well as Antelopes,
Goats, Bison, and Oxen. Many species of Dinotherium and
Mastodons flourished ; a Chimpanzee, a Semnopithecus, a
Cynocephalus, and a Baboon bear witness to the great variety
of Monkeys at this epoch. To this fauna belong also
Brahmatherium, Vishnutherium, and later on Sivatherhim and
Hydaspitherimn, all large-horned Giraffes.

South America, now separated from North America, was
behind the other continents. In the Lower Neogene Period
the Paucituberculata still lived there, as well as Typotherium,
along with the Marsupials properly so-called, the Sparasso-
donts, Toxodonts, and the Amblypods (Astrapotherium) ,

1 Tetraprolodon.

316 TOWARDS THE HUMAN FORM

but the Chinchillas and Cabiais, among the Rodents, were
already specialized, and representatives of the Edentata
were the gigantic Megatherium, Mylodon, Megalonyx, the true
Armadillos, and true Ant-Eaters. The Perissodactyla
belonged to two families, Prototheridae and Macrauchenidae.
Finally, Ameghino has described under the name Homunculidse
a series of Monkeys in which he chose to see the distant
ancestors of all the Monkeys and of Man himself.

In the following period, which is our own, the fauna of South
America continued its special evolution, but North American
elements had already penetrated it, especially in the basin of
Parana belonging to the Upper Neogene. These newcomers
were Carnivora of various groups — Bears (Proarctotherium) ,
Dogs (Amphicyon) , Raccoons, and, right at the end of the
period, a Ruminant (Microtragulus).

Man himself was now on the point of making his
appearance.

CHAPTER IV

The Human Form

TX7HILE the Mammals we have just described were
* * specializing in various ways of life, to which they
closely restricted themselves, certain among them, whose
exalted destiny nothing as yet suggested, continued to adapt
themselves to a most varied diet, to life on the ground, or up
in the trees that offered them such safe refuge, employing their
limbs in running, leaping, climbing, and grasping, according
to their will and the needs of the moment, thus providing the
maximum stimulus for their cerebral system, and provoking
its development by the activity imposed on it. In striking con-
trast to this continuous elaboration of the brain, the limbs and
the various organs retained their initial indeterminate character
and their almost primitive forms. These mammals have been
grouped together in the order of Primates. Their common
characteristic was the opposability of the inner digit on
each of the four limbs, which allowed them to take hold of
and feel objects in a variety of ways, and thus to gather new
and precise information, which, in its turn, contributed to the
evolution of the brain. There these impressions were combined
with those received by the other senses, and provoked more
and more frequently the exercise of deliberate volition.

This order to-day comprises Lemurs and Monkeys. The
Lemurs live in India, Equatorial Africa, and more especially
in Madagascar, where they are numerous and varied. The
Monkeys form two large groups, the Platyrrhina, with
separated nostrils and thirty-six teeth, except in the case of
Marmosets, and the Catarrhina with a narrow nasal septum
and only thirty-two teeth distributed according to the
same formula as the human teeth. The first belong to the New
World, the second to Africa and Asia ; in Europe they are
represented only by the Magot or Barbary Ape, localized
in a district near Gibraltar. Among the largest members of the
Monkey tribe of the Old World, the Gibbons of India, the

318 TOWARDS THE HUMAN FORM

Orang-Outangs of the Sunda Islands, the Chimpanzees, and
the Gorillas of Central Africa have lost their tails, and the
absence of this appendage accentuates their resemblance to
Man. They are called Anthropomorphous Apes, i.e. apes
shaped like Man.

At the beginning of the Eocene Period there lived in America
numerous species of Lemurs (Hyopsodus), which lacked only
one pair of incisors to conform to the complete dental formula
of the early placental Mammals, with its four molars and three
premolars. We may perhaps even consider Pelycodus of
the Wasatch, which did conform to the complete dental
formula, to be Lemurs. But we may say that true Primates
in this period are characterized by a reduction of their incisors
to two pairs, which persisted throughout the whole series.
Animals of the Upper Eocene with an analogous dental
formula — Adapts — have been found in the basin of Paris ;
but Cuvier, who was the first to describe them, had only seen
their skulls, and took them for Pachydermata. Further, the
angle of the lower jaw is slightly curved inward, as in
the Marsupials. Adapts is therefore very near to the
primitive placental Mammals, and we are thus led to admit
that the Primates evolved on parallel lines to the other
placental Mammals, without mingling with them The Lemurs
form a highly diversified group, as witness the long muzzles
and straight, pointed ears, giving them a special physiognomy
which has earned them the description of Fox-faced Monkeys,
the multiple mammae and varied dentition sometimes including
only one pair of lower incisors (Propithecus, Tarsius), and some-
times only a single one in the upper jaw (Aye-Aye), which, thus
deprived of canines, resembles that of a Rodent — all of which
characters go with a retention of the four prehensile hands.
Some lemurian forms have given rise to the American Monkeys,
which have retained their four primitive premolars. The
Lemurs were distributed throughout the world, and it is very
likely that somewhere in this varied group the ancestors of both
New and Old World Monkeys evade us. For, even though both
these ancestors were Lemurs, they need not necessarily have
been identical. The New World Monkeys have a maximum of
thirty-six teeth, those of the Old World only thirty-two. But
these two types differ among themselves, because the New-
World Monkeys have a milk dentition which always includes

THE HUMAN FORM 319

three premolars in the upper jaw, even when the total number
of teeth is only thirty-two, whereas the Old World Monkeys
have only two. This is considered to be an argument in favour
of the greater antiquity of the American Monkeys.

From the numerical point of view the dentition of Man
resembles that of the Old World Monkeys ; it differs chiefly
in the smaller size of the canines. The reduction in the formula
continues as the ascent is made from Lemurs to Man, in whom
it reaches its minimum limit of thirty-two teeth, already
attained in the catarrhine Monkeys. We can only seek
the cause of this reduction in a character common to all
these animals, and the most logical to which we can
attribute it is the faculty of prehension acquired by
the hand, which thus relieves the jaws of a great deal of
the work that had hitherto exclusively devolved upon them.
Thenceforth, having no longer to exercise traction in the
seizure and removal of objects, and being no longer stretched
by this traction— which counted for at least one important
factor in their peculiar elongation, and no doubt provoked the
special conformation of the herbivorous head — the jaws became
shorter and more compact. Thus was the passage effected
from the fox-like muzzle of the Lemur tribe to the flat-nosed
face of the Monkey. This shortening was not accomplished
without some amelioration of the conditions in which they
obtained their food, which perhaps explains the thinning of
the hair on this almost naked face.

Furthermore, the variety of attitudes necessarily assumed
by climbing animals living in trees must have prepared them
for the erect position that the large Apes only partially
succeeded in accomplishing. These various transformations
were early realized. In the Eocene deposits of Patagonia the
brothers Ameghino discovered a whole series of Primates which
they named Homunculus, Tetraprothomo, TriprotJwmo, and
Diprothomo, meaning respectively miniature man, great-great-
great-grandfather, great-great-grandfather, and great-grand-
father of man. According to them the cradle of mankind was
not, as de Quatrefages believed, at the foot of the great Tibetan
Highland, where the different human races are still found in
proximity, but in South America. Unfortunately, as Marcellin
Boule has shown in his brilliant memoir on the Chappelle-aux-
Saints Man, all the Ameghino Homunculi are still too far
removed from Man to be included anywhere in his genealogy.

320 TOWARDS THE HUMAN FORM

In the Eocene layers of Wasatsch in North America Cope
discovered in Anaptomorphus the first link in the chain con-
necting the Lemurs with the Monkeys. Analogous animals
first multiplied in North America, only to leave it and migrate
towards South America, where they originated the agile
and prehensile-tailed Monkeys (the Sajous) inhabiting that
region. Lemurs came to Europe about the same time, and,
probably on account of the cooling of the temperature,
evidently considered that the safest refuge was in their present
homes — India, tropical Africa, and Madagascar. Lemurs
and Sajous are even found associated in the Eocene
deposits of the Fayum, where the former are represented by
Parapithecus and the latter by Mceropithecus. But, side by side
with these, palaeontologists were very much surprised to find
an anthropomorphous Ape, Propliopithecus hceckeli, not far
removed from a Gibbon, and no doubt related to Pithe-
canthropus erectus, discovered in Java by Dr. Dubois, and
■certainly the direct ancestor of Pliopitheciis, discovered by
Lartet in the Miocene of Sansans. Thus the anthropoid
Apes, which were supposed to represent the final stage in the
evolution of the Monkeys, because they are nearest to Man,
are seen to go back to the very beginning of the Tertiary epoch,
which removes any unlikelihood of the existence of Man himself
at this time. Hence the Gorillas and the Chimpanzees would
only come after the graceful Gibbons, the most Man-like of all
the Apes, which are venerated in India, and the grimacing tribes
of tailed Monkeys of the old continents would be even more
recent ; Mesopithecus of Pentelicus, described by Albert Gaudry,
is Miocene, so that in admitting our genealogical relationship
with the Monkeys we need not include among our ancestors any
of those repulsive beings such as Hamadryas, Mandrills with
their streaked and variegated heads, or those other dog-headed
Monkeys whose grotesque faces we can see in menageries.

On the other hand, we must recognize — however vexatious
to our feelings it may be — that the characteristic features of
Man's body are not very far removed from those of the Gibbon,
and that, as Lamarck has already said, it is easy to explain those
characters which are peculiar to him. They are almost all
derived from his absolute vertical posture. It is this which has
freed the hands from tasks other than prehension and the
examination of objects and the construction and manipulation

THE HUMAN FORM 321

of defensive weapons. Thanks to these, the jaws entirely ceased
to bite and tear, as they had already ceased to seize, and
limited themselves to the mastication of food. On account of
this less arduous work, they became shorter and lighter. In
the larger Apes the muscles that raise the lower jaw
are very powerful, being inserted in the temporal fossa
during youth ; but, as the animal grows older, they creep
gradually up the lateral walls of the skull, as in Carnivora,
till they finally meet at the vertex, where they cause
the development of a median crest at the point of their
attachment. Henceforth this crest prevents any ex-
pansion of the skull, whose bones are definitely sutured
along the median line. When the muscles attached to it contract
they even tend to compress the walls of the skull laterally, and
thus to compress, and so arrest the development of, the brain.
This is probably one reason why old Monkeys are more
capricious, more evilly disposed, and more stupid than young
ones. In Man the muscles that raise the lower jaw have ceased
to migrate in this way. They are inserted in the temporal
fossa, like those of the young Monkeys, and their contraction
can exercise no pressure upon the brain ; on the contrary,
they tend to separate the frontal and parietal bones and so to
relieve the brain, thus favouring its development. The head is
so balanced on the vertebral column that it projects to
an equal extent before and behind ; and it likewise develops
in height, a fact which has important consequences. The
frontal development of the skull and the brain naturally
bring forward the base of the nose, whereas the retraction of the
jaws permits of the nostrils opening freely above them — hence,
the nasal salient so characteristic of Man. The same retraction
gives freedom of movement to the lips, now no longer strained
forward over projecting teeth, and it becomes possible for them
to smile. As the skull grows in height, it dominates the ears,
already immobile in Monkeys, and, as it widens at the
same time, it brings the eyes, more or less laterally placed in
most Mammals, to a frontal position. Thus all the characteristic
features of the human face are consequent on the development
of the brain, in itself stimulated by the new importance of the
hand. In the same way the characteristic features of the
Vertebrates have been determined by the predominance
assumed by the nervous system, so that the evolution of the

322 TOWARDS THE HUMAN FORM

human form and mental character would appear to have been
essentially brought about by the progress of the intelligence.
It must have been at a very early date that the development of
man's ancestors was orientated in this direction.

Once past the lemurian stage, which in Adapids was still
one that had links with the Marsupials, it would appear that
the simple erection of the body into the vertical position,
without any modification of the structural type, at once opened
the way that was to lead rapidly to the human form by the
uninterrupted and almost exclusive progress of the organs of
intelligence and reason. Elsewhere, limbs, dentition,
tegumentary dependencies, and visceral organs themselves
were modified in all directions, especially adapting themselves
to purely material functions. Here, on the contrary, effort was
concentrated in the perfecting of the nervous system and the
cerebral apparatus, so that Man, separated at the outset from
existing members of the Monkey tribe, has no direct relation-
ship with any other Mammal.

Is this to claim on behalf of Man, from a purely material
viewpoint, a place apart in nature ? Every fact set down in
this book leads to a contrary conclusion. Following the
example of the geologists, who, refusing to attribute the
explanation of the configuration and structure of the globe
to unknown causes, have succeeded so brilliantly in explaining
all by a unique consideration of the causes yet at work around
us, I have sought to establish that laws still regulating life
are adequate to explain the formation and evolution of the
principal organic types — a problem that seems to me of greater
importance than the pursuit of the factors determining
variation of species, which is but a fractional part of the main
problem.

Thus the human form explains itself like the others. It would
seem, indeed, that across the fluent sea of living forms those
that set their course towards the human type have left a wake
that is wonderfully direct. Sponges, Polyps, Bryozoa,
Arthropods, Flat-worms, Star-fish and the world of
Echinoderms to which they give rise, Molluscs, Tunicates,
Bony Fishes, tailless Batrachians, Reptiles, Birds, hoofed
and clawed placental Mammals — all these are off that main
track. Moreover, whereas purely mechanical conditions or
attitudinal changes have led to the early forms and subsequent

THE HUMAN FORM 323

mutations of other organic types, the structural mutations
that led from Invertebrates up to Vertebrates were due to
the volume acquired by the nervous system, whose centres,
especially the brain, thereupon gradually perfected themselves.
It is, above all, in the size and the special arrangement of his
brain that Man differs from the other Vertebrates.

That which has raised man above the animals whose structure
he retains, and which inspires the horror he feels at the idea of
kinship with them, is his consciousness of exceptional
mentality. Nevertheless, we must acquiesce in the knowledge
that we are made, like the lowliest of living creatures, from a
few common substances. The white corpuscles of oar blood
have retained the structure and amoeboid movements of the
lowest of the rhizopod Protozoa ; the olfactory membrane
of our nose, our trachea, and various other of our body cavities
are lined with cells provided with vibratile cilia like those of
the Infusoria ; our nerve-cells have a common external
character with those of all other animals ; our muscular fibres
do not differ essentially from those of other Vertebrates, and
even had their counterparts in certain Invertebrata ; our body
is divided into segments like the segments of the Worm ; our
teeth do not differ from the resistant plates which form the
dermal skeleton of the Sharks, and of which the teeth of these
Fishes are but a modification ; the scales of Fish have formed
the bones of the vault of their skull — and of our own, as
Geoffroy Saint-Hilaire discovered ; our sternum and clavicles
are allied with the external bony plates of Batrachians. As
in them, so in the human embryo are there rudimentary
branchial arches, and the Batrachians inherited theirs from the
Ctenobranch Fishes. We reproduce our kind by means of cells
similar to the reproductive cells of all other living creatures,
and the development of our body is modelled on that of
the Reptiles, the Birds, and the humblest Mammals.

We must resign ourselves to these affinities. Whatever we
may think, we shall never have bodies made of moonbeams
like Victor Hugo's sylphs, nor shimmering wings like those
outspread by Wells' angel in the course of the "Wonderful
Visit " he imprudently paid to our earth. On the other hand,
we may take the greater pride in our intelligence since our
body has been its work, and because in our evolution —
paradoxical as it may appear — mind has ever dominated

324 TOWARDS THE HUMAN FORM

matter. It is our desire to know, to see further and from a
greater height, that has made us rise to the completely erect
attitude of which we are so proud, and which has incited us to
use our liberated hands for the palpation and appreciation of
everything they touch, or to fashion raw material into
implements exactly suited to a purpose clearly conceived. It
is this same desire that has stimulated the evolution of our
brain, given to the human countenance its noble aspect, and
prepared our lips for language and laughter.

What matters the material — be it living flesh or inert dust —
on which intelligence has been at work, if intelligence has ever
and without intermission ennobled that material by its
presence ? What matter those transformations that the body
of Man has had to undergo, if, in a radiant course across the
abyss of all living form, Mind has brought it to those heights
from which Reason now dominates the world ?

CONCLUSION

CTARTING from the origin of matter, we have now arrived
^ at the realization of the human form, linking these two
extremes by a continuous chain of facts, solidly riveted by
careful arguments based on a small number of principles.
Most of these principles were formulated long ago, discussed
and then abandoned, because they were first stated in a general
form and afterwards discovered to be inadequate. Each,
however, had a value of its own, and it was only necessary to
give them intelligent co-ordination in order to obtain a rational
explanation of Life and its activities.

It is undoubtedly true, as Cuvier x had already insisted in
opposition to many of his contemporaries, and as Pasteur
has since triumphantly demonstrated, that the spontaneous
generation of living beings no longer occurs in Nature ; but it
has been equally well demonstrated that the sun alone can
sustain life on earth, and that if the sun were extinguished
life would vanish with it. But this makes it probable that life
was born from rays which the sun has lost,2 but which we may
now actually hope to produce by artificial means, thus opening
the door to the realization of the wildest anticipations. It is
also true that the variations in plant and animal species are so
gradual, or so slight when they are sudden, that we might
suppose their forms to be fixed, as the majority of naturalists
once believed; yet these variations do nevertheless take place,
and, slow though they may be, we can, by expending great
care, induce plants to vary from their original condition. But
time is needed, and in the days when Cuvier defended the fixity
of species, no one considered the shortness of the period during
which we have made any observations at all, as compared
with one of the geological periods whose history we have been
able to reconstruct.

Lamarck attributed the variations of species to habits
imposed upon animals by the stimuli of their external

1 Regne animal, 3rd edition, vol. i, p. 9.

2 Cf. p. 70.

326 CONCLUSION

environment. He was right, but only up to a certain point,
and this limitation caused his doctrine to be discarded. Darwin
admitted that variations were due to all manner of causes,
preserved by heredity, and reinforced by natural selection,
but there could be no natural selection unless it could exert
its influence upon a great number and variety of beings already
in existence. Whence did they come ? He does not say.

Every conception of this kind — we might make a long list
of them — can be defended by arguments drawn from facts,
though none can cover all the facts. But all must be allowed a
part, though only a part, in the explanation of living forms.
As a matter of fact, they have all at some time or other con-
tributed to the determination of forms ; and not only these,
but many others as well. In addition to the external
causes of modification, there are powerful internal causes,
often intimately connected with them ; for instance, the
modifications of muscles and bones by habitual movements
provoked by stimuli in the environment, according to the
formula of Lamarck. Every structural cell associated in the
task of building up an organism, while it contributes to that
organism's life, none the less continues to live for its own sake.
On the basis of this " independance des elements anatomiques ",
Claude Bernard founded his entire physiological doctrine. Even
this is inadequate when taken literally. Each cell does, in fact,
contribute its quota to the construction of the common founda-
tions, in which all share. Thence it draws all the nourishment
it requires ; into it it empties in return all the residue of its
nutrition and the products of its activity. This residue and these
products constitute the internal secretions, to which Brown-
Sequard first called attention, but which, far from being the
property of certain glands long regarded as functionless, as
we have become accustomed to say, are really the work of
all the structural cells. Through the medium of this environ-
ment, which they are perpetually modifying, and upon which
react all the modifications that they themselves undergo,
whether these are due to the action of the external environment
itself or to other causes, the cells combined in one and the
same organism — even those associated temporarily and
accidentally — influence one another, however widely separated.
An organism, therefore, carries within itself endless causes of
modification, which give it sufficient plasticity to enable it

CONCLUSION 327

to adapt itself in a constant manner to its surroundings.
Nothing could better illustrate the effects of this distance-
action than such experiments as M. L. Pezard has performed
upon Birds, showing that not only their external appearance
but their psychology may be changed — by castration, for
instance, or genital grafts.1 These operations profoundly
modified the development of the cock's plumage, and even
incited the hen to adopt his crow — a purely psychological
effect. It is not surprising, then, that these modifications
should react upon the structure of the reproductive cells them-
selves in order to become functional, which from the time of the
repeated segmentation whereby they are able to reconstitute
an organism similar to the one from which they came, must
recapitulate, in inverse order, the stages through which the
latter has passed in order to reach its final form. This is what
constitutes heredity. It perpetuates the individual in his
progeny. But the substances which accumulate within the
individual not only modify him ; unfortunately they encumber
him, and he ends by succumbing to the burden, after passing
through the phase of gradual decay which we call old age.

The regeneration through the reproductive cells of the
successive characters of the ancestral organism from which
they came, led Etienne Geoffroy Saint-Hilaire to conceive the
embryogeny of living forms, both animal and vegetable, as
consisting in a rapid epitome of their descent. The
increasing rapidit}' with which the ancestral characters succeed
one another in an embryo, unequal though it be for different
organs, ensures that these characters are finally telescoped one
into another, so to speak, while, at the same time, those which
evolve most rapidly by a sort of inter-organic struggle for
existence take the place and absorb the nourishment of those
that develop more slowly. To this acceleration in the succession
of embryogenetic phenomena, resulting from the definitive
modification of the adult form, we have given the name of
tachygenesis. Thanks to its influence, heredity becomes, by a
sort of paradox, a modifying instead of a conservative force.
The importance of tachygenesis as a cause of organic trans-
formation cannot be over-estimated. We have seen how it
produced the Vertebrate type. But tachygenesis is itself a

1 Le conditionnement physiologique des caracteres sexuels secondaires chez
les Oiseaux. These de Paris (Sciences), 1918.

328 CONCLUSION

result of something else, and we are far from understanding
how it is produced in the first instance.

Embryogeny does not reproduce only ancestral characters.
Free embryos, in the course of their development, very
frequently modify their mode of life ; they return to the con-
ditions in which these characters were achieved, thus allowing
us to discover their causes, so that we are able to emphasize
the importance of attitudinal changes in the realization of
organic types, whose structure did not appear at first sight to
be referable to any causes within the scope of our observation.
This conviction led Cuvier to postulate his four immutable
structural types, of which, however, only one, the Vertebrata,
was clearly delimited by constant and precise characters. For
Cuvier's four " embranchements " we have to-day substituted
nine : Protozoa, Porifera, Ccelenterata, Chitinophora (Arthropoda
and Nemathelminthes) , Vermes, Echinodermata, Mollusca,
Vertebrata, and, related to the last-named by a process of
degeneration due to the fixation of their embryos to objects
below the surface of the sea, Tunicata. But for each one of these
phyla a clear explanation has been given of the characters
that distinguish it. It is extremely improbable that deep-sea
research will provide us with any new phyla, for it would
seem as though those we already know correspond to all the
types that are rationally possible. But only four of these
phyla have dowered the freshwater or the solid land with a
numerous posterity ; to wit, the Chitinophora, whose essential
types are represented by the Arachnida and Insecta ; the
Vermes, Mollusca, and Vertebrata. We have already seen how
the hermaphroditism of the Vermes and the lacustrine and land
Molluscs has raised the question of conditions which determine
the production of this or that sex.

It would seem that the males of the lower forms show little
aptitude for development, and are relatively weak, and that
those of the higher forms show a disposition to squander their
food reserves in the production of useless ornaments such as the
brilliant plumes of male birds, the decorations of numerous
male insects, the mane of the lion, the beard of man, etc., or
in organs of defence and attack such as the horns of the various
male ruminants, the tusks of elephants, or the enormous
mandibles of the stag-beetle. The females, on the contrary,
at least in the Animal Kingdom, generally appear to sacrifice

CONCLUSION 329.

all unnecessary ornaments — in certain insects, even their
wings — to the accumulation of reserves to be utilized as food
for their eggs. Under these conditions, we have been led to ask
whether the determination of sex is not simply a matter of
nutrition, and whether it would not therefore be possible to
produce either sex at will, or, at least, to foretell, at any given
time, which one would appear. There is nothing chimerical
about such hopes. In certain Bees, the workers, during the egg-
laying season, prepare special cells for those larvae which are
to develop into males and for those which are to develop into-
females ; and we know that our common Bee can even trans-
form, during the course of their evolution, the larva designed to-
yield a sterile worker into one that will develop into a fertile
female, by means of appropriate nourishment. If this result
could be generalized, man could obtain control over a
phenomenon which has hitherto seemed to him a profound
mystery. If he possessed the power to determine the sex of an
organism in its early stages, and knew all the phases through
which it must pass, why should he not try to mould it to his will
and obtain new forms which he could anticipate in advance,
instead of merely exploiting the uncertain caprices of cross-
breeding ? The infinite number of races of Dogs, Fowls,
Pigeons, Rabbits, etc., which have been obtained almost by
chance, show how readily species respond to experiments, and,
as we have seen, the determination of forms is above all a
matter of chemistry. Unfortunately, despite all the advances
made in organic chemistry during the last half-century, despite
all its successful work in reconstructing varied and complex
substances, especially the albuminoids, the problem of the
composition, structure, and possible transformations of
substances and their mutual relations has by no means been
solved, and we have need of its solution if we wish to make
rapid progress in the history of life. The very question of the
nature of life may soon be removed to an entirely new sphere.
For instance, the microbes which pass through porcelain
filters and are only visible to the ultra-microscope are con-
sidered to be alive. On the other hand, albuminoid substances,
do not pass through these filters, because of the size of their
molecules. Hence these molecules approach the limits of
visibility. It is questionable whether an " organized '
microbe differs very much from a simple chemical compound
which, by reason of the size and the small number of its com-

330 CONCLUSION

►

ponent molecules, has abandoned the geometrical shape of

ordinary crystals and assumed the forms of granules, straight,
curved, and even helicoidal rods which the microbiologists
call micrococci, bacilli, bacteria, spirilla, etc. Elementary life,
from this point of view, would be nothing more than a form of
chemical reaction in which the living molecule, instead of
destroying itself by abandoning the debris to substances with
which it is in contact, breaks these up for its own profit and
increases indefinitely at their expense, not by augmenting its
surface volume as the crystals do, but by letting itself be
penetrated, and by multiplying itself by the division of its
mass in proportion to its growth. Nutrition would thus appear
to be the cause of reproduction, which assures mastery of the
world to organized beings which multiply by geometrical
progression.

The countless variety of flowers which the horticulturists
can produce demonstrate that organisms are much more
docile than is commonly believed. It can only be the presence
within them of some special substances, or even of a single
substance, which determines the formation of these varieties,
and it is by no means beyond the present power of chemistry
to define these substances and produce them synthetically.
If man can work successfully along these lines, he will become a
creator. Henceforth the whole history of vanished organisms,
which palaeontology has been so painfully yet brilliantly
reconstructing since Professor Marcellin Boule succeeded in
rediscovering the entire ancestral series both of the large groups
and also of our present species — all this wonderful history of
a dimly remote past, whose first pages were deciphered by
Cuvier, will then receive experimental confirmation.
Undoubtedly the great majority of the genealogies with which
we must content ourselves are built up on simple hereditary
resemblances. As for the primitive characters whose gradual
modification we have observed in our reconstituted series,
their causes escape us completely, or can only be imagined by
a comparison with those we see about us. In this book we have
sought to place the organisms whose story we have recounted
in the environment where they evolved by referring, so far
as possible, the modifications they have undergone to the
conditions of their environment. These modifications result
partly from the direct action of physical agents such as heat,

CONCLUSION 331

light, and others connected with electricity, which up till now
have been hardly suspected — the currents that traverse the
muscles and the nerves, or those involved in the phenomena
or radio-activity ; but, above all, they depend upon the
chemical reactions that take place between the countless
products of the activity or decay of structural cells. To
isolate these products, to determine their chemical com-
position, to study the action of each of them on the con-
stituent elements of a given organism, is a piece of experimental
work requiring great patience, which will probably never be
finished but which will certainly lead to results of the greatest
importance if boldly undertaken and methodically planned.
It is along these lines that man can hope to complete his con-
quest of life. This task must naturally have disheartened
the savants of the eighteenth century, who could not possibly
perceive how to set about it, but who essayed to take the place
of the philosophers. A beginning was made by the scientists
of the nineteenth century, not without a measure of success ;
and it has already kindled among those of the twentieth a
passionate enthusiasm, which the results already obtained in the
domain of biological chemistry must fan to a whiter heat.

In their attempts to fathom the composition of the living
cell, biologists discovered first of all that it was surprisingly
complex, but of a nature to explain the mystery of life.
We have long known that the nucleus is really a complex
apparatus notably containing two special globules, the cen-
trosomes, a network of a substance that has great power in
fixing carmine chromatin, a network that is transformed
at the time of the cell-division into a festooned ribbon composed
of a constant number of loops in all the cells of one organism
and all the organisms of the same species. These loops are
capable of becoming isolated and then forming chromosomes.

The botanists, in their own sphere, have recognized and
described the green chlorophyll granules by virtue of which the
plant manufactures sugar and exhales oxygen under the action
of the sun. They also know the leucoplasts which produce starch.
Within recent times discovery has been heaped upon discovery.
In 1887 Dr. Raphael Dubois 1 found within the plasma of cells
certain active and special forms to which he gave the name of
vacnolides ; Altmann later on called them bioplasts, and to-day

1 R. Dubois, " Les Vacuolides," Comptes rendus de la Societe de Biologie,
8th ser., vol. iv, 1887.

332 CONCLUSION

they are generally designated as mitochondria, a term given
them by Benda, while the whole mass is known as
the chondriome. But the chondriome itself is not simple,
and in analysing it by means of various strains, Dangard
has distinguished, at least among the plants, three categories
of cells constituting what he calls the vacuome, the
plastidime,1 and the spherome. These various elements increase
in size, change their forms and their manner of grouping, and
produce, as Guillermond has shown, various substances. In
short they nourish themselves very much in the manner of the
beneficent microbes which aid the cell to live instead of
destroying it as ordinary microbes do, and they stand in the
same relation to the chondriome as the algae, which live in
community, or, as we say, in symbiosis, stand in relation to
Radiolarians or to Worms of the genus Convolnta. That is what
Portier implied when he called them symbiota. We are thus
led back by the circuitous route of symbiosis to the question
which we previously raised, of the nature of Life.

The vast horizons which open before us in the future
go beyond the old bounds of science. Modern science seeks
positive solutions for questions which a short time ago were
considered to be outside the domain of observation and
experience, and fit only for philosophical speculation. What
connexion, for instance, may there be between the motor
reactions of Infusoria, simple inevitable reflexes of external
stimuli ; the vague and blind sensibility of Sponges and
Ccelenterates ; the obscure instinct of Worms ; the remarkably
accurate hereditary prescience of the Insect, the free intelligence
of the superior animals, and human reason ? How is it that
some among so many structural cells have been able to make
sensibility their exclusive property, and to concentrate into
nervous centres without breaking their co-ordination with
all the other cells ; to receive information from them ; to
command them by means of a mechanism representing the
combined forces of matter, heat, electricity, light, and perhaps
other agents between which we now recognize unexpected
affinities ? 2 How did thought expand in this environment,
and acquire the power to embrace unflinchingly the immensity
of the cosmos, to face the enigma of the universe and endeavour
to resolve it ? That is the secret of the future.

1 Comptes rendus de VAcademie des sciences, 1st December, 1919, 9th
February and 1st March, 1920.

2 Cf. the excellent book of Jean Perrin, Les A tomes.

MAPS

333

Map I. — Conformation of Land and Sea in the Northern Hemisphere at the

beginning of the Primary Period.

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being strictly classified.)

Ch.

Ch.

H

H

INDEX

Adaptation, 77

Africa, 23-6, 29, 48, 96, 157, 243, 282

Agassiz (Alex.), 14S

Agassiz (Louis), 208, 230, 245

Age of the Earth, 31-3

Albuminoids, 63, 67, 70-2

Algae, 78, 96-8

Algonkian, 20, 22

Allantois, 180, 1S5

Allmann, 195, 207

Alps, 17, 19, 26, 29, 30, 47, 49, 52

Alsace, 50

Altai, 17

Ameghino, 285, 316, 319

America, 13, 17, 21-3, 27, 29, 30, 32,

33, 46, 47, 79, 210, 234, 236, 243,

281,282,287, 312, 315
Ammonites, 75, 161
Amnion, 180, 185
Ampere, 141 /

Amphineura, 136
Amphioxus, 79, 92, 125, 134, 142,

143, 156, 162, 167,227
Angiosperms, 101, 102, 111, 244
Animal Colonies, 126
Animal Heat, 46, 181
Annam, 17
Annelid, 124
Anthony, Dr., 247
Antilles, 74
Apennines, 17
Apalachian Mtns., 16, 24
Arabia, 22
Arachnida, 168, 169
Archaean, 20, 22
Aristotle, 304
Armogony, armogenesis, 93
Arrhenius (Svante), 5, 62
Artiozoa, 209

Arthropods, 123, 124, 130, 147, 209
Artois, 30

Asia, 13, 17, 22, 2S2, 315
Astronomical Year, 41
Atlantic, 22, 29, 30, 47, 49, 282
Atoms, 3, 4
Attitude, 126 ; ii, v
Attraction, 4
Australia, 13, 17, 24, 26, 28, 29, 47,

157, 232, 287, 289

Bacteria, 74,
Bajocia, 27
Balbiani, 86
Balbiano, 72
Balfour, 141

97

Barysphere, 36

Barrande (J. de), 23

BataMon, 79

Batracians, 46, 175-9, 182, 185, 236,

258
Beaumont (Eliede), 18
Becquerel, 62
Belgium, 25, 26, 48
Benda, 332

Bernard (Claude), 60, 79, 255, 326
Berthelot (Daniel), 70
Berthelot (Marcellin), 61, 66
Birds, 181, 182, 192, 237, 238, 285,

286
Black Forest, 16, 25
Blainville, 76
Blandet, 44
Blaringhem, 104, 105
Blastoderm, 179
Blastomeres, 79
Blastopore, 115
Blastula, 115
Blavet, 103
Bode, 10
Bohemia, 17, 25
Bonnet (Charles), 76
Bordage, 103
Borneo, 27
Bosler, 44

Boule, 303, 319, 330
Bourquelot, 90
Bouvier, 140
Brachiopods, 219-22
Brazil, 24, 26, 28-30, 48
Bridal apparel, 218
Bridel, 90
Britain (Great) (British Isles), 22,26,

28,29, 48,50, 51,53, 281
Brittany, 17, 29-31, 51, 281
Brongniart, 216
Brown-Sequard, 326
Bryozoa, 116
Buffon, 9, 95
Bunsen, 8
Burmeister, 395

Caledonian (chain), 16, 18, 19, 34,

47, 52, 239
Calyx, 102, 107
Cambrian, 20-47
Canada, 21, 23, 24, 26, 46
Cape (the), 26, 28, 46, 47
Carboniferous, 22, 48
Carbo-hydrates, 63-5, 67
Carnivora, 293, 303, 310

342

INDEX

Carnegie, 264

Carnot, 5

Carpels, 103

Carrel (A,), 79

Carribean Sea, 13, 28

Caspian, 26

Catkin, 102, 160

Caveux, 204

Cells, 78, 117

Cellulose, 96, 242

Cetaceans, 148, 306, 308

Ceylon, 32

Channel (English), 23

Chatelier (de), 44

Chauvin (M. de), 355

China, 24, 26, 28, 29, 47

Chlorophyll, 67, 68, 97

Chromatin, 85

Claparede, 214

Clarke (J.), 205

Club mosses, 46,48, 100

Coblentzian, 24

Coelom, 115

Cohn, 62

Comparative Anatomy, 133

Conifers, 45, 46, 111, 202

Cope, 295, 320

Copepods, 39, 147

Corals, 20, 45, 47, 50, 120, 121, 148,

152, 208, 209, 245, 246
Cretaceous, 20, 21, 28, 51, 244. 255,

278
Croll, 53
Crookes, 4
Crustaceans, 124, 126, 134, 150-5,

162, 172, 173,212-14
Cryptogams, 46, 99, 100, 102, 110,

111,201, 202
Cuvier, 31, 45, 49, 61, 75, 76, 96, 124,

140, 144, 161, 271, 304, 307, 310,

325, 328, 330

Dana, 208

Dangard , 332

Darwin, 76, 131, 144, 190, 255-7,

314, 326
Davaul, 103
David (A.), 46
Delage, 90
Demes, 117
Deperet, 269
Determinism, 60
Devonian, 20, 47
Diastases, 65
Dicotyledons, 51, 107, 108, 202, 203,

244, 245
Dinantian, 24, 25
Discs (imaginal), 83
Dohrn (A.), 133, 143, 180
Dollo, 274
Douarnenez, 19, 35

Douville, 25, 75, 245, 248
Driesch, 79
Dubois, 320, 331

Earthquakes, 35, 36, 40
Echinoderms, 122, 125, 126, 133-5,

147, 222, 240
Ecliptic, 41, 54
Ectoderm, 115
Egypt, 300, 312, 320
Electrons 4
Embrvogeny, 77 ff., 91-3, 114, 115,

123, 133, 176-81, 183, 184, 204,

328
Entomostraca, 124
Environment, 76, 84
Eocene, 20
Eogene, 20

Epirogenic (movements), 52
Equinoxes, 42, 43
Erzgebirge, 16
Ether, 3, 36
Europe, 13, 24, 53
Evolution, 75, 83, 314

Fabre (J. H.), 257

Fats, 63, 64

Fernandez (Miquel), 80

Ferns, 45, 46, 99-101, 110, 111, 201

Filhol, 307, 310, 311

Finland, 21, 22, 24, 52, 200, 241

Fischer, 71,72, 140

Flowers, 102, 103, 107-10

Foraminifera, 26, 112, 204

Foucault, 8

France, 17, 22-6, 30, 31, 50-3

Frasnian, 24

Frauenhofer (lines), 8

Frich (F.), 226

Fuego, Terra del, 17

Fungi, 68, 69, 78, 96-8

Fusulina, 26

Gadow (H.), 275

Gastrula, 115

Gaudechon, 70

Gaudry (A.), 234, 237, 312, 314, 320

Gautier (A.), 66, 88, 195

Gegenbaur, 233

Geikie, 53

Geothermic (degrees), 34

Germany, 22, 24, 49, 53

Germen, 83

Giard, 93, 196

Glacial (climate), 34, 45, 46, 54 ;
(periods), 19, 52, 53 ; (glaciers),
25, 34, 46-8, 50, 52, 53

Glands, 89, 167, 182, 184

Goethe (theory of), 111

Gondwana, 25, 27, 48, 49, 168, 210,
236, 289, 311

INDEX

343

Gothlandian, 23
Grand'Eury, 101,202
Gravier, 155

Greenland, 16, 21, 25, 26, 283
Grube, 214

Gymnosperms, 100-2, 110, 111, 202,
244

Haacke, 103

Haeckel, 39, 60, 91, 92

Hariot, 103

Harz, 16

Haug, 75, 226

Heer (O.), 284

Heinrichs, 10

Helium, 9, 32, 71

Helmholtz, 62

Herbivora, 292, 293, 299

Herbst, 80

Hercynian (chain), 16-19, 24, 25, 34,

47, 48, 50, 52, 239, 243
Heredity, 83-5, 87, 89-92, 104, 126,

145, 160, 185, 186
Hermaphroditism, 160, 162-5
Himalaya, 17, 19, 29-30, 34, 47, 52
Hirn, 5

Histoblasts, 83
Hitchcock, 265

Holland (Professor), 264, 307
Holland, 25

Holothurians, 127, 149, 150
Horns, 304-6, 313
Houssay, 227
Hugo (Victor), 214
Huronian (chain), 16, 19, 21, 39, 239
Huxley, 60, 66, 266
Hydra, 79, 116-20, 206
Hyponomeutitae, 80

Independent Creations, 75

India, 22, 24-6, 29, 47, 48, 315, 320

Indo-China, 17, 22, 26

Infusoria, 113, 114, 204

Inostranzeff, 201

Insects, 171-4, 213, 215-8, 254-8

Instincts. 255-8,280

Intelligence, 280, 322, 323

Italy, 22, 25, 26, 29

Janssen, 8
Japan, 22, 52, 74
] eh ring (von), 80
Joly, 59
Joule, 5
Jurassic, 20

Kayser (E.),226

Kelvin (Lord), 32, 44, 62

Kent (Saville), 246

Keyserling, 61

King, 262

Kirchoff , 8

Klein, 103

Korea, 22

Kossel, 71

Ko^alevsky (\V.), 296, 303

Kiinckcl d'Herculais, 83

Labitte, 218

Lacaze-Duthiers, 208

Lamarck, 31, 59, 95, 131, 134, 144,

184, 219, 299, 314, 320, 325
Lamy, 169
Lang (A.), 137, 138
Laplace, 6, 9
Lartet, 307, 320
Leaves, 99-100
Leibnitz, 76
Lefebvre, 46
Lemoine, 310
Light, 3
Lignier, 1 10
Limbs, 293-9
Lithosphere, 35
Locomotion, 121-3
Lyell (Sir Charles), 95

MacLeod, 168, 169

Madagascar, 22, 26, 28, 29, 48, 282,

283
Maillard, 71. 72
Malaya, 17, 26
Mammals, 182-6, 192, 259-60, 278,

280-2, 286-316
Mammoth, 45, 53
Marchal, 80
Marion, 208

Mating (plumage, etc.), 89, 218
Matter, 3, 4
Maupas, 163
Mayer, 5

Meditenanean, 13, 22, 28, 54, 282
Medusas, 119-20
Mendeleef, 4
Mercerat, 285
Merids, 116, 118-21
Meseta, 17,29, 281
Metamorphosis, 15
Meunier (Stan.), 35
Milne-Edwards, 214, 286
Mimetism, 147
Miocene, 20
Mollasca, 51,74,125, 126, 128, 136-40,

147, 156, 223, 225-7, 240, 246-50
Monocotyledons, 51, 109, 110, 245
Monlivault (de), 61
Moreneo, 285
Morgan (de), 79
Morse, 219, 220, 260
Moselcy, 208

Mtosjisowicz (von), 75, 226
Mosses, 98-100, 110,201
Movement, 4, 5, 40. 45

344

INDEX

Munier-Chalmas, 225, 250
Musset, 59
Myriapods, 213, 214

Naudin (C), 195
Natural Selection, 76, 190
Nauplii, 124
Nebulum, 6
Nematodes, 163
Nervous System, 140-3, 321
Neumayer, 27, 75, 245
Nutrition, 65

Oken, 60, 68
d'Orbigny (A.), 75
Orbit, 41,54
Organic Chemistry, 66
Orogenesis, 19
Osborn (H. F.), 309
Owen, 290

99

Pacific (ocean, continent), 17, 21,

24, 243, 245, 283
Pasteur, 59, 61,325
Patrogony, 92
Perez (J.), 196

Perevaslawzeva (Marie), 168
Peridot, 35
Permian, 20
Perrin, 332
Petchili, 17
Pezard, 327
Placenta, 184,288,289
Plankton, 39
Plasma, 83
Plastids, 78, 112, 117
Pleistocene, 20
Pliocene, 20, 53, 75
Poincare (H.), 1 1
Poles, 13, 16, 40, 41, 47, 55
Pollen, 102

Polyps, 116, 121,208,239
Portier, 332
Portlandian, 27
Pouchet, 59
Preadaptations, 133, 152, 156, 165,

173, 194
Preyer, 62
Primordial slime, 60
Primates, 288,317-21
Protoplasm, 60

Quatrefages (de), 118, 214, 319

Radiolaria, 112, 204, 240, 246
Radium, 3, 31, 32
Rayleigh (Lord), 4, 36
Renaud (B.), 202, 242
Reproduction, 65

Reptiles, 131, 186, 187, 237-9, 258,
259, 261-75, 278-80, 299, 304

Respiratory Apparatus, 165-70, 174

Rhizopods, 113

Richter, 62

Riesengebirge, 16

Roche, 36

Rodents, 300, 303, 309, 315

Rontgen rays, 4

Romanes, 255, 257

Ruedemann, 207

Ruminants, 304-6, 311

Russia, 22, 24, 25, 27, 49, 53, 239, 243

Sahara, 24, 25, 28

Saint-Hilaire (Geoffroy), 76, 91, 143,

175, 306, 323
Saint-Hilaire (Etienne Geoffroy), 94,

141, 327
Saintonge, 19
Salles-Guyon, 62
Savigny, 133
Scandinavia, 16, 21, 22, 24-6, 28, 47,

53
Schulze (F. E.), 230
Schutzenberger, 71
Scotland, 16, 25, 26, 28, 281
Secondary (Period), 19, 20, 50 ; III,

2, 276
Semper, 78
Serre (A.), 91

Sex, 87, 89, 95, 102-5, 328, 329
Siberia, 16, 21, 22, 24, 27-9
Silesia, 25, 26
Silurian, 20, 47
Social (life), 77
Spain, 17, 22, 25, 29, 30, 243
Spawning, 157, 178
Spegazzini, 103

Sponges, 116, 152, 204, 205, 239
Spontaneous Generation, 59, 61
Spores, 62, 70, 99
Stamens, 101,102,107, 108
Stratigi-aphv, 18
Structure (types of), 125, 126, 133,

138, 139
Struggle for Existence, 190
Strutt, 32

Sudden Variations, 195
Suess, 23, 25
Sun Spots, 40
Switzerland, 50, 52
Synclines, 16

Tachygenesis, 82, 93, 94, 176, 178,
190, 202, 235, 241, 327

Tactism, 135, 255

Tectonics, 18

Teeth, 259, 260, 289-91, 299-306,
308, 309, 318, 319

Telegony, 186

Ternary (Compounds), 63

Tertiary, 19,20

Theromorpha, 259, 260

INDEX

345

Tethys, 25, 27-9, 51, 212, 245, 282

Thevenin, 239

Tieghem (van), 62, 203

Trasciatti, 72

Trembley, 79, 116, 117

Triasic, 20, 27, 260, 286

Trilobites, 46, 124, 211-14, 231-33,

240
Tyndall, 5

United States, 16, 23, 27

Vejdowsky, 164

Vermes, 116, 124

Vertebrates,' 123, 125, 126, 129, 133,

141-3, 145, 174, 177, 181, 1S5,

227-39, 258-80, 2S4
Violle, 44

Vire, 151
Vitalism, 60
Viviparity, 189
Volcanoes, 17, 243
Volition, 299, 318
Vosges, 17, 25, 51
Vries (De), 195

Weismann, 83, 87

Wertheim, 36

Westphalian deposits, 24

Wings, 171-4, 192,292

Worms (Annelid), 123, 124, 126,

134-6, 140, 145, 161, 163-6, 206,

218 235
Worms (Flat), 159, 164

Zoids, 117

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