← catalogue

The Whence and the Whither of Man

by John M. Tyler · English · Gutenberg #14834 · 564,236 chars · public domain (US)

The Project Gutenberg eBook of The Whence and the Whither of Man
    
This eBook is for the use of anyone anywhere in the United States and
most other parts of the world at no cost and with almost no restrictions
whatsoever. You may copy it, give it away or re-use it under the terms
of the Project Gutenberg License included with this eBook or online
at www.gutenberg.org. If you are not located in the United States,
you will have to check the laws of the country where you are located
before using this eBook.

Title: The Whence and the Whither of Man

Author: John M. Tyler


        
Release date: January 29, 2005 [eBook #14834]
                Most recently updated: October 28, 2024

Language: English

Other information and formats: www.gutenberg.org/ebooks/14834

Credits: E-text prepared by Janet Kegg and the Project Gutenberg Online Distributed Proofreading Team


*** START OF THE PROJECT GUTENBERG EBOOK THE WHENCE AND THE WHITHER OF MAN ***

Note: Project Gutenberg also has an HTML version of this
      file which includes the original illustrations.
      See 14834-h.htm or 14834-h.zip:
      (https://www.gutenberg.org/dirs/1/4/8/3/14834/14834-h/14834-h.htm)
      or
      (https://www.gutenberg.org/dirs/1/4/8/3/14834/14834-h.zip)





THE WHENCE AND THE WHITHER OF MAN

A Brief History of His Origin and Development through Conformity
to Environment

Being the Morse Lectures of 1895

by

JOHN M. TYLER
Professor of Biology, Amherst College

New York
Charles Scribner's Sons

1896







          Morse Lectures

    1893--THE PLACE OF CHRIST IN
      MODERN THEOLOGY. By Rev. A.M.
      Fairbairn, D.D. 8vo, $2.50

    1894--THE RELIGIONS OF JAPAN. By Rev.
      William Elliot Griffis, D.D.
      12mo, $2.00.

    1895--THE WHENCE AND THE WHITHER OF
      MAN. By Professor John M. Tyler.
      12mo, $1.75.





TABLE OF CONTENTS



INTRODUCTION


CHAPTER I

THE PROBLEM: THE MODE OF ITS SOLUTION

The question.--The two theories of man's origin.--The argument
purely historical.--Means of tracing man's ancestry and
history.--Classification.--Ontogenesis and Phylogenesis.


CHAPTER II

PROTOZOA TO WORMS: CELLS, TISSUES, AND ORGANS

Amoeba: Its anatomy and physiology.--Development of the
cell.--Hydra: The development of digestive and reproductive organs,
and of tissues.--Forms intermediate between amoeba and hydra:
Magosphæra, volvox.--Embryonic development.--Turbellaria: Appearance
of a body wall, of ganglion, and nerve-cords.


CHAPTER III

WORMS TO VERTEBRATES: SKELETON AND HEAD

Worms and the development of organs.--Mollusks: The external
protective skeleton leads to degeneration or stagnation.--Annelids
and arthropods: The external locomotive skeleton leads
to temporary rapid advance, but fails of the goal.--Its
disadvantages.--Vertebrates: The internal locomotive skeleton leads
to backbone and brain.--Reasons for their dominance.--The primitive
vertebrate.


CHAPTER IV

VERTEBRATES: BACKBONE AND BRAIN

The advance of vertebrates from fish through amphibia and reptiles
to mammals.--The development of skeleton, appendages, circulatory
and respiratory systems, and brain.--Mammals: The oviparous
monotremata.--Marsupials.--Placental mammals.--Development of the
placenta.--Primates.--Arboreal life and the development of the
hand.--Comparison of man with the highest apes.--Recapitulation of
the history of man's origin and development.--The sequence of
dominant functions.


CHAPTER V

THE HISTORY OF MENTAL DEVELOPMENT AND ITS SEQUENCE OF FUNCTIONS

Mode of investigation.--Intellect.--Sense-perceptions.--Association.
--Inference and understanding.--Rational intelligence.--Modes of mental
or nervous action.--Reflex action, unconscious and comparatively
mechanical.--Instinctive action: The actor is conscious, but guided
by heredity.--Intelligent action.--The actor is conscious, guided by
intelligence resulting from experience or observation.--The will
stimulated by motives.--Appetites.--Fear and other prudential
considerations.--Care for young and love of mates.--The dawn of
unselfishness.--Motives furnished by the rational intelligence:
Truth, right, duty.--Recapitulation: The will, stimulated by ever
higher motives, is finally to be dominated by unselfishness and love
of truth and righteousness.--These rouse the only inappeasable
hunger, and are capable of indefinite development.--Strength of
these motives.--Their complete dominance the goal of human
development.


CHAPTER VI

NATURAL SELECTION AND ENVIRONMENT

The reversal of the sequence of functions leads to extermination,
degeneration, or, rarely, to stagnation.--Natural selection becomes
more unsparing as we go higher.--Extinction.--Severity of the
struggle for life.--Environment one.--But lower animals come into
vital relation with but a small part of it.--It consists of a myriad
of forces, which, as acting on a given form, may be considered as
one grand resultant.--Environment is thus a power making at first
for digestion and reproduction, then for muscular strength and
activity, then for shrewdness, finally for unselfishness and
righteousness.--An ultimate "power, not ourselves, making for
righteousness," a personality.--Our knowledge of this personality
may be valid, even though very incomplete.--Religion.--Conformity to
the spiritual in or behind environment is likeness to God.--The
conservative tendency in evolution.


CHAPTER VII

CONFORMITY TO ENVIRONMENT

Human environment.--The development of the family as the school of
man's training.--The family as the school of unselfishness and
obedience.--The family as the basis of social life.--Society as an
aid to conformity to environment by increasing intelligence and
training conscience.--Mental and moral heredity.--Personal
magnetism.--Man's search for a king.--The essence of
Christianity.--Conformity to environment gives future supremacy, but
often at the cost of present hardship.--Conformity as obedience to
the laws of our being.--Environment best understood through the
study of the human mind.--Productiveness and prospectiveness of
vital capital.--Faith.


CHAPTER VIII

MAN

Composed of atoms and molecules, hence subject to chemical and
physical laws.--As a living being.--As an animal.--As a
vertebrate.--As a mammal.--As a social being.--As a personal and
moral being.--The conflict between the higher and the lower in
man.--As a religious being.--As hero.--He has not yet
attained.--Future man.--He will utilize all his powers, duly
subordinating the lower to the higher.--The triumph of the common
people.


CHAPTER IX

THE TEACHINGS OF THE BIBLE

Subject of the Bible.--_Man_: Body, intellect, heart.--_God_:
Law, sin, and penalty.--God manifested in Christ.--Salvation, the divine
life permeating man--Faith.--Prayer.--Hope.--The Church.--The
battle.--The victory.--The crown.


CHAPTER X

PRESENT ASPECTS OF THE THEORY OF EVOLUTION

The struggle for existence.--Natural selection.--Correlation of
organs.--Fortuitous variation.--Origin of the fittest.--Nägeli's
theory: Initial tendency supreme.--Weismann and the Neo-Darwinians:
Natural selection omnipotent.--The Neo-Lamarckians.--Comparison of
the Neo-Darwinian and the Neo-Lamarckian views.--"Individuality" the
controlling power throughout the life of the organism.--Transmission
of special effects of use and disuse.--Summary.


CHART SHOWING SEQUENCE OF ATTAINMENTS AND OF DOMINANT FUNCTIONS


PHYLOGENETIC CHART OF THE ANIMAL KINGDOM


INDEX





INTRODUCTION


In the year 1865 Professor Samuel Finley Breese Morse, to whom the
world is indebted for the application of the principles of
electro-magnetism to telegraphy, gave the sum of ten thousand
dollars to Union Theological Seminary to found a lectureship in
memory of his father, the Rev. Jedediah Morse, D.D., theologian,
geographer, and gazetteer. The subject of the lectures was to have
to do with "The relations of the Bible to any of the sciences." The
ten chapters of this book correspond to ten lectures, eight of which
were delivered as Morse Lectures at Union Theological Seminary
during the early spring of 1895. The first nine chapters appear in
form and substance as they were given in the lectures, except that
Chapters VI. and VII. were condensed in one lecture. Chapter X. is
new, and I have not hesitated to add a few paragraphs wherever the
argument seemed especially to demand further evidence or
illustration.

One of my friends, reading the title of these lectures, said: "Of
man's origin you know nothing, of his future you know less." I fear
that many share his opinion, although they might not express it so
emphatically.

It would seem, therefore, to be in order to show that science is now
competent to deal with this question; not that she can give a final
and conclusive answer, but that we can reach results which are
probably in the main correct. We may grant very cheerfully that we
can attain no demonstration; the most that we can claim for our
results will be a high degree of probability. If our conclusions are
very probably correct, we shall do well to act according to them;
for all our actions in life are suited to meet the emergencies of a
probable but uncertain course of events.

We take for granted the probable truth of the theory of evolution as
stated by Mr. Darwin, and that it applies to man as really as to any
lower animal. At the same time it concerns our argument but little
whether natural selection is "omnipotent" or of only secondary
importance in evolution, as long as it is a real factor, or which
theory of heredity or variation is the more probable.

If man has been evolved from simple living substance protoplasm, by
a process of evolution, it will some day be possible to write a
history of that process. But have we yet sufficient knowledge to
justify such an attempt?

Before the history of any period can be written its events must have
been accurately chronicled. Biological history can be written only
when the successive stages of development and the attainments of
each stage have been clearly perceived. In other words, the first
prerequisite would seem to be a genealogical[A] tree of the animal
kingdom. The means of tracing this genealogical tree are given in
the first chapter, and the results in the second, third, and fourth
chapters of this book.

  [Footnote A: See Phylogenetic Chart, p. 310.]

Now, for some of the ancestral stages of man's development a very
high degree of probability can be claimed. One of man's earliest
ancestors was almost certainly a unicellular animal. A little later
he very probably passed through a gastræa stage. He traversed fish,
amphibian, and reptilian grades. The oviparous monotreme and the
marsupial almost certainly represent lower mammalian ancestral
stages. But what kind of fish, what species of amphibian, what form
of reptiles most closely resembles the old ancestor? How did each of
these ancestors look? I do not know. It looks as if our ancestral
tree were entirely uncertain and we were left without any foundation
for history or argument.

But the history of the development of anatomical details, however
important and desirable, is not the only history which can be
written, nor is it essential. It would be interesting to know the
size of brain, girth of chest, average stature, and the features of
the ancient Greeks and Romans. But this is not the most important
part of their history, nor is it essential. The great question is,
What did they contribute to human progress?

Even if we cannot accurately portray the anatomical details of a
single ancestral stage, can we perhaps discover what function
governed its life and was the aim of its existence? Did it live to
eat, or to move, or to think? If we cannot tell exactly how it
looked, can we tell what it lived for and what it contributed to the
evolution of man?

Now, the sequence of dominant functions or aims in life can be
traced with far more ease and safety, not to say certainty, than one
of anatomical details. The latter characterize small groups, genera,
families, or classes; while the dominant function characterizes all
animals of a given grade, even those which through degeneration
have reverted to this grade.

Even if I cannot trace the exact path which leads to the
mountain-top, I may almost with certainty affirm that it leads from
meadow and pasture through forest to bare rock, and thence over snow
and ice to the summit; for each of these forms a zone encircling the
mountain. Very similarly I find that, whatever genealogical tree I
adopt, one sequence in the dominance of functions characterizes them
all; digestion is dominant before locomotion and locomotion before
thought.

And it is hardly less than a physiological necessity that it should
be so. The plant can and does exist, living almost purely for
digestion and reproduction, and the same is true of the lowest and
most primitive animals. A muscular system cannot develop and do its
work until some sort of a digestive system has arisen to furnish
nutriment, any more than a steam-engine can run without fuel. And a
brain is of no use until muscle and sense-organs have appeared.

This sequence of dominant functions,[A] of physiological dynasties,
would seem therefore to be a fact. And our series of forms described
in the second, third, and fourth chapters is merely a concrete
illustration showing how this sequence may have been evolved. The
substitution of other terms in the anatomical series there
described--amoeba, volvox, etc.--would not affect this result. By
a change in the form of our history we have eliminated to a large
extent the sources of uncertainty and error. And the dominant
function of a group throws no little light on the details of its
anatomy.

  [Footnote A: See condensed Chart of Development, etc., p. 309.]

If we can be satisfied that ever higher functions have risen to
dominance in the successive stages of animal and human development,
if we can further be convinced that the sequence is irreversible, we
shall be convinced that future man will be more and more completely
controlled by the very highest powers or aims to which this sequence
points. Otherwise we must disbelieve the continuity of history. But
the germs of the future are always concealed in the history of the
present. Hence--pardon the reiteration--if we can once trace this
sequence of dominant functions, whose evolution has filled past
ages, we can safely foretell something at least of man's future
development.

The argument and method is therefore purely historical. Here and
there we will try to find why and how things had to be so. But all
such digressions are of small account compared with the fact that
things were or are thus and so. And a mistaken explanation will not
invalidate the facts of history.

The subject of our history is the development, not of a single human
race nor of the movements of a century, but the development of
animal life through ages. And even if our attempts to decipher a few
pages here and there in the volumes of this vast biological history
are not as successful as we could hope, we must not allow ourselves
to be discouraged from future efforts. Even if our translation is
here and there at fault, we must never forget the existence of the
history. Some of the worst errors of biologists are due to their
having forgotten that in the lower stages the germs of the higher
must be present, even though invisible to any microscope. Our study
of the worm is inadequate and likely to mislead us, unless we
remember that a worm was the ancestor of man. And a biologist who
can tell us nothing about man is neglecting his fairest field.

Conversely history and social science will rest on a firmer basis
when their students recognize that many human laws and institutions
are heirlooms, the attainments, or direct results of attainments, of
animals far below man. We are just beginning to recognize that the
study of zoölogy is an essential prerequisite to, and firm
foundation for, that of history, social science, philosophy, and
theology, just as really as for medicine. An adequate knowledge of
any history demands more than the study of its last page. The
zoölogist has been remiss in not claiming his birthright, and in
this respect has sadly failed to follow the path pointed out by Mr.
Darwin.

For palæontology, zoölogy, history, social and political science,
and philosophy are really only parts of one great science, of
biology in the widest sense, in distinction from the narrower sense
in which it is now used to include zoölogy and botany. They form an
organic unity in which no one part can be adequately understood
without reference to the others. You know nothing of even a
constellation, if you have studied only one of its stars. Much less
can the study of a single organ or function give an adequate idea of
the human body.

Only when we have attained a biological history can we have any
satisfactory conception of environment. As we look about us in the
world, environment often seems to us to be a chaos of forces aiding
or destroying good and bad, fit and unfit, alike.

But our history of animal and human progress shows us successive
stages, each a little higher than the preceding, and surviving, for
a time at least, because more completely conformed to environment.
If this be true, and it must be true unless our theory of evolution
be false, higher forms are more completely conformed to their
environment than lower; and man has attained the most complete
conformity of all. Our biological history is therefore a record of
the results of successive efforts, each attaining a little more
complete conformity than the preceding. From such a history we ought
to be able to draw certain valid deductions concerning the general
character and laws of our environment, to discover the direction in
which its forces are urging us, and how man can more completely
conform to it.

If man is a product of evolution, his mental and moral, just as
really as his physical, development must be the result of such a
conformity. The study of environment from this standpoint should
throw some light on the validity of our moral and religious creeds
and theories. It would seem, therefore, not only justifiable, but
imperative to attempt such a study.

Our argument is not directly concerned with modern theories of
heredity, or variation, or with the "omnipotence" or secondary
importance of natural selection. And yet Nägeli, and especially
Weismann, have had so marked an influence on modern thought that we
cannot afford to neglect their theories. We will briefly notice
these in the closing chapter.




CHAPTER I

THE PROBLEM: THE MODE OF ITS SOLUTION


The story of a human life can be told in very few words. A youth of
golden dreams and visions; a few years of struggle or of neglected
opportunities; then retrospect and the end.

        "We come like water, and like wind we go."

But how few of the visions are realized. Faust sums up the whole of
life in the twice-repeated word _versagen_, renounce, and history
tells a similar story. Terah died in Haran; Abraham obtained but a
grave in the land promised him and his children; Jacob, cheated in
marriage, bitterly disappointed in his children, died in exile,
leaving his descendants to become slaves in the land of Egypt; and
Moses, their heroic deliverer, died in the mountains of Moab in
sight of the land which he was forbidden to enter. You may answer
that it is no injury that the promise is too large, the vision too
grand, to be fulfilled in the span of a single life, but must become
the heritage of a race. But what has been the history of Abraham's
descendants? A death-grapple for existence, captivity, and
dispersion. Their national existence has long been lost.

Was there ever a nation of grander promise than Greece or Rome? But
Greece died of premature old age, and Rome of rottenness begotten
of sin. But each of them, you will say, left a priceless heritage to
the immortal race. But if Greece and Rome and a host of older
nations, of which History has often forgotten the very name, have
failed and died, can anything but ultimate failure await the race?
Is human history to prove a story told by an idiot, or does it
"signify" something? Is the great march of humanity, which Carlyle
so vividly depicts, "from the inane to the inane, or from God to
God?"

This is the sphinx question put to every thinking man, and on his
answer hangs his life. For according to that answer, he will either
flinch and turn back, or expend every drop of blood and grain of
power in urging on the march.

To this question the Bible gives a clear and emphatic answer. "God
created man in his own image," and then, as if men might refuse to
believe so astounding a statement, it is repeated, "in the image of
God created he him." When, and by what mode or process, man was
created we are not told. His origin is condensed almost into a line,
his present and future occupy all the rest of the book. Whence we
came is important only in so far as it teaches us humility and yet
assures us that we may be Godlike because we are His handiwork and
children, "heirs of God and joint heirs with Christ of a heavenly
inheritance."

Now has Science any answer to this vital question? Perhaps. But this
much is certain; it can foretell the future only from the past. Its
answer to the question _whither_ must be an inference from its
knowledge as to _whence_ we have come. The Bible looks mainly at the
present and future; Science must at least begin with the study of
the past. The deciphering of man's past history is the great aim of
Biology, and ultimately of all Science. For the question of Man's
past is only a part of a greater question, the origin of all living
species.

We may say broadly that concerning the origin of species two
theories, and only two, seem possible. The first theory is that
every species is the result of an act of immediate creation. And
every true species, however slightly it may differ from its nearest
relative, represents such a creative act, and once created is
practically unchangeable. This is the theory of immutability of
species. According to the second theory all higher, probably all
present existing, species are only mediately the result of a
creative act. The first living germ, whenever and however created,
was infused with power to give birth to higher species. Of these and
their descendants some would continue to advance, others would
degenerate. Each theory demands equally for its ultimate explanation
a creative act; the second as much as, if not more than, the first.
According to the first theory the creative power has been
distributed over a series of acts, according to the second theory it
has been concentrated in one primal creation. The second is the
theory of the mutability of species, or, in general, of evolution,
but not necessarily of Darwinism alone.

The first theory is considered by many the more attractive and
hopeful. Now a theory need not be attractive, nor at first sight
appear hopeful, provided only it is true. But let me call your
attention to certain conclusions which, as it appears to me, are
necessarily involved in it. Its central thought is the practical
immutability of species. Each one of these lives its little span of
time, for species are usually comparatively short-lived, grows
possibly a very little better or worse, and dies. Its progress has
added nothing to the total of life; its degeneration harmed no one,
hardly even itself; it was doomed from the start. Progress there has
been, in a sense. The Creator has placed ever higher forms on the
globe. But all the progress lies in the gaps and distances between
successive forms, not in any advance made, or victory won, by the
species or individual. The most "aspiring ape," if ever there was
such a being, remains but an ape. He must comfort himself with the
thought that, while he and his descendants can never gain an inch,
the gap between himself and the next higher form shall be far
greater than that between himself and the lowest monkey.

And if this has been the history of thousands of other species, why
should it not be true of man also? Who can wonder that many who
accept this theory doubt whether the world is growing any better, or
whether even man will ever be higher and better than he now is?
Would it not be contrary to the whole course of past history, if you
can properly call such a record a history, if he could advance at
all? Now I have no wish to misrepresent this or any honestly
accepted theory, but it appears to me essentially hopeless, a record
not of the progress of life on the globe, but of a succession of
stagnations, of deaths. I can never understand why some very good
and intelligent people still think that the theory of the immediate
creation of each species does more honor to the Creator and his
creation than the theory of evolution. Evolution is a process, not
a force. The power of the Creator is equally demanded in both cases;
only it is differently distributed. And evolution is the very
highest proof of the wisdom and skill of the Creator. It elevates
our views of the living beings, must it not give a higher conception
of Him who formed them?

The plant in its first stages shows no trace of flowers, but of
leaves only. Later a branch or twig, similar in structure to all the
rest, shortens. The cells and tissues which in other twigs turn into
green leaves here become the petals and other organs of the rose or
violet. Let us suppose for a moment that every rose and violet
required a special act of immediate creation, would the springtime
be as wonderful as now? Would the rose or violet be any more
beautiful, or are they any less flowers because developed out of
that which might have remained a common branch? The plant at least
is glorified by the power to give rise to such beauty. And is not
the creation of the seed of a violet or rose something infinitely
grander than the decking of a flowerless plant with newly created
roses? The attainment of the highest and most diversified beauty and
utility with the fewest and simplest means is always the sign of
what we call in man "creative" genius. Is not the same true of God?
I think you all feel the force of the argument here.

There were at one time no flowering plants. The time came at last
for their appearance. Which is the higher, grander mode of producing
them, immediate creation of every flowering species, or development
of the flower out of the green leaves of some old club moss or
similar form? The latter seems to me at least by far the higher
mode. And to have created a ground-pine which could give rise to a
rose seems far more difficult and greater than to have created both
separately. It requires more genius, so to speak. It gives us a far
higher opinion of the ground-pine; does it disgrace the rose? We can
look dispassionately at plants. The rose is still and always a rose,
and the oak an oak, whatever its origin. And I believe that we shall
all readily admit that evolution is here a theory which does the
highest honor to the wisdom and power of the Creator. What if the
animal kingdom is continually blossoming in ever higher forms? Does
not the same reasoning hold true, only with added force? I firmly
believe that we should all unhesitatingly answer, yes, could we but
be assured that all men would everywhere and always believe that we,
men, were the results of an immediate creative act.

But why do we so strenuously object to the application to ourselves
of the theory of evolution? One or two reasons are easily seen. We
have all of us a great deal of innate snobbery, we would rather have
been born great than to have won greatness by the most heroic
struggle. But is man any less a man for having arisen from something
lower, and being in a fair way to become something higher? Certainly
not, unless I am less a man for having once been a baby. It is only
when I am unusually cross and irritable that I object to being
reminded of my infancy. But a young child does not like to be
reminded of it. He is afraid that some one will take him for a baby
still. And the snob is always desperately afraid that some one will
fail to notice what a high-born gentleman he is.

Now man can relapse into something lower than a brute; the only
genuine brute is a degenerate man. And we all recognize the strength
of tendencies urging us downward. Is not this the often unrecognized
kern of our eagerness for some mark or stamp that shall prove to all
that we are no apes, but men? It is not the pure gold that needs the
"guinea stamp." If we are men, and as we become men, we shall cease
to fear the theory of evolution. Now this is not the only, or
perhaps the greatest, objection which men feel or speak against the
theory. But I must believe that it has more weight with us than we
are willing to admit.

But some say that the theory of immediate creation and immutability
of species is the more natural and has always been accepted, while
the theory of evolution is new and very likely to be as short-lived
as many another theory which has for a time fascinated men only to
be forgotten or ridiculed.

But the idea of evolution is as old as Hindu philosophy. The old
Ionic natural philosophers were all evolutionists. So Aristophanes,
quoting from these or Hesiod concerning the origin of things, says:
"Chaos was and Night, and Erebus black, and wide Tartarus. No earth,
nor air nor sky was yet; when, in the vast bosom of Erebus (or
chaotic darkness) winged Night brought forth first of all the egg,
from which in after revolving periods sprang Eros (Love) the much
desired, glittering with golden wings; and Eros again, in union with
Chaos, produced the brood of the human race." Here the formative
process is a birth, not a creation; it is evolution pure and simple.
"According to the ancient view," says Professor Lewis, "the present
world was a growth; it was born, it came from something antecedent,
not merely as a cause but as its seed, embryo or principium.
Plato's world was a 'zoon,' a living thing, a natural production."

Furthermore, to the ancient writers of the Bible the idea of origin
by birth from some antecedent form--and this is the essential idea
of evolution--was perfectly natural. They speak of the "generations
of the heavens and the earth" as of the "generations" of the
patriarchs. The first book of the Bible is still called Genesis, the
book of births. The writer of the ninetieth Psalm says, "Before the
mountains were born, or ever thou hadst brought to birth the earth
and the world." And what satisfactory meaning can you give to the
words, "Let the earth bring forth," and "the earth brought forth,"
in immediate proximity to the words, "and God made," unless while
the ultimate source was God's creative power, the immediate process
of formation was one of evolution.

The Bible is big and broad enough to include both ideas, the human
mind is prone to overestimate the one or the other. Traces, at
least, of a similar mode of thought persisted by the Greek Fathers
of the Church, and disappeared, if ever, with the predominance of
Latin theology. To the oriental the idea of evolution is natural.
The earth is to him no inert, resistant clod; she brings forth of
herself.

But our ancestors lived on a barren soil beneath a forbidding sky.
They were frozen in winter and parched in summer. Nature was to them
no kind foster-mother, but a cruel stepmother, training them by
stern discipline to battle with her and the world. They peopled the
earth with gnomes and cobolds and giants, and their nymphs were the
Valkyre. Their God was Thor, of the thunderbolt and hammer, and who
yet lived in continual dread of the hostile powers of Nature. A
Norse prophet or prophetess standing beside Elijah at Horeb would
have bowed down before the earthquake or the fire; the oriental
waited for the "still small voice." And we are heirs to a Latin
theology grafted on to the Thor-worship of our pagan ancestors. The
idea of a Nature producing beneficently and kindly at the word of a
loving God is foreign to all our inherited modes of thought. And our
views of the heart of Nature are about as correct as those of our
ancestors were of God. A little more of oriental tendencies of
thought would harm neither our theology nor our life.

What, then, is the biblical idea of Nature? God speaks to the earth,
in the first chapter of Genesis, and the earth responds by "giving
birth" to mountains and living beings. It is evidently no mere
lifeless, inert clod, but pulsating with life and responsive to the
divine commands. While yet a chaos it had been brooded over by the
Divine Spirit. It is like the great "wheels within wheels," with
rings full of eyes round about, which Ezekiel saw in his vision by
the river Chebar. "When the living creatures went, the wheels went
by them; and when the living creatures were lifted up from the
earth, the wheels were lifted up. Whithersoever the spirit was to
go, they went, thither was their spirit to go; and the wheels were
lifted up over against them: for the spirit of the living creatures
(or of life) was in the wheels." And above the living creatures was
the firmament and the throne of God. So Nature may be material, but
it is material interpenetrated by the divine; if you call it a
fabric, the woof may be material but the warp is God. This view
contains all the truth of materialism and pantheism, and vastly
more than they, and it avoids their errors and omissions.

To the old metaphysical hypothesis of evolution Mr. Darwin gave a
scientific basis. It had always been admitted that species were
capable of slight variation and that this divergence might become
hereditary and thus perhaps give rise to a variety of the parent
species. But it was denied that the variation could go on increasing
indefinitely, it seemed soon to reach a limit and stop. Early in the
present century Lamarck had attempted to prove that by the use and
disuse of organs through a series of generations a great divergence
might arise resulting in new species. But the theory was crude,
capable at best of but limited application, and fell before the
arguments and authority of Cuvier. The times were not ripe for such
a theory. Some fifty years later, Mr. Darwin called attention to the
struggle for existence as a means of aggregating these slight
modifications in a divergence sufficient to produce new species,
genera, or families. His argument may be very briefly stated as
follows:

1. There is in Nature a law of heredity; like begets like.

2. The offspring is never exactly like the parent; and the members
of the second generation differ more or less from one another. This
is especially noticeable in domesticated plants and animals, but no
less true of wild forms. If the parent is not exactly like the other
members of the species, some of its descendants will inherit its
peculiarities enhanced, others diminished.

3. Every species tends to increase in geometrical progression. But
most species actually increase in number very slowly, if at all. Now
and then some insect or weed escapes from its enemies, comes under
favorable food conditions, and multiplies with such rapidity that it
threatens to ravage the country. But as it multiplies it furnishes
an abundance of food for the enemies which devour it, or of food and
place for the parasites in and upon it; and they increase with at
least equal rapidity. Hence while the vanguard increases
prodigiously in numbers, because it has outrun these enemies, the
rear is continually slaughtered. And thus these plagues seem in
successive generations to march across the continent.

And yet even they give but a faint idea of the reproductive powers
of plants and animals. The female fish produces often many
thousands, sometimes hundreds of thousands of eggs. Insects
generally from a hundred to a thousand. Even birds, slowly as they
increase, produce in a lifetime probably at least from twelve to
twenty eggs. Now let us suppose that all these eggs developed, and
all the birds lived out their normal period of life, and reproduced
at the same rate. After not many centuries there would not be
standing room on the globe for the descendants of a single pair.

Again, of the one hundred eggs of an insect let us suppose that only
sixty develop into the first larval, caterpillar, stage. Of these
sixty, the number of members of the species remaining constant, only
two will survive. The other fifty-eight die--of starvation,
parasites, or other enemies, or from inclement weather. Now which
two of all shall survive? Those naturally best able to escape their
enemies or to resist unfavorable influences; in a word, those best
suited to their conditions, or, to use Mr. Darwin's words,
"conformed to their environment."

Now if any individual has varied so as to possess some peculiarity
which enables it even in slight degree to better escape its enemies
or to resist unfavorable conditions, those of its descendants who
inherit most markedly this peculiar quality or variation will be the
most likely to escape, those without it to perish. If a form varies
unfavorably, becomes for instance more conspicuous to its enemies,
it will almost certainly perish. Thus favorable variations tend to
increase and become more marked from generation to generation.

Now it has always been known that breeders could produce a race of
markedly peculiar form or characteristics by selecting the
individuals possessing this quality in the highest degree and
breeding only from these. The breeder depends upon heredity,
variation, and his selection of the individuals from which to breed.
Similarly in nature new species have arisen through heredity,
variation, and a selection according to the laws of nature of those
varying in conformity with their environment. And this Mr. Darwin
called natural, in contrast with the breeder's artificial,
"selection," arising from the "struggle for existence," and
resulting in what Mr. Spencer has called the "survival of the
fittest."

Let us take a single illustration. Many of the species of beetles on
oceanic islands have very rudimentary wings, or none at all, and yet
their nearest relatives are winged forms on some neighboring
continent. Mr. Darwin would explain the origin of these evidently
distinct wingless species as follows: They are descended from winged
ancestors blown or otherwise transported thither from the
neighboring continent. But beetles are slow and clumsy fliers, and
on these wind-swept islands those which flew most would be blown out
to sea and drowned. Those which flew the least, and these would
include the individuals with more poorly developed wings, would
survive. There would thus be a survival in every generation of a
larger proportion of those having the poorest wings, and destruction
of those whose wings were strong, or whose habits most active. We
have here a natural selection which must in time produce a species
with rudimentary or aborted wings, just as surely as a human
breeder, by artificial selection can produce such an animal as a pug
or a poodle. These, like sin, are a human device; nature should not
be held responsible for them.

But you may urge that the variation which would take place in a
single generation would be, as a rule, too slight to be of any
practical value to the animal, and could not be fostered by natural
selection until greatly enhanced by some other means. Let us think a
moment. If ten ordinary men run in a foot-race, the two foremost may
lead by several feet. But if the number of runners be continually
increased the finish will be ever closer until finally but an atom
more wind or muscle or pluck would make all the difference between
winning and losing the prize.

Similarly the million or more young of any species of insect in a
given area may be said to run a race of which the prize is life, and
the losing of which means literally death. The competition is
inconceivably severe. How indefinitely slight will be the difference
between the poorest of the 2,000 or 20,000 survivors and the best
of the more than 900,000 which perish. The very slightest favorable
variation may make all the difference between life and sure death.
And yet these indefinitely slight variations continued and
aggregated through ages would foot up an immense total divergence.
The chalk cliffs of England have been built up of microscopic
shells.

I have tried to give you very briefly a sketch of the essential
points of Mr. Darwin's theory of evolution. But you should all read
that marvel of patience, industry, clear insight, close reasoning,
and grand honesty, the "Origin of Species." I have no time to give
the arguments in its favor or to attempt to meet the objections
which may arise in your minds. I ask you to believe only this much;
that the theory is accepted with practical unanimity by scientific
men because it, and it alone, furnishes an explanation for the facts
which they discover in their daily work. And this is the strongest
proof of the truth of any accepted theory.

Inasmuch as it is accepted by all scientists and largely by the
public, it is certainly worth your while to know whether it has any
bearing on the great moral and religious questions which you are
considering. And in these lectures I shall take for granted, what
some scientists still doubt, that man also is a product of
evolution. For the weight of evidence in favor of this view is
constantly increasing, and seems already to strongly preponderate.
Also I wish in these lectures to grant all that the most ardent
evolutionist can possibly claim. Not that I would lower man's
position, but I have a continually increasing respect for the
so-called "lower animals."

Now if the theory of evolution be true, and really only on this
condition, life has had a history; and human history began ages
before man's actual appearance on the globe, just as American
history began to be fashioned by Anglo-Saxons, Danes, and Normans
before they set foot even in England. We study history mainly to
deduce its laws; and that knowing them we may from the past forecast
the future, prepare for its emergencies, and avoid or wisely meet,
its dangers. And we rely on these laws of history because they are
the embodiment of ages of human experience.

Whatever be our system of philosophy we all practically rely on past
experience and observation. Fire burns and water drowns. This we
know, and this knowledge governs our daily lives, whatever be our
theories, or even our ignorance, of the laws of heat and
respiration. Now human history is the embodiment of the experience
of the race; and we study it in the full confidence that, if we can
deduce its laws, we can rely on racial experience certainly as
safely as on that of the individual. Furthermore, if we can discover
certain great movements or currents of human action or progress
moving steadily on through past centuries, we have full confidence
that these movements will continue in the future. The study of
history should make us seers.

But the line of human progress is like a mountain road, veering and
twisting, and often appearing to turn back upon itself, and having
many by-roads, which lead us astray. If we know but a few miles of
it we cannot tell whether it leads north or south or due west. But
if from any mountain-top we can gain a clear bird's-eye view of its
whole course, we easily distinguish the main road, its turns become
quite insignificant, we see that it leads as directly as any
engineering skill could locate it through the mountains to the
fertile plains and rich harvests beyond.

Now our knowledge of the history of man covers so brief a period
that we can scarcely more than hazard a guess as to the trend of
human progress. Many of the most promising social movements are like
by-roads which, at first less steep and difficult, end sooner or
later against impassable obstacles. And even if there be a main line
of march, advance seems to alternate with retreat, progress with
retrogression. To illustrate further, the great waves rush onward
only to fall back again, and we can hardly tell whether the tide is
flowing or ebbing.

Yet already certain tendencies appear fairly clear. Governments tend
to become democratic, if we define democracy as "any form of
government in which the will of the people finds sovereign
expression." The tendency of society seems to be toward furnishing
all its members equality of opportunity to make the most of their
natural endowments. But if we are convinced that these statements
express even vaguely the tendency of human development in all its
past history, we are confident that these tendencies will continue
in the future for a period somewhat proportional to their time of
growth in the past. If we are wise, we try to make our own lives and
actions, and those of our fellows, conform to and advance them.
Otherwise our lives will be thrown away.

But if the theory of evolution be true, human history is only the
last page of the one history of all life. If we are to gain any
adequate, true, extensive view of human progress, we must read more
than this. We must take into account the history of man when he was
not yet man. And if we believe in the future continuance of
tendencies of a few centuries' growth, we shall rest assured of the
permanence of tendencies which have grown and strengthened through
the ages.

Our confidence in the results of historical study is therefore
proportioned to the extent and thoroughness of the experience which
they record, and to the time during which these laws can be proven
to have held good. If I can make it even fairly probable that these
laws, on obedience to which human progress and success seem to
depend, are merely quoted from a grander code applicable to all life
in all times, your confidence in them will be even greater. I trust
I can prove to you that the animal kingdom has not drifted aimlessly
at the mercy of every wind and tide and current of circumstance. I
hope to show that along one line it has from the beginning through
the ages held a steady course straight onward, and that deviation
from this course has always led to failure or degeneration. From so
vast a history we may hope to deduce some of the great laws of true
success in life. Furthermore, if along this central line, at the
head of which man stands, there always has been progress, we cannot
doubt that future progress will be as certain, and perhaps far more
rapid. In all the struggle of life we shall have the sure hope of
success and victory; if not for ourselves still for those who shall
come after us. "We are saved by hope." And we may be confident that
this hope will never make us ashamed.

Finally, even from our present knowledge of the past progress of
life we shall hope to catch hints at least that man's only path to
his destined goal is the straight and narrow road pointed out in the
Bible. If in this we are even fairly successful we shall find a
relation and bond between the Bible and Science worthy of all
consideration. And this is the only agreement which can ever satisfy
us.

If I wished to bring before you a view of the development of man, I
should best choose individuals or families from various periods of
human history from the earliest times down to the present. I should
try to tell you how they looked and lived. But if anyone should
attempt to condense into three lectures such a history of even one
line of the human race, you would probably think him insane. Even if
he succeeded in giving a fairly clear view of the different stages,
the successive stages would be so remote from one another, such vast
changes would necessarily remain unnoticed or unexplained that you
would hardly believe that they could have any genetic relation or
belong to one developmental series.

But the history which I must attempt to condense for you is measured
by ages, and the successive terms of the series will be indefinitely
more remote from each other than the life and thoughts of Lincoln or
Washington from those of our most primitive Aryan ancestor or of the
rudest savage of the Stone Age. The series must appear exceedingly
disconnected. Systems of organs will apparently spring suddenly into
existence, and we shall have no time to trace their origin or
earlier development. Even if we had an abundance of time many gaps
would still remain; for the forms, which according to our theory
must have occupied their place, have long since disappeared and
left no trace nor sign. We have generally no conception at all of
the amount of extermination and degeneration which have taken place
in past ages.

I grant frankly that I do not believe that the forms which I have
selected represent exactly the ancestors of man. They have all been
more or less modified. I claim only that in the balance and relative
development of their organic systems--muscular, digestive, nervous,
etc.--they give us a very fair idea of what our ancestor at each
stage must have been. But it is on this balance and relative
development of the different systems, that is, whether an animal is
more reproductive, digestive, or nervous, that my argument will in
the main be based.

But if the older ancestors have so generally disappeared, and their
surviving relatives have been so greatly modified, how can we make
even a shrewd guess at the ancestry of higher forms? The genealogy
of the animal kingdom has been really the study of centuries,
although the earlier zoölogists did not know that this was to be the
result of their labors. The first work of the naturalist was
necessarily to classify the plants and animals which he found, and
catalogue and tabulate them so that they might be easily recognized,
and that later discovered forms might readily find a place in the
system. Hypotheses and theories were looked upon with suspicion.
"Even Linnæus," says Romanes, "was express in his limitations of
true scientific work in natural history to the collecting and
arranging of species of plants and animals." The question, "What is
it?" came first; then, "How did it come to be what it is?" We are
just awakening to the question, "Why this progressive system of
forms, and what does it all mean?"

Let us experiment a little in forming our own classification of a
few vertebrates. We see a bat flying through the air. We mistake it
for a bird. But a glance at it shows that it is a mammal. It is
covered with hair. It has fore and hind legs. Its wings are
membranes stretched between the fingers and along the sides of the
body. It has teeth. It suckles its young. In all these respects it
differs from birds. It differs from mammals only in its wings. But
we remember that flying squirrels have a membrane stretching along
the sides of the body and serving as a parachute, though not as
wings. We naturally consider the wings as a sort of after-thought
superinduced on the mammalian structure. We do not hesitate to call
it a mammal.

The whale makes us more trouble; it certainly looks remarkably like
a fish. But the fin of its tail is horizontal, not vertical. Its
front flippers differ altogether from the corresponding fins of
fish; their bones are the same as those occurring in the forelegs of
mammals, only shorter and more crowded together. Later we find that
it has lungs, and a heart with four chambers instead of only two, as
in fish. The vertebræ of its backbone are not biconcave, but flat in
front and behind. And, finally, we discover that it suckles its
young. It, too, is in all its deep-seated characteristics a mammal.
It is fish-like only in characteristics which it might easily have
acquired in adaptation to its aquatic life. And there are other
aquatic mammals, like the seals, in which these characteristics are
much less marked. Their adaptation has evidently not gone so far.

Now the first attempts resulted in artificial classifications, much
like our grouping of bats with birds and whales with fish. All
animals, like coral animals and starfishes, whose similar parts were
arranged in lines radiating from a centre, were united as radiates,
however much they might differ in internal structure and grade of
organization. But this radiate structure proved again to be largely
a matter of adaptation.

Practically all animals having a heavy calcareous shell were grouped
with the snails and oysters as mollusks. But the barnacle did not
fit well with other mollusks. Its shell was entirely different. It
had several pairs of legs; and no mollusk has legs. The barnacle is
evidently a sessile crab or better crustacean. Its molluscan
characteristics were only skin-deep, evidently an adaptation to a
mode of life like that of mollusks. The old artificial systems were
based too much on merely external characteristics, the results of
adaptation. When the internal anatomy had been thoroughly studied
their groups had to be rearranged.

Reptiles and amphibia were at first united in one class because of
their resemblance in external form. Our common salamanders look so
much like lizards that they generally pass by this name. But the
young salamander, like all amphibia, breathes by gills, its skeleton
differs greatly from, and is far weaker than, that of the lizard,
and there are important differences in the circulatory and other
systems. Moreover, practically all amphibia differ from all reptiles
in these respects. Evidently the fact that the alligator and many
snakes and turtles (of which neither the young nor the embryos ever
breathe by gills) live almost entirely in the water, is no better
reason for classifying these with amphibia than to call a whale a
fish, and not a mammal, because of its form and aquatic life.

When the comparative anatomy of fish, amphibia, and reptiles had
been carefully studied it was evident that the amphibia stood far
nearer the fish in general structure, while the higher reptiles
closely approached birds. Then it was noticed that our common fish
formed a fairly well-defined group, but that the ganoids, including
the sturgeons, gar-pikes, and some others, had at least traces of
amphibian characteristics. Such generalized forms, with the
characteristics of the class less sharply marked, were usually by
common consent placed at the bottom of the class. And this suited
well their general structure, while in particular characteristics
they were often more highly organized than higher groups of the same
class.

The palæontologist found that the oldest fossil forms belonged to
these generalized groups, and that more highly specialized
forms--that is, those in which the special class distinctions were
more sharply and universally marked--were of later geological
origin. Thus the oldest fish were most like our present ganoids and
sharks, though differing much from both. Our common teleost fish,
like perch and cod, appeared much later. The oldest bird, the
archæopteryx, had a long tail like that of a lizard, and teeth; and
thus stood in many respects almost midway between birds and
reptiles. And most of the earliest forms were "comprehensive,"
uniting the characteristics of two or more later groups. Thus as the
classification became more natural, based on a careful comparison of
the whole anatomy of the animals, its order was found to coincide in
general with that of geological succession.

Then the zoölogist began to ask and investigate how the animal grew
in the egg and attained its definite form. And this study of
embryology brought to light many new and interesting facts. Agassiz
especially emphasized and maintained the universality of the fact
that there was a remarkable parallelism between embryos of later
forms and adults of old or fossil groups. The embryos of higher
forms, he said, pass through and beyond certain stages of structure,
which are permanent in lower and older members of the same group.

You remember that the fin on the tail of a fish is as a rule
bilobed. Now the backbone of a perch or cod ends at a point in the
end of the tail opposite the angle between the two lobes, without
extending out into either of them. In the shark it extends almost to
the end of the upper lobe. Now we have seen that sharks and ganoids
are older than cod. In the embryo of the cod or perch the backbone
has, at an early stage, the same position as in the shark or ganoid;
only at a later stage does it attain its definite position.

So Agassiz says the young lepidosteus (a ganoid fish), long after it
is hatched, exhibits in the form of its tail characters thus far
known only among the fossil fishes of the Devonian period. The
embryology of turtles throws light upon the fossil chelonians. It is
already known that the embryonic changes of frogs and toads coincide
with what is known of their succession in past ages. The
characteristics of extinct genera of mammals exhibit everywhere
indications that their living representatives in early life resemble
them more than they do their own parents. A minute comparison of a
young elephant with any mastodon will show this most fully, not only
in the peculiarities of their teeth, but even in the proportion of
their limbs, their toes, etc. It may therefore be considered as
a general fact that the phases of development of all living
animals correspond to the order of succession of their extinct
representatives in past geological times. The above statements are
quoted almost word for word from Professor Agassiz's "Essay on
Classification." The larvæ of barnacles and other more degraded
parasitic crustacea are almost exactly like those of Crustacea in
general. The embryos of birds have a long tail containing almost or
quite as many vertebræ as that of archæopteryx. But most of these
never reach their full development but are absorbed into the pelvis,
or into the "ploughshare" bone supporting the tail feathers. Thus
older forms may be said to have retained throughout life a condition
only embryonic in their higher relatives. And the natural
classification gave the order not only of geological succession but
also of stages of embryonic development. Thus the system of
classification improved continually, although more and more
intermediate forms, like archæopteryx, were discovered, and certain
aberrant groups could find no permanent resting-place.

But why should the generalized comprehensive forms stand at the
bottom rather than the top of the systematic arrangement of their
classes? Why should the system of classification coincide with the
order of geologic occurrence, and this with the series of embryonic
stages? Above all, why should the embryos of bird and perch form
their tails by such a roundabout method? Why should the embryo of
the bird have the tail of a lizard? No one could give any
satisfactory explanation, although the facts were undoubted.

Mr. Darwin's theory was the one impulse needed to crystallize these
disconnected facts into one comprehensible whole. The connecting
link was everywhere common descent, difference was due to the
continual variation and divergence of their ancestors. The
classification, which all were seeking, was really the ancestral
tree of the animal kingdom. Forms more generalized should be placed
lower down on the ancestral tree, and must have had an earlier
geological occurrence because they represented more nearly the
ancestors of the higher. But this explains also the facts of
embryonic development.

According to Mr. Darwin's theory all the species of higher animals
have developed from unicellular ancestors. It had long been known
that all higher forms start in life as single cells, egg and
spermatozoon. And these, fused in the process of fertilization, form
still a single cell. And when this single cell proceeds through
successive embryonic stages to develop into an adult individual it
naturally, through force of hereditary habit, so to speak, treads
the same path which its ancestors followed from the unicellular
condition to their present point of development. Thus higher forms
should be expected to show traces of their early ancestry in their
embryonic life. Older and lower adult forms should represent
persistent embryonic stages of higher. It could not well be
otherwise.

But the path which the embryo has to follow from the egg to the
adult form is continually lengthening as life advances ever higher.
From egg to sponge is, comparatively speaking, but a step; it is a
long march from the egg to the earthworm; and the vertebrate embryo
makes a vast journey. But embryonic life is and must remain short.
Hence in higher forms the ancestral stages will often be slurred
over and very incompletely represented. And the embryo may, and
often does, shorten the path by "short-cuts" impossible to its
original ancestor. Still it will in general hold true, and may be
recognized as a law of vast importance, that any individual during
his embryonic life repeats very briefly the different stages through
which his ancestors have passed in their development since the
beginning of life. Or, briefly stated, ontogenesis, or the embryonic
development of the individual, is a brief recapitulation of
phylogenesis, or the ancestral development of the phylum or group.

The illustration and proof of this law is the work of the
embryologist. We have time to draw only one or two illustrations
from the embryonic development of birds. We have already seen that
the embryonic bird has the long tail of his reptilian ancestor. In
early embryonic life it has gill-slits leading from the pharynx to
the outside of the neck like those through which the water passes in
the respiration of fish. The Eustachian tube and the canal of the
external ear of man, separated only by the "drum," are nothing but
such an old persistent gill-slit. No gills ever develop in these,
but the great arteries run to them, and indeed to all parts of the
embryo, on almost precisely the same general plan as in the adult
fish. Only later is the definite avian circulation gradually
acquired.

This law is even more strikingly illustrated in the embryonic
development of the vertebral column and skull, if we had time to
trace their development. And the development of the excretory system
points to an ancestor far more primitive than even the fish. Our
embryonic development is one of the very strongest evidences of our
lowly origin.

Thus we have three sources of information for the study of animal
genealogy. First, the comparative anatomy of all the different
groups of animals; second, their comparative embryology; and third,
their palæontological history. Each source has its difficulties or
defects. But taken all together they give us a genealogical tree
which is in the main points correct, though here and there very
defective and doubtful in detail. The points in which we are left
most in doubt in regard to each ancestor are its modes of life and
locomotion, and body form. But these may temporarily vary
considerably without affecting to any great extent the general plan
of structure and the line of development of the most important
deep-seated organs.

I have chosen a line composed of forms taken from the comparative
anatomical series. All such present existing forms have probably
been modified during the lapse of ages. But I shall try to tell you
when they have diverged noticeably from the structure of the
primitive ancestor of the corresponding stage. It is much safer for
us to study concrete, actual forms than imaginary ones, however real
may have been the former existence of the latter. And, after all,
their lateral divergence is of small account compared with the great
upward and onward march of life, to the right and left of which they
have remained stationary or retrograded somewhat, like the tribes
which remained on the other side of Jordan and never entered the
Promised Land.

To recapitulate: Our question is the Whence and the Whither of man.
To this question the Bible gives a clear and definite answer. Can
Science also give an answer, and is this in the main in accord with
the answer of Scripture? Science can answer the question only by the
historical method of tracing the history of life in the past and
observing the goal toward which it tends. If the evolution theory be
true, the record of human achievement and progress forms only one
short chapter in the history of the ages. If from the records of
man's little span of life on the globe we can deduce laws of history
on whose truth we can rely, with how much greater confidence and
certainty may we rely on laws which have governed all life since its
earliest appearance?--always provided that such can be found.

Our first effort must therefore be to trace the great line of
development through a few of its most characteristic stages from the
simplest living beings up to man. This will be our work in the three
succeeding lectures. And to these I must ask you to bring a large
store of patience. Anatomical details are at best dry and
uninteresting. But these dry facts of anatomy form the foundation on
which all our arguments and hopes must rest.

But if you will think long and carefully even of anatomical facts,
you will see in and behind them something more and grander than
they. You will catch glimpses of the divinity of Nature. Most of us
travel threescore years and ten stone-blind in a world of marvellous
beauty. Why does the artist see so much more in every fence-corner
and on every hill-side than we, set face to face with the grandest
landscapes? Primarily, I believe, because he is sympathetic, and
looks on Nature as a comrade as near and dear as any human sister
and companion. As Professor Huxley has said, "they get on rarely
together." She speaks to the artist; to us she is dumb, and ought to
be, for we are boorishly careless of her and her teachings.

Nature, to be known, must be loved. And though you have all the
knowledge of a von Humboldt, and do not love her, you will never
understand her or her teachings. You will go through life with her,
and yet parted from her as by an adamantine wall.

I do not suppose that the author of the book of Job had ever studied
geology, or mineralogy, or biology, but read him, and see whether
this old prince of scientific heroes had loved, and understood, and
caught the spirit of Nature. And what a grand, free spirit it was,
and what a giant it made of him. I do not believe that Paul ever had
a special course of anatomy or botany. But if he had not pondered
long and lovingly on the structure of his body, and the germination
of the seed, he never could have written the twelfth and fifteenth
chapters of the first letter to the Corinthians. And time fails to
speak of David and all the writers of the Psalms, and of those
heroic souls misnamed the "Minor" Prophets.

Study the teachings of our Lord. How he must have considered the
lilies of the field, and that such a tiny seed as that of the
mustard could have produced so great an herb, and noticed and
thought on the thorns and the tares and the wheat, and watched the
sparrows, and pondered and wondered how the birds were fed. All his
teaching was drawn from Nature. And all the study in the world could
never have taught him what he knew, if it had not been a loving and
appreciative study.

There is one strange and interesting passage in John's Gospel, xv.
1: "I am the true vine." My father used to tell us that the Greek
word [Greek: alêthinê], rendered true, is usually employed of the
genuine in distinction from the counterfeit, the reality in
distinction from the shadow and image. Is not this perhaps the clew
to our Lord's use of natural imagery? Nature was always the
presentation to his senses of the divine thought and purpose. He
studied the words of the ancient Scripture, he found the same words
and teachings clearly and concretely embodied in the processes of
Nature. The interpretation of the Parable of the Sower was no mere
play of fancy to him; it was the genuine and fundamental truth,
deeper and more real than the existence of the sower, the soil, and
the seed. The spiritual truth was the substance; the tangible soil
and seed really only the shadow. And thus all Nature was to him
divine.

We all of us need to offer the prayer of the blind man, "Lord, that
our eyes may be opened." Let us learn, too, from the old heathen
giant, Antæus, who, after every defeat and fall, rose strengthened
and vivified from contact with his mother Earth. You will experience
in life many a desperate struggle, many a hard fall. There is at
such times nothing in the world so strengthening, healing, and
life-giving as the thoughts and encouragements which Nature pours
into the hearts and minds of her loving disciples. She will set you
on your feet again, infused with new life, filled with an
unconquerable spirit, with unfaltering courage, and an iron will to
fight once more and win. In every battle her inspiring words will
ring in your ears, and she will never fail you. We may not see her
deepest realities, her rarest treasures of thought and wisdom; but
if we will listen lovingly for her voice, we may be assured that she
will speak to us many a word of cheer and encouragement, of warning
and exhortation. For, to paraphrase the language of the nineteenth
Psalm, "She has no speech nor language, her voice is not heard. But
her rule is gone out throughout all the earth, and her words to the
end of the world."




CHAPTER II

PROTOZOA TO WORMS: CELLS, TISSUES, AND ORGANS


The first and lowest form in our ancestral series is the amoeba, a
little fresh-water animal from 1/500 to 1/1000 of an inch in
diameter. Under the microscope it looks like a little drop of
mucilage. This semifluid, mucilaginous substance is the Protoplasm.
Its outer portion is clear and transparent, its inner more granular.
In the inner portion is a little spheroidal body, the nucleus. This
is certainly of great importance in the life of the animal; but just
what it does, or what is its relation to the surrounding protoplasm
we do not yet know. There is also a little cavity around which the
protoplasm has drawn back, and on which it will soon close in again,
so that it pulsates like a heart. It is continually taking in water
from the body, or the outside, and driving it out again, and thus
aids in respiration and excretion. The animal has no organs in the
proper sense of the word, and yet it has the rudiments of all the
functions which we possess.

A little projection of the outer, clearer layer of protoplasm, a
pseudopodium, appears; into this the whole animal may flow and thus
advance a step, or the projection may be withdrawn. And this power
of change of form is a lower grade of the contractility of our
muscular cells. Prick it with a needle and it contracts. It
recognizes its food even at a microscopic distance; it appears
therefore to feel and perceive. Perhaps we might say that it has a
mind and will of its own. It is safer to say that it is irritable,
that is, it reacts to stimuli too feeble to be regarded as the cause
of its reaction. It engulfs microscopic plants, and digests them in
the internal protoplasm by the aid of an acid secretion. It breathes
oxygen, and excretes carbonic acid and urea, through its whole body
surface. Its mode of gaining the energy which it manifests is
therefore apparently like our own, by combustion of food material.

  [Illustration: 1. AMOEBA PROTEUS. HERTWIG, FROM LEIDY.
  _ek_, ectosarc; _en_, endosarc; _N_, food particles;
  _n_, nucleus; _cv_, contractile vesicle.]

It grows and reaches a certain size, then constricts itself in the
middle and divides into two. The old amoeba has divided into two
young ones, and there is no parent left to die, and death, except by
violence, does not occur. But this absence of death in other rather
distant relatives of the amoeba, and probably in the amoeba
itself, holds true only provided that, after a series of
self-divisions, reproduction takes place after another mode. Two
rather small and weak individuals fuse together in one animal of
renewed vigor, which soon divides into two larger and stronger
descendants. We have here evidently a process corresponding to the
fertilization of the egg in higher animals; yet there is no egg,
spermatozoon, or sex.

It is a little mass of protoplasm containing a nucleus, and
corresponds, therefore, to one of the cells, most closely to the
egg-cell or spermatozoon of higher animals. If every living being is
descended from a single cell, the fertilized egg, it is not hard to
believe that all higher animals are descended from an ancestor
having the general structure or lack of structure of the amoeba.

But is the amoeba really structureless? Probably it has an
exceedingly complex structure, but our microscopes and technique are
still too imperfect to show more than traces of it. Says Hertwig:
"Protoplasm is not a single chemical substance, however complicated,
but a mixture of many substances, which we must picture to ourselves
as finest particles united in a wonderfully complicated structure."
Truly protoplasm is, to borrow Mephistopheles' expression concerning
blood, a "quite peculiar juice." And the complexity of the nucleus
is far more evident than that of the protoplasm. Is protoplasm
itself the result of a long development? If so, out of what and how
did it develop? We cannot even guess. But the beginning of life may,
apparently must, have been indefinitely farther back than the
simplest now existing form. The study of the amoeba cannot fail to
raise a host of questions in the mind of any thoughtful man.

As we have here the animal reduced, so to speak, to lowest terms, it
may be well to examine a little more closely into its physiology and
compare it briefly with our own.

The amoeba eats food as we do, but the food is digested directly
in the internal protoplasm instead of in a stomach; and once
digested it diffuses to all parts of the cell; here it is built up
into compounds of a more complex structure, and forms an integral
part of the animal body. The dead food particle has been transformed
into living protoplasm, the continually repeated miracle of life.
But it does not remain long in this condition. In contact with the
oxygen from the air it is soon oxidized, burned up to furnish the
energy necessary for the motion and irritability of the body. We are
all of us low-temperature engines. The digestive function exists in
all animals merely to bring the food into a soluble, diffusible
form, so that it can pass to all parts of the body and be used for
fuel or growth. In our body a circulatory system is necessary to
carry food and oxygen to the cells and to remove their waste. For
most of our cells lie at a distance from the stomach, lungs, and
kidney. But in a small animal the circulatory system is often
unnecessary and fails. Breathing and excretion take place through
the whole surface of the body. The body of the frog is devoid of
scales, so that the blood is separated from the surrounding water
only by a thin membrane, and it breathes and excretes to a certain
extent in the same way.

But another factor has to be considered. If we double each dimension
of our amoeba, we shall increase its surface four times, its mass
eight-fold. Now the power of absorbing oxygen and excreting waste is
evidently proportional to the excretory and respiratory surface, and
much the same is true of digestion. But the amount of oxygen
required, and of waste to be removed is proportional to the mass;
for every particle of protoplasm requires food and oxygen, and
produces waste. The particles of protoplasm in our new, larger
amoeba can therefore receive only half as much oxygen as before,
and rid themselves of their waste only half as fast. There is
danger of what in our bodies would be called suffocation and
blood-poisoning. The amoeba having attained a certain size meets
this emergency by dividing into two small individuals, the division
is a physical adaptation. But the many-celled animal cannot do this;
it must keep its cells together. It gains the additional surface by
folding and plaiting. And the complicated internal structure of
higher animals is in its last analysis such a folding and plaiting
in order to maintain the proper ratio between the exposed surface of
the cells and their mass. And each cell in our bodies lives in one
sense its own individual life, only bathed in the lymph and
receiving from it its food and oxygen instead of taking it from the
water.

But in another sense the cells of our body live an entirely
different life, for they form a community. Division of labor has
taken place between them, they are interdependent, correlated with
one another, subject therefore to the laws of the whole community or
organism. There are many respects in which it is impossible to
compare Robinson Crusoe with a workman in a huge watch factory; yet
they are both men.

Both the amoeba and we live in the closest relation to our
environment, and conformity to it is evidently necessary: life has
been defined as the adjustment of internal relations to external
conditions. We continually take food, use it for energy and growth,
and return the simpler waste compounds. We are all of us, as
Professor Huxley has said, "whirlpools on the surface of Nature;"
when the whirl of exchange of particles ceases we die. We have seen
that the fusion of two amoebæ results in a new rejuvenated
individual. Why is a mixture of two protoplasms better than one? We
can frame hypotheses; we know nothing about it. What of the mind of
the amoeba? A host of questions throng upon us and we can answer
no one of them. All the great questions concerning life confront us
here in the lowest term of the animal series, and appear as
insoluble as in the highest.

Our second ancestral form is also a fresh-water animal, the hydra.
This is a little, vase-shaped animal, which usually lives attached
to grass-stems or sticks, but has the power to free itself and hang
on the surface of the water or to slowly creep on the bottom. The
mouth is at the top of the vase, and the simple, undivided cavity
within the vase is the digestive cavity. Around the mouth is a ring
of from four to ten hollow tentacles, whose cavities communicate
freely underneath with the digestive cavity. Not only is food taken
in at the mouth, but indigestible material is thrown out here. The
animal may thus be compared to a nearly cylindrical sack with a
circle of tubes attached to it above. The body consists of two
layers of cells, the ectoderm on the outside and the entoderm lining
the digestive cavity. Between these two is a structureless, elastic
membrane, which tends to keep the body moderately expanded.

The food is captured by the tentacles; but digestion takes place
only partially in the digestive cavity, for each surrounding cell
engulfs small particles of food and digests them within itself. The
entodermal cells behave in this respect much like a colony of
amoebæ. The cells of both layers have at their bases long muscular
fibrils, those of the ectodermal cells running longitudinally, those
of the entoderm transversely. The animal can thus contract its body
in both directions, or, if the body contain water and the transverse
muscles are contracted, the pressure of the water lengthens the body
and tends to extend the tentacles.

On the outside of the elastic membrane, just beneath the ectoderm,
is a plexus or cobweb of nervous cells and fibrils. As in every
nervous system, three elements are here to be found. 1. An afferent
or sensory nerve-fibril, which under adequate stimulus is set in
vibration by some cell of the epidermis or ectoderm, which is
therefore called a sensory cell. 2. A central or ganglion
cell, which receives the sensory impulse, translates it into
consciousness, and is the seat of whatever powers of perception,
thought, or will the animal possesses. This also gives rise to the
efferent or motor impulses, which are conveyed by (3) a motor fibril
to the corresponding muscle, exciting its contraction. But there are
also nerve-fibrils connecting the different ganglion cells, so that
they may act in unison. In the higher animals we shall find these
central or ganglion cells condensed in one or a few masses or
ganglia. But here they are scattered over the whole surface of the
elastic supporting membrane.

The reproductive organs for the production of eggs and spermatozoa
form little protuberances on the outside of the body below the
tentacles. But hydra reproduces mostly by budding; new individuals
growing out of the side of the old one, like branches from the trunk
of a tree, but afterward breaking free and leading an independent
life. There are special forms of cells besides those described;
nettle cells for capturing food, interstitial cells, etc., but these
do not concern us.

The distance from the single-celled amoeba to hydra is vast,
probably really greater than that between any other successive terms
of our series. It may therefore be useful to consider one or two
intermediate forms and the parallel embryonic stages of higher
animals, and to see how the higher many-celled animal originates
from the unicellular stage.

The amoeba is an illustration of a great kingdom of similar,
practically unicellular forms, which have played no unimportant part
in the geological history of the globe. These are the protozoa. They
include, first of all, the foraminifera, which usually have shells
composed of carbonate of lime. These shells, settling to the bottom
of the ocean, have accumulated in vast beds, and when compacted and
raised above the surface, form chalk, limestone, or marble,
according to the degree and mode of their hardening.

The protozoa include also the flagellata, a great, very poorly
defined mass of forms occupying the boundary between the plant and
animal kingdoms. They are usually unicellular, and their protoplasm
is surrounded by a thin, structureless membrane. This prevents their
putting out pseudopodia as organs of motion. Instead of these they
have at one end of the ovoid or pear-shaped body a long,
whiplash-like process or thread, a flagellum, and by swinging this
they propel themselves through the water. These flagellata seem to
have a rather marked tendency to form colonies. The first individual
gives rise to others by division. But the division is not complete;
the new individuals remain connected by the undivided rear end of
the body. And such a colony may come to contain a large number of
individuals.

  [Illustration: 2. MAGOSPHÆRA PLANULA. LANG, FROM HAECKEL.]

Such a colony is represented by magosphæra. This is a microscopic
globular form, discovered by Professor Haeckel on the coast of
Norway. It consists of a large number of conical or pear-shaped
individual cells, whose apices are turned toward the centre of the
sphere. The cells are cemented together by a mucilaginous substance.
Around their exposed larger ends, which form the surface of the
sphere, are rows of flagella, by whose united action the colony
rolls through the water. After a time each individual absorbs its
flagella, the colony is broken up, the different individuals settle
to the bottom, and each gives rise by division to a new colony. This
group of cells may be considered as a colony or as an individual.
Each term is defensible.

Volvox is also a spheroidal organism, composed often of a very large
number of flagellated cells. But it differs from magosphæra in
certain important respects. In the first place its cells have
chlorophyl, the green coloring matter of plants. It lives therefore
on unorganized fluid nourishment, carbon dioxide, nitrates, etc. It
is a plant. But certain characteristics render it probable that it
once lived on solid food and was therefore an animal. For where
almost the sole difference between plants and animals is in the
fluid or solid character of their food, a change from the one form
into the other is not as difficult or improbable as one might
naturally think. And plants and animals are here so near together,
and travelling by roads so nearly parallel, that, even if volvox
never was an animal, it might still serve very well to illustrate a
stage through which animals must have passed.

The cells of volvox do not form a solid mass, but have arranged
themselves in a single layer on the outer surface of the sphere. For
a time, under favorable circumstances, volvox reproduces very much
like magosphæra, and each cell can give rise to a new, many-celled
individual. But after a time, especially under unfavorable
circumstances, a new mode of reproduction appears. Certain cells
withdraw from the outer layer into the interior of the colony. Here
they are nourished by the other cells and develop into true
reproductive elements, eggs and spermatozoa. Fertilization, that is,
the union of egg and spermatozoon, or mainly of their nuclei, takes
place; and the fertilized egg develops into a new organism. But the
other cells, which have been all the time nourishing these, seem now
to lack nutriment, strength, or vitality to give rise to a new
colony. They die.

We find thus in volvox division of labor and corresponding
difference of structure or differentiation; certain cells retain the
power of fusing with other corresponding cells, and thus of
rejuvenescence and of giving rise to a new organism. And these
cells, forming a series through all generations, are evidently
immortal like the protozoa. Natural death cannot touch them. These
are the reproductive cells. The other cells nourish and transport
them and carry on the work of excretion and respiration. These
latter correspond practically to our whole body. We call them
somatic cells. In volvox they are entirely subservient to, and exist
for, the reproductive cells, and die when they have completed their
service of these. The body is here only a vehicle for ova.
Furthermore, in volvox there has arisen such an interdependence of
cells that we can no longer speak of it as a colony. The colony has
become an individual by division of labor and the resulting
differentiation in structure.

But hydra gives us but a poor idea of the coelenterata, to which
kingdom it belongs. The higher coelenterata have nearly or quite
all the tissues of higher animals--muscular, connective, glandular,
etc. And by tissues we mean groups of cells modified in form and
structure for the performance of a special work or function. The
protozoa developed the cell for all time to come, the coelenterata
developed the tissues which still compose our bodies. But they had
them mainly in a diffuse form. A sort of digestive and reproductive
system they did possess. But the work of arranging these tissues and
condensing them into compact organs was to be done by the next
higher group, the worms.

Let us now take a glance at certain stages of embryonic development
which correspond to these earliest ancestral forms. We should expect
some such correspondence from the fact already stated that the
embryonic development of the individual is a brief recapitulation of
the ancestral development of the species or larger group. The egg of
the lowest vertebrate, amphioxus, shows these changes in a simple
and apparently primitive form.

  [Illustration: 3. IMMATURE EGG-SHELL FROM OVARY OF ECHINODERM.
  HATSCHEK, FROM HERTWIG.]

The fertilized egg of any animal consists of a single cell, a little
mass of protoplasm containing a nucleus and surrounded by a
structureless membrane. The egg is globular. The nucleus undergoes
certain very peculiar, still but little understood, changes and
divides into two. The protoplasm also soon divides into two masses
clustering each around its own nucleus. The plane of division will
be marked around the outside by a circular furrow, but the cells
will still remain united by a large part of the membrane which
bounds their adjacent, newly formed, internal faces.

Let us suppose that the egg lay so that the first plane of division
was vertical and extending north and south. Each cell or half of the
egg will divide into two precisely as before. The new plane of
division will be vertical, but extending east and west. Each plane
passes through the centre of the egg, and the four cells are of the
same form and size, like much-rounded quarters of an orange. The
third plane will lie horizontal or equatorial, and will divide each
of these quarters into an upper and lower octant. The cells keep on
dividing rapidly, the eight form sixteen, then thirty-two, etc. The
sharp angle by which the cells met at the centre has become rounded
off, and has left a little space, the segmentation cavity, filled
with fluid in the middle of the embryo. The cells continue to press
or be crowded away from the centre and form a layer one cell deep on
the surface of the sphere.

This embryo, resembling a hollow rubber ball filled with fluid, is
called a blastosphere. It corresponds in structure with the fully
developed volvox, except, of course, in lacking reproductive cells.

  [Illustration: 4. GASTRULA. HATSCHEK, FROM HERTWIG.
  Outer layer is the ectoderm; inner layer, the entoderm; internal
  cavity, the archenteron; mouth of cavity, blastopore.]

If the rubber ball has a hole in it so that I can squeeze out the
water, I can thrust the one-half into the other, and change the ball
into a double-walled cup. A similar change takes place in the
embryo. The cells of the lower half of the blastosphere are slightly
larger than those of the upper half. This lower hemisphere flattens
and then thrusts itself, or is invaginated, into the upper
hemisphere of smaller cells and forms its lining. This cup-shaped
embryo is called the gastrula. The cup deepens somewhat and becomes
ovoid. Take a boiled egg, make a hole in the smaller end and remove
the yolk, and you have a passable model of a gastrula. The shell
corresponds to the ectoderm or outer layer of smaller cells; the
layer of "white" represents the entoderm or lining of larger cells.
The space occupied by the yolk corresponds to the archenteron or
primitive digestive cavity; and the opening at the end to the
primitive mouth or blastopore. Ectoderm and entoderm unite around
the mouth. Both the blastosphere and gastrula often swim freely by
flagella.

You can hardly have failed to notice how closely the gastrula
corresponds to a hydra, and many facts lead us to believe that the
still earlier ancestor of the hydra was free swimming, and that the
tentacles are a later development correlated with its adult sessile
life. Yet we must not forget that the hydra is even now not quite
sessile, it moves somewhat. And our ancestor was almost certainly a
free swimming gastræa, or hypothetical form corresponding in form
and structure to the gastrula. The ancestor of man never settled
down lazily into a sessile life.

But how is an adult worm or vertebrate formed out of such a
gastrula? To answer this would require a course of lectures on
embryology. But certain changes interest us. Between the ectoderm
and entoderm of the gastrula, in the space occupied by the
supporting membrane of hydra, a new layer of cells, the mesoderm,
appears. This has been produced by the rapid growth and reproduction
of certain cells of the entoderm which have migrated, so to speak,
into this new position. In higher forms it becomes of continually
greater importance, until finally nearly all the organs of the body
develop from it. In our bodies only the lining of the mid-intestine
and of its glands has arisen from the entoderm. And only the
epidermis, or outer layer of our skin, and the nervous system and
parts of our sense-organs have arisen from the ectoderm. But our
mid-intestine is still the greatly elongated archenteron of the
gastrula.

We may therefore compare the hydra or gastrula to a little portion
of the lining of the human mid-intestine covered with a little flake
of epidermis. This much the hydra has attained. But our bones and
muscles and blood-vessels all come from the mesoderm by folding,
plaiting, and channelling, and division of labor resulting in
differentiation of structure. Of all true mesodermal structures the
hydra has actually none, but in the ectodermal and entodermal cells
he has the potentiality of them all. We must now try to discover how
these potentialities became actualities in higher forms.

The third stage in our ancestral series is the turbellarian. This is
a little, flat, oval worm, varying greatly in size in different
species, and found both in fresh and salt water. Some would deny
that this worm belonged in our series at all. But, while doubtless
considerably modified, it has still retained many characteristics
almost certainly possessed by our primitive bilateral ancestor. The
different parts of hydra were arranged like those of most flowers,
around one main vertical axis; it was thus radiate in structure,
having neither front nor rear, right nor left side. But our little
turbellaria, while still without a head, has one end which goes
first and can be called the front end. The upper or dorsal surface
is usually more colored with pigment cells than the lower or ventral
surface, on which is the mouth. It has also a right and left side.
It is thus bilateral.

The gastræa swam by cilia, little eyelash-like processes which urge
the animal forward like a myriad of microscopic oars. In our bodies
they are sometimes used to keep up a current, _e.g._, to remove
foreign particles from the lungs. The turbellaria is still covered
with cilia, probably an inheritance from the gastræa; for, while in
smaller forms they may still be the principal means of locomotion,
in larger ones the muscles are beginning to assume this function and
the animal moves by writhing. The bilateral symmetry has arisen in
connection with this mode of locomotion and is thus a mark of
important progress.

In the turbellaria we find for the first time a true body-wall
distinct from underlying organs. The outer layer of this is a
ciliated epithelium or layer of cells. Under this an elastic
membrane may occur. Then come true body muscles, running
transversely, longitudinally and dorso-ventrally. Between the
external transverse and the internal longitudinal layers we often
find two muscular layers whose fibres run diagonally. The body is
well provided with muscles, but their arrangement is still far from
economical or effective.

Within the body-wall is the parenchym. This is a spongy mass of
connectile tissue in which the other organs are embedded. The mouth
lies in the middle, or near the front of the ventral surface. The
intestine varies in form, but is provided with its own layers of
longitudinal and transverse muscles, and usually has paired pouches
extending out from it into the body parenchym. These seem to
distribute the dissolved nutriment; hence the whole cavity is still
often called a gastro-vascular cavity as serving both digestion and
circulation. There is no anal opening, but indigestible material is
still cast out through the mouth.

The animal can gain sufficient oxygen to supply its muscles and
nerves, which are the principal seats of combustion, through the
external surface. It has, therefore, no special respiratory organs.
But the waste matter of the muscles cannot escape so easily, for
these are becoming deeper seated. Hence we find an excretory system
consisting of two tubes with many branches in the parenchym, and
discharging at the rear end of the body. This again is a sign that
the muscles are becoming more important, for the excretory system is
needed mainly to remove their waste. These tubes maybe only greatly
enlarged glands of the skin.

  [Illustration: 5. TURBELLARIAN. LANG.
  _va_ and _ha_, front and rear branches of gastro-vascular cavity;
  _ph_, pharynx. The dark oval with fine branches represents the
  nervous system.]

The nervous system consists of a plexus of fibres and cells, the
cells originating impulses and the fibres conveying them. But this
much was present in hydra also. Here the front end of the body goes
foremost and is continually coming in contact with new conditions.
Here the lookout for food and danger must be kept. Hence, as a
result of constant exercise, or selection, or both, the
nerve-plexus has thickened at this point into a little compact mass
of cells and fibres called a ganglion. And because this ganglion
throughout higher forms usually lies over the oesophagus, it is
called the supra-oesophogeal ganglion. This is the first faint and
dim prophecy of a brain, and it sends its nerves to the front end of
the body. But there run from it to the rear end of the body four to
eight nerve-cords, consisting of bundles of nerve-threads like our
nerves, but overlaid with a coating of ganglion cells capable of
originating impulses. These cords are, therefore, like the plexus
from which they have condensed, both nerves and centres;
differentiation has not gone so far as at the front of the body.
Sense organs are still very rudimentary. Special cells of the skin
have been modified into neuro-epithelial cells, having sensory hairs
protruding from them and nerve-fibrils running from their bases.

  [Illustration: 6. CROSS-SECTION OF TURBELLARIAN. HATSCHEK, FROM
  JIJIMA.
  _e_, external skin; _rm_, lateral muscles; _la_ and _li_,
  longitudinal muscles; _mdv_, dorso-ventral muscles; _pa_,
  parenchyma; _h_, testicle; _ov_, oviduct; _dt_, yolk-gland; _n_,
  ventral nerve; _i_, gastro-vascular cavity.]

In a very few turbellaria we find otolith vesicles. These are
little sacks in the skin, lined with neuro-epithelial cells and
having in the middle a little concretion of carbonate of lime hung
on rather a stiffer hair, like a clapper in a bell. Such organs
serve in higher animals as organs of hearing, for the sensory hairs
are set in vibration by the sound-waves. It is quite as probable
that they here serve as organs for feeling the slightest vibrations
in the surrounding water, and thus giving warning of approaching
food or danger. The animal has also eyes, and these may be very
numerous. They are not able to form images of external objects, but
only of perceiving light and the direction of its source. A little
group of these eyes lies directly over the brain, near the front end
of the body; the others are distributed around the front or nearly
the whole margin of the body.

The turbellaria, doubtless, have the sense of smell, although we can
discover no special olfactory organ. This sense would seem to be as
old as protoplasm itself.

This distribution of the eyes around a large portion of the margin,
and certain other characteristics of the adult structure and of the
embryonic development, are very interesting, as giving hints of the
development of the turbellaria from some radiate ancestor. The mouth
is in a most unfavorable position, in or near the middle of the
body, rarely at the front end, as the animal has to swim over its
food before it can grasp it. The animal only slowly rids itself of
old disadvantageous form and structure and adapts itself completely
to a higher mode of life.

By far the most highly developed system in the body is the
reproductive. It is doubtful whether any animal, except, perhaps,
the mollusk, has as complicated and highly developed reproductive
organs. By markedly higher forms they certainly grow simpler.

And here we must notice certain general considerations. We found
that reproduction in the amoeba could be defined as growth beyond
the limit normal to the individual. This form of growth benefits
especially the species. The needs and expenses of the individual
will therefore first be met and then the balance be devoted to
reproduction. Now the income of the animal is proportional to its
surface, its expense to its mass, and activity. And the ratio of
surface to mass is most favorable in the smallest animals.[A] Hence,
smaller animals, as a rule, increase faster than larger ones; and
this is only one illustration of the fact that great size in an
animal is anything but an unmixed advantage to its possessor. But
muscles and nerves are the most expensive systems; here most of the
food is burned up. Hence energetic animals have a small balance
remaining. Now the turbellarian is small and sluggish, with a fair
digestive system. With a great amount of nutriment at its disposal
the reproductive system came rapidly to a high development, and
relatively to other organs stands higher than it almost ever will
again.

  [Footnote A: Cf. p. 35.]

It is only fair to state that good authorities hold that so
primitive an animal could not originally have had so highly
developed a system, and that this characteristic must be acquired,
not ancestral.

That certain portions of it may be later developments may be not
only possible but probable. But anyone who has carefully studied the
different groups of worms, will, I think, readily grant that in the
stage of these flat worms reproduction was the dominant function,
which had most nearly attained its possible height of development.
From this time on the muscular and nervous systems were to claim an
ever-increasing share of the nutriment, and the balance for
reproduction is to grow smaller.

At the close of this lecture I wish to describe very briefly a
hypothetical form. It no longer exists; perhaps it never did. But
many facts of embryology and comparative anatomy point to such a
form as a very possible ancestor of all forms higher than flat
worms, viz., mollusks, arthropods, and vertebrates.

It was probably rather long and cylindrical, resembling a small
and short earthworm in shape. The skin may have been much like
that of turbellaria. Within this the muscles run in only
two-directions--longitudinally and transversely. Between these and
the intestine is a cavity--the perivisceral cavity--like that of our
own bodies, but filled with a nutritive fluid like our lymph. This
cavity seems to have developed by the expansion and cutting off of
the paired lateral outgrowths of the digestive system of some old
flat worm. But other modes of development are quite possible. The
intestine has now an anal opening at or near the rear end of the
body. The food moves only from front to rear, and reaches each part
always in a certain condition. Digestion proper and absorption have
been distributed to different cells, and the work is better done.
Three portions can be readily distinguished: fore-intestine with the
mouth, mid-intestine, as the seat of digestion and absorption, and
hind-intestine, or rectum, with the anal opening. The front and
hind-intestine are lined with infolded outer skin.

The nervous system consists of a supra-oesophageal ganglion with
four posterior nerve-cords--one dorsal, two lateral, and one (or
perhaps two) ventral. There were probably also remains of the old
plexus, but this is fast disappearing. The excretory system consists
of a pair of tubes discharging through the sides of the body-wall,
and having each a ciliated, funnel-shaped opening in the
perivisceral cavity. These have received the name of nephridia.
Through these also the eggs and spermatozoa are discharged. The
reproductive organs are modified patches of the peritoneum, or
lining of the perivisceral cavity.

The number of muscles or muscular layers has been reduced in this
animal. But such a reduction in the number of like parts in any
animal is a sign of progress. And the longitudinal muscles have
increased in size and strength, and the animal moves by writhing.
Such a worm has the general plan of the body of the higher forms
fairly well, though rudely, sketched. Many improvements will come,
and details be added. But the rudiments of the trunk of even our own
bodies are already visible. Head, in any proper sense of the term,
and skeleton are still lacking; they remain to be developed.

And yet, taking the most hopeful view possible concerning the animal
kingdom, its prospects of attaining anything very lofty seem at this
point poor. Its highest representative is a headless trunk, without
skeleton or legs. It has no brain in any proper sense of the word,
its sense-organs are feeble; it moves by writhing. Its life is
devoted to digestion and reproduction. Whatever higher organs it has
are subsidiary to these lower functions. And yet it has taken ages
on ages to develop this much. If _this_ is the highest visible
result of ages on ages of development, what hope is there for the
future? Can such a thing be the ancestor of a thinking, moral,
religious person, like man? "That is not first which is spiritual,
but that which is natural (animal, sensuous); and afterward that
which is spiritual." First, in order of time, must come the body,
and then the mind and spirit shall be enthroned in it. The little
knot of nervous material which forms the supra-oesophageal
ganglion is so small that it might easily escape our notice; but it
is the promise of an infinite future. The atom of nervous power
shall increase until it subdues and dominates the whole mass.




CHAPTER III

WORMS TO VERTEBRATES: SKELETON AND HEAD


In tracing the genealogy of any American family it is often
difficult or impossible to say whether a certain branch is descended
from John Oldworthy or his cousin or second cousin. In the latter
cases to find the common ancestor we must go back to the grandfather
or great-grandfather. The same difficulty, but greatly enhanced,
meets us when we try to make a genealogical tree of the animal
kingdom. Thus it seems altogether probable that all higher forms are
descended from an ancestor of the same general structure and grade
of organization as the turbellaria, although probably free swimming,
and hence with somewhat different form and development, especially
of the muscular system. It seems to me altogether probable that all,
except possibly Mollusca, are descended from a common ancestor
closely resembling the schematic worm last described. Some would,
however, maintain that they diverged rather earlier than even the
turbellaria; others after the schematic worm, if such ever existed.
As far as our argument is concerned it makes little difference which
of these views we adopt.

From our turbellaria, or possibly from some even more primitive
ancestor, many lines diverged. And this was to be expected. The
coelenterata, as we saw in hydra, had developed rude digestive and
reproductive systems. The higher groups of this kingdom had
developed all, or nearly all, the tissues used in building the
bodies of higher animals--muscular, reproductive, connectile,
glandular, nervous, etc. But these are mostly very diffuse. The
muscular fibrils of a jelly-fish are mostly isolated or parallel in
bands, rarely in compact well-defined bundles. The tissues have
generally not yet been moulded into compact masses of definite form.
There are as yet very few structures to which we can give the name
of organs. To form organs and group them in a body of compact
definite form was the work pre-eminently of worms. The material for
the building was ready, but the architecture of the bilateral animal
was not even sketched. And different worms were their own
architects, untrammelled by convention or heredity, hence they built
very different, sometimes almost fantastic, structures.

We must remember, too, the great age of this group. They are present
in highly modified forms in the very oldest palæozoic strata, and
probably therefore came into existence as the first traces of
continental areas were beginning to rise above the primeval ocean.
They are literally "older than the hills." They were exposed to a
host of rapidly changing conditions, very different in different
areas. This prepares us for the fact that the worms represent a
stage in animal life corresponding fairly well to the Tower of Babel
in biblical history. The animal kingdom seems almost to explode into
a host of fragments. Our genealogical tree fairly bristles with
branches, but the branches do not seem to form any regular whorls or
spirals. Few of them have developed into more than feeble growths.
They now contain generally but few species. Many of them are
largely or entirely parasitic, and in connection with this mode of
life have undergone modifications and degeneration which make it
exceedingly difficult to decipher their descent or relationships.

Four of these branches have reached great prominence in numbers and
importance. One or two others were formerly equally numerous and
have since become almost extinct; so the brachiopoda, which have
been almost entirely replaced by mollusks. The same may very
possibly be true of others. For of the amount of extinction of
larger groups we have generally but an exceedingly faint conception.
Indeed in this respect the worms have been well compared to the
relics which fill the shelves of one of our grandmother's
china-closets.

The four great branches are the echinoderms, mollusks, articulates,
and vertebrates. The echinoderms, including starfishes, sea-urchins,
and others straggled early from the great army. We know as yet
almost nothing of their history; when deciphered it will be as
strange as any romance. The vertebrates are of course the most
important line, as including the ancestors of man. But we must take
a little glance at mollusks, including our clams, snails, and
cuttle-fishes; and at the articulates, including annelids and
culminating in insects. The molluscan and articulate lines, though
divergent, are of great importance to us as throwing a certain
amount of light on vertebrate development; and still more as showing
how a certain line of development may seem, and at first really be,
advantageous, and still lead to degeneration, or at best to but
partial success.

When we compare the forms which represent fairly well the direction
of development of these three lines, a snail or a clam with an
insect and a fish, we find clearly, I think, that the fundamental
anatomical difference lies in the skeleton; and that this resulted
from, and almost irrevocably fixed, certain habits of life.

We may picture to ourselves the primitive ancestor of mollusks as a
worm having the short and broad form of the turbellaria, but much
thicker or deeper vertically. A fuller description can be found in
the "Encyclopædia Britannica," Art., Mollusca. It was hemi-ovoid in
form. It had apparently the perivisceral cavity and nephridia of the
schematic worm, and a circulatory system. In this latter respect it
stood higher than any form which we have yet studied. Its nervous
system also was rather more advanced. It had apparently already
taken to a creeping mode of life and the muscles of its ventral
surface were strongly developed, while its exposed and far less
muscular dorsal surface was protected by a cap-like shell covering
the most important internal organs. But the integument of the whole
dorsal surface was, as is not uncommon in invertebrates, hardening
by the deposition of carbonate of lime in the integument. And this
in time increased to such an extent as to replace the primitive,
probably horny, shell.

Into the anatomy of this animal or of its descendants we have no
time to enter, for here we must be very brief. We have already
noticed that the most important viscera were lodged safely under the
shell. And as these increased in size or were crowded upward by the
muscles of the creeping disk, their portion of the body grew upward
in the form of a "visceral hump." Apparently the animal could not
increase much in length and retain the advantage of the protection
of the shell; and the shell was the dominating structure. It had
entered upon a defensive campaign. Motion, slow at the outset,
became more difficult, and the protection of the shell therefore all
the more necessary. The shell increased in size and weight and
motion became almost impossible. The snail represents the average
result of the experiment. It can crawl, but that is about all; it is
neither swift nor energetic. Even the earthworm can outcrawl it. It
has feelers and eyes, and is thus better provided with sense-organs
than almost any worm. It has a supra-oesophageal ganglion of fair
size.

The clams and oysters show even more clearly what we might call the
logical results of molluscan structure. They increased the shell
until it formed two heavy "valves" hanging down on each side of the
body and completely enclosing it. They became almost sessile, living
generally buried in the mud and gaining their food, consisting
mostly of minute particles of organic matter, by means of currents
created by cilia covering the large curtain-like gills. Their
muscular system disappeared except in the ploughshare-shaped "foot"
used mostly for burrowing, and in the muscles for closing the shell.
That portion of the body which corresponds to the head of the snail
practically aborted with nearly all the sense-organs. The nervous
system degenerated and became reduced to a rudiment. They had given
up locomotion, had withdrawn, so to speak, from the world; all the
sense they needed was just enough to distinguish the particles of
food as they swept past the mouth in the current of water. They have
an abundance of food, and "wax fat." The clam is so completely
protected by his shell and the mud that he has little to fear from
enemies. They have increased and multiplied and filled the mud.
"Requiescat in pace."

But zoölogy has its tragedies as well as human history. Let us turn
to the development of a third molluscan line terminating in the
cuttle-fishes. The ancestors of these cephalopods, although still
possessed of a shell and a high visceral hump, regained the swimming
life. First, apparently, by means of fins, and then by a simple but
very effective use of a current of water, they acquired an often
rapid locomotion. The highest forms gave up the purely defensive
campaign, developed a powerful beak, led a life like that of the old
Norse pirates, and were for a time the rulers and terrors of the
sea. With their more rapid locomotion the supra-oesophageal
ganglion reached a higher degree of development, and it was served
by sense-organs of great efficiency. They reduced the external
shell, and succeeded, in the highest forms, of almost ridding
themselves of this burden and encumbrance. Traces of it remain in
the squids, but transformed into an internal quill-like, supporting,
not defensive, skeleton. They have retraced the downward steps of
their ancestors as far as they could. And the high development of
their supra-oesophageal ganglion and sense-organs, and their
powerful jaws and arms, or tentacles, show to what good purpose they
have struggled. But the struggle was in vain, as far as the
supremacy of the animal kingdom was concerned. Their ancestors had
taken a course which rendered it impossible for their descendants to
reach the goal. Their progress became ever slower. They were
entirely and hopelessly beaten by the vertebrates. They struggled
hard, but too late.

The history of mollusks is full of interest. They show clearly how
intimately nervous development is connected with the use of the
locomotive organs. The snail crept, and slightly increased its
nervous system and sense-organs. The clam almost lost them in
connection with its stationary life. The cephalopods were
exceedingly active, developed, therefore, keen sense-organs and a
very large and complicated supra-oesophagal ganglion, which we
might almost call a brain.

The articulate series consists of two groups of animals. The higher
group includes the crabs, spiders, thousand-legs, and finally the
insects, and forms the kingdom of arthropoda. The lower members are
still usually reckoned as worms, and are included under the
annelids. Of these our common earthworm is a good example, and near
them belong the leeches. But the marine annelids, of which nereis,
or a clam-worm, is a good example, are more typical. They are often
quite large, a foot or even more in length. They are composed of
many, often several hundred, rings or segments. Between these the
body-wall is thin, so that the segments move easily upon each other,
and thus the animal can creep or writhe.

These segments are very much alike except the first two and the
last. If we examine one from the middle of the body we shall find
its structure very much like that of our schematic worm. Outside we
find a very thin, horny cuticle, secreted by the layer of cells just
beneath it, the hypodermis. Beneath the skin we find a thin layer of
transverse muscles, and then four heavy bands of longitudinal
muscles. These latter have been grouped in the four quadrants, a
much more effective arrangement than the cylindrical layer of the
schematic worm. Furthermore, the animal has on each segment a pair
of fin-like projections, stiffened with bristles, the parapodia.
These are moved by special muscles and form effective organs of
creeping.

  [Illustration: 7. EUNICE LIMOSA (ANNELID). LANG, FROM EHLERS.
  Front and hind end seen from dorsal surface.
  _fa, fp, fc_, feelers; _a_, eye; _k_, gill;
  _p_, parapodia; _ac_, anal cirri.]

Within the muscles is the perivisceral cavity, and in its central
axis the intestine, segmented like the body-wall. The reproductive
organs are formed from patches of the lining of the perivisceral
cavity, and the reproductive elements, when fully developed, fall
into the perivisceral fluid and are carried out by nephridia, just
such as we found in the schematic worm. Beside the perivisceral
cavity and its fluid there is a special circulatory system. This
consists mainly of one long tube above the intestine and a second
below, with often several smaller parallel tubes. Transverse
vessels run from these to all parts of the body. The dorsal tube
pulsates and thus acts as a heart. The surface of the body no longer
suffices to gather oxygen, hence we find special feathery gills on
the parapodia. But these gills are merely expanded portions of the
body wall, arranged so as to offer the greatest possible amount of
surface where the capillaries of the blood system can be almost
immediately in contact with the surrounding water.

  [Illustration: 8. CROSS-SECTION OF BODY SEGMENT OF ANNELID. LANG.
  _dp_ and _vp_, dorsal and ventral halves of parapodia; _b_ and _ac_,
  bristles; _k_, gill; _dc_ and _vc_, feelers; _rm_, lateral muscles;
  _lm_, longitudinal muscles; _vd_, dorsal blood-vessel; _vo_, ventral
  blood-vessel; _bm_, ventral ganglion; _ov_, ovary; _tr_, opening of
  nephridium in the perivisceral cavity; _np_, tubular portion of
  nephridium. The circles containing dots represent eggs floating in
  the perivisceral fluid.]

The nervous system consists of a large supra-oesophageal ganglion
in the first segment; then of a chain of ganglia, one to each
segment, on the ventral side of the body. With one ganglion in each
segment there is far more controlling, perceptive, ganglionic
material than in lower worms. Furthermore the supra-oesophageal
ganglion is relieved of a large part of the direct control of the
muscles of each segment, and is becoming more a centre of control
and perception for the body as a whole. It is more like our brain,
commander-in-chief, the other ganglia constituting its staff. The
sense-organs have improved greatly. There are tentacles and otolith
vesicles as very delicate organs of feeling, or possibly of hearing
also.

But the annelids were probably the first animals to develop an eye
capable of forming an image of external objects. The importance of
this organ in the pursuit of food or the escape from enemies can
scarcely be over-estimated. The lining of the mouth and pharynx can
be protruded as a proboscis, and drawn back by powerful muscles, and
is armed with two or more horny claws. Eyes and claws gave them a
great advantage over their not quite blind but really visionless and
comparatively defenceless neighbors, and they must have wrought
terrible extinction of lower and older forms. But while we cannot
over-estimate the importance of these eyes, we can easily exaggerate
their perfectness. They were of short range, fitted for seeing
objects only a few inches distant, and the image was very imperfect
in detail. But the plan or fundamental scheme of these eyes is
correct and capable of indefinitely greater development than the
organs of touch or smell, perhaps greater even than the otolith
vesicle.

And the reflex influence of the eye on the brain was the greatest
advantage of all. Hitherto with feeble muscles and sense-organs it
has hardly paid the animal to devote more material to building a
larger brain. It was better to build more muscle. But now with
stronger muscles at its command, and better sense-organs to report
to it, every grain of added brain material is beginning to be worth
ten devoted to muscle. The muscular system will still continue to
develop, but the brain has begun an almost endless march of
progress. The eye becomes of continually increasing advantage and
importance because it has a capable brain to use it; and brain is a
more and more profitable investment, because it is served by an
ever-improving eye.

  [Illustration: 9. MYRMELEO FORMICARIUS. ANT-LION. HERTWIG, FROM
  SCHMARDA.
  1, adult; 2, larva; 3, cocoon.]

The annelid had hit upon a most advantageous line of development,
which led ultimately to the insect. The study of the insect will
show us clearly the advantages and defects of the annelid plan.
First of all, the insect, like the mollusk, has an external
skeleton. But the skeleton of the mollusk was purely protective, a
hindrance to locomotion. That of the insect is still somewhat
protective, but is mainly, almost purely, locomotive. It is never
allowed to become so heavy as to interfere with locomotion. In the
second place, the insect has three body regions, having each its own
special functions or work. And one of these is a head. The annelid
had two anterior segments differing from those of the rest of the
body; these may, perhaps, be considered as the foreshadowings of a
structure not yet realized; they can only by courtesy be called a
head. Thirdly, the insect has legs. The annelid had fin-like
parapodia, approaching the legs of insects about as closely as the
fins of a fish approach the legs of a mammal. The reproductive and
digestive systems, while somewhat improved, are not very markedly
higher than those of annelids. The excretory system has more work to
perform and reaches a rather higher development.

But in these organs there is no great or striking change; the time
for marked and rapid development of the digestive and reproductive
systems has gone by. Material can be more profitably invested in
brain or muscle. Air is carried to all parts of the body by a
special system of air-sacks and tubes. This is a very advantageous
structure for small animals with an external skeleton. In very large
animals, or where the skeleton is internal, it would hardly be
practicable; the risk of compression of the tubes at some point, and
of thus cutting off the air-supply of some portion of the body,
would be altogether too great.

The circulatory system is very poor. It consists practically only of
a heart, which drives the blood in an irregular circulation between
the other organs of the body much as with a syringe you might keep
up a system of currents in a bowl of water. But the rapidity of the
flow of the blood in our bodies is mainly to furnish a supply of
oxygen to the organs. A tea-spoonful of blood can carry a fair
amount of dissolved solid nutriment like sugar, it can carry at each
round but a very little gas like oxygen. Hence the blood must make
its rounds rapidly, carrying but a little oxygen at each circuit.
But in the insect the blood conveys only the dissolved solid
nutriment, the food; hence a comparatively irregular circulation
answers all purposes.

The skeleton is a thickening of the horny cuticle of the annelid on
the surface of each segment. The horny cylinder surrounding each
segment is composed of several pieces, and on the abdomen these are
united by flexible, infolded membranes. This allows the increase in
the size of the segment corresponding to the varying size of the
digestive and reproductive systems. In this part of the body the
skeletal ring of each segment is joined to that of the segments
before and behind it in the same manner. But in other parts of the
body we shall find the skeletal pieces of each segment and the rings
of successive segments fused in one plate of mail. The legs are the
parapodia of annelids carried to a vastly higher development. They
are slender and jointed, and yet often very powerful. A large
portion of the muscular system of the body is attached to these
appendages.

But the insect has also jaws. The annelid had teeth or claws
attached to the proboscis. But true jaws are something quite
different. They always develop by modifying some other organ. In the
insect they are modified legs. This is shown first by their
embryonic development. But the king- or horseshoe-crab has still no
true jaws, but uses the upper joints of its legs for chewing. There
are primitively three pairs of jaws of various forms for the
different kinds of food of different species or higher groups. But
some of them may disappear and the others be greatly modified into
awls for piercing, or a tube for sucking honey. Into the wonderful
transformations of these modified legs we cannot enter.

The muscles are no longer arranged to form a sack as in annelids.
Transverse muscles, running parallel to the unyielding plates of
chitin or horn could accomplish nothing. They have largely
disappeared. The work of locomotion has been transferred from the
trunk to the legs.

The abdomen of the insect is as clearly composed of distinct
segments as the body of the annelid. Of these there are perhaps
typically eleven. The thorax is composed of three segments, distinct
in the lowest forms, fused in the highest. This fusion of segments
in the thorax of the highest forms furnishes a very firm framework
for the attachment of wings and muscles. These wings are a new
development, and how they arose is still a question. But they give
the insect the capability of exceedingly rapid locomotion.

The three pairs of jaws, modified legs, in the rear half of the head
show that this portion is composed of three segments. For only one
pair of legs is ever developed on a single segment. Embryology has
shown that the portion of the head in front of the mouth is also
composed of three segments. Possibly between the præ- and post-oral
portions still another segment should be included, making a total of
seven in the head. The head has thus been formed by drawing forward
segments from the trunk, and fusing them successively with the first
or primitive head segment. This is difficult to conceive of in the
fully developed insect, where the boundary between head and thorax
is very sharp. But the ancestors of insects looked more like
thousand-legs or centipedes, and here head and thorax are much less
distinct. But in the annelid the mouth is on the second segment;
here it is on the fourth. It has evidently travelled backward. That
the mouth of an animal can migrate seems at first impossible, but if
we had time to examine the embryology of annelids and insects, it
would no longer appear inconceivable or improbable. And its backward
migration brought it among the legs which were grasping and chewing
the food. And in vertebrates the mouth has changed its position,
though not in exactly the same way. Our present mouth is probably
not at all the mouth of the primitive ancestor of vertebrates. Thus
in the insect three segments have fused around the mouth, and three,
possibly four, in front of it. This makes a head worthy of the name.
The ganglia of the three post-oral segments, which bear the jaws,
have fused in one compound ganglion innervating the mouth and jaws.
Those of the three præ-oral segments have fused to form a brain.
Eyes are well developed, giving images sometimes accurate in detail,
sometimes very rude. Ears are not uncommon. The sense of smell is
often keen.

Perhaps the greatest advance of the insect is its adaptation to land
life. This gives it a larger supply of oxygen than any aquatic
animal could ever obtain. This itself stimulates every function, and
all the work of the body goes on more energetically. Then the heat
produced is conducted off far less rapidly than in aquatic forms.
Water is a good conductor of heat, and nearly all aquatic animals
are cold-blooded. The few which are warm-blooded are protected by a
thick layer of non-conducting fat. In all land animals, even when
cold-blooded, the work of the different systems is aided by the
longer retention of the heat in the body.

Let us recapitulate. The schematic worm had a body composed of two
concentric tubes. The outer was composed of the muscles of the body
covered by the protective integument. The inner tube was the
alimentary canal with its special muscles. Between these two was the
perivisceral cavity, filled with nutritive fluid, lymph, and
furnishing a safe lodging-place for the more delicate viscera. It
represented fairly the trunk of higher animals.

The annelid added segmentation, and thus greater freedom of motion
by the parapodia. But the segments were still practically alike. In
the insect division of labor took place, that is, each group of
segments was allotted its own special work; and these groups of
segments were modified in structure to best suit the performance of
this part of the work of the body. The abdomen was least modified
and its eleven segments were devoted to digestion, reproduction, and
excretion--the old vegetative functions. Three segments were united
in the thorax; all their energy was turned to locomotion, and the
insect became thus an exceedingly active, swift animal. The third
body-region, the head, includes six segments, of which three
surrounded the mouth and furnished the jaws, while two more were
crowded or drawn forward in order that their ganglia might be added
to the old supraoesophageal ganglion and form a brain. It is
interesting to note that a form, peripatus, still exists which
stands almost midway between annelids and insects and has only four
segments in the head. The formation of the head was thus a gradual
process, one segment being added after another.

In the turbellaria the dominant functions were digestion and
reproduction, and their organs composed almost the whole body. Here
only eleven segments at most are devoted to these functions, and
nine in head and thorax to locomotion and brain. Head and thorax
have increased steadily in importance, while the abdomen has
decreased as steadily in number of segments. And the brain is
increasing thus rapidly because there are now muscles and
sense-organs of sufficient power to make such a brain of value. And
this brain perceives not only objects and qualities, but invisible
relations between these, and this is an advance amounting to a
revolution. It remembers, and uses its recollections. It is capable
of learning a little by experience and observation. The A, B, C of
thinking was probably learned long before the insect's time, and the
bee shows a fair amount of intelligence.

The line of development which the insect followed was comparatively
easy and its course probably rapid. Certain crustacea, aquatic
arthropoda, are among the oldest fossils, and it is possible that
insects lived on the land before the first fish swam in the sea.
They had fine structure and powers; and yet during the later
geologic periods they have scarcely advanced a step, and are now
apparently at a standstill. They ran splendidly for a time, and then
fell out of the race. What hindered and stopped them?

One vital defect in their whole plan of organization is evident. The
external skeleton is admirably suited to animals of small size, but
only to these. In larger animals living on land it would have to be
made so heavy as to be unwieldy and no longer economical. Their mode
of breathing also is fitted only for animals of small size having
an external skeleton. Whatever may be our explanation the fact
remains that insects are always small. This is in itself a
disadvantage. Very small animals cannot keep up a constant high
temperature unless the surrounding air is warm, for their radiating
surface is too large in comparison with their heat-producing mass.
At the first approach of even cool weather they become chilled and
sluggish, and must hibernate or die. They are conformed to but a
limited range of environment in temperature.

But small size is, as a rule, accompanied by an even greater
disadvantage. It seems to be almost always correlated with short
life. Why this is so, or how, we do not know. There are exceptions;
a crow lives as long as a man; or would, if allowed to. But, as a
rule, the length of an animal's days is roughly proportional to the
size of its body. And the insect is, as a rule, very short-lived. It
lives for a few days or weeks, or even months, but rarely outlasts
the year. It has time to learn but little by experience. The same
experience must be passed, the same emergency arise and be met, over
and over again during the lifetime of the same individual if the
animal is to learn thereby. And intelligence is based upon
experience. Hence insects can and do possess but a low grade of
intelligence. But instinct is in many cases habit fixed by heredity
and improved by selection. The rapid recurrence of successive
generations was exceedingly favorable to the development of
instincts, but very unfavorable to intelligence. Insects are
instinctive, the highest vertebrates intelligent. The future can
never belong to a tiny animal governed by instincts. Mollusks and
insects have both failed to reach the goal; another plan of
structure than theirs must be sought if the animal kingdom is to
have a future.

The future belonged to the vertebrate. To begin with less
characteristic organs the digestive system is much like that of the
annelid or schematic worm, but with greatly increased glandular and
absorptive surfaces. The present mouth of nearly all vertebrates is
probably not primitive. It is almost certainly one of the gill-slits
of some old ancestor of fish, such as now are used to discharge the
water which is used for respiration. The jaws are modified branchial
arches or the cartilaginous or bony rods which in our present fish
support the fringe of gills. These have formed a pair of exceedingly
effective and powerful jaws. The reproductive system holds still to
the old type and shows little if any improvement. The excretory
organs, kidneys, are composed primitively of nephridial tubes like
those of the schematic worm or annelid, but immensely increased in
number, modified, and improved in certain very important
particulars. The muscles in simplest forms are composed of heavy
longitudinal bands, especially developed toward the dorsal surface
of the body to the right and left of the axial skeleton. Locomotion
was produced by lashing the tail right and left, as still in fish.
There is improvement in all these organs, except perhaps the
reproductive, but nothing very new or striking. The great
improvement from this time on was not to be sought in the vegetative
organs, or even directly to any great extent in muscles.

The new and characteristic organ was not the vertebral column, or
series of vertebræ, or backbone, from which the kingdom has derived
its name. This was a later production. The primitive skeleton was
the notochord, still appearing in the embryos of all vertebrates and
persisting throughout life in fish. This is an elastic rod of
cartilage, lying just beneath the spinal marrow or nerve-cord, which
runs backward from the brain. The nerve-centres are therefore here
all dorsal, and the notochord or skeleton lies between these and the
digestive or alimentary canal. The skeleton of the clam or snail is
purely protective and a hindrance to locomotion. That of the insect
is almost purely locomotive, but external, that of the vertebrate
purely locomotive and internal. It does not lie outside even of the
nervous system, although this system especially required, and was
worthy of, protection. It does not protect even the brain; the skull
of vertebrates is an after-thought. It is almost the deepest seated
of all organs. But lying in the central axis of the body it
furnishes the very best possible attachment for muscles. Around this
primitive notochord was a layer of connectile tissue which later
gave rise to the vertebræ forming our backbone.

  [Illustration: 10. CROSS-SECTION OF AXIAL SKELETON OF PETROMYZON.
  HERTWIG, FROM HIEDERSHEIM.
  _SS_, skeletogenous layer; _Ob_, _Ub_, dorsal and ventral processes
  of _SS_; _C_, notochord; _Cs_, sheath of notochord; _Ee_, elastic
  external layer of sheath; _F_, fatty tissue; _M_, spinal marrow;
  _P_, sheath of _M_.]

The nervous system on the dorsal surface of the notochord consists
of the brain in the head and the spinal marrow running down the
back. The brain of all except the very lowest vertebrates consists
of four portions: 1. The cerebrum, or cerebral lobes, or simply
"forebrain," the seat of consciousness, thought, and will, and from
which no nerves proceed. Whether the primitive vertebrate had any
cerebrum is still uncertain. 2. The mid-brain, which sends nerves to
the eyes, and in this respect reminds us of the brain of insects.
Its anterior portion appears from embryology to be very primitive.
3. The small brain, or cerebellum, which in all higher forms is the
centre for co-ordination of the motions of the body. 4. The medulla,
which controls especially the internal organs. The spinal marrow, or
that portion of the nervous system which lies outside of the head,
is at the same time a great nerve-trunk and a centre for reflex
action of the muscles of the body. But the development of these
distinct portions and the division of labor between them must have
been a long and gradual process.

We have every reason to believe that here, as in insects, the head
has been formed by annexation of segments from the rump and the
fusion of their nervous matter with that of the brain. But here,
instead of only three segments, from nine to fourteen have been
fused in the head to furnish the material for the brain. Notochord
and backbone may be the most striking and apparent characteristic of
vertebrates, but their predominant characteristic is brain. On this
system they lavished material, giving it from three to four times as
much as any lower or earlier group had done. They very early set
apart the cerebral lobes to be the commander-in-chief and centre of
control for all other nerve-centres. To this all report, and from it
all directly or indirectly receive orders. It can say to every
other organ in the body, "Starve that I may live." It is the seat of
thought and will. The other portions of the brain report to it what
they have gathered of vision or sound; it explains the vision or
song or parable. It is relieved as far as possible from all lower
and routine work that it may think and remember and govern. The
vertebrate built for mind, not neglecting the body.

Every trait of vertebrates is a promise of a great future. Its
internal skeleton gives it the possibility of large size. This gave
it in time the victory in the struggle with its competitors, as to
whether it should eat or be eaten. It is vigorous and powerful, for
all its organs are at the best. It gives the possibility of later,
on land, becoming warm-blooded, _i.e._, of maintaining a constant
high temperature. It is thus resistant to climate and hardship. In
time its descendants will face the arctic winter as well as the heat
of the tropics.

But it has started on the road which leads to mind. The greater size
is correlated with longer life. The lessons of experience come to it
over and over again, and it can and must learn them. It is the
intelligent, remembering, thinking type. The insect had begun to
peer into the world of invisible and intangible relations, the
vertebrate will some day see them. This much is prophecied in his
very structure. He must be heir to an indefinite future.

       *       *       *       *       *

You have probably noticed that the vertebrate differs greatly from
all his predecessors. The gulf between him and them is indeed wide
and deep. His origin and ancestry are yet far from certain. But an
attempt to decipher his past history, though it may lead to no sure
conclusions, will yet be of use to us. Practically all aquatic
vertebrates lead a swimming life, neither sessile nor creeping. The
embryonic development of our appendages leads to the same
conclusion. We must never forget that the embryonic development of
the individual recapitulates briefly the history of the development
of the race. Now the legs and arms, or fore- and hind-legs, of
higher vertebrates and the corresponding paired fins of fish develop
in the embryo as portions of a long ridge extending from front to
rear of the side of the body.

This justifies the inference that the primitive vertebrate ancestor
had a pair of long fins running along the sides of the body, but
bending slightly downward toward the rear so as to meet one another
and continue as a single caudal fin behind the anal opening. Such
fins, like the feathers of an arrow, could be useful only to keep
the animal "on an even keel" as it was forced through the water by
the lateral sweeps of the tail. They would have been useless for
creeping.

But there is another piece of evidence that he was a free swimming
form. All vertebrates breathe by gills or lungs, and these are
modified portions of the digestive system, of the walls of the
oesophagus, from which even the lung is an embryonic outgrowth.
Now practically all invertebrates breathe through modified portions
of the integument or outer surface of the body, and their gills are
merely expansions of this. In the annelid they are projections of
the parapodia, in the mollusk expansions of the skin, where the foot
or creeping sole joins the body. Why did the vertebrate take a new
and strange, and, at first sight, disadvantageous mode of
breathing? There must have been some good reason for this. The most
natural explanation would seem to be that he had no projections on
his outer surface which could develop into gills, and farther, that
he could not afford to have any. Now projections on the lower
portion of the sides of the body would be an advantage in creeping,
but a hindrance in any such mode of swimming as we have described,
or indeed in any mode of writhing through the water.

Furthermore, if he lived, not a creeping life on the bottom, but
swimming in the water above, he would have to live almost entirely
on microscopic animals and embryos; and these would be most easily
captured by a current of water brought in at the mouth. The whole
branchial apparatus in its simplest forms would seem to be an
apparatus for sifting out the microscopic particles of food and only
later a purely respiratory apparatus. Moreover, we have seen that
the parapodia of annelids naturally point to the development of an
external skeleton, for their muscles are already a part of the
external body-wall and attached to the already existing horny
cuticle. The logical goal of their development was the insect.

Now I do not wish to conceal from you that many good zoölogists
believe that the vertebrate is descended from annelids; but for this
and other reasons such a descent appears to me very improbable. It
would seem far more natural to derive the vertebrate from some free
swimming form like the schematic worm, whose largest nerve-cord lay
on the dorsal surface because its branches ran to heavy muscles much
used in swimming. Later the other nerve-cords degenerated, for such
a degeneration of nerve-cords is not at all impossible or
improbable. "No thoroughfare" is often written across paths
previously followed by blood or nervous impulses, when other paths
have been found more economical or effective.

But where did the notochord come from? I do not know. It always
forms in the embryo out of the entoderm or layer which becomes the
lining of the intestine. Now this is a very peculiar origin for
cartilage, and the notochord is a very strange cartilage even if we
have not made a mistake in calling it cartilage at all. My best
guess would be that it is simply a thickened portion of the upper
median surface of the intestine to keep the "balls" of digesting
nutriment or other hard particles in the intestine from "grinding"
against the nerve-cord as they are crowded along in the process of
digestion. Once started its elasticity would be a great aid in
swimming.

Professor Brooks has called attention to the fact that the higher a
group stands in development, the longer its ancestors have
maintained a swimming life. Thus we have noticed that the sponges
were the first to settle; then a little later the mass of the
coelenterates followed their example. But the etenophora, the
nearest relatives of bilateral animals, have remained free swimming.
Then the flat worms and mollusks took to a creeping mode of life,
while the annelids and vertebrates still swam. Then the annelids
settled to the bottom and crept, and all their descendants remained
creeping forms. The vertebrates alone remained swimming, and
probably neither they nor their descendants ever crept until they
emerged on the land, or as amphibia were preparing for land
life. If this be true, it is a fact worthy of our most careful
consideration. The swimming life would appear to be neither as easy
nor as economical as the creeping. It is certainly hard to believe
that food would not have been obtained with less effort and in
greater abundance at the bottom than in the water above. The
swimming life gave rise to higher and stronger forms; but did its
maintenance give immediate advantage in the struggle for existence?
This is an exceedingly interesting and important question, and
demands most careful consideration. But we shall be better prepared
to answer it in a future lecture.

The period of development of mollusks, articulates, and vertebrates,
is really one. They developed to a certain extent contemporaneously.
The development of vertebrates was slow, and they were the last to
appear on the stage of geological history.

You must all have noticed that development, during this period,
takes on a much more hopeful form than during that described in the
last chapter. Then digestion and reproduction were dominant. Now
muscle is of the greatest importance. If this fails of development,
as in mollusks, the group is doomed to degeneration or at best
stagnation. But we have seen the dawn of a still higher function. In
insects and vertebrates the brain is becoming of importance, and
absorbing more and more material. This is the promise of something
vastly higher and better. Better sense-organs are appearing, fitted
to aid in a wider perception of more distant objects. The vertebrate
has discovered the right path; though a long journey still lies
before it. The night is far spent, the day is at hand.




CHAPTER IV

VERTEBRATES: BACKBONE AND BRAIN


In tracing man's ancestry from fish upward we ought properly to
describe three or four fish, an amphibian, a reptile, and then take
up the series of mammalian ancestors. But we have not sufficient
time for so extended a study, and a simpler method may answer our
purpose fairly well. Let us fix our attention on the few organs
which still show the capacity of marked development, and follow each
one of these rapidly in its upward course.

We must remember that there are changes in the vegetative organs.
The digestive and excretory systems improve. But this improvement is
not for the sake of these vegetative functions. Brain and muscle
demand vastly more fuel, and produce vastly more waste which must be
removed. At almost the close of the series the reproductive system
undergoes a modification which is almost revolutionary in its
results. But we shall find that this modification is necessitated by
the smaller amount of material which can be spared for this
function; not by its increasing importance, still less its dominance
for its own worth. The vertebrate is like an old Roman; everything
is subordinated to mental and physical power. He is the world
conqueror.

The important changes from fish upward affect the following organs:
1. The skeleton. A light, solid framework must be developed for the
body. 2. The appendages start as fins, and end as the legs and arms
of man. 3. The circulatory and respiratory systems developed so as
to carry with the utmost rapidity and certainty fuel and oxygen to
the muscular and nervous high-pressure engines. Or, to change the
figure, they are the roads along which supplies and munitions can be
carried to the army suddenly mobilized at any point on the frontier.
4. Above all, the brain, especially the cerebrum, the crown and goal
of vertebrate structure. The improvement is now practically
altogether in the animal organs of locomotion and thought. Still,
among these animal organs, the lower systems will lead in point of
time. The brain must to a certain extent wait for the skeleton.

1. The skeleton. The axial skeleton consists, in the lowest fish, of
the notochord, a cylindrical unsegmented rod of cartilage running
nearly the length of the body. This is surrounded by a sheath of
connective tissue, at first merely membranous, later becoming
cartilaginous or gristly. Pieces of cartilage extend upward over the
spinal marrow, and downward around the great aortic artery, forming
the neural and hæmal arches. These unite with the masses of
cartilage surrounding the notochord to form cartilaginous vertebræ,
which may be stiffened by an infiltration of carbonate of lime. The
vertebral column of sharks has reached this stage. Then the
cartilaginous vertebræ ossify and form a true backbone. I have
described the process as if it were very simple. But only the
student of comparative osteology can have any conception of the
number of experiments which were tried in different groups before
the definite mode of forming a bony vertebra was attained. At the
same time the skull was developing in a somewhat similar manner. But
the skull is far more complex in origin and undergoes far more
numerous and important changes than the simpler vertebral column.
Into its history we have no time to enter.

And what shall we say of bone itself as a mere material or tissue,
with its admirable lightness, compactness, and flawlessness. And
every bone in our body is a triumph of engineering architecture. No
engineer could better recognize the direction of strain and stress,
and arrange his rods and columns, arches and buttresses, to suitably
meet them, than these problems are solved in the long bone of our
thigh. And they must be lengthened while the child is leaping upon
them. An engineer is justly proud if he can rebuild or lengthen a
bridge without delaying the passage of a single train. But what
would he say if you asked him to rebuild a locomotive, while it was
running even twenty miles an hour? And yet a similar problem had to
be solved in our bodies.

But the vertebral column is not perfected by fish. The vertebræ with
few exceptions are hollow in front and behind, biconcave; and
between each two vertebræ there is a large cavity still occupied by
the notochord. Thus these vertebræ join one another by their edges,
like two shallow wine-glasses placed rim to rim. Only gradually is
the notochord crowded out so that the vertebræ join by their whole
adjacent surfaces. Even in highest forms, for the sake of mobility,
they are united by washer-like disks of cartilage. Biconcave
vertebræ persisted through the oldest amphibia, reptiles, and
birds. But finally a firm backbone and skull were attained.

2. The appendages. Of these we can say but little. The fish has
oar-like fins, attached to the body by a joint, but themselves
unjointed. By the amphibia legs, with the same regions as our own
and with five toes, have already appeared. The development of the
leg out of the fin is one of the most difficult and least understood
problems of vertebrate comparative anatomy. The legs are at first
weak and scarcely capable of supporting the body. Only gradually do
they strengthen into the fore- and hind-legs of mammals, or into the
legs and wings of birds and old flying reptiles.

3. Changes in the circulatory and respiratory systems. The fish
lives altogether in the water and breathes by gills, but the dipnoi
among fishes breathes by lungs as well as gills. As long as
respiration takes place by gills alone, the circulation is simple;
the blood flows from the heart to the gills, and thence directly all
over the body; the oxygenated blood from the gills does not return
directly to the heart. But the blood from the lungs does return to
the heart; and there at first mixes in the ventricle with the impure
blood which has returned from the rest of the body. Gradually a
partition arises in the ventricle, dividing it into a right and left
half. Thus the two circulations of the venous blood to the lungs,
and of the oxygenated blood over the body, are more and more
separated until, in higher reptiles, they become entirely distinct.

As the animal came on land and breathed the air, more completely
oxygenated blood was carried to the organs, and their activity was
greatly heightened. As more and more heat was produced by the
combustion in muscular and nervous tissues, and less was lost by
conduction, the temperature of the body rose, and in birds and
mammals becomes constant several degrees above the highest summer
temperature of the surrounding air.

The changes in the brain affect mainly the large and small brain.
The cerebellum increases with the greater locomotive powers of the
animal. But its development is evidently limited. The large brain,
or cerebrum, is in fish hardly as heavy as the mid-brain; in
amphibia the reverse is true. In higher recent reptiles the cerebrum
would somewhat outweigh all the other portions of the brain put
together. In mammals it extends upward and backward, has already in
lower forms overspread the mid-brain, and is beginning to cover the
small brain. But this was not so in the earliest mammals. Here the
cerebrum was small, more like that of reptiles. But during the
tertiary period the large brain began to increase with marvellous
rapidity. It was very late in arriving at the period of rapid
development, but it kept on after all the other organs of the body
had settled down into comparative rest, perhaps retrogression.

We have given thus a rapid sketch in outline of the changes in the
most characteristic systems between fish and mammals. Some of the
changes which took place in mammals were along the same lines, but
one at least is so new and unexpected that this highest class
demands more careful and detailed examination.

The mammal is a vertebrate. Hence all its organs are at their best.
But mammals stand, all things considered, at the head of
vertebrates. The skeleton is firm and compact. The muscles are
beautifully moulded and fitted to the skeleton so as to produce the
greatest effect with the least mass and weight of tissue. The
sense-organs are keen, and the eye and ear especially delicate, and
fitted for perception at long range. Yet in all these respects they
are surpassed by birds. As a mere anatomical machine the bird always
seems to me superior to the mammal. It is not easy to see why it
failed, as it has, to reach the goal of possibility of indefinite
development and dominance in the animal world. Why he stopped short
of the higher brain development I cannot tell. The fact remains that
the mammal is pre-eminent in brain power, and that this gave him the
supremacy.

But mammals came very late to the throne, and the probability of
their ever gaining it must for ages have appeared very doubtful.
They seem to have been a fairly old group with a very slow early
development. Reptiles especially, and even birds, were far more
precocious than these slower and weaker forms which crept along the
earth. But reptiles and birds, like many other precocious children,
soon reached the limit of their development. They had muscle, the
mammal brain and nerve; the mammal had the staying power and the
future. Bitter and discouraging must have been the struggle of these
feeble early mammals with their larger, swifter, and more powerful,
reptilian relatives. And yet, perhaps, by this very struggle the
mammal was trained to shrewdness and endurance.

The primitive mammals laid eggs like reptiles or birds. Only two
genera, echidna and platypus, survive to bear witness of these old
oviparous groups, and these only in New Zealand. These retain
several old reptilian characteristics. Their lower position is shown
also by the fact that the temperature of their bodies is, at least,
ten degrees Fahrenheit below that of higher mammals. One of these
carries the egg in a pouch on the ventral surface; the other, living
largely in water, deposits its eggs in a nest in a burrow in the
side of the bank of the stream.

After these came the marsupials. In these the eggs develop in a sort
of uterus; but there is no placenta, in the sense of an organic
connection between the embryo and the uterus of the mother. The
young are at birth exceedingly small and feeble. The adult giant
Kangaroo weighs over one hundred pounds; the young are at birth not
as large as your thumb. They are placed by the mother in a marsupial
pouch on her ventral surface, and here nourished till able to care
for themselves.

Pardon a moment's digression. The marsupials, except the opossum,
are confined to Australia, and the oviparous mammals, or monotremes,
to New Zealand. Formerly the marsupials, at least, ranged all over
Europe and Asia, for we have indisputable evidence in their fossil
remains. But they have survived only in this isolated area, and here
apparently only because their isolation preserved them from the
competition with higher forms. If the Australian continent had not
been thus early cut off from all the rest of the world, the only
trace of both these lower groups would have been the opossum in
America and certain peculiarities in the development of the egg in
higher mammals. This shows us how much weight should be assigned to
the formerly popular argument of the "missing links." The wonder is
not that so many links are missing, but that any of these primitive
forms have come down to us. For we see here another proof of the
fearful extermination of lower forms during the progress of life on
the globe. It seems as if the intermediate forms were less common
among these most recent animals than among the older types. This may
not be true, for it is not easy to compare the gap between two
mammals with that between two worms or insects, and mistakes are
very easily made. But it seems as if extermination had done its work
more ruthlessly among these highest forms than among their humbler
and lower ancestors. I would not lay much weight on such an opinion;
but, if true, it has a meaning and is worthy of study.

In higher, true, placental mammals the period of pregnancy is much
longer, and the young are born in a far higher stage of development,
or rather, growth. The stage of growth at which the young are born
differs markedly in different groups. A new-born kitten is a much
feebler, less developed being than a new-born calf. An embryonic
appendage, the allantois, used in reptiles and birds for
respiration, has here been turned to another purpose. It lays itself
against the walls of the uterus, uterine projections interlock with
those which it puts forth, and the blood of the mother circulates
through a host of capillaries separated from those of the blood
system of the embryo only by the thinnest membrane. This is the
placenta, developed, in part from the allantois of the embryo, in
part from the uterus of the mother. It is not a new organ, but an
old one turned to better and fuller use. In these closely
associated systems of blood-vessels, nutriment and oxygen diffuse
from the blood of the mother into that of the embryo, and thus rapid
growth is assured. The importance and far-reaching effect of this
new modification in the old reproductive system cannot be
over-estimated. The internal intra-uterine development of the young,
and the mammalian habit of suckling them, far more than any other
factors, have made man what he is. Some explanation must be sought
for such a fact.

We have already seen that any animal devotes to reproduction the
balance between income and expenditure of nutriment. Now, the
digestive system is here well developed, and the income is large.
But we have already noticed that, as animals grow larger, the ratio
between the digestive surface and the mass to be supported grows
continually smaller. On account of size alone the mammal has but a
small balance. But the amount of expenditure is proportional to the
mass and activity of the muscular and nervous systems. And the
mammal is, and from the beginning had to be, an exceedingly active,
energetic, and nervous animal. The income has increased, but the
expenses have far outrun the increase. The mammal can devote but
little to reproduction.

Moreover, it requires a large amount of material to form a mammalian
egg, such as that of the monotreme. It requires indefinitely more
nutriment to build a mammal than a worm, for the former is not only
larger and more perfect at birth; it is also vastly more
complicated. The embryonic journey has, so to speak, lengthened out
immensely. One monotreme egg represents more economy and saving than
a thousand eggs of a worm. Moreover, where the individuals are
longer lived and the generations follow one another at longer
intervals, the number of favorable variations and the possibility of
conformity to environment through these is greatly lessened. In such
a group it is of the utmost importance that every egg should
develop; the destruction of a single one is a real and important
loss to the species. It is not enough to produce such an egg; it
must be most scrupulously guarded. Even the egg of the platypus is
deposited in a nest in a hole in the bank, and the female Echidna
carries the egg in a marsupial pouch until it develops.

Notice further that among certain species of fish, amphibia, and
reptiles, the females carry the eggs in the body until the embryos
or young are fairly developed. Viviparous forms are unknown by
birds, probably because this mode of development is incompatible
with flight, their dominant characteristic. Putting these facts
together, what more probable than that certain primitive egg-laying
mammals should have carried the eggs as long as possible in the
uterus. The embryo under these conditions would be better nourished
by a secretion of the uterine glands than by a very large amount of
yolk. The yolk would diminish and the egg decrease in size, and thus
the marsupial mode of development would have resulted. And, given
the marsupial mode of development and an embryo possessing an
allantois, it is almost a physiological necessity that in some forms
at least a placenta should develop. That the placenta has resulted
from some such process of evolution is proven by its different
stages of development in different orders of mammals. And even the
feeblest attachment of the allantois of the embryo to the wall of
the uterus would be of the greatest advantage to the species.

This is not the whole explanation; other factors still undiscovered
were undoubtedly concerned. But even this shows us that the internal
development of the young and the habit of suckling them was a
logical result of mammalian structure and position. The grand
results of this change we shall trace farther on.

The changes from the lower true mammals to the apes are of great
interest, but we can notice only one or two of the more important.
The prosimii, or "half apes," including the lemurs, are nearly all
arboreal forms. Perhaps they were driven to this life by their more
powerful competitors. The arboreal life developed the fingers and
toes, and most of these end, not with a claw, but with a nail. The
little group has much diversity of structure, and at present finds
its home mainly in Madagascar; though in earlier times apparently
occurring all over the globe. The brain is more highly developed
than in the average mammal, but far inferior to that of the apes.
They have a fairly opposable thumb.

The highest mammals are the primates. Their characteristics are the
following: Fingers and toes all armed with nails, the eyes
comparatively near together and fully enclosed in a bony case. The
cerebrum with well-developed furrows covers the other portions of
the brain. There is but one pair of milk-glands, and these on the
breast. The differences between hand and foot become most strongly
marked by the "anthropoid" apes. These have become accustomed to an
upright gait in their climbing; hence the feet are used for
supporting the body and the hands for grasping. Both thumb and
great toe are opposable; but the foot is a true foot, and the hand a
true hand, in anatomical structure. The face, hands, and feet have
mainly lost the covering of hair. They have no tail, or rather its
rudiments are concealed beneath the skin. These include the gibbon,
the orang, the gorilla, and the chimpanzee.

We can sum up the few attainments of mammals in a line. The lower
forms attained the placental mode of embryonic development; the
higher attained upright gait, hands and feet, and a great increase
of brain. Anatomically considered these were but trifles, but the
addition of these trifles revolutionized life on the globe. The
principal anatomical differences between man and the anthropoid ape
are the following: Man is a strictly erect animal. The foot of the
ape is less fitted for walking on the ground, where he usually "goes
on all fours." The skull is almost balanced on the condyles by which
it articulates with the neck, and has but slight tendency to tip
forward. The facial portion, nose and jaws, is less developed and
retracted beneath the larger cranium or brain-case. This has greatly
changed the appearance of the head. Protruding jaws and chin, even
when combined with large cranium and brain, always give man the
appearance of brutality and low intelligence.

The pelvis is broad and comparatively shallow. The legs, especially
the thighs, are long. The foot is long and strong, and rests its
lower surface, not merely the outer margin as in apes, on the
ground. The elastic arch of the instep must be excepted in the above
description, and adds lightness and swiftness to his otherwise slow
gait. The great toe is short and generally not opposable. The
muscles of the leg are heavy and the knee-joint has a very broad
articulating surface. But the great result of man's erect posture is
that the hand is set free from the work of locomotion, and has
become a delicate tactile and tool-using organ. The importance of
this change we cannot over-estimate. The hand was the servant of the
brain for trying all experiments. Had not our arboreal ancestors
developed the hand for us we could never have invented tools nor
used them if invented. And its reflex influence in developing the
brain has been enormous. The arm is shorter and the hand smaller.
The brain is absolutely and relatively large, and its surface
greatly convoluted. This gives place for a large amount of "gray
matter," whose functions are perception, thought, and will. For this
gray matter forms a layer on the outside of the brain.

Thus, even anatomically, man differs from the anthropoid apes. His
whole structure is moulded to and by the higher mental powers, so
that he is the "Anthropos" of the old Greek philosophers, the being
who "turns his face upward." Yet in all these anatomical respects
some of the apes differ less from him than from the lower apes or
"half apes." And every one of these can easily be explained as the
result of progressive development and modification. Whoever will
deny the possibility or probability of man's development from some
lower form must argue on psychological, not on anatomical, grounds;
and it grows clearer every day that even the former but poorly
justify such a denial.

But it is interesting to note that no one ape most closely
approaches man in all anatomical respects. Thus among the
anthropoids the orang is perhaps most similar to man in cerebral
structure, the chimpanzee in form of skull, the gorilla in feet and
hands. No evolutionist would claim that any existing ape represents
the ancestor of man. The anthropoids represent very probably the
culmination of at least three distinct lines of development. But we
must remember that in early tertiary times apes occurred all over
Europe, and probably Asia, many degrees farther north than now. In
those days, as later, the fauna and flora of northern climates were
superior in vigor and height of development to that of Africa or
Australia. It is thus, to say the least, not at all improbable that
there existed in those times apes considerably, if not far, superior
to any surviving forms. Whether the palæontologist will find for us
remains of such anthropoids is still to be seen.

But you will naturally ask, "Is there not, after all, a vast
difference between the brain of man and that of the ape?" Let us
examine this question as fully as our very brief time will allow.
Considerable emphasis used to be laid on the facial angle between a
line drawn parallel to the base of the skull and one obliquely
vertical touching the teeth and most prominent portion of the
forehead. Now this angle is in man very large--from seventy-five to
eighty-five degrees, or even more, and rarely falling below
sixty-five degrees. But this angle depends largely on the protrusion
of the jaws, and varies greatly in species of animals showing much
the same grade of intelligence. In some not especially intelligent
South American monkeys the facial angle amounts to about sixty-five
degrees. In this respect the skull of a chimpanzee reminds us of a
human skull of small cranial capacity and large jaws, in which the
cranium has been pressed back and the jaws crowded forward and
slightly upward.

The weight of the brain in proportion to that of the body has been
considered as of great importance, and within certain limits this is
undoubtedly correct. Thus, according to Leuret, the weight of the
brain is to that of the whole body: In fish, 1:5,668; in reptiles,
1:1,320; in birds, 1:212; in mammals, 1:186. These figures give the
averages of large numbers of observations and have a certain
amount of value. But within the same class the ratio varies
extraordinarily. Thus the weight of the brain is to that of the
whole body: In the elephant, 1:500; in the largest dogs, 1:305; in
the cat, 1:156; in the rat, 1:76; in the chimpanzee, 1:50; in man,
1:36; in the field-mouse, 1:31; in the goldfinch, 1:24.

From this series it is evident that the relative weight of the brain
is no index of the intelligence of the animal. Indeed if the brain
were purely an organ of mind, there is no reason that it should be
any larger in an elephant than in a mouse, provided they had the
same mental capacity. As animals grow larger the weight of the
brain, relatively to that of the body, decreases, and considering
the size of man it is remarkable that it should form so large a
fraction of his weight. Still the fraction in the chimpanzee is not
so much smaller. It is still possible that this fraction is above
the normal for the chimpanzee, for some of the observations may have
been taken on animals which had died of consumption or some other
wasting disease. I have not been able to find whether this
possibility of error has been scrupulously avoided.

A fair idea of the size of the brain may be obtained by measuring
the cranial capacity. This varies in man from almost one-hundred
cubic inches to less than seventy. In the gorilla its average is
perhaps thirty, in the orang and chimpanzee rather less, about
twenty-eight. This is certainly a vast difference, especially when
we remember that the gorilla far exceeds man in weight.

Le Bon tells us that of a series of skulls forty-five per cent, of
the Australian had a cranial capacity of 1,200 to 1,300 c.c., while
46.7 per cent. of modern Parisian skulls showed a capacity of
between 1,500 and 1,600 c.c. The skull of the gorilla contains about
five hundred and seventy cubic centimetres. Broca found that the
cranial capacity of 115 Parisian skulls, of probably the higher
classes from the twelfth century, averaged about 1,426 cubic
centimetres, while ninety of those of the poorer classes of the
nineteenth century averaged about 1,484. His observations seemed to
prove that there has been a steady increase in Parisian cranial
capacity from the twelfth to the nineteenth century.

Turning to the actual weight of the brain, that of Cuvier weighed
64.5 ounces, and a few cases of weights exceeding 65 ounces have
been recorded. The lowest limit of weight in a normal human brain
has not yet been accurately determined. From 34 to 31 ounces have
been assigned by different writers. The brain of a Bush woman was
computed by Marshall at 31.5 ounces, and weights of even 31 ounces
have been recorded without any note to show that the possessors were
especially lacking in intelligence. As Professor Huxley says in his
"Man's Place in Nature," a little book which I cannot too highly
recommend to you all, "It may be doubted whether a healthy human
adult brain ever weighed less than 31 or 32 ounces, or that the
heaviest gorilla brain has ever exceeded 20 ounces. The difference
in weight of brain between the highest and the lowest men is far
greater, both relatively and absolutely, than that between the
lowest man and the highest ape. The latter, as has been seen, is
represented by 12 ounces of cerebral substance absolutely, or by
32:20 relatively. But as the largest recorded human brain weighed
between 65 and 66 ounces, the former difference is represented by 33
ounces absolutely, or by 65:32 relatively."

But there is another characteristic of the brain which seems to bear
a close relation to the degree of intelligence. The surface of the
human brain is not smooth but covered with convolutions, with
alternating grooves or sulci, which vastly increase its surface and
thus make room for more gray matter. Says Gratiolett: "On comparing
a series of human and simian brains we are immediately struck with
the analogy exhibited in the cerebral forms in all these creatures.
There is a cerebral form peculiar to man and the apes; and so in the
cerebral convolutions, wherever they appear, there is a general
unity of arrangement, a plan, the type of which is common to all
these creatures." Professor Huxley says: "It is most remarkable
that, as soon as all the principal sulci appear, the pattern
according to which they are arranged is identical with the
corresponding sulci in man. The surface of the brain of the monkey
exhibits a sort of skeleton map of man's, and in the man-like apes
the details become more and more filled in, until it is only in
minor characters that the chimpanzee's or orang's brain can be
structurally distinguished from man's."

The facts of anatomy, at least, are all against us. Struggle as we
may, be as snobbish as we will, we cannot shake off these poor
relations of ours. Our adult anatomy at once betrays our ancestry,
if we attempt to deny it. Read the first chapter of that remarkable
book by Professor Drummond on the "Ascent of Man," the chapter on
the ascent of the body, and the second chapter on the scaffolding
left in the body. The tips of our ears and our rudimentary ear
muscles, the hair on hand and arm, and the little plica semilunaris,
or rudimentary third eyelid in the inner angle of our eyes, the
vermiform appendage of the intestine, the coracoid process on our
shoulder-blades, the atlas vertebra of our necks--to say nothing of
the coccyx at the other end of the backbone--many malformations, and
a host of minor characteristics all refute our denial.

If we appeal from adult anatomy to embryology the case becomes all
the worse for us. Our ear is lodged in the gill-slit of a fish, our
jaws are branchial arches, our hyoid bone the rudiment of this
system of bones supporting the gills. Our circulation begins as a
veritable fish circulation; our earliest skeleton is a notochord;
Meckel's cartilage, from which our lower jaw and the bones of our
middle ear develop, is a whole genealogical tree of disagreeable
ancestors. Our glandula thyreoidea has, according to good
authorities, an origin so slimy that it should never be mentioned in
polite society. The origin of our kidneys appears decidedly vermian.
Time fails me to read merely the name of the witnesses which could
be summoned from our own bodies to witness against us.

Even if the testimony of some of these witnesses is not as strong
as many think, and we have misunderstood several of them, they are
too numerous and their stories hang too well together not to impress
an intelligent and impartial jury. But what if it is all true? What
if, as some think, our millionth cousin, the tiger or cat, is
anatomically a better mammal than I? His teeth and claws and
magnificent muscles are of small value compared with man's mental
power.

What a comedy that man should work so hard to prove that his chief
glory is his opposable thumb, or a few ounces of brain matter! Man's
glory is his mind and will, his reason and moral powers, his vision
of, and communion with, God. And supposing it be true, as I believe
it is true, that the animal has the germ of these also, does that
cloud my mind or obscure my vision or weaken my action? It bids me
only strive the harder to be worthy of the noble ancestors who have
raised me to my higher level and on whose buried shoulders I stand.
Whatever may have been our origin, whoever our ancestors, we are
men. Then let us play the man. If we will but play our part as well
as our old ancestors played theirs, if we will but walk and act
according to our light one-half as heroically and well as they
groped in the darkness, we need not worry about the future. That
will be assured.

Says Professor Huxley: "Man now stands as on a mountain-top far
above the level of his humble fellows, and transfigured from his
grosser nature by reflecting here and there a ray from the infinite
source of truth. And thoughtful man, once escaped from the blinding
influences of traditional prejudice, will find in the lowly stock
whence man has sprung the best evidence of the splendor of his
capacities, and will discern in his long progress through the past a
reasonable ground of faith in his attainment of a nobler future."

We have sketched hastily and in rude outline the anatomical
structure of the successive stages of man's ancestry; let us now, in
a very brief recapitulation, condense this chronicle into a
historical record of progress.

We began with the amoeba. This could not have been the beginning.
In all its structure it tells us of something earlier and far
simpler, but what this earlier ancestor was we do not know. Rather
more highly organized relatives of the amoeba, the flagellata,
have produced a membrane, and swim by means of vibratile,
whiplash-like flagella. We must emphasize that these little animals
correspond in all essential respects to the cells of our bodies;
they are unicellular animals. And the cell once developed remains
essentially the same structure, modified only in details, throughout
higher animals. And these unicellular animals have the rudiments of
all our functions. Their protoplasm and functions seem to differ
from those of higher animals only in degree, not in kind. And the
more we consider both these facts the more remarkable and suggestive
do they become.

Cells with membranes can unite in colonies capable of division of
labor and differentiation. And magosphæra is just such a little
spheroidal colony. But the cells are still all alike, each one
performs all functions equally well. But in volvox division of labor
and differentiation of structure have taken place. Certain cells
have become purely reproductive, while the rest gather nutriment for
these, but are at the same time sensitive and locomotive, excretory
and respiratory. The first function to have cells specially devoted
to it is the reproductive; this is a function absolutely necessary
for the maintenance of the species. For the nutritive cells die when
they have brought the reproductive cells to their full development.
These few nutritive cells represent the body of all higher animals
in contrast with the reproductive elements. And with the development
of a body, death, as a normal process, enters the world. The
dominant function is here evidently the reproductive, and the whole
body is subservient to this.

In hydra the union and differentiation of cells is carried further.
But the cells are still much alike and only slowly lose their own
individuality in that of the whole animal. This is shown in the fact
that each entodermal cell digests its own particles of food,
although the nutriment once digested diffuses to all parts of the
body. Also almost any part of the animal containing both ectoderm
and entoderm can be cut off and will develop into a new animal.

But beside the reproductive cells and tissues hydra has developed a
very simple digestive system, in which the newly caught food at
least macerates and begins to be dissolved. This is the second
essential function. The animal can, and the plant as a rule does,
exist with only the lowest rudiments of anything like nervous or
muscular power; but no species can exist without good powers of
digestion and reproduction. These essential organs must first
develop and the higher must wait. And the inner, digestive, layer of
cells persists in our bodies as the lining of the mid-intestine. We
compared hydra therefore to a little patch of the lining of our
intestine covered with a flake of epidermis; only these layers in
hydra possess powers lost to the corresponding cells of our bodies
in the process of differentiation. Notice, please, that when cell or
organ has once been developed it persists, as a rule, modified, but
not lost. Nature's experiments are not in vain; her progress is very
slow but sure. But hydra has also the promise of better things,
traces of muscular and nervous tissue. There are still no compact
muscles, like our own, much less ganglion or brain or nerve-centre
of individuality. The tissues are diffuse, but they are the
materials out of which the organs of higher animals will
crystallize, so to speak. Notice also that these higher muscles and
nerves are here entirely subservient to, and exist for, digestion
and reproduction.

In the turbellaria the reproductive system has reached a very high
grade of development. It is a complex and beautifully constructed
organ. The digestive system has also vastly improved; it has its own
muscular layers, and often some means of grasping food. But it is
slower in reaching its full development than the reproductive
system. But all the muscles are no longer attached to the stomach;
they are beginning to assert their independence, and, in a rude way,
to build a body-wall. But they are in many layers, and run in almost
all directions. Some of these layers will disappear, but the most
important ones, consisting of longitudinal and transverse fibres,
will persist in higher forms. Locomotion by means of these muscles
is slowly coming into prominence. They are no longer merely slaves
of digestion.

But a muscular fibril contracts only under the stimulus of a nervous
impulse. More nerve-cells are necessary to control these more
numerous muscular fibrils. The animal now moves with one end
foremost, and that end first comes in contact with food, hindrances,
or injurious surroundings. Here the sensory cells of feeling and
their nerve fibrils multiply. Remember that these neuro-epithelial
sensory cells are suited to respond not merely to pressure, but to a
variety of the stimuli, chemical, molecular, and of vibration, which
excite our organs of smell, taste, and hearing. Such organs and the
directive eyes appear mainly at this anterior end. But a ganglion
cell sends an impulse to a muscle because it has received one along
a sensory nerve from one or more of these sensory cells. Hence the
ganglion cells will increase in number. The old cobweb-like plexus
condenses into a little knot, the supra-oesophageal ganglion. This
ganglion cannot do much, if any, thinking; it is rather a steering
organ to control the muscles and guide the animal. It is the servant
of the locomotive system. Yet it is the beginning of the brain of
higher animals, and probably still persists as an infinitesimal
portion of our human brain. And all this is the prophecy of a head
soon to be developed. An excretory system has appeared to carry off
the waste of the muscles and nerves.

In the schematic worm and annelid the reproductive system is
simpler, though perhaps equally effective. It takes the excess of
nutriment of the body. The muscular system has taken the form of a
sack composed of longitudinal and transverse fibres. The
perivisceral cavity, formed perhaps by cutting off and enlarging the
lateral pouches of the turbellarian digestive system, serves as a
very simple but serviceable circulatory system. But in the annelid
and all higher forms a special system of tubes has developed to
carry the nutriment, and usually oxygen also, needed to keep up the
combustion required to furnish the energy in these active organs.
The digestive system has attained its definite form with the
appearance of an anal opening and the accompanying division of labor
and differentiation into fore-, mid-, and hind-intestine.

The digestive and reproductive systems have thus nearly attained
their final form. From the higher worms upward the digestive system
will improve greatly. Its lining will fold and flex and vastly
increase the digestive and absorptive surfaces. The layer of cells
which now secrete the digestive fluids will in part be replaced by
massive glands. Far better means of grasping food than the horny
teeth of annelids will yet appear. But all these changes are
inconsiderable compared with the vast advance made by the muscular
and nervous systems. Reproduction and digestion are losing their
supremacy in the animal body. Their advance and improvement will
require but little further attention.

In the annelid especially, and to some extent in the schematic worm,
the supra-oesophageal ganglion is relieved in part of the direct
control of the muscular fibrils and has become an organ of
perception and the seat of government of lower nervous centres. In
all higher forms it innervates directly only the principal
sense-organs of the head. And at this stage the light-perceiving
directive eye has developed into a form-perceiving, eidoscopic
organ. The eye was short of range and its images were perhaps rude
and imperfect, but it was a visual eye and had vast possibilities.
The animal is taking cognizance of ever more subtle elements in its
environment. Perhaps it is not too much to say that the eidoscopic
eye first awakened the slumbering animal mind, for its reflex effect
upon the supra-oesophageal ganglion cannot be over-estimated. The
animal will very soon begin to think.

Between the turbellarian and the annelid many aberrant lines
diverged. Some of these attained a comparatively high level and then
seemed to meet insuperable obstacles, while others came to an end or
turned downward very early. Three of these demanded attention, those
leading to mollusks, insects, and vertebrates. And it is interesting
to notice that the fundamental difference between these three lines
was the skeleton, or perhaps we ought to say it was the habit of
life which led to the development of such a skeleton.

The mollusk took to a sluggish, creeping mode of life, under an
external purely protective skeleton; the insect to a creeping mode
of life, with an external but almost purely locomotive skeleton; the
vertebrate kept on swimming and developed an internal locomotive
skeleton. And it must already have become clear to you that the
destiny of these different lines was fixed not so much directly by
the skeleton itself as by its reflex effect in moulding the
muscular, and ultimately the nervous, system.

The insects formed their skeleton by thickening the horny cuticle of
the annelid. They transformed the annelid parapodia into legs and
developed wings. They attained life in the air. They devoted the
muscles of the body largely to the extremities and gained swift
locomotion. They have a fair circulatory and an excellent
respiratory system. Best of all, they developed a head and a brain
by fusing the three anterior ganglia of the body. The insect could
and does think. Such a structure ought to lead to great and high
results. But actually their possibilities were very limited. They
have not progressed markedly during the last geological period.
Their external skeleton was easily attained and brought speedy
advantages, which for a time placed them far above all competitors.
But it limited their size and length of life and opportunities, and
finally their intelligence. They remained largely the slaves of
instinct. They followed an attractive and exceedingly promising
path, but it led to the bottom of a cliff, not to the summit.

The mollusks, clams, and snails took an easier, down-hill road. They
formed a shell, and it developed large enough to cover them. It
hampered and almost destroyed locomotion and reduced nerve to a
minimum. But nerves are nothing but a nuisance anyhow. And why
should they move? Food was plenty down in the mud, and if danger
threatened, they withdrew into the shell. They stayed down in the
mud and let the world go its way. If grievously afflicted by a
parasite they produced a pearl--to save themselves from further
discomfort. They developed just enough muscle and nervous system to
close the shell or drag it a little way; that was all. Digestion and
reproduction retained the supremacy. They were fruitful and
multiplied, and produced hosts of other clams and snails. The
present was enough for them and they had that.

For if the winner in the struggle for existence is the one who gains
the most food, the most entire protection against discomfort, danger
from enemies or unfavorable surroundings, and the most fruitful and
rapid reproduction--and these are all good--then the clam is the
highest product of evolution. It never has been surpassed--I venture
to say it never can be--except possibly by the tape-worms. I can
never help thinking with what contempt these primitive oysters, if
they had had brains enough, would have looked down upon the toiling,
struggling, discontented, fighting, aspiring primitive vertebrates.
How they would have wondered why God allowed such disagreeable,
disturbing, unconventional creatures to exist, and thanked him that
he had made the world for them, and heaven too, if there be such a
place for mollusks. Their road led to the Slough of Contentment.

But even in molluscan history there was a tragic chapter. The squids
and cuttle-fishes regained the swimming life, and in their latest
forms gave up the protective shell. But its former presence had so
modified their structure that any great advance was impossible. It
was too late. The sins of the fathers were visited upon the children
in the thousandth generation.

The vertebrate developed an internal skeleton. This was necessarily
a slow growth, and the type came late to supremacy. The longitudinal
muscles are arranged in heavy bands on each side of the back, and
the animal swims rapidly. The sense-organs are keen. The brain
contains the ganglia of several or many segments and is highly
differentiated. It has a special centre of perception, thought, and
will; it is an organ of mind. The vertebrate has the physical and
mental advantages of large size.

First the definite form and mode of developing a vertebra is
attained. Then the vertebral column is perfected. The fins are
modified into legs. The lungs increase in size and the heart becomes
double. The animal emerges on land; and, with a better supply of
oxygen and less loss of heat, all the functions are performed with
the highest possible efficiency. First, apparently, amphibia, then
reptiles, and finally mammals of enormous size and strength
appeared. It looked as if the earth were to be an arena where
gigantic beasts fought a never-ending battle of brute force. But
these great brutes reproduced slowly, had therefore little power of
adaptation, were fitted to special conditions, and when the
conditions changed they disappeared. The bird tried once more the
experiment of developing the locomotive powers to the highest
possible extent. It became a flying machine, and every organ was
moulded to suit this life. Every ounce of spare weight was thrown
aside, the muscles were wonderfully arranged and of the highest
possible efficiency. The body temperature is higher than that of
mammals. The whole organization is a physiological high-pressure
engine. The sense-organs are perhaps the finest and keenest in the
whole animal kingdom. The brain is inferior only to that of mammals.
The experiment could not have been tried under more favorable
conditions; it was not a failure, it certainly was not a success
when compared with that of mammals.

The possibilities of every system except one had been practically
exhausted. Only brain development remained as the last hope of
success. Here was an untried line, and the mammals followed it.
During the short tertiary period the brain in many of their genera
seems to have increased tenfold. By the arboreal life of the highest
forms the hand is developed as the instrument of the thinking brain.
The battle is beginning to become one of wits, and the crown will
soon pass from the strongest to the shrewdest. Mind, not muscle,
much less digestion or reproduction, is the goal of the animal
kingdom. And we shall see later that the mammalian mode of
reproduction and of care of the young led to an almost purely mental
and moral advance. For these could have but one logical outcome,
family life. And the family is the foundation of society. And family
and social life have been the school in which man has been compelled
to learn the moral lessons, the application of which has made him
what he is.

You must all, I think, have noticed that the different systems of
organs succeed one another in a certain definite order; and that
each stage from the lowest to the highest is characterized by the
predominance of a certain function or group of functions. This
sequence of functions is not a deduction but a fact. Place side by
side all possible genealogical trees of the animal kingdom, whether
founded on comparative anatomy, embryology, palæontology, or all
combined. They will all disclose this sequence of functions arranged
in the same order. Let me call your attention to the fact that this
order is not due to chance, but rests upon a physiological basis. We
might almost claim that if the evolution of man from the single cell
be granted, no other order of their occurrence is possible.

The protozoa are mostly, though not purely, nutritive and
reproductive. These functions are essential to the existence of the
species. Naturally in the early protozoan colonies, and in forms
like hydra, these functions predominated. But mere digestive tissue
is not enough for digestion. Muscles are needed to draw the food to
the mouth, to keep the digestive sack in contact with it, and for
other purposes. A little higher they are used to enable the animal
to go in search of its food. They are still, however, more or less
entirely subservient to digestion. But in the highest worms we are
beginning to see signs that muscles are predominating in the body;
and we feel that, while mutually helpful, the digestive system
exists for the muscles, and these latter are becoming the aim of
development. From worms upward there is a marked advance in physical
activity and strength. The muscles thicken and are arranged in
heavier bands. Skeleton and locomotive appendages and jaws follow in
insects and vertebrates. The direct battle of animal against animal,
and of strength opposed to strength or activity, becomes ever
sharper. The strongest and most active are selected and survive.

And yet this is not the whole truth. Some power of perception is
possessed by every animal. But until muscles had developed the
nervous system could be of but little practical value. Knowledge of
even a great emergency is of little use, if I can do nothing about
it. But when the muscles appeared, nerves and ganglion cells were
necessary to stimulate and control them. And this highest system
holds for a long time a position subordinate to that of the lower
muscular organ. Its development seems at first sight extraordinarily
slow. Only in insects and vertebrates has it become a centre of
instinct and thought. Through the sense-organs it is gaining an ever
clearer, deeper, and wider knowledge of its environment. First it is
affected only by the lower stimuli of touch, taste, and smell. Then
with the development of ear and eye it takes cognizance of ever
subtler forces and movements. Memory comes into activity very early.
The animal begins to learn by experience. The brain is becoming not
merely a steering but a thinking organ. More and more nervous
material is crowded into it and detailed for its work. Wits and
shrewdness are beginning to count for something in the battle. Not
only the animal with the strongest muscles, but the one with the
best brain survives. And thus at last the brain began to develop
with a rapidity as remarkable as its long delay. Thus each higher
function is called into activity by the next lower, serves this at
first, and only later attains its supremacy.

And yet the advance of the different functions is not altogether
successive. Muscle and nerve do not wait for digestion and
reproduction to show signs of halting before they begin to advance.
They all advance at once. But the progress of reproduction and
digestion is most rapid at first, and it appears as if they would
outrun the others. But in the ascending series the others follow
after, and soon overtake and pass by them. And these lower
functions, when out-marched, do not lag behind, but keep in touch
with the others, forming the rear-guard and supply-train of the
army. And notice that each organ holds the predominance about as
long as it shows the power of rapid improvement. The length of its
reign is pretty closely proportional to its capacity of development.
The digestive system reaches that limit early, the muscular system
is capable of indefinitely higher complexity, as we see in our hand.
But the muscular system has nearly or quite reached its limit. The
body had seen its day of dominance before man arrived on the globe.

But where is the limit to man's mental or moral powers? Every
upward step in knowledge, wisdom, and righteousness only opens our
eyes to greater heights, before unperceived and still to be
attained. These capacities, even to our dim vision, are evidently
capable of an indefinite, perhaps infinite, development. What, as
yet only partially developed, faculty remains to supersede them? As
being capable of an endless development and without a rival, may we
not, _must_ we not, consider them as ends in themselves? They are
evidently what we are here for. Everything points to a spiritual end
in animal evolution. The line of development is from the
predominantly material to the predominance of the non-material. Not
that the material is to be crowded out. It is to reach its highest
development in the service of the mind. The body must be sustained
and perfected, but it is not the end. The goal is mind, the body is
of subordinate importance.

But if this is true, we must study carefully the development of mind
in the animal. The question pre

Showing first 200,000 characters. Full text: gutenberg.org/ebooks/14834