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THE

PRINCIPLES OF BIOLOGY

BY

HERBERT SPENCER
w

AUTHOR OF SOCIAL STATICS, EDUCATION, STUDY OF SOCIOLOGY,

ESSAYS : SCIENTIFIC, POLITICAL, AND SPECULATIVE,

FACTORS OF ORGANIC EVOLUTION, ETC.

IN TWO VOLUMES
VOL. I

NEW YORK
APPLETON AND COMPANY
1897

Copyright, 18G6,
By D. APPLETON AND COMPANY.

QH307

PREFACE TO THE AMERICAN EDITION.

The System of Philosophy now in course of publication by
Mr. Herbert Spencer begins with a volume of First Princi-
ples, which was republished in this country a year or two
since. The subject of Biology comes next in order, and is to
be treated in two volumes, of which the present is the first ;
Volume II. will probably appear toward the close of the year.
In accordance with the author's plan, the doctrine or method
of Evolution unfolded in First Principles and applied to Biol-
ogy in the present work, will be carried out in the subsequent
treatment of the Principles of Psychology and the Principles
of Sociology.

In the preface to the English edition, Mr. Spencer remarks :

" The aim of this work is to set forth the general truths of
Biology, as illustrative of, and as interpreted by, the laws of
Evolution : the special truths being introduced only so far as
is needful for elucidation of the general truths.

" For aid in executing it, I owe many thanks to Prof. Hux-
ley and Dr. Hooker. They have supplied me with informa-
tion where my own was deficient ; and in looking through
the proof-sheets, have pointed out errors of detail into which
I had fallen. By having kindly rendered me this valuable
assistance, they must not, however, be held committed to any
of the enunciated doctrines that are not among the recog-
nized truths of Biology."

New York, March, 18GG.

CONTENTS OF VOL. I.

PART I.— THE DATA OF BIOLOGY.

CHAP. PAGE

I. — ORGANIC MATTER ...... 3

II. — THE ACTIONS OF FORCES OX ORGANIC MATTER . 25

III. THE RE-ACTIONS OF ORGANIC MATTER ON FORCES 42

IV. PROXIMATE DEFINITION OF LIFE .... 59

V. THE CORRESPONDENCE BETWEEN LIFE AXD ITS CIR-
CUMSTANCES ...... T2

VI. THE DEGREE OF LIFE VARIES AS THE DEGREE OF

CORRESPONDENCE ..... 82

VII. THE SCOPE OF BIOLOGY ..... 94

PART II.— THE INDUCTIONS OF BIOLOGY.

I. GROWTH 107

II. DEVELOPMENT

III. FUNCTION .

IV. — WASTE AND REPAIR

V. ADAPTATION

VI. INDIVIDUALITY .

VII. — GENESIS

133

1513

169

184

201

209

Vlll

CONTENTS.

CHAP.

VIII. HEREDITY .....

IX. VARIATION

X. GENESIS, HEREDITY, AND VARIATION

XI. — CLASSIFICATION ....
XII. DISTRIBUTION ....

PAGE

239
257
273
292
311

PART III.— THE EVOLUTION OF LIFE.

I. PRELIMINARY 331

II. GENERAL ASPECTS OF THE SPECIAL-CREATION-HY-
POTHESIS ....... 333

III. — GENERAL ASPECTS OF THE EVOLUTION-HYPOTHESIS 346

IV. THE ARGUMENTS FROM CLASSIFICATION . .356

V. — THE ARGUMENTS FROM EMBRYOLOGY . . . 365

VI. — THE ARGUMENTS FROM MORPHOLOGY . . . 380

VII. THE ARGUMENTS FROM DISTRIBUTION . ' . . 388

VIII. — HOW IS ORGANIC EVOLUTION CAUSED?. . . 402

IX. EXTERNAL FACTORS . . . . . .411

X. INTERNAL FACTORS ...... 420

XL — DIRECT EQUILIBRATION ..... 432

XII. INDIRECT EQUILIBRATION ..... 443

XIII. THE CO-OPERATION OF THE FACTORS . . ." 464

XIV. THE CONVERGENCE OF THE EVIDENCES . . 470

PART I.

THE DATA OF BIOLOGY.

CHAPTEE I.

ORGANIC MATTER.

§ 1. Of tlie four chief elements which, in various com-
binations, make up living bodies, three are gaseous. While
carbon is known only as a solid, oxygen, hydrogen, and
nitrogen habitually maintain the aeriform state. Only by
intense pressures joined with extreme refrigerations have
two out of the three (some say all) been reduced to the liquid
form. There is a certain significance in this. When we
remember how those re-distributions of Matter and Motion
which constitute Evolution, structural and functional, imply
motions in the units that are re-distributed ; we shall see a
probable meaning in the fact that organic bodies, which
exhibit the phenomena of Evolution in so high a degree, are
mainly composed of ultimate units having extreme mobility.
The properties of substances, though destroyed to sense by
combination, are not destroyed in reality : it follows from the
persistence of force, that the properties of a compound are
resultants of the properties of its components — resultants in
which the properties of the components are severally in full
action, though greatly obscured by each other. One of the
leading properties of each substance is its degree of molecular
mobility ; and its degree of molecular mobility more or
less sensibly affects the molecular mobilities of the various
compounds into which it enters. Hence we may infer some
relation between the gaseous form of three out of the four

WOFERTT LMAAT
v t State Collet*

4 THE DATA OF BIOLOGY.

chief organic elements, and that comparative readiness dis-
played by organic matters to undergo those changes in the
arrangement of parts which we call development, and those
transformations of motion which we call function.

Considering them chemically instead of physically, it is
to be remarked that three out of these four main components
of organic matter, have affinities which are narrow in their
range and low in their intensity. Hydrogen combines with
comparatively few other elements ; and such chemical energy
as it does show, is scarcely at all shown within the limits of
the organic temperatures. Of carbon it may similarly be said
that it is totally inert at ordinary heats ; that the number of
substances with which it unites is not great ; and that in
most cases its tendency to unite with them is but feeble.
Lastly, this chemical indifference is shown in the highest
degree by nitrogen — an element which, as we shall hereafter
see, plays the leading part in organic changes.

Among the organic elements, including under the title
not only the four chief ones, but also the less conspicuous re-
mainder, that capability of assuming different states, called
allotropism, is frequent. Carbon presents itself in the three
unlike conditions of diamond, graphite, and charcoal. Under
certain circumstances, oxygen takes on the form in which it
is called ozone. Sulphur and phosphorus (both, in small
proportions, essential constituents of organic matter) have
allotropic modifications. Silicon, too, is allotropic ; while
its oxide, silica, which is an indispensable constituent of
many lower organisms, exhibits the analogue of allotropism
— isomerism. And even of the iron which plays an active
part in higher organisms, and a passive part in some lower
ones, it may be said that though not known to be itself allo-
tropic, yet isomerism characterizes those compounds of it that
are found in living bodies. Allotropism being interpretable
as some change of molecular arrangement, this frequency
of its occurrence among the components of organic matter,
is significant as implying a further kind of molecular mobility.

ORGANIC MATTER. 5

One more fact, that is here of great interest for ns, must
be set down. These four elements of which organisms are
almost wholly composed, present us with certain extreme
antitheses. "While between two of them we have an unsur-
passed contrast in chemical activity ; between one of them
and the other three, we have an unsurpassed contrast in
molecular mobility. "While carbon, by successfully resisting
fusion and volatilization at the highest temperatures that can
be produced, shows us a degree of atomic cohesion greater
than that of any other known element, hydrogen, oxygen, and
nitrogen, show the least atomic cohesion of all elements. And
while oxygen displays, alike in the range and intensity of its
affinities, a chemical energy exceeding that of any other sub-
stance (unless fluorine be considered an exception), nitrogen
displays the greatest chemical inactivity. Now on calling to
mind one of the general truths arrived at when analyzing
the process of Evolution the probable significance of this
double difference will be seen. It was shown {First Principles,
§ 123) that, other things equal, unlike units are more easily
separated by incident forces than like units' are — that an inci-
dent force falling on units that are but little dissimilar does
not readily segregate them ; but that it readily segregates
them if they are widely dissimilar. Thus, these two extreme
contrasts, the one between physical mobilities, and the other
between chemical activities, fulfil, in the highest degree, a
a certain further condition to facility of differentiation and
integration.

§ 2. Among the binary, combinations of these four chief
organic elements, we find a molecular mobility much less
than that of these elements themselves ; at the same time
that it is much greater than that of binary compounds in
general. Of the two products formed by the union

of oxygen with carbon, the first, called carbonic oxide, which
contains one atom of carbon to one of oxygen (expressed by
the symbol C O), is an incondensible gas ; and the second

THE DATA OF BIOLOGY.

carbonic acid, containing an additional atom of oxygen (C 02)
assumes a liquid form only under a pressure of nearly forty
atmospheres. The several compounds of oxygen with

nitrogen, present us with an instructive gradation. Protoxide
of nitrogen, which contains one atom of each element (N O),
is a gas condensible only under a pressure of some fifty at-
mospheres ; deutoxide of nitrogen (N 02) is a gas hitherto
uncondensed (the molecular mobility remaining undiminished
in consequence of the volume of the united gases remaining
unchanged) ; nitrous acid (N 03) is gaseous at ordinary
temperatures, but condenses into a very volatile liquid at the
zero of Fahrenheit ; peroxide of nitrogen (N 04) is gaseous at
71°, liquid between that and 16°, and becomes solid at a tem-
perature below this ; while nitric acid (N 05) may be obtained
in crystals wmicli melt at 85° and boil at 113°. In this
series we see, though not with complete uniformity, a de-
crease of molecular mobility as the weights of the compound
molecules are increased. The hydro-carbons illus-

trate the same general truth still better. One series of them
will suffice. Marsh gas (C2 H^ is permanently gaseous.
Olefiant gas (C4 H4) may be liquefied by pressure. Oil
gas, which is identical with olefiant gas in the proportions
of its constituents but has double the atomic weight, (C8 H8\
becomes liquid without pressure at the zero of Fahrenheit.
Amylene (Ci0 Hio) is a liquid which boils to 102°. And the suc-
cessively higher multiples, caproylene (C12 H12), caprylene
(C16 Hi6), elaene (C18 H18) and paramylene (C^ H20), are liquids
which boil respectively at 102°, 131°, 257°, 230°, and 329°.
Cetylene (C^ HS2) is a liquid which boils at 527° ; while pa-
raffine (C54 H54) and mylene (C60 H60) are solids. Only

one compound of hydrogen with nitrogen has been obtained
in a free state — ammonia (H3 N) ; and this, which is gaseous,
is liquefiable by pressure, or by reducing its temperature to
— 40° F. In cyanogen, which is composed of nitro-

gen and carbon (N C2), we have a gas that becomes liquid at a
pressure of four atmospheres and solid at — 30° F. And, in

ORGANIC MATTER. /

paracyanogen, formed of the same proportions of these ele-
ments in higher multiples (N3 C8), we have a solid which does
not fuse or volatilize at ordinary temperatures. Lastly,

in the most important member of this group, water, (H O
or else as many chemists now think H2 02) we have a com-
pound of two incondensible gases which assumes both the
fluid state and the solid state within ordinary ranges of
temperature ; while its molecular mobility is still such that
its fluid or solid masses are continually passing into the form
of vapour, though not with great rapidity until the temper-
ature is raised to 212°.*

Considering them chemically, it is to be remarked of
these binary compounds of the four chief organic elements,
that they are, on the average, less stable than binary com-
pounds in general. Water, carbonic oxide, and carbonic
acid, are, it is true, difficult to decompose. But omitting
these, the usual strength of union among the elements of the
above-named substances is low considering the simplicity

* This immense loss of molecular mobility which oxygen and hydrogen un-
dergo on uniting to form water — a loss far greater than that seen in other binary
compounds of analogous composition — suggests the conclusion that the atom of
water is a multiple atom. Thinking that if this conclusion be true, some evidence
of the fact must be afforded by the heat-absorbing power of aqueous vapour,
I lately put the question to Prof. Tyndall, whether it resulted from his ex-
periments that the vapour of water absorbs more heat than the supposed sim-
plicity of its atom would lead him to expect. I learned from him that it has an
excessive absorbent power — an absorbent power more like that of the complex-
atomcd vapours than like that of the simple-atomed vapours — an absorbent
power that therefore harmonizes with the supposition that its atom is a multiple
one. Besides this anomalous loss of molecular mobility and this anomalous heat-
absorbing power, there are other facts which countenance the supposition. The
unparalleled evolution of heat during the combination of oxygen and hydrogen is
one. Another is that exceptional property which water possesses, of beginning to
expand when its temperature is lowered below 40° ; since this exceptional property
is explicable only on the assumption of some change of molecular arrangement — a
change which is comprehensible if the molecules are multiple ones. And yet a
further confirmatory fact is the ability of water to assume a colloid condition ; for
as this implies a capacity in its atoms for aggregating into high multiples, it
suggests, by analogy with known cases, that they have a capacity for aggregating
into lower multiples.

8 THE DATA OF BIOLOGY.

of the substances. With the exception of acetylene, the
various hydro-carbons are not producible by directly com-
bining their elements ; and the elements of most of them are
readily separated by heat without the aid of any antagonistic
affinity. Nitrogen and hydrogen do not unite with each
other immediately ; and the ammonia which results from
their mediate union, though it resists heat, yields to the
electric spark. Cyanogen is stable : not being resolved into
its components at a red heat, unless in iron vessels. Much
less stable however are the several oxides of nitrogen. The
protoxide, it is true, does not yield up its elements below a
red heat ; but nitrous acid cannot exist if water be added to
it; hypo-nitric acid is decomposed both by water. and by
contact with the various bases ; and nitric acid not only
readily parts with its oxygen to many metals, but when
anhydrous, spontaneously decomposes. Here it will

be well to note, as having a bearing on what is to follow, how
characteristic of most nitrogenous compounds is this special
instability. In all the familiar cases of sudden and violent
decomposition, the change is due to the presence of nitrogen.
The explosion of gunpowder results from the readiness with
which the nitrogen contained in the nitrate of potash, yields
up the oxygen combined with it. The explosion of gun-cot-
ton, which also contains nitric acid, is a substantially par-
allel phenomenon. The various fulminating salts are all
formed by the union with metals, of a certain nitrogenous
acid called fulminic acid ; which is so unstable that it cannot
be obtained in a separate state. Explosiveness is a property
of nitro-mannite, and also of nitro-glycerin. Iodide of nitrogen
detonates on the slightest touch, and often without any assign-
able cause. Percussion produces detonation in sulphide of
nitrogen. And the body which explodes with the most
tremendous violence of any that is known, is the chloride of
nitrogen. Thus these easy and rapid decompositions, due to
the chemical indiiference of nitrogen, are characteristic.
When we come hereafter to observe the part which nitrogen

ORGANIC MATTER. 9

plays in organic actions, we shall see the significance of this
extreme readiness shown by its compounds to undergo
change. Returning from these facts parenthetically

introduced, we have next to note that though among these
binary compounds of the four chief organic elements, there
are a few active ones, yet the majority of them display a
smaller degree of ehemical energy than the average of binary
compounds. Water is the most neutral of bodies : usually pro-
ducing little chemical alteration in the substances with which
it combines ; and being expelled from most of its combinations
by a moderate heat. Carbonic acid is a relatively feeble acid :
the carbonates being decomposed by the majority of other acids
and by ignition. The various hydro-carbons are but narrow
in the range of their comparatively weak affinities. The
compounds formed by ammonia have not much stability : they
are readily destroyed by heat, and by the other alkalies.
The affinities of cyanogen are tolerably strong ; though they
yield to those of the chief acids. Of the several oxides of ni-
trogen it is to be remarked, that while those containing the
smaller proportions of oxygen are chemically inert, that con-
taining the greatest proportion of oxygen (nitric acid) though
chemically active, in consequence of the readiness with which
one part of it gives up its oxygen to oxidize a base with
which the rest combines, is nevertheless driven from all its
combinations by a red heat.

These binary compounds, like their elements, are to a con-
siderable degree characterized by the prevalence among
them of allotropism ; or, as it is more usually called when
displayed by compound bodies — isomerism. Professor Graham
finds reason for thinking that a change in atomic arrange-
ment of this nature, takes place in water, at or near the
melting point of ice. The relation between cyanogen and
paracyanogen is, as we saw, an isomeric one. In the above-
named series of hydro-carbons, differing from each other only
in the multiples in which the elements are united, we find
isomerism becoming what is distinguished as polymerism.

10 THE DATA OF BIOLOGY.

The like is still more conspicuous in other groups of the
hydro-carbons, as in the essential oils : sixteen to twenty of
which are severally isomeric with essential oil of turpentine.
Here the particular kind of molecular mobility implied by
these metamorphoses, is well shown : essential oil of turpen-
tine being converted into a mixture of several of these poly-
merides, by simple exposure to a heat of 460°.

There is one further fact respecting these binary compounds
of the four chief organic elements, which must not be over-
looked. Those of them which form parts of the living tissues
of plants and animals (excluding water which has a me-
chanical function, and carbonic acid which is a product of
decomposition) are confined to one group — the hydro-carbons.
And of this group, which is on the average characterized by
comparative instability and inertness, these hydro-carbons
found in living tissues, are among the most unstable and
inert.

§ 3. Passing now to the substances which contain three
of these chief organic elements, we have first to note that
along with the greater atomic weight which mostly accom-
panies their increased complexity, there is, on the average,
a further marked decrease of molecular mobility. Scarcely any
of them maintain a gaseous state of ordinary temperatures.
One class of them only, the alcohols and their derivatives,
evaporate under the usual atmospheric pressure ; but not
rapidly unless heated. The fixed oils, though they show that
molecular mobility implied by an habitually liquid state,
show this in a lower degree than the alcoholic compounds ;
and they cannot be reduced to the gaseous state without de-
composition. In their allies, the fats, which are solid unless
heated, the loss of molecular mobility is still more marked.
And throughout the whole series of the fatty acids, in which
to a fixed proportion of oxygen there are successively added
higher equimultiples of carbon and hydrogen, we see how
the molecular mobility decreases with the increasing sizes of

ORGANIC MATTER. 11

the atoms. In the amylaceous and saccharine group of com-
pounds, solidity is the habitual state : such of them as can
assume a liquid form, doing so only when heated to 300° or
400° F. ; and decomposing when further heated, rather than
become gaseous. Resins and gums exhibit general physical
properties of like character and meaning.

In chemical stability these ternary compounds, considered
as a group, are in a marked degree below the binary ones.
The various sugars and kindred bodies, decompose at no very
high temperatures. The oils and fats are also readily carbon-
ized by heat. Resinous and gummy substances are easily
made to render up some of their constituents. And the
alcohols with their allies, have no great power of resisting
decomposition. These bodies, formed by the union of

oxygen, lrydrogen, and carbon, are also, as a class, chemically
inactive. The formic and acetic are doubtless energetic
acids ; but the higher members of the fatty-acid series are
easily separated from the bases with which they combine.
Saccharic acid, too, is an acid of considerable power ; and
sundry of the vegetal acids possess a certain activity,
though an activity far less than that of the mineral acids.
But throughout the rest of the group, there is shown but a
small tendency to combine with other bodies ; and such com-
binations as are formed have usually little permanence.

The phenomena of isomerism and polymerism are of fre-
quent occurrence in these ternary compounds. Starch and
dextrine are isomeric. Fruit sugar, starch sugar, eucalvn,
sorbin, and inosite, are polymeric. Sundry of the vegetal
acids exhibit similar modifications. And among the resins
and gums, with their derivatives, molecular re-arrangements
of this kind are not uncommon.

One further fact respecting these compounds of carbon,
oxygen and hydrogen, should be mentioned ; namely, that
they are divisible into two classes — the one consisting of sub-
stances that result from the destructive decomposition of
organic matter, and the other consisting of substances that

12 THE DATA OF BIOLOGY.

exist as such in organic matter. These two classes of sub-
stances exhibit in different degrees, the properties to which
we have been directing our attention. The lower alcohols,
their allies and derivatives, which possess greater molecular
mobility and chemical stability than the rest of these ternary
compounds, are not found in animal or vegetal bodies. While
the sugars and amylaceous substances, the fixed oils and fats,
the gums and resins, which have all of them much less mole-
cular mobility, and are, chemically considered, more unstable
and inert, are components of the living tissues of plants and
animals.

§ 4. Among compounds containing all the four chief
organic elements, a division analogous to that just named
may be made. There are some which result from the decom-
position of living tissues ; there are others which make
parts of living tissues in their state of integrity ; and these
two groups are contrasted in their properties in the same way
as are the parallel groups of ternary compounds.

Of the first division, certain products found in the animal
excretions are the most important, and the only ones that
need be noted ; such, namely, as urea, kreatine, kreatinine.
These animal bases exhibit much less molecular mobility than
the average of the substances treated of in the last section :
being solid at ordinary temperatures, fusing, where fusible at
all, at temperatures above that of boiling water, and having
no power to assume a gaseous state. Chemically considered,
their stability is low, and their activity but small, in com-
parison with the stabilities and activities of the simpler com-
pounds.

It is, however, the nitrogenous constituents of living tis-
sues, that display most markedly, those characteristics of which
we have been tracing the growth. Albumen, fibrin, casein,
and their allies, are bodies in which that molecular mobility
exhibited by three of their components in so high a degree,
is reduced to a minimum. These substances are known only

ORGANIC MATTER. 13

in the solid state : that is to say, when deprived of the water
usually mixed with them, they do not admit of fusion, much
less of volatilization. To which add, that they have not even
that molecular mobility which solution in water implies;
since though the}' form viscid mixtures with water, they do
not dissolve in the same perfect way as do inorganic com-
pounds. The chemical characteristics of these sub-
stances, are instability and inertness carried to the extreme.
How rapidly albumenoid matters decompose under ordinary
conditions, is daily seen : the difficulty of every house-wife
being to prevent them from decomposing. It is true that
when desiccated and kept from contact with air, they may be
preserved unchanged for a long period ; but the fact that they
can only be thus preserved, proves their great instability. It is
true, also, that these most complex nitrogenous principles are
not absolutely inert; since they enter into combinations with
some bases ; but their unions are very feeble.

It should be noted, too, of these bodies, that though they
exhibit in the lowest degree that kind of molecular mobility,
which implies facile vibration of the atoms as wholes, they ex-
hibit in a high degree that kind of molecular mobility resulting
in isomerism, which implies permanent changes in the posi-
tions of adjacent atoms with respect to each other. Each of
them has a soluble and insoluble form. In some cases there
are indications of more than two such forms. And it appears
that their metamorphoses take place under very slight
changes of conditions.

In these most unstable and inert organic compounds, we
find that the atomic complexity reaches a maximum : not
only since the four chief organic elements are here united
with small proportions of sulphur and phosphorus; but also
since they are united in high multiples. The peculiarity
which we found characterized even binary compounds of the
organic elements, that their atoms are formed not of single
equivalents of each component, but of two, three, four and
more equivalents, is carried to the greatest extreme in these

14 THE DATA OF BIOLOGY.

compounds, that take the leading part in organic actions.
According to Mulder, the formula of albumen is 10 (C40 H81
R5 qi2j _|_ g2 p That is to sa}7, with the sulphur and phos-
phorus there are united ten equivalents of a compound atom
containing forty atoms of carbon, thirty-one of hydrogen,
live of nitrogen, and twelve of oxygen : the atom being thus
made up of nearly nine hundred ultimate atoms.

§ 5. Did space permit, it would be useful here to consider
in detail, the interpretations that may be given of the pecu-
liarities we have been tracing : bringing to their solution,
those general mechanical principles which are now found to
hold true of molecules as of masses. But it must suffice
briefly to indicate the conclusions that such an inquiry pro-
mises to bring out.

Proceeding on mechanical principles, it may be argued that
the molecular mobility of a substance must depend partly on
the inertia of its molecules; partly on the intensity of their
mutual polarities; partly on their mutual pressure, as deter-
mined by the density of their aggregation, and (where the
molecules are compound) partly on the molecular mobilities
of their component molecules. Whence it is to be inferred
that any three of these remaining constant, the molecular
mobility will vary as the fourth. Other things equal, there-
fore, the molecular mobility of atoms must decrease as their
masses increase ; and so there must result that general pro-
gression we have traced, from the high molecular mobility
of the uncombined organic elements, to the low molecular
mobility of those large-atomed substances into which they are
ultimately compounded.

Applying to atoms the mechanical law which holds of
masses, that since inertia and gravity increase as the cubes
of the dimensions while cohesion increases as their squares,
the self-sustaining power of a body becomes relatively
smaller as its bulk becomes greater ; it might be argued that
these large, aggregate atoms which constitute organic sub-

ORGANIC MATTER. 15

stance, arc mechanically weak — are less able than simpler
atoms to bear, without alteration, the forces falling on them.
That very massiveness which renders them less mobile, enables
the physical forces acting on them more readily to change the
relative positions of their component atoms ; and so to pro-
duce what we know as re-arrangements and decompositions.
Further, it seems a not improbable conclusion, that this
formation of large aggregates of elementary atoms, and re-
sulting diminution of self-sustaining power, must be accom-
panied by a decrease of those contrasts of dimension to
which polarity is ascribable. A sphere is the figure of equi-
librium which any aggregate of units tends to assume, under
the influence of simple mutual attraction. AVhere the num-
ber of units is small and their mutual polarities are decided,
this proclivity towards spherical grouping will be overcome
by the tendency towards some more special form, determined
by their mutual polarities. But it is manifest that in pro-
portion as an aggregate atom becomes larger, the effects of
simple mutual attraction must become relatively greater ;
and so must tend to mask the effects of polar attraction.
There will consequently be apt to result in highly com-
pound atoms like these organic ones containing nine hun-
dred elementary atoms, such approximation to the spherical
form as must involve a less distinct polarit}T than in simpler
atoms. If this inference be correct, it supplies us with an ex-
planation both of the chemical inertness of these most com-
plex organic substances, and of their inability to crystallize.

j; 6. Here we are naturally introduced to another aspect of
our subject — an aspect of great interest. Professor Graham
has recently published a series of important researches, which
promise to throw much light on the constitution and changes
of organic matter. He shows that solid substances exist un-
der two forms of aggregation — the colloid or jelly-like, and the
crystalloid or crystal-like. Examples of the last are too fa-
miliar to need specifying. Of the first may be named such

16 THE DATA OF BIOLOGY.

instances as " hydrated silicic acid, hydrated alumina, and
other metallic peroxides of the aluminous class, when they exist
in the soluble form ; with starch, dextrine and the gums, cara-
mel, tannin, albumen, gelatine, vegetable and animal extractive
matters." Describing the properties of colloids, Professor
Graham says : — " Although often largely soluble in water,
they are held in solution by a most feeble force. They ap-
pear singularly inert in the capacity of acids and bases, and
in all the ordinary chemical relations." * * * "Al-
though chemically inert in the ordinary sense, colloids
possess a compensating activity of their own arising out of
their physical properties. "While the rigidity of the crystal-
line structure shuts out external impressions, the softness of
the gelatinous colloid partakes of fluidity, and enables the
colloid to become a medium of liquid diffusion, like water
itself." * * * " Hence a wide sensibility on the part of
colloids to external agents. Another and eminently charac-
teristic quality of colloids is their mutability." * * * " The
solution of hydrated silicic acid, for instance, is easily obtain-
ed in a state of purity, but it cannot be preserved. It may
remain fluid for days or weeks in a sealed tube, but is sure to
gelatinize and become insoluble at last. Nor does the change
of this colloid appear to stop at that point ; for the mineral
forms of silicic acid, deposited from water, such as flint, are
often found to have passed, during the geological ages of
their existence, from the vitreous or colloidal into the crystal-
line condition (H. Rose). The colloid is, in fact,. a dynami-
cal state of matter, the crystalloidal being the statical
condition. The colloid possesses energia. It may be looked
upon as the primary source of the force appearing in the
phenomena of vitality. To the gradual manner in which
colloidal changes take place (for they always demand time as
an element) may the characteristic protraction of chemico-
organic changes also be referred."

The class of colloids includes not only all those most com-
plex nitrogeneous compounds characteristic of organic tissue^

ORGANIC MATTER. 17

and sundry of the oxy-hvdro-carbons found along with them ;
but, significantly enough, it includes several of those sub-
stances classed as inorganic, which enter into organized
structures. Thus silica, which is a component of many
plants, and constitutes the spicules of sponges as well as the
shells of many foraminifera and infusoria, has a colloid, as
well as a crystalloid, condition. A solution of hyd rated silicic
acid, passes in the course of a few days into a solid jelly that
is no longer soluble in water ; and it may be suddenly thus
coagulated by a minute portion of an alkaline carbonate, as
well as by gelatine, alumina, and peroxide of iron. This last-
named substance, too — peroxide of iron — which is an ingre-
dient in the blood of mammals and composes the shells of
certain protozoa, has a colloid condition. " Water containing
about one per cent, of hydrated peroxide of iron in solution,
has the dark red colour of venous blood." * * * " The
red solution is coagulated in the cold by traces of sulphuric
acid, alkalies, alkaline carbonates, sulphates, and neutral salts
in general." * * * " The coagulum is a deep red-coloured
jelly, resembling the clot of blood but more transparent.
Indeed, the coagulum of this colloid is highly suggestive
of that of blood, from the feeble agencies which suffice to
effect the change in question, as well as from the appearance
of the product." The jelly thus formed soon becomes, like
the last, insoluble in water. Lime also, which is so important
a mineral element in living bodies, animal and vegetal
enters into a compound belonging to this class. " The
well-known solution of lime in sugar, forms a solid coagulum
when heated. It is probably, at a high temperature, entirely
colloidal."

Generalizing some of the facts which he gives, Professor
Graham says — "The equivalent of a colloid appears to be
always high, although the ratio between the elements of the
substance may be simple. Gummic acid, for instance, may
be represented by C12 Hu O1 ; but, judging from the small
proportions of lime and potash which suffice to neutralize this

18 THE DATA OF BIOLOGY.

acid, the true numbers of its formula must be several times
greater. It is difficult to avoid associating the inertness of
colloids with their high equivalents, particularly where the
high number appears to be attained by the repetition of a
small number. The inquiry suggests itself whether the col-
loid molecule may not be constituted by the grouping
together of a number of smaller crystalloid molecules, and
whether the basis of colloidality may not really be this com-
posite character of the molecule."

§ 7. A further contrast between colloids and crystalloids,
is equally significant in its relations to vital phenomena.
Professor Graham points out that the marked differences in
volatility displayed by different bodies, are paralleled by
differences in the rates of diffusion of different bodies through
liquids. As alcohol and ether at ordinary temperatures, and
various other substances at higher temperatures, diffuse them-
selves in a gaseous form through the air; so a substance in
aqueous solution, when placed in contact with a mass of
water (in such way as to avoid mixture by circulating currents)
diffuses itself through this mass of water. And just as there
are various degrees of rapidity in evaporation, so there are
various degrees of rapidity in diffusion : " the range also in
the degree of diffusive mobility exhibited by different sub-
stances appears to be as wide as the scale of vapour-tensions."
This parallelism is what might have been looked for ; since
the tendency to assume a gaseous state, and the tendency to
spread in solution through a liquid, are both consequences of
molecular mobility. It also turns out, as was to be expected,
that diffusibility, like volatility, has, other things equal, a re-
lation to atomic weight — (other things equal, we must say,
because molecular mobility must, as pointed out in § 5, be
affected by other properties of atoms, besides their inertia).
Thus the substance most rapidly diffused of any on which
Professor Graham experimented, was hydro-chloric acid — a
compound which is of low atomic weight, is gaseous save

ORGANIC MATTER. 19

under a pressure of forty atmospheres, and ordinarily exists
as a liquid, only in combination with water. Again, " hydrate
of potash may be said to possess double the velocity of diffu-
sion of sulphate of potash, and sulphate of potash again double
the velocity of sugar, alcohol, and sulphate of magnesia," —
differences which have a general correspondence with differ-
ences in the massiveness of the atoms.

But the fact of chief interest to us here, is that the rela-
tively small -atomed crystalloids have immensely greater
diffusive power than the relatively large -atomed colloids.
Among the crystalloids themselves, there are marked differ-
ences of diffusibility ; and among the colloids themselves,
there are parallel differences, though less marked ones. But
these differences are small compared with that between the
diffusibility of the crystalloids as a class, and the diffusibility
of the colloids as a class. Hydro-chloric acid is seven times
as diffusible as sulphate of magnesia ; but it is fifty times
as diffusible as albumen, and a hundred times as diffusible
as caramel.

These differences of diffusibility manifest themselves with
nearly equal distinctness, when a permeable septum is placed
between the solution and the water. And the result is, that
when a solution contains substances of different diffusibilities,
the process of dialysis, as Professor Graham calls it, becomes
a means of separating the mixed substances : especially when
such mixed substances are partly crystalloids and partly col-
loids. The bearing of this fact on organic processes will be
obvious. Still more obvious will its bearing be, on

joining it with the remarkable fact, that while crystalloids
can diffuse themselves through colloids nearly as rapidly as
through water, colloids can scarcely diffuse themselves at all
through other colloids. From a mass of jelly containing
salt, into an adjoining mass of jelly containing no salt, the
salt spread more in eight days than it spread through water
in seven days; while the spread of "caramel through the
jelly appeared scarcely to have begun after eight days had

20 THE DATA OF BIOLOGY.

elapsed." So that we must regard the colloidal compounds
of which organisms are built, as having by their physical
nature, the ability to separate colloids from crystalloids, and
to let the crystalloids pass through them with scarcely any
resistance.

One other result of these researches on the relative diffu-
sibilities of different substances, has a meaning for us. Pro-
fessor Graham rinds, that not only does there take place by
dialysis, a separation of mixed substances which are unlike in
their molecular mobilities ; but also that combined substances
between which the affinity is feeble, will separate on the
dialyzer, if their molecular mobilities are strongly -con-
trasted. Speaking of the hydro-chlorate of peroxide of
iron, he says, " such a compound possesses an element of
instability in the extremely unequal diffusibility of its
constituents ; " and he points out that when dialyzed, the
hydro-chloric acid gradually diffuses away, leaving the
colloidal peroxide of iron behind. Similarly, he remarks of
the peracetate of iron, that it " may be made a source of
soluble peroxide, as the salt referred to is itself decomposed
to a great extent by diffusion on the dial}7zer." Now this
tendency to separate displayed by substances that differ
widely in their molecular mobilities, though usually so
far antagonized by their affinities as not to produce sponta-
neous decomposition, must, in all cases, induce a certain
readiness to change which would not else exist. The un-
equal mobilities of the combined atoms, must give disturbing
forces a greater power to work transformations than they
would otherwise have. Hence the probable significance of a
fact named at the outset, that while three of the chief organic
elements have the greatest atomic mobilities of any elements
known, the fourth, carbon, has the least atomic mobility of
known elements. Though, in its simple compounds, the
affinities of carbon for the rest are strong enough to prevent
the effects of this great difference from clearly showing them-
selves ; yet there seems reason to think, that in those com-

ORGANIC MATTER. 21

plex compounds composing organic bodies — compounds in
which there are various cross affinities leading to a state
of chemical tension — this extreme difference in the molecular
mobilities must be an important aid to molecular re-arrange-
ments. In short, we are here led by concrete evidence to the
conclusion which we before drew from first principles, that
this great unlikeness among the combined units must facili-
tate differentiations.

§ 8. A portion of organic matter in a state to exhibit those
phenomena which the biologist deals with, is, however, some-
thing far more complex than the separate organic matters
we have been studying ; since a portion of organic matter in
its integrity, contains several of these.

In the first place, no one of those colloids which make up
the mass of a living body, appears capable of carrying on
vital changes by itself : it is always associated with other
colloids. A portion of animal-tissue, however minute, almost
always contains more than one form of protein-substance :
different chemical modifications of albumen and gelatine are
present together, as well as, probably, a soluble and insoluble
modification of each ; and there is usually more or less of
fatty matter. In a single vegetal cell, the minute quantity
of nitrogenous colloid present, is imbedded in colloids of the
non-nitrogenous class. The microscope makes it at once
manifest, that even the smallest and simplest organic forms
are not absolutely homogeneous.

Further, we have to contemplate organic tissue, formed
of mingled colloids in both soluble and insoluble states, as
permeated throughout by crystalloids. Some of these crys-
talloids, as oxygen,* water, and perhaps certain salts, are
agents of decomposition ; some, as the saccharine and fatty

* It will perhaps seem strange to class oxygen as a crystalloid. But inasmuch
as the crystalloids are distinguished from the colloids by their atomic simplicity,
and inasmuch as sundry gases are reducible to a crystalline state, we are justi-
fied in so classing it.

22 THE DATA OF BIOLOGY.

matters, are probably materials for decomposition ; and some,
as carbonic acid, water, urea, kreatine, and kreatinine, are
products of decomposition. Into the mass of mingled colloids,
mostly insoluble and where soluble of very low molecular
mobility or diffusive power, we have constantly passing, crys-
talloids of high molecular mobility or diffusive power, that
are capable of decomposing these complex colloids ; and from
these complex colloids, so decomposed, there result other
crystalloids (the two chief ones extremely simple and mobile,
and the rest comparatively so) which diffuse away as rapidly
as they are formed.

And now we may clearly see the necessity for that pecu-
liar composition which we find in organic matter. On the
one hand, were it not for the extreme molecular mobility
possessed by three of its chief elements out of the four ; and
were it not for the consequently high molecular mobility of
their simpler compounds ; there could not be this quick escape
of the waste products of organic action ; and there could not
be that continuously active change of matter which vitality
implies. On the other hand, were it not for the union of
these extremely mobile elements into immensely complex
compounds, having relatively vast atoms that are made com-
paratively immobile by their inertia, there could not result
that mechanical fixity which prevents the components of liv-
ing tissue from diffusing away along with the effete matters
produced by the decomposition of tissue.

§ 9. Thus in the substances of which organisms are com-
posed, the conditions necessary to that re-distribution of
Matter and Motion which constitutes Evolution, are fulfilled
in a far higher degree than at first appears.

The mutual affinities of the chief organic elements are
not active within the limits of those temperatures at which
organic actions take place ; and one of these elements is
especially characterized by its chemical indifference. The
compounds formed by these elements in ascending grades of

ORGANIC MATTER. 23

complexity, become progressively less stable. And those
most complex compounds into which all these four elements
enter, together with small proportions of two other elements
that very readily oxidize, have an instability so great that
decomposition ensues under ordinary atmospheric conditions.

Among these elements out of which living bodies are built,
there is an unusual tendency to unite in multiples ; and so to
form groups of products which have the same chemical com-
ponents, but, being different in their modes of aggregation,
possess different properties. This prevalence among them of
isomerism and polymerism, shows, in another way, the special
fitness of organic substances for undergoing re-distributions.

In those most complex compounds that are instrumental
to vital actions, there exists a kind and degree of molecular
mobility which constitutes the plastic quality fitting them for
organization. Instead of the extreme molecular mobility
possessed by three out of the four organic elements in their
separate states — instead of the diminished, but still great,
molecular mobility possessed by their simpler combinations,
the gaseous and liquid characters of which unfit them for
showing to any extent the process of Evolution — instead of
the properties of their less simple combinations, which,
when not made unduly mobile by heat, assume the unduly
rigid form of crystals ; we have in these colloids, of which
organisms are mainly composed, just the required com-
promise between fluidity and solidity. They cannot be re-
duced to the unduly mobile conditions of liquid and gas ; and
yet they do not assume the unduly fixed conditions usually cha-
racterizing solids. The absence of power to unite together in
polar arrangement, leaves their atoms with a certain freedom
of relative movement which makes them sensitive to small
forces, and produces plasticity in the aggregates composed
of them.

While the relatively great inertia of these large and com-
plex organic atoms, renders them comparativelj" incapable
of being set in motion by the ethereal undulations, and so re-

24 THE DATA OF BIOLOGY.

duced to less coherent forms of aggregation ; there is reason
to think that this same inertia facilitates changes of arrange-
ment among their constituent atoms; since, in proportion as
an incident force impresses but little motion on a mass, it is
the better able to impress motion on the parts of the mass in
relation to each other. And it is further probable that the
extreme contrasts in molecular mobilities among the compo-
nents of these highly complex atoms, aid in producing modi-
liability of arrangement among them.

Lastly, the great difference in diiiusibility between colloids
and crystalloids, makes possible in the tissues of organisms,
a specially rapid re-distribution of matter and motion ; both
because colloids, being easily permeable by crystalloids, can
be chemically acted on throughout their whole mass, in-
stead of only on their surfaces ; and because the products of
decomposition, being also crystalloids, can escape as fast as
they are produced, leaving room for further like transforma-
tions. So that while the composite atoms of which organic
tissues are built up, possess that low molecular mobility fit-
ting them for plastic purposes, it results from the extreme
molecular mobilities of their ultimate constituents, that the
waste products of vital activity escape as fast as they are
formed.

To all which add, that the state of warmth, or increased
molecular vibration, in* which all the higher organisms are
kept, increases these various facilities for re-distribution : not
only as aiding chemical changes, but as accelerating the dif-
fusion of crystalloid substances.

ff. C State CM**

CHAPTER II.

THE ACTIONS OF FOKCES ON OKGANIC MATTER.

§ 10. To some extent, the parts of every body are changed
in their arrangement by any incident mechanical force.
But in organic bodies, the changes of arrangement produced
by mechanical forces are usually conspicuous. It is a dis-
tinctive mark of colloids, that they yield with great readiness
to pressures and tensions ; and that they yet recover, more
or less completely, their original shapes, when the pres-
sures or tensions cease. It is clear that without this
pliability and elasticity, most organic actions would be im-
possible. Not only temporary but permanent alter-
ations of form are facilitated by this colloid character of
organic matter. Continued pressure on living tissue, by
modifying the processes going on in it, (perhaps retarding
the absorption of new material to replace the old that has
decomposed and diffused away,) gradually diminishes and
finally destroys its power of resuming the outline it had at
first. Thus the matter of which organisms are built up, is
modifiable by arrested momentum or by continuous strain,
in a far greater degree than is ordinary matter.

§ 11. Sensitiveness to certain forces that are quasi-
mechanical, if not mechanical in the usual sense, is seen in
two closely-related peculiarities displayed by organic matter

3 25

26 THE DATA OF BIOLOGY.

as well as other matter that assumes the same state of mole-
cular aggregation.

Colloids take up by a power that has been called " capillary
affinity," a large quantity of water : undergoing at the same
time great increase of bulk with change of form. Conversely,
with like readiness, they give up this water by evaporation :
resuming more or less completely their original states.
Whether resulting from capillarity, or from the relatively
great diffusibility of water, or from both ; these changes
are to be here noted as showing another mode in which
the arrangement of parts in organic bodies, is affected by
mechanical forces.

In what is called osmose, we have a further mode of allied
kind. When on opposite sides of a permeable septum, and
especially a septum of colloidal substance, are placed miscible
solutions of different densities, a double transfer takes place :
a large quantity of the less dense solution finds its way through
the septum into the more dense solution ; and a small quan-
tity of the more dense finds its way into the less dense — one
result being a considerable increase in the bulk of the more
dense at the expense of the less dense. This process, which
appears to depend on several conditions, is not yet fully un-
derstood. But be the explanation what it may, the process
is one that tends continually to work alterations in organic
bodies. Through the surfaces of plants and animals, transfers
of this kind are ever taking place. Very many of the con-
spicuous changes of form undergone by organic germs, are
due mainly to the permeation of their limiting membranes
by the surrounding liquids.

It should be added that besides the direct alterations which
the imbibition and transmission of water and watery solutions
by colloids produce in organic matter, they produce indirect
alterations. Being instrumental in conveying into the tissues
the agents of chemical change, and conveying out of them
the products of chemical change, they aid in carrying on
other re-distributions.

THE ACTIONS OF FORCES ON ORGANIC MATTER. 27

§ 12. As elsewhere shown {First Principles, § 103) Heat, or
a raised state of molecular vibration, enables incident forces
more easily to produce changes of molecular arrangement in
organic matter. But besides this, it conduces to certain vital
changes in so direct a way as to become their chief cause.

The power of the organic colloids to imbibe water, and to
bring along with it into their substance the materials which
work transformations, would not be continuously operative
if the water imbibed were to remain. It is because it escapes,
and is replaced by more containing more materials, that the
succession of changes is maintained. Among the higher
animals and higher plants its escape is facilitated by evapor-
ation. And the rate of evaporation is, other things equal,
determined by heat. Though the current of sap in

a tree is mainly caused by some action, probably osmotic,
that is at work in the roots ; yet the loss of water from
the surfaces of the leaves, and the consequent absorption
of more sap into the leaves by capillary attraction, must
largely aid the circulation. The drooping of a plant when
exposed to the sunshine while the earth round its roots is
dry, shows us how evaporation empties the sap-vessels ; and
the quickness with which a withered slip revives on being
placed in water, shows us the part which capillary action
plays. In so far then, as the evaporation from a plant's sur-
face helps to produce currents of sap through the plant,
we must regard the heat which produces this evaporation
as a part-cause of those re-distributions of matter which
these currents effect. In terrestrial animals, heat

similarly aids the changes that are going on. The exha-
lation of vapour from the lungs and the surface of the skin,
forming the chief escape of the water that is swallowed,
conduces to the maintenance of those currents through the
tissues, without which the functions would cease. For
though the vascular system distributes nutritive fluids in
ramiried channels through the body ; yet the absorption of
these fluids into tissues, partly depends on the escape of fluids

28 THE DATA OF BIOLOGY.

which the tissues already contain. Hence, to the extent that
such escape is facilitated by evaporation, and this evaporation
facilitated by heat, heat becomes an agent of re-distribution
in the animal organism.

§ 13. Light, which is now known to modify many inor-
ganic compounds — which works those chemical changes
utilized in photography, causes the combination of certain
gases, alters the molecular arrangements of many crystals,
and leaves traces of its action even on substances that are ex-
tremely stable, — may be expected to produce marked effects
on substances so complex and unstable as those which make
up organic bodies. It does produce such marked effects ;
and some of them are among the most important that
organic matter undergoes.

The molecular changes wrought by light in animals, are
but of secondary moment. There is the darkening of the
skin that follows exposure to the sun's rays. There are
those alterations in the retina which cause in us sensations
of colours. And on certain eyeless creatures that are semi-
transparent, the light permeating their substance works
some effect evinced by movement. But speaking generally,
the opacity of animals limits the action of light to their
surfaces ; and so renders its direct physiological influence
but small.* On plants, however, the solar rays that

produce in us the impression of yellow, are the immediate
agents of those molecular changes through which are hourly
accumulated the materials for further growth. Experiments
have shown that when the sun shines on living leaves, they
begin to exhale oxygen and to accumulate carbon and
hydrogen — results which are traced to the decomposition by
the solar rays, of the carbonic acid and water absorbed.
It is now an accepted conclusion that, by the help of certain

* The increase 01 respiration found to result from the presence of light, is
probably an indirect effect. ±x is most likely due to the recention of more viviu
impressions through the eyes, and to the consequent nervous stimulation.

THE ACTIONS OF FORCES ON ORGANIC MATTER. 29

classes of the ethereal undulations penetrating their leaves,
plants are enabled to separate from the associated oxygen,
those two elements of which their tissues are chiefly built
up.

This transformation of ethereal undulations into certain
molecular re-arrangements of an unstable kind, on the over-
throw of which the stored-up forces are liberated in new
forms, is a process that underlies all organic phenomena. It
will therefore be well, if we pause a moment to consider whe-
ther any proximate interpretation of it is possible. Certain
recent researches in molecular physics, give us some clue to
its nature.

The elements of the problem are these : — The atoms of
several ponderable matters exist in combination : those that
are combined having strong affinities, but having also affin-
ities less strong for some of the surrounding atoms that are
otherwise combined. The atoms thus united, and thus mixed
among others with which they are capable of uniting, are
exposed to the undulations of a medium that is relatively so
rare as to seem imponderable. These undulations are of
numerous kinds : they differ greatly in their lengths, or in
the frequency with which they recur at any given point.
And under the influence of undulations of a certain frequency,
some of these atoms are transferred from atoms for which they
have a stronger affinity, to atoms for which they have a weaker
affinity. That is to say, particular orders of waves of a rela-
tively imponderable matter, remove particular atoms of pon-
derable matter from their attachments, and carry them within
reach of other attachments. Now the discoveries of

Bunsen and Kirchoff respecting the absorption of particular
luminiferous undulations by the vapours of particular sub-
stances, joined with Prof. Tyndall's discoveries respecting
the absorption of heat by gases, show very clearly that the
atoms of each substance have a rate of vibration in harmony
with ethereal waves of a certain length, or rapidity of recur-
rence. Every special kind of atom can be made to oscillate

30 THE DATA OF BIOLOGY.

by a special order of ethereal waves, which are absorbed in
producing its oscillations ; and can by its oscillations generate
this same order of ethereal waves. Whence it appears that
immense as is the difference in density between ether and
ponderable matter, the waves of the one can set the atoms of
the other in motion, when the successive impacts of the waves
are so timed as to correspond with the oscillations of the
atoms. The effects of the waves are, in such case, cumula-
tive; and each atom gradually acquires a momentum made up
of countless infinitesimal momenta. Note further,

that unless the members of a chemically-compound atom are
so bound up as to be incapable of any relative movements (a
supposition at variance with the conceptions of modern science)
we must conceive them as severally able to vibrate in unison
or harmony with those same classes of ethereal waves that
affect them in their uncombined states. While the compound
atom as a whole, will have some new rate of oscillation de-
termined by its attributes as a whole ; its components will
retain their original rates of oscillation, subject only to modifi-
cations by mutual influence. Such being the cir-
cumstances of the case, we may partially understand how
the sun's rays can effect chemical decompositions. If the
members of a binary atom stand so related to the undulations
falling on them, that one is thrown into a state of increased
oscillation and the other not ; it is manifest that there
must arise a tendency towards the dislocation of the two — a
tendency which may or may not take effect, according to the
weakness or strength of their union, and according to the
presence or absence of collateral affinities. This inference is
in harmony with several significant facts. Dr. Draper
remarks that " among metallic substances (compounds) those
first detected to be changed by light, such as silver, gold,
mercury, lead, have all high atomic weights ; and such as
sodium and potassium, the atomic weights of which are low,
appeared to be less changeable." As here interpreted, the
fact specified amounts to this ; that the compounds most

THE ACTIONS OF FORCES ON ORGANIC MATTER. 31

readily decomposed by light, are those in which there
is a marked contrast between the atomic weights of the
constituents, and probably therefore a marked contrast
between the rapidities of their vibrations. The circumstance,
too, that different chemical compounds are decomposed or
modified in different parts of the spectrum, implies that there
is a relation between special orders of undulations and special
orders of composite atoms — doubtless a correspondence
between the rates of these undulations and the rates of
oscillation which some of the components of such atoms
will assume. Strong confirmation of this view may

be drawn from the decomposing actions of those longer
ethereal waves which we perceive as heat. On contemplating
the whole series of binary compounds, we see that the ele-
ments which are most remote in their atomic weights, as
hvdrogen and the noble metals, will not combine at all : their
vibrations are so unlike that they cannot keep together
under any conditions of temperature. If again we look at a
smaller group, as the metallic oxides, we see that whereas
those metals that have atoms nearest in weight to the atoms
of oxygen, cannot be separated from oxygen by heat, even
when it is joined by a powerful collateral affinity ; those
metals which differ more widely from oxygen in their atomic
weights, can be de-oxidized by carbon at high temperatures ;
and those which differ from it most widely, combine with it
very reluctantly, and yield it up if exposed to thermal undu-
lations of moderate intensity. And here indeed, remem-
bering the relations among the atomic weights in the two
eases, may we not suspect a close analogy between the de-
oxidation of a metallic oxide by carbon under the influence
of the longer ethereal waves, and the de-carbonization of
carbonic acid by hydrogen under the influence of the shorter
ethereal waves ?

These conceptions help us to some dim notion of the mode
in which changes are wrought by light in the leaves of plants.
Among the several elements concerned, there are wide differ-

32 THE DATA OF BIOLOGY.

ences in molecular mobility, and probably in the rates of
molecular vibration. Each is combined with one of the others ;
but is capable of forming various combinations with the rest.
And they are severally in presence of a complex compound
into which they all enter, and which is ready to assimilate
with itself the new compound atoms that they form. Certain
of the ethereal waves falling on them when thus arranged,
there results a detachment of some of the combined atoms
and a union of the rest. And the conclusion suggested is,
that the induced vibrations among the various atoms as at
first arranged, are so incongruous as to produce instability ;
and to give collateral affinities the power to work a re-
arrangement, which, though less stable under other conditions,
is more stable in the presence -of these particular undula-
tions. There seems, indeed, no choice but to conceive
the matter thus. An atom united with one for which it has
a strong affinity, has to be transferred to another for which
it has a weaker affinity. This transfer implies motion. The
motion is given by the waves of a medium that is relatively
imponderable. No one wave of this imponderable medium
can give the requisite motion to this atom of ponderable
matter : especially as the atom is held by a positive force besides
its inertia. The motion required can hence be given only
by successive waves ; and that these may not destroy each
other's effects, it is needful that each shall strike the atom
just when it has completed that recoil produced by the impact
of previous ones. That is, the ethereal undulations must
coincide in rate with the oscillations of the atom, determined
by its inertia and the forces acting on it. It is also requisite
that the rate of oscillation of the atom to be detached, shall
differ from that of the atom with which it is united ; since
if the two oscillated in unison, the ethereal waves would not
tend to separate them. And, finally, the successive impacts
of the ethereal waves must be accumulated, until the resulting
oscillations have become so wide in their sweep as greatly to
weaken the cohesion of the united atoms, at the same time

THE ACTIONS OF FORCES ON ORGANIC MATTER. 33

that they bring one of them within reach of other atoms with
which it will combine. In this way only does it seem possible
for such a force to produce such a transfer. More-

over, while we are thus enabled to conceive how light may
work the*e molecular changes; we also gain an insight into
the method by which the insensible motions propagated to
us from the sun, are treasured up in such way as afterwards
to generate sensible motions. Bv the accumulation of in-
finitesimal impacts, atoms of ponderable matter are made to
oscillate. The quantity of motion which each of them
eventually acquires, effects its transfer to a position of un-
stable equilibrium, from which it can afterwards be readily
dislodged. And when so dislodged, along with other atoms
similarly and simultaneously affected, there is suddenly given
out all the motion which had been before impressed on it.

Speculation aside, however, that which it concerns us to
notice, is the broad fact that light is an all-important agent
of molecular changes in organic substances. It is not here
necessary for us to ascertain how light produces these compo-
sitions and decompositions : it is necessary only for us to
observe that it does produce them. That the characteristic
matter called chlorophyll, which gives the green colour to
leaves, makes its appearance whenever the blanched shoots of
plants are exposed to the sun ; that the petals of flowers,
uncoloured while in the bud, acquire their bright tints as
they unfold ; and that on the outer surfaces of animals,
analogous changes are induced ; are wide inductions which
are enough for our present purpose.

§ 14. "We come next to the agency of chief importance
among those that work changes in organic matter ; namely,
chemical affinity. How readily vegetal and animal substances
are modified by other substances put in contact with them,
we see daily illustrated. Besides the many compounds which
cause the death of an organism into which they are put, we
have the much greater number of compounds which work

34 THE DATA OF BIOLOGY.

those milder effects termed medicinal — effects implying, like
the others, molecular re-arrangements. Indeed, nearly all
soluble chemical compounds, natural and artificial, produce,
when taken into the body, alterations that are more or less
conspicuous in their results.

After what was shown in the last chapter, it will be mani-
fest that this extreme modifiability of organic matter by
chemical agencies, is the chief cause of that active molecular
re-arrangement which organisms, and especially animal or-
ganisms, display. In the two fundamental functions of
nutrition and respiration, we have the means by which the
supply of materials for this active molecular re-arrangement
is maintained.

Thus the process of animal nutrition consists in the absorp-
tion, partly of those complex substances that are thus highly
capable of being chemically altered, and partly in the absorp-
tion of simpler substances capable of chemically altering
them. The tissues always contain small quantities of alka-
line and earthy salts, which enter the system in one form
and are excreted in another. Though we do not know spe-
cifically the parts which these salts play, yet from their
universal presence, and from the transformations which they
undergo in the body, it may be safely inferred that their
chemical affinities are instrumental in working some of the
metamorphoses ever going on.

The inorganic substance, however, on which mainly depend
these metamorphoses in organic matter, is not swallowed
along with the solid and liquid food, but is absorbed from
the surrounding medium — air or water, as the case may be.
Whether the oxygen taken in, either, as by the lowest
animals, through the general surface, or, as by the higher
animals, through respiratory organs, is the immediate cause
of those molecular changes that are ever going on through-
out the living tissues ; or whether the oxygen, playing the
part of scavenger, merely aids these changes by carrying
away the products of decompositions otherwise caused ; it

THE ACTIONS OF FORCES ON ORGANIC MATTER. 35

equally remains true, that these changes are maintained by
its instrumentality. Whether the oxygen absorbed and
diffused through the system, effects a direct oxidation of the
organic colloids which it permeates ; or whether it first leads
to the formation of simpler and more oxidized compounds,
that are afterwards further oxidized and reduced to still
simpler forms ; matters not, in so far as the general result is
concerned. In any case it holds good, that the substances
of which the animal body is built up, enter it in a but
slightly oxidized and highly unstable state ; while the great
mass of them leave it in a fully oxidized and stable state.
It follows, therefore, that whatever the special changes gone
through, the general process is a falling from a state of un-
stable chemical equilibrium, to a state of stable chemical
equilibrium. Whether this process be direct or indirect,
the total molecular re-arrangement and the total motion
given out in effecting it, must be the same.

§ 15. There is another species of re-distribution among
the component units of organisms, which is not immediately
effected by the affinities of the units concerned, but is me-
diately effected by other affinities ; and there is reason to
think that the re-distribution thus caused, is important in
amount, if not indeed the most important. In ordinary cases
of chemical action, the two or more substances concerned,
themselves undergo changes of molecular arrangement ; and
the changes are confined to the substances themselves. But
there are other cases in which the chemical action going on,
does not end with the substances at first concerned ; but sets
going chemical actions, or changes of molecular arrangement,
among surrounding substances that would else remain qui-
escent. And there are yet further cases in which mere
contact with a substance that is itself quiescent, will cause
other substances to undergo rapid metamorphoses. In

what we call fermentation, the first species of this communi-
cated chemical action is exemplified. One part of yeast,

36 THE DATA OF BIOLOGY.

while itself undergoing molecular changes, will convert 100
parts of sugar into alcohol and carbonic acid ; and during its
own decomposition, one part of diastase " is able to effect the
transformation of more than 1000 times its weight of starch
into sugar." As illustrations of the second species,

may be mentioned those changes which are suddenly produced
in many colloids by minute portions of various substances
added to them — substances that are not undergoing any
manifest transformation, and suffer no appreciable effect
from the contact. The nature of the first of these two

kinds of communicated molecular change, which here chiefly
concerns us, may be rudely represented by certain visible
changes that are communicated from mass to mass, when a
series of masses has been arranged in a special way. The
simplest example is that furnished by the child's play of
setting bricks on end in a row, in such positions that when
the first is overthrown it overthrows the second ; the second,
the third ; the third, the fourth ; and so on to the end of the
row. Here we have a number of units severally placed in
unstable equilibrium, and in such relative positions that each,
while falling into a state of stable equilibrium, gives an im-
pulse to the next, sufficient to make the next, also, fall from
unstable to stable equilibrium. Now since among mingled
compound atoms, no one can undergo change in the arrange-
ment of its parts without a molecular motion that must cause
some disturbance all around ; and since an adjacent atom
disturbed by this communicated motion, may have the arrange
ment of its constituent molecules altered, if it is not a stable
arrangement ; and since we know, both that the atoms which
are changed by this so-called catalysis are unstable, and that
the atoms resulting from their change are more stable ; it
seems probable that the transformation is really analogous,
in principle, to the familiar one named. "Whether thus
interpretable or not, however, there is great reason for think-
ing that to this kind of action, is due a large amount of vital

THE ACTIONS OF FORCES OX ORGANIC MATTER. 37

metamorphosis. Let us contemplate the several groups of
facts which point to this conclusion.

In the last chapter (§ 2) we incidentally noted the extreme
instability of nitrogenous compounds in general. We saw
that sundry of them are liable to explode on the slightest
incentive — sometimes without any apparent cause ; and that
of the rest, the great majority are very easily decomposed by
heat, and by other substances. We shall perceive much
significance in this general characteristic, when we join it
with the fact, that the substances capable of initiating extensive
molecular changes in the manner above described, are all
nitrogenous ones. Yeast consists of vegetal cells containing
nitrogen, — cells that grow by assimilating the nitrogenous
matter contained in wort. Similarly, the " vinegar-plant,"
which so greatly facilitates the formation of acetic acid from
alcohol, is a fungoid growth, that is doubtless, like others of
its class, rich in nitrogenous compounds. Diastase, by which
the transformation of starch into sugar is effected, during
the process of malting, is also a nitrogenous body. So too
is a substance called synaptase — an albumenous principle
contained in almonds, that has the power of working several
metamorphoses in the matters associated with it. These
nitrogenized compounds, like the rest of their family, are
remarkable for the rapidity with which they decompose ; and
the extensive changes produced by them in the accompanying
oxy-hydro-carbons, are found to vary in their kinds accord-
ing as the decompositions of the ferments vary in their
stages. We have next to note, as having here a

meaning for us, the chemical contrasts between those organ-
isms which carry on their functions by the help of external
forces, and those which carry on their functions by forces
evolved from within. If we compare animals and plants, we
see that whereas plants, characterized as a class by containing
but little nitrogen, are dependent on the solar rays for their
vital activities ; animals, the vital activities of which are not

38 THE DATA OF BIOLOGY.

thus dependent, mainly consist of nitrogenous substances.
There is one marked exception to this broad distinction, how-
ever; and this exception is specially instructive. Among
plants, there is a considerable group — the Fungi — many mem-
bers of which, if not all, can live and grow in the dark ; and
it is their peculiarity that they are very much more nitro-
genous than other plants. Yet a third class of facts
of like significance, is disclosed when we compare different
portions of the same organisms. The seed of a plant contains
nitrogenous substance in a far higher ratio than the rest of
the plant ; and the seed differs from the rest of the plant in
its ability to initiate, in the absence of light, extensive vital
changes — -the changes constituting germination. Similarly
in the bodies of animals, those parts which carry on active
functions are nitrogenous ; while parts that are non-nitro-
genous— as the deposits of fat— carry on no active functions.
And we even find that the appearance of non-nitrogenous
matter, throughout tissues normally composed almost wholly
of nitrogenous matter, is accompanied by loss of activity :
what is called fatty degeneration, being the concomitant of
failing vitality. One more fact which serves to make
still clearer the meaning of the foregoing ones, still remains —
the fact, namely, that in no part of any organism where vital
changes are going on, is nitrogenous matter wholly absent.
It is common to speak of plants — or at least all parts of
plants but the seeds — as non-nitrogenous. But they are only
relatively so ; not absolutely. The quantity of albumenoid
substance contained in the tissues of plants, is extremely small
compared with the quantity contained in the tissues of ani-
mals ; but all plant-tissues which are discharging active
functions, contain some albumenoid substance. In every
living vegetal cell there is a certain part that contains nitro-
gen. This part initiates those changes which constitute the
development of the cell. And if it cannot be said that the
primordial utricle, as this nitrogenous part is called, is the
worker of all subsequent changes undergone by the cell, it

THE ACTIONS OF FORCES ON OEGANIC MATTER. 39

nevertheless continues to be the part in which the independent
activity is most marked.

Looking at the evidence thus brought together, do we
not get an insight into the part played by nitrogenous
matter in organic changes ? We see that nitrogenous com-
pounds in general, are extremely prone to decompose : their
decomposition often involving a sudden and great evolution
of force. We see that the substances classed as ferments,
which, during their own molecular changes, set up molecular
changes in the accompanying oxy-hydro carbons, are all
nitrogenous. We see that among classes of organisms, and
among the parts of each organism, there is a relation between
the amount of nitrogenous matter present and the amount of
independent activity. And we see that even in organisms
and parts of organisms where the activity is least, such
changes as do take place are initiated by a substance contain-
ing nitrogen. Does it not seem probable, then, that these
extremely unstable compounds, have everywhere the effect of
communicating to the less unstable compounds associated
with them, molecular movements towards a stable state, like
those they are themselves undergoing ? The changes which
we thus suppose nitrogenous matter to produce in a body,
are clearly analogous to those which we see it produce out of
the body. Out of the body, certain oxy-hydro-carbons in con-
tinued contact with nitrogenous matter, are transformed into
carbonic acid and alcohol,- and unless prevented the alcohol
is transformed into acetic acid : the substances formed being
thus more highly oxidized and more stable than the substances
destroyed. In the body, these same oxy-hydro-carbons
together with some hydro-carbons, in continued contact with
nitrogenous matter, are transformed into carbonic acid and
water : substances which are also more highly oxidized and
more stable than those from which they result. And since
acetic acid is itself resolved by further oxidation into carbonic
acid and water ; we see that the chief difference between the
two cases, is, that the process is more completely effected in

40 THE DATA OF BIOLOGY.

the bodj^, than it is out of the body.* Thus, to carry further the
simile used above, the atoms of hydro-carbons and oxy-hydro-
carbons contained in the tissues, are, like bricks on end, not in
the stablest equilibrium, but still in an equilibrium so stable,
that they cannot be overthrown by the chemical and thermal
forces which the body brings to bear on them. On the other
hand, being like similarly-placed bricks that have very nar-
row ends, the nitrogenous atoms contained in the tissues are
in so unstable an equilibrium that they cannot withstand
these forces. And when these delicately-poised nitrogenous
atoms fall into stable arrangements, they give impulses to
the more firmly-poised non-nitrogenous atoms, which cause
them also to fall into stable arrangements. It is a

curious and significant fact, that in the arts, we not only
utilize this same principle of initiating extensive changes
among comparatively stable compounds, by the help of com-
pounds much less stable ; but we employ for the purpose
compounds of the same general class. Our modern method
of firing a gun, is to place in close proximity with the gun-
powder which we wish to decompose or explode, a small por-
tion of fulminating powder, which is decomposed or exploded
with extreme facility ; and which, on decomposing, communi-
cates the consequent molecular disturbance to the less-easily
decomposed gunpowder. When we ask what this fulminating
powder is composed of, we find that it is a nitrogenous salt.

Thus various evidences point to the conclusion, that besides
the molecular re-arrangements produced in organic matter by
direct chemical action, there are others of kindred importance
produced by indirect chemical action. Indeed, the inference

* May it not be well to inquire whether alcohol is not, in a greater or less
measure, transformed in the body into acetic acid ? If, when in contact with
changing nitrogenous matter, in presence of oxygen, alcohol undergoes this
transformation out of the body, it seems not improbable that it does so in the body
— especially as the raised temperature which aids the change in the one case exists
in the other. It would be out of place here to set down the sundry facts which
countenance this hypothesis. I may say, however, that it apparently removes
some of the difficulties which at present perplex the question.

THE ACTIONS OF FORCES ON ORGANIC MATTER. 41

that some of the leading transformations occurring in the
animal organism, are due to this so-called catalysis, appears
necessitated by the general aspect of the facts ; apart from
any such detailed interpretations as the foregoing. "We know
that various amylaceous and saccharine matters taken as food,
are decomposed in their course through the body. We know
that these matters do not become components of the tissues,
but only of the fluids circulating through them ; and that
thus their metamorphosis is not an immediate result of the
organic activities. We know that their stability is such that
the thermal and chemical forces to which they are exposed
in the body, cannot alone decompose them. The only explan-
ation open to us, therefore, is that the transformation of these
oxy-hydro-carbons, into carbonic acid and water, is due to
communicated chemical action.

§ 16. This chapter will have served its purpose if it has
given a conception of the extreme modifiability of organic
matter by surrounding agencies. Even did space permit,
it would be needless to describe in detail the immensely
varied and complicated changes which the forces from mo-
ment to moment acting on them, work in living bodies.
Dealing with biology in its general principles, it concerns us
only to notice how specially sensitive are the substances of
which organisms are built up, to the varied influences that
act upon organisms. And their special sensitiveness has been
made sufficiently manifest, in the several foregoing sections.

CHAPTER III.

THE RE-ACTIONS OF ORGANIC MATTER ON FORCES.

§ 17. Re-distributions of Matter, imply concomitant re-
distributions of Motion. That which under one of its aspects
we contemplate as an alteration of arrangement among the
parts of a body, is, under a correlative aspect, an alteration
of arrangement among certain momenta whereby these parts
are impelled to their new positions. At the same time that
a force, acting differently on the different units of an aggre-
gate, changes their relations to each other ; these units, re-
acting differently on the different parts of the force, work
equivalent changes in the relations of these to one another.
Inseparably connected as they are, these two orders of phe-
nomena are liable to be confounded together. It is very
needful, however, to distinguish between them. In the last
chapter, we took a rapid survey of the re-distributions which
forces produce in organic matter ; and here we must take a
like survey of the simultaneous re-distributions undergone by
the forces.

At the outset we are met by a difficulty. The parts of an
inorganic mass undergoing re-arrangement by an incident
force, are, in most cases, passive — do not complicate those
necessary re-actions that result from their inertia, by other
forces which they originate. But in organic matter, the
re-arranged parts do not re-act in virtue of their inertia only ;
they are so constituted that the incident force usually sets up

42

THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 43

in them other actions which are much more important. In-
deed, what we may call the indirect re-actions thus caused,
are so great in their amounts compared with the direct re-
actions, that they quite obscure them.

In strictness, these two kinds of re-action should not be
dealt with together. The impossibility of separating them,
however, compels us to disregard the distinction between
them. Under the above general title, we must include both
the immediate re-actions and those re-actions mediately
produced, which are among the most conspicuous of vital
phenomena.

§ 18. From organic matter, as from all other matter,
incident forces call forth that re-action which we know as
heat. More or less of molecular vibration almost necessarily
results, when, to the forces at work among the molecules
of any aggregate, other forces are added. Experiment
abundantly demonstrates this in the case of inorganic
masses ; and it must equally hold in the case of organic
masses. In both cases the force which, more mark-

edly than any other, produces this thermal re-action, is that
which causes the union of different substances with each
other. Though inanimate bodies admit of being greatly
heated by pressure and by the electric current, yet the
evolutions of heat thus induced, are neither so common, nor
in most cases so conspicuous, as those resulting from chemical
combination. And though in animate bodies, there are
doubtless certain amounts of heat generated by other actions ;
yet these are all secondary to the heat generated by the
action of oxygen on the substances composing the tissues and
the substances contained in them. Here, however,

we see one of the characteristic distinctions between inani-
mate and animate bodies. Among the first, there are but
few which ordinarily exist in a condition to evolve the heat
caused by chemical combination ; and such as are in this
condition soon cease to be so, when chemical combination

44 TIIE DATA OF BIOLOGY.

and genesis of heat once begin in them. Whereas among
the second, there universally exists the ability, more or less
decided, thus to evolve heat ; and the evolution of heat, in
some cases very slight and in no cases very great, continues
as long as they remain animate bodies.

The relation between active change of matter and re-active
genesis of atomic vibration, is clearly shown by the contrasts
between different organisms, and between different states and
parts of the same organism. In plants, the genesis of heat is
extremely small, in correspondence with their extremely
small production of carbonic aid : those portions only, as
flowers and germinating seeds, in which considerable oxidation
is going on, having a decidedly raised temperature. Among
animals, we see that the hot-blooded are those which expend
much force and respire actively. We see that though such
creatures as insects are scarcely at all warmer than the surround-
ing air when they are still, they rise several degrees above it
when they exert themselves ; and that in creatures like our-
selves, which habitually maintain a heat much greater than
that of their medium, exercise is accompanied by an ad-
ditional production of heat, often to an inconvenient extent.

This molecular agitation accompanying the molecular
re-arrangements that are caused by oxygen taken into the
animal organism, must result both from the union of oxygen
with those nitrogenous matters of which the tissues are
composed, and from its union with those non-nitrogenous
matters which are diffused through the tissues. Just as much
heat as would be caused by the oxidation of such matters
out' of the body, must be caused by their oxidation in the
body. In the one case as in the other, the heat must be re-
garded as a concomitant. Whether the distinction
made by Liebig between nitrogenous substances as tissue-
food, and non-nitrogenous substances as heat-food, be true or
not in a narrower sense, it cannot be accepted in the sense
that tissue-food is not also heat-food. Indeed he does not
himself assert it in this sense. The ability of carnivorous

THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 4:5

animals to live and generate heat while consuming matter that
is almost exclusively nitrogenous, to say nothing of the con-
stant relation above shown between functional activity and the
evolution of heat, suffices to prove that the nitrogenous com-
pounds forming the tissues are heat-producers, as well as the
non-nitrogenous compounds circulating among and through
the tissues. But it is possible that this antithesis is not

true even in the more restricted sense. It seems quite an
admissible hypothesis that the hydro-carbons and oxy-hydro-
carbons which, in traversing the system, are transformed by
communicated chemical action, evolve during their transform-
ation, not heat alone, but also other kinds of force. It may be
that as the nitrogenous matter, while falling into more stable
molecular arrangements, generates both that molecular agi-
tation called heat, and such other molecular movements as are
resolved into forces expended by the organism ; so, too, does
the non-nitrogenous matter. Or perhaps the concomitants of
this metamorphosis of non-nitrogenous matter, vary with the
conditions. Heat alone may result when it is transformed
while in the circulating fluids, but partly heat, and partly
another force, when it is transformed in some active tissue that
has absorbed it : just as coal, though producing little else but
heat as ordinarily burnt, has its heat partially transformed into
mechanical motion if burnt in a steam-engine furnace. In
such case, the antithesis of Liebig would be reduced to this ;
— that whereas nitrogenous substance is tissue-food both as
material for building-up tissue and as material for its function ;
non-nitrogenous substance is tissue-food only as material for
function.

There can be no doubt that this thermal re-action which
chemical action from moment to moment produces in the body,
is from moment to moment an aid to further chemical
action. We before saw (First Principles, § 103) that a state
of raised molecular vibration, is favourable to those re-dis-
tributions of matter and motion which constitute Evolution.
We saw that in organisms distinguished by the amount and

46 THE DATA OF BIOLOGY.

rapidity of such re-distributions, this raised state of molecular
vibration is conspicuous. And we here see that this raised
state of molecular vibration, is itself a continuous consequence
of the continuous molecular re-distributions it facilitates.
The heat generated by each increment of chemical change,
makes possible the succeeding increment of chemical change.
In the body this connexion of phenomena is the same as we
see it to be out of the body. Just as in a burning piece of
wood, the heat given out by the portion actually combining
with oxygen, raises the adjacent portion to a temperature at
which it also can combine with oxygen ; so, in a living
animal, the heat produced by oxidation of each portion of
tissue, maintains the temperature at which the unoxidized
portions can be readily oxidized.

§ 19. Among the forces called forth from organisms by
re-action against the actions to which they are subject, is
Light. Phosphorescence is in some few cases displayed by
plants — especially by certain fungi. Among animals it is
comparatively common. All know that there are several
kinds of luminous insects ; and many are familiar with the
fact that luminosity is a characteristic of various marine
creatures.

Most of the evidence goes to show that this evolution of
light, as well as the evolution of heat, is consequent on oxi-
dation of the tissues. Light, like heat, is the expression of a
raised state of molecular vibration : the diiference between
them being a difference in the rates of vibration. Hence by
chemical action on substances contained in the organism, heat
or light may be produced, according to the character of the
resulting molecular vibrations. The inference that

oxidation is the cause of this luminosity, does not, however,
rest only on d priori grounds. It is supported by experi-
mental evidence. In phosphorescent insects, the continuance
of the light is found to depend on the continuance of respira-
tion ; and any exertion which renders respiration more active,

THE KE-ACTIONS OF ORGANIC MATTER ON FOKCES. 47

increases the brilliancy of the light. Moreover, by separating
the luminous matter, Prof. Matteucci has shown that its
emission of light is accompanied by absorption of oxygen
and escape of carbonic acid. The phosphorescence

of marine animals has been referred to other causes than
oxidation. In some cases, however, it is, I think, explicable,
without assuming any more special agency. Considering that
in creatures of the genus Noctiluea, for example, to which the
phosphorescence most commonly seen on our own coasts is
due, there is no means of keeping up a constant circulation,
we may infer that the movements of aerated fluids through
their tissues, must be greatly affected by impulses received
from without. Hence it may be that the sparkles visible at
night when the waves break gently on the beach, or when an
oar is dipped into the water, are called forth from these
creatures by the concussion, not because of any unknown
influence it excites, but because, being propagated through
their delicate tissues, it produces a sudden movement of the
fluids and a sudden increase of chemical action. Neverthe-
less, in other phosphorescent animals inhabiting the sea, as
in the Pyrosoma and in certain Annelida, light seems to be
really produced, not by direct reaction on the action of
oxygen, but by some indirect re-action involving a trans-
formation of force.

§ 20. The re-distributions of matter in general, are accom-
panied by electrical disturbances ; and there is abundant
evidence that electricity is generated during those re-distri-
butions that are ever taking place in organisms. Experi-
ments have shown " that the skin and most of the internal
membranes are in opposite electrical states ; " and also that
between different internal organs, as the liver and the stomach,
there are electrical contrasts — such contrasts being greatest
where the processes going on in the compared parts are most
unlike. It has been proved by M. du Bois-Keymond that
when any point in the longitudinal section of a muscle is

48 THE DATA OF BIOLOGY.

connected by a conductor with any point in its transverse
section, an electric current is established ; and further, that
like results occur when nerves are substituted for muscles.
The special causes of these phenomena have not yet been
determined. Considering that the electric contrasts are most
marked where active secretions are going on — considering,
too, that while they do not exist between external parts
which are similarly related to the vascular currents, they do
exist between external parts which are dissimilarly related
to the vascular currents — and considering also that they
are extremely difficult to detect where there are no appre-
ciable movements of fluids ; it may be that they are due
simply to the friction of heterogeneous substances, which is
universally a cause of electric disturbance. But whatever be
the. interpretation, the fact remains the same, that there is
throughout the living organism, an unceasing production of
differences between the electric states of different parts ; and
consequently an unceasing restoration of electric equilibrium
by the establishment of currents among these parts.

Besides these general, and not conspicuous, electrical phe-
nomena which appear to be common to all organisms, vegetal
as well as animal, there are certain special and strongly
marked ones. I refer, of course, to those which have made
the Torpedo and the Gymnotus objects of so much interest.
In these creatures we have a genesis of electricity that is not
incidental on the performance of their different functions by
the different organs ; but one which is itself a function,
having an organ appropriate to it. The character of this
organ in both these fishes, and its largely-developed con-
nexions with the nervous centres, have raised the suspicion,
which various experiments have thus far justified, that in it
there takes place a transformation of what we call nerve-force
into the force known as electricity : this conclusion being
more especially supported by the fact, that substances, such as
morphia and strychnia, which are known to be powerful

THE RE-ACTIOXS OF ORGANIC MATTER ON FORCES. 4:9

nervous stimulants, greatly increase the violence and rapidity
of the electric discharges.

But whether general or special, and in whatever manner
produced these evolutions of electricity are among the
re-actions of organic matter, called forth by the actions to
which it is subject. Though these re-actions are not direct,
but seem rather to be remote consequences of those changes
wrought by external agencies on the organism, they are yet
incidents in that general re-distribution of motion, which
these external agencies initiate ; and as such must here be
noticed.

§ 21. To these known modes of motion, has next to be
added an unknown one. Heat, Light, and Electricity are
emitted by inorganic matter when undergoing changes, as
well as by organic matter. But there is a kind of force mani-
fested in some classes of living bodies, which we cannot
identify with any of the forces manifested by bodies that are
not alive, — a force which is thus unknown, in the sense that
it cannot be assimilated with any otherwise-recognized class.
I allude to what is called nerve-force.

This is habitually generated in all animals, save the lowest,
by incident forces of every kind. The gentle and violent
mechanical contacts, which in ourselves produce sensations
of touch and pressure — the additions and abstractions of mole-
cular vibration, which in ourselves produce sensations of
heat and cold ; produce in all creatures that have nervous
systems, certain nervous disturbances — disturbances which,
as in ourselves, are either communicated to the chief nervous
centre, and there constitute consciousness, or else result in
merely physical processes that are set going elsewhere in the
organism. In special parts distinguished as organs of sense,
other external actions bring about other nervous re-actions ;
that show themselves either as special sensations, or as ex-
citements which, without the intermediation of consciousness,

50 THE DATA OF BIOLOGY.

beget actions in muscles or other organs. Besides

neural discharges that follow the direct incidence of external
forces, there are others ever being caused by the incidence of
forces which, though originally external, have become internal
by absorption into the organism of the agents exerting them.
For thus may be classed those neural discharges that from
moment to moment result from modifications of the tissues,
wrought by substances carried to them in the blood. That
the unceasing change of matter which oxygen and other
agents produce throughout the system, is accompanied by a
genesis of nerve-force, is shown by various facts ; — by the fact
that nerve-force is no longer generated, if oxygen be with-
held, or the blood prevented from circulating ; by the fact that
when the chemical transformation is diminished, as during
sleep with its slow respiration and circulation, there is a
diminution in the quantity of nerve-force ; in the fact that an
excessive expenditure of nerve-force, involves excessive re-
spiration and circulation, and excessive waste of tissue. To
these proofs that nerve-force is evolved in greater or less quan-
tity, according as the conditions to rapid molecular change
throughout the body, are well or ill fulfilled ; may be added
proofs that certain special molecular actions, are the causes
of these special re-actions. The effects of alcohol, ether,
chloroform, and the vegeto-alkalies, put beyond doubt the
inference, that the overthrow of molecular equilibrium by
chemical affinity, when it occurs at certain places in the body,
results in the overthrow of equilibrium in the nerves pro-
ceeding from these places — results, that is, in the propagation

through these nerves, of the change called a nervous dis-
cs J G

charge. Indeed, looked at from this point of view,

the two classes of nervous changes — the one initiated from
without and the other from within — are seen to merge into
one class. Both of them may be traced to metamorphosis of
tissue. There can be little doubt that the sensations of
touch and pressure, are consequent on accelerated changes of
matter, produced by mechanical disturbance of the mingled

THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 51

fluids and solids composing the parts affected. There is
abundant evidence that the sensation of taste, is due to the
chemical actions set up by particles which find their way
through the membrane covering the nerves of taste ; for, as
Prof. Graham points out, sapid substances all belong to the
class of crystalloids, which are able rapidly to permeate
animal tissue, while colloids, which cannot pass through
animal tissue, are all insipid. Similarly with the sense of
smell. Substances which excite this sense, are necessarily
more or less volatile ; and their volatility being the result of
their molecular mobility, implies that they have in a high
degree, the power of getting at the olfactory nerves by pene-
trating their mucous investment. Again, the facts which
photography has familiarized us with, make it clear that
those nervous impressions called colours, are primarily due
to certain changes wrought by light in the substance of the
retina. And though, in the case of hearing, we cannot so
clearly trace the connexion of cause and effect ; yet as we see
that the auditory apparatus is one fitted to intensify those
vibrations constituting sound, and to convey them to a recep-
tacle containing fluid in which nerves are immersed ; it can
scarcely be doubted that the sensation of sound proximately
results from atomic re-arrangements caused in these nerves
by the vibrations of the fluid : knowing, as we do, that the
re-arrangement of atoms is in all cases aided by agita-
tion. Perhaps, however, the best proof that nerve-
force, whether peripheral or central in its origin, results from
chemical transformation, lies in the fact that most of the
chemical agents which powerfully affect the nervous system,
affect it whether applied at the centre or the periphery. Vari-
ous acids, mineral and vegetal, are tonics — the stronger ones
being usually the stronger tonics ; and this which we call
their acidity, implies a power in them of acting on the nerves
of taste, while the tingling or pain that follows their absorp-
tion through the skin, implies that the nerves of touch are
acted on by them. Similarly with certain vegeto-alkalies

52 THE DATA OF BIOLOGY.

which are peculiarly bitter. These by their bitterness, show
that they affect the extremities of the nerves ; while by their
tonic properties, they show that they affect the nervous
centres — the most intensely bitter among them, strychnia,
being the most powerful nervous stimulant. However true
it may be that this relation in not a regular one, since opium,
hashish, and some other drugs, which work marked effects on
the brain, are not remarkably sapid — however true it may be
that there are relations between particular substances and
particular parts of the nervous system ; yet such instances
do but qualify, without negativing, the general proposition.
The truth of this proposition can scarcely be doubted when,
to the evidence above given, is added the fact that various
condiments and aromatic drugs are given as nervous stimu-
lants ; and the fact that anaesthetics, besides the general effects
they produce when inhaled or swallowed, produce local effects
of like kind when absorbed through the skin ; and the fact
that ammonia, which in consequence of its extreme molecular
mobility, so quickly and so violently excites the nerves be-
neath the skin, as well as those of the tongue and the nose,
is a rapidly-acting stimulant when taken internally.

Whether we shall ever know anything more of this nerve-
force, than that it is some species of molecular disturbance
that is propagated from end to end of a nerve, it is impossi-
ble to say. Whether a nerve is merely a conductor, which
delivers at one of its extremities an impulse received at the
other ; or whether, as some now think, it is itself a generator
of force which is initiated at one extremity and accumulates
in its course to the other extremity ; are also questions which
cannot yet be answered. All we know is, that forces capable
of working molecular changes in nerves, are capable of
calling forth from them manifestations of activity — dis-
charges of some force, which, though probably allied to elec-
tricity, is not identical with it. And our evidence that nerve-
force is thus originated, consists not only of such facts as the
above, but also of more conclusive facts established by direct

THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 53

experiments on nerves — experiments which show that nerve-
force is generated when the cut end of a nerve is either me-
chanically irritated, or acted on by some chemical agent, or
subject to the galvanic current — experiments which thus
prove that nerve-force is liberated by whatever disturbs the
molecular equilibrium of nerve-substance. And this is all
which it is necessary for us here to understand.

§ 22. The most important of these re-actions called forth
from organisms by surrounding actions, remains to be noticed.
To the above various forms of insensible motion thus caused,
we have to add sensible motion. On the production of this
mode of force, more especially depends the possibility of all
vital phenomena. It is, indeed, usual to regard the power of
generating sensible motion, as confined to one out of the two
organic sub-kingdoms ; or, at any rate, as possessed by but
few members of the other. On looking closer into the matter,
however, we see that plant-life as well as animal-life, is uni-
versally accompanied by certain manifestations of this power ;
and that plant-life could not otherwise continue.

Through the humblest, as well as through the highest, ve-
getal organisms, there are ever going on certain re-distribu-
tions of matter. In protophytes the microscope shows us an
internal transposition of parts, which when not active enough
to be immediately visible, is proved to exist by the changes
of arrangement that become manifest in the course of hours
and days. In the individual cells of many higher plants, an
active movement among the contained granules may be wit-
nessed. And well-developed cryptogams in common with all
phanerogams, exhibit this genesis of mechanical motion still
more conspicuously in the circulation of sap. It might, in-
deed, be concluded a prion, that through plants displaying
much differentiation of parts, an internal movement must be
going on ; since, without it, the mutual dependence of organs
having unlike functions would seem impossible. Be-

sides these motions of fluids kept up internally, plants, espe-

54 THE DATA OF BIOLOGY.

cially of the lower orders, are able to move their external
parts in relation to each other, and also to move about from
place to place. Illustrations in abundance will occur to all
students of recent Natural History — such illustrations as the
active locomotion of the zoospores of many Algee, the rhyth-
mical bendings of the Oscillator ice, the rambling progression
of the Diatomacem. In fact many of these smallest vegetals,
and many of the larger ones in their early stages, display a
mechanical activity not distinguishable from that of the
simplest animals. Among well-organized plants, which are
never locomotive in their adult states, we still not unfre-
quently meet with relative motions of parts. To such fami-
liar cases as those of the Sensitive plant and the Venus'
fly-trap, many others may be added. When its base is
irritated, the stamen of the Berberry flower leans over and
touches the pistil. If the stamens of the common wild Cistus
be gently brushed with the finger, they spread themselves —
bending away from the seed-vessel. And some of the orchid-
flowers, as Mr. Darwin has recently shown, shoot out masses
of pollen on to the entering bee, when its trunk is thrust
down in search of honey.

Though the power of moving is not, as we see, a character-
istic of animals alone, yet in them, considered as a class, it is
manifested to an extent so marked, as practically to become
one of their distinctive characters — indeed, we may say, their
most distinctive character. For it is by their immensely
greater ability to generate mechanical motion, that animals
are enabled to perform those actions which constitute their
visible lives; and it is by their immensely greater ability to
generate mechanical motion, that the higher orders of animals
are most obviously distinguished from the lower orders.
Though, on remembering the seemingly active movements of
infusoria, some will perhaps question this last named con-
trast ; yet, on comparing the quantities of matter propelled
through given spaces in given times, they will see that the
momentum evolved is far less in the protozoa than in the

THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 55

teleozoa. These sensible motions of animals are effected

by various organs under various stimuli. In the humblest
forms, and even in some of the more developed ones which
inhabit the water, locomotion results from the vibrations of
cilia : the contractility resides in these waving hairs that
grow from the surface. Some of the Acale-phce, and their
allies the Polypes, move when mechanically irritated : the
long pendant tentacle of a Physalia is suddenly drawn up if
touched ; and, as well as its tentacles, the whole body of a
Hydra collapses if roughly handled, or jarred by some shock
in its neighbourhood. In all the higher animals however,
and to a smaller degree in many of the lower, sensible mo-
tion is generated by a special tissue, under the special ex-
citement of a neural discharge. Though it is not strictly true
that such animals show no sensible motions otherwise caused ;
since all of them have certain ciliated membranes, and since
the circulation of fluid in them is partially due to osmotic and
capillary actions; yet, generally speaking, we. may say that
their movements are effected only by muscles that contract
only through the agency of nerves.

"What special transformations of force generate these various
mechanical changes, we do not, in most cases, know. Those
re-distributions of fluid, with the alterations of form sometimes
caused by them, that result from osmose, are not, indeed,
quite incomprehensible. Certain motions of plants which,
like those of the " animated oat," follow contact with water,
are easily interpreted ; as are also such other vegetal motions
as those of the Touch-me-not, the Squirting Cucumber, and the
Carpobolus. But we have as yet no clue to the mode in which
molecular movement is transformed into the movement of
masses, in animals. We cannot refer to known causes the
rhythmical action of a Medusa's disc, or that slow decrease of
bulk that spreads throughout the mass of an Alcyonium, when
one of its component individuals has been irritated. Nor
are we any better able to say how the insensible motion
transmitted through a nerve, gives rise to sensible motion in

56 THE DATA OF BIOLOGY.

a muscle. It is true that Science has given to Art, several
methods of changing insensible into sensible motion. By ap-
plying heat to water we vaporize it ; and the movement of its
expanding vapour, we transfer to solid matter ; but it is clear
that the genesis of muscular movement is in no way analogous
to this. The force evolved during chemical transformations
in a galvanic battery, we communicate to a soft iron magnet
through a wire coiled round it ; and it would be quite possi-
ble, by placing near to each other several magnets thus
excited, to obtain, through the attraction of each for its
neighbours, an accumulated movement made up of their
separate movements, and thus to mechanically imitate a mus-
cular contraction ; but from what we know of organic mat-
ter, and the structure of muscle, there is no reason to suppose
that anything analogous to this takes place in it. We

can, however, through one kind of molecular change, produce
sensible changes of aggregation such as possibly might, when
occurring in organic substance, cause sensible motion in
it : I refer to allotropic change. Sulphur, for example, as-
sumes different crystalline and non-crystalline forms at dif-
ferent temperatures; and maybe made to pass backwards
and forwards from one form to another, by slight variations
of temperature : undergoing each time an alteration of bulk.
We know that this allotropism, or rather its analogue iso-
merism, prevails among colloids — inorganic and organic.
We also know that some of these metamorphoses among col-
loids, are accompanied by visible re-arrangements : instance
hydrated silicic acid, which, after passing from its soluble
state to the state of an insoluble jelly, begins, in a few days,
to contract, and to give out part of its contained water. Now,
considering that such isomeric changes of organic as well as
inorganic colloids, are often very rapidly produced by very
slight causes, it seems not impossible that some of the colloids
constituting muscle, may be thus changed by a nervous dis-
charge— resuming their previous condition when the dis-
charge ceases. And it is conceivable that by structural

THE RE- ACTIONS OF ORGANIC MATTER ON FORCES. 57

arrangements, minute sensible motions so caused, may be ac-
cumulated into large sensible motions. There is, however,
no evidence to support this supposition.

§ 23. But the truths which it is here our business espe-
cially to note, are quite independent of hypotheses or inter-
pretations. It is sufficient for the ends we have in view, to
observe that organic matter does exhibit these several conspi-
cuous re-actions, when acted on by incident forces : it is not
requisite that we should know how these re-actions originate.

In the last chapter were set forth the several modes in
which incident forces cause re-distributions of organic mat-
ter ; and in this chapter have been set forth the several modes
in which is manifested the motion accompanying this re-dis-
tribution. There we contemplated under its several aspects,
the general fact, that in consequence of its extreme instability,
organic matter undergoes extensive molecular re-arrange-
ments, on very slight changes of conditions. And here we
have contemplated under its several aspects, the correlative
general fact, that during these extensive molecular re-arrange-
ments, there are necessarily evolved large amounts of force.
In the one case the atoms of which organic matter consists,
are regarded as changing from positions of unstable equi-
librium to positions of stable equilibrium ; and in the other
case they are regarded as giving out in their falls from
unstable to stable equilibrium, certain momenta — momenta
that may be manifested as heat, light, electricity, nerve-
force or mechanical motion, according as the conditions
determine.

I will add only that these evolutions of force are rigor-
ously dependent on these changes of matter. It is a corol-
lary from that primordial truth which, as we have seen,
underlies all other truths, {First Principles, §§ 76, 141,)
that whatever amount of power an organism expends in
any shape, is the correlate and equivalent of a power that
was taken into it from without. On the one hand, it

58 THE DATA OF BIOLOGY.

follows from the persistence of force, that each portion of
mechanical or other energy which an organism exerts, im-
plies the transformation of as much organic matter as con-
tained this energy in a latent state. And on the other hand,
it follows from the persistence of force that no such trans-
formation of organic matter containing this latent energy
can take place, without the energy being in one shape or
other manifested.

CHAPTER IV *

PROXIMATE DEFINITION OF LIFE.

§ 24. To those who accept the general doctrine of Evolu-
tion, it needs scarcely to be pointed out that classifications are
subjective conceptions, which have no absolute demarcations
in Nature corresponding to them. They are appliances by
which we limit and arrange the matters under investigation ;
and so facilitate our thinking. Consequently, when we at-
tempt to define anything complex, or make a generalization
of facts other than the most simple, we can scarcely ever
avoid including more than we intended, or leaving out some-
thing that should be taken in. Thus it happens that on
seeking a definition of Life, we have great difficulty in find-
ing one that is neither more nor less than sufficient. Let
us look at a few of the most tenable definitions that have
been given. While recognizing the inspects in which they
are defective, we shall see what requirements a more com-
plete one must fulfil.

* This chapter and the following two chapters originally appeared in Part
III. of the Principles of Psychology : forming a preliminary which, though indis-
pensable to the argument there developed, was somewhat parenthetical. Having
now to deal with the general science of Biology before the more special one of
Psychology, it becomes possible to transfer these chapters to their proper place.
They have been carefully revised.

59

60 THE DATA OF BIOLOGY.

Schelling said that Life is the tendency to individuation.
This formula, until studied, conveys little meaning. But it
needs only to consider it as illustrated by the facts of develop-
ment, or by the contrasts between lower and higher forms of
life, to recognize its value ; especially in respect of compre-
hensiveness. As before shown, however, {First Principles,
§ 56), it is objectionable, partly on the ground that it refers,
not so much to the functional changes constituting Life, as to
the structural changes of those aggregations of matter which
manifest Life ; and partly on the ground that it includes
under the idea Life, much that we usually exclude from it :
for instance — crystallization.

The definition of Richerand, — " Life is a collection of
phenomena which succeed each other during a limited time
in an organized body," — is liable to the fatal criticism, that
it equally applies to the decay which goes on after death.
For this, too, is " a collection of phenomena which succeed
each other during a limited time in an organized body."

" Life," according to De Blainville, " is the two-fold
internal movement of composition and decomposition, at once
general and continuous." This conception is in some re-
spects too narrow, and in other respects too wide. On the
one hand, while it expresses what physiologists distinguish as
vegetative life, it excludes those nervous and muscular
functions which form the most conspicuous and distinctive
classes of vital phenomena. On the other hand, it describes
not only the integrating and disintegrating processes going on
in a living body, but it equally well describes those going on
in a galvanic battery ; which also exhibits a " two-fold in-
ternal movement of composition and decomposition, at once
general and continuous."

Elsewhere, I have myself proposed to define Life as " the
co-ordination of actions ; " * and I still incline towards this de-
finition as one answering to the facts with tolerable precision.

* See Westminster Review for April, 1852— Art. IV. "A Theory of Popu-
lation."

PROXIMATE DEFINITION OF LIFE. 01

It includes all organic changes, alike of the viscera, the
limbs, and the brain. It excludes the great mass of inor-
ganic changes ; which display little or no co-ordination. By
making co-ordination the specific characteristic of vitality,
it involves the truths, that an arrest of co-ordination is
death, and that imperfect co-ordination is disease. More-
over, it harmonizes with our ordinary ideas of life in its dif-
ferent gradations : seeing that the organisms which we rank
as low in their degree of life, are those which display but
little co-ordination of actions ; and seeing that from these up
to man, the recognized increase in degree of life corresponds
with an increase in the extent and complexity of co-ordina-
tion. But, like the others, this definition includes too much ;
for it may be said of the Solar System, with its regularly-
recurring movements and its self-balancing perturbations,
that it, also, exhibits co-ordination of actions. And how-
ever plausibly it may be argued that, in the abstract, the
motions of the planets and satellites are as properly compre-
hended in the idea of life, as the changes going on in a
motionless, unsensitive seed ; yet, it must be admitted that
they are foreign to that idea as commonly received, and
as here to be formulated.

It remains to add the definition since suggested by Mr.
G. H. Lewis — " Life is a series of definite and successive
changes, both of structure and composition, which take place
within an individual without destroying its identity." The
last fact which this statement has the merit of brino-ins: into
view — the persistence of a living organism as a whole, in
spite of the continuous removal and replacement of its parts
— is important. But otherwise it may be argued, that since
changes of structure and composition, though probably the
causes of muscular and nervous actions, are not the muscular
and nervous actions themselves, the definition excludes the
more visible movements with which our idea of life is most
associated ; and further, that in describing vital changes as
a series, it scarcely includes the fact that many of them, as

G2 THE DATA OF BIOLOGY.

Nutrition, Circulation, Respiration, and Secretion, in their
many subdivisions, go on simultaneously.

Thus, however well each of these definitions expresses
the phenomena of life under some of its aspects, no one of
them is more than approximately true. It may turn out, that
to find a formula which will bear every test is impossible.
Meanwhile, it is possible to frame a more adequate formula
than any of the foregoing. As we shall presently find,
these all omit an essential peculiarity of vital changes in
general — a peculiarity which, perhaps more than any other,
distinguishes them from non-vital changes. Before specify-
ing this peculiarity, however, it will be well to trace our way,
step by step, to as complete an idea of Life as may be reached
from our present stand-point : by doing which, we shall both
see the necessity for each limitation as it is made, and ulti-
mately be led to feel the need for a further limitation.

And here, as the best mode of determining what are those
general characteristics which distinguish vitality from non-
vitality, we shall do well to compare the two most unlike
kinds of vitality, and see in what they agree. Manifestly,
that which is essential to Life must be that which is common
to Life of all orders. And manifestly, that which is common
to all forms of Life, will most readily be seen on contrasting
those forms of Life which have the least in common, or are
the most unlike.*

§ 25. Choosing assimilation, then, for our example of
bodily life, and reasoning for our example of that life
known as intelligence ; it is first to be observed, that they
are both processes of change. Without change, food cannot
be taken into the blood nor transformed into tissue : without

* This paragraph replaces a sentence that, in The Principles of Psychology,
referred to a preceding chapter on " Method ; " in which the mode of procedure
here indicated, was set forth as a mode to be systematically pursued in the choice
of hypotheses. Should opportunity ever permit, this chapter on Method will be
embodied, along with other matter on the same topic, in a General Introduction
to First Principles.

PROXIMATE DEFINITION OF LIFE. C3

change, there can be no getting from premisses to conclusion.
And it is this conspicuous manifestation of change, which
forms the substratum of our idea of Life in general. Doubt-
less we see innumerable changes to which no notion of vital-
ity attaches : inorganic bodies are ever undergoing changes
of temperature, changes of colour, changes of aggregation.
But it will be admitted that the great majority of the phe-
nomena displayed by inorganic bodies, are statical and not
dynamical ; that the modifications of inorganic bodies are
mostly slow and unobtrusive ; that on the one hand, when
we see sudden movements in inorganic bodies, we are apt to
assume living agency, and on the other hand, when we see
no movements in organic bodies, we are apt to assume death.
From all which considerations it is manifest, that be the
requisite qualifications what they may, a definition of Life
must be a definition of some kind of change or changes.

On further comparing assimilation and reasoning, with a
view of seeing in what respect the change displayed in both
differs from non-vital change, we find that it differs in being
not simple change, but change made up of successive changes.
The transformation of food into tissue, involves mastication,
deglutition, chymification, chylification, absorption, and those
various actions gone through after the lacteal ducts have
poured their contents into the blood. Carrying on an argu-
ment necessitates a long chain of states of consciousness;
each implying a change of the preceding state. Inorganic
changes, however, do not in any considerable degree exhibit
this peculiarity. It is true that from meteorologic causes,
inanimate objects are daily, sometimes hourly, undergoing
modifications of temperature, of bulk, of hygrometric and
electric condition. Not only, however, do these modifications
lack that conspicuousness and that rapidity of succession
which vital ones possess, but vital ones form an additional
series. Living as well as not-living bodies are affected
by atmospheric influences ; and beyond the changes which
these produce, living bodies exhibit other changes, more nu-

64 THE DATA OF BIOLOGY.

merous and more marked. So that though organic change
is not rigorously distinguished from inorganic change by
presenting successive phases — though some inanimate objects,
as watches, display phases of change both quick and nu-
merous— though all objects are ever undergoing change of
some kind, visible or invisible — though there is scarcely any
object which does not, in the lapse of time, undergo a con-
siderable amount of change that is fairly divisible into phases;
yet, vital change so greatly exceeds other change in its dis-
play of varying phases, that we may consider this as prac-
tically one of its characteristics. Life, then, as thus roughly
differentiated, may be regarded as change presenting succes-
sive phases ; or otherwise, as a series of changes. And it
should be observed, as a fact in harmony with this concep-
tion, that the higher the life the more conspicuous the varia-
tions. On comparing inferior with superior organisms, these
last will be seen to display more rapid changes, or a more
lengthened series of them, or both.

Contemplating afresh our two typical phenomena, we
may see that vital change is further distinguished from non-
vital change, by being made up of many simultaneous changes.
Assimilation is not simply a series of actions, but includes
many actions going on together. During mastication the
stomach is busy with the food already swallowed ; on which
it is both pouring out solvent fluids and expending muscular
efforts. While the stomach is still active, the intestines are
performing their secretive, contractile, and absorbent func-
tions ; and at the same time that one meal is being digested,
the nutriment obtained from a previous meal is undergoing
that transformation into tissue which constitutes the final act
of assimilation. So also is it, in a certain sense, with mental
changes. Though the states of consciousness which make up
an argument occur in series, yet, as each of these states is
complex — implies the simultaneous excitement of those many
faculties by which the perception of any object or relation
has been effected ; it is obvious that each such change in

PROXIMATE DEFINITION OF LIFE. 65

consciousness implies manj7 component changes. In

this respect too, however, it must be admitted that the
distinction between animate and inanimate is not precise.
No mass of dead matter can have its temperature altered,
without at the same time undergoing an alteration in bulk,
and sometimes also in hygrometric state. An inorganic
body cannot be oxidized, without being at the same time
changed in weight, colour, atomic arrangement, temperature,
and electric condition. And in some vast and mobile aggre-
gates like the sea, the simultaneous as well as the successive
changes displayed, outnumber those going on in an animal.
Nevertheless, speaking generally, a living thing is distin-
guished from a dead thing, by the multiplicity of the changes
at any moment taking place in it. Add to which, that by
this peculiarity, as by the previous one, not only is the vital
more or less clearly marked off from the non-vital ; but
creatures possessing high vitality are marked off from those
possessing low vitality. It needs but to contrast the many
organs co-operating in a mammal, with the few in a polype,
to see that the actions which are progressing together in the
body of the first, as much exceed in number the actions pro-
gressing together in the body of the last, as these do those
in a stone. As at present analyzed, then, Life consists of
simultaneous and successive changes.

Continuing the comparison, we next find that vital changes,
both visceral and cerebral, differ from other changes in their
heterogeneity. Neither the simultaneous acts nor the serial
acts, which together constitute the process of digestion, are
at all alike. The states of consciousness comprised in any
ratiocination are not repetitions of each other, either in com-
position or in modes of dependence. Inorganic processes, on
the other hand, even when like organic ones in the number
of the simultaneous and successive changes they involve, are
unlike them in the homogeneity of these changes. In the
case of the sea, just referred to, it is observable that count-
less as are the actions at any moment going on, they are

G6 the data of biology.

mostly mechanical actions that are to a great degree similar ;
and in this respect widely differ from the actions of any mo-
ment taking place in an organism : which not only belong to
the several classes, mechanical, chemical, thermal, electric, but
present under each of these classes, innumerable unlike actions.
Even where life is nearly simulated, as by the working of a
steam-engine, we may see that considerable as is the number
of simultaneous changes, and rapid as are the successive ones,
the regularity with which they soon recur in the same order
and degree, renders them unlike those varied changes exhi-
bited by a living creature. Still, it will be found that
this peculiarity, like the foregoing ones, does not divide the
two classes of changes with precision ; inasmuch as there are
inanimate things which exhibit considerable heterogeneity of
change : for instance, a cloud. The variations of state which
this undergoes, both simultaneous and successive, are many
and quick ; and they differ widely from each other both in
quality and quantity. At the same instant there may occur
in a cloud, change of position, change of form, change of
size, change of density, change of colour, change of tem-
perature, change of electric state ; and these several kinds of
change are continuously displayed in different degrees and
combinations. Yet notwithstanding this, when we consider
that very few inorganic objects manifest heterogeneity of
change in a marked manner, while all organic objects mani-
fest it ; and further, that in ascending from low to high forms
of life, we meet with an increasing variety in the kinds and
amounts of changes displayed ; we see that there is here
a further leading distinction between organic and inorganic
actions. According to this modified conception, then, Life is
made up of heterogeneous changes both simultaneous and
successive.

If now we look for some point of agreement between the
assimilative and logical processes, by which they are distin-
guished from those inorganic processes that are most like
them in the heterogeneity of the simultaneous and successive

PROXIMATE DEFINITION OF LIFE. 67

changes they comprise, we discover that they are distinguish-
ed by the combination subsisting among their constituent
changes. The acts that make up digestion are mutually de-
pendent. Those composing a train of reasoning are in close
connection. And generally, it is to be remarked of vital
changes, that each is made possible by all, and all are affected
by each. Respiration, circulation, absorption, secretion, in
their many sub-divisions, are bound up together. Muscular
contraction involves chemical change, change of temperature,
and change in the excretions. Active thought influences the
operations of the stomach, of the heart, of the kidneys. But we
miss this union among inorganic processes. Life-like as may
seem the action of a volcano in respect of the heterogeneity
of its many simultaneous and successive changes, it is not life-
like in respect of their combination. Though the chemical,
mechanical, thermal, and electric phenomena exhibited, have
some inter-dependence ; yet the emission of stones, mud, lava,
flame, ashes, smoke, steam, usually takes place irregularly in
quantity, order, intervals, and mode of conjunction. Even
here, however, it cannot be said that inanimate things pre-
sent no parallels to animate ones. A glacier may be instanced
as showing nearly as much combination in its changes as a
plant of the lowest organization. It is ever growing and
ever decaying ; and the rates of its composition and decom-
position preserve a tolerably constant ratio. It moves ; and
its motion is in immediate dependence on its thawing. It
emits a torrent of water, which, in common with its motion,
undergoes annual variations, as plants do. During part
of the year the surface melts and freezes alternately ; and
on these changes are dependent the variations in movement,
and in efflux of water. Thus we have growth, decay, changes
of temperature, changes of consistence, changes of velocity,
changes of excretion, all going on in connexion ; and it may
be as truly said of a glacier as of an animal, that by cease-
less integration and disintegration it gradually undergoes an
entire change of substance without losing its individuality.

G8 THE DATA OF BIOLOGY.

This exceptional instance, however, will scarcely be held to
obscure that broad distinction from inorganic processes,
which organic processes derive from the combination among
their constituent changes. And the reality of this distinction
becomes yet more manifest when we find that, in common
with previous ones, it not only marks off the living from the
not-living, but also things which live little from things which
live much. For while the changes going on in a plant or a
zoophyte are so imperfectly combined that they can continue
after it has been divided into two or more pieces, the com-
bination among the changes going on in a mammal is so
close that no part cut off from the rest can live, and any con-
siderable disturbance of one function causes a cessation of the
others. Life, therefore, as we now regard it, is a com-
bination of heterogeneous changes, both simultaneous and
successive.

Once more looking for a characteristic common to these
two kinds of vital action, we perceive that the combinations
of heterogeneous changes which constitute them, differ from
the few combinations which they otherwise resemble, in re-
spect of definiteness. The associated changes going on in a
glacier, admit of indefinite variation. Under a conceivable
alteration of climate, its thawing and its progression may be
stopped for myriads of years, without disabling it from again
displaying these phenomena under appropriate conditions.
By a geological convulsion, its motion may be arrested with-
out an arrest of its thawing ; or by an increase in the in-
clination of the surface it slides over, its motion may be
accelerated without accelerating its rate of dissolution.
Other things remaining the same, a more rapid deposit of
snow may cause an indefinite increase of bulk ; or, conversely,
the accretion may entirely cease, and yet all the other actions
continue until the mass disappears. Here, then, the combina-
tion has none of that definiteness which, in a plant, marks
the mutual dependence of assimilation, respiration, and cir-
culation ; much less has it that definiteness seen in the

PROXIMATE DEFINITION OF LIFE. 69

mutual dependence of the chief animal functions : no one of
which can be varied without varying the rest : no one of
which can go on unless the rest go on. It is this definiteness
of combination which distinguishes the changes occurring
in a living body from those occurring in a dead one. Decom-
position exhibits both simultaneous and successive changes,
which are to some extent heterogeneous, and in a sense com-
bined ; but they are not combined in a definite manner. They
vary according as the surrounding medium is air, water, or
earth. They alter in nature with the temperature. If the local
conditions are unlike, they progress differently in different
parts of the mass, without mutual influence. They may end in
producing gases, or adipocire, or the dry substance of which
mummies consist. They may occupy a few days, or thousands
of years. Thus, neither in their simultaneous nor in their suc-
cessive changes, do dead bodies display that definiteness of
combination which characterizes living ones. It is

true that in some inferior creatures the cycle of successive
changes admits of a certain indefiniteness — that it may
be apparently suspended for a long period by desiccation or
freezing ; and may afterwards go on as though there had
been no breach in its continuity. But the circumstance
that only a low order of life permits the cycle of its changes
to be thus modified, serves but to suggest that, like the pre-
vious characteristics, this characteristic of definiteness in its
combined changes, distinguishes high vitality from low vital-
ity, as it distinguishes low vitality from inorganic processes.
Hence, our formula as further amended reads thus : — Life is
a definite combination of heterogeneous changes, both simul-
taneous and successive.

Finally, we shall still better express the facts, if, instead of
saying a definite combination of heterogeneous changes, we
say the definite combination of heterogeneous changes. As
it at present stands, the definition is defective both in allow-
ing that there may be other definite combinations of hetero-
geneous changes, and in directing attention to the hetero-

70 THE DATA OF BIOLOGY.

geneous changes rather than to the definiteness of their
combination. Just as it is not so much its chemical elements
which constitute an organism, as it is the arrangement of
them into special tissues and organs ; so it is not so much its
heterogeneous changes which constitute Life, as it is the de-
finite combination of them. Observe what it is that ceases
when life ceases. In a dead body there are going on hetero-
geneous changes, both simultaneous and successive. What
then has disappeared ? The definite combination has dis-
appeared. Mark, too, that however heterogeneous the simul-
taneous and successive changes exhibited by an inorganic
object, as a volcano, we much less tend to think of it as
living, than we do a watch or a steam-engine, which, though
displaying homogeneous changes, displays them definitely
combined. So dominant an element is this in our idea of
Life, that even when an object is motionless, yet, if its parts
be definitely combined, we conclude either that it has had
life, or has been made by something having life. Thus then,
we conclude that Life is — the definite combination of hetero-
geneous changes, both simultaneous and successive.

§ 26. Such is the conception at which we arrive without
changing our stand-point. It is, however, an incomplete
conception. This ultimate formula (which is to a consider-
able extent identical. with one above given — "the co-ordina-
tion of actions ; " seeing that " definite combination " is
synonymous with " co-ordination," and " changes both si-
multaneous and successive" are comprehended under the
term " actions ; '' but which differs from it in specifying the
fact, that the actions or changes are " heterogeneous ") — this
ultimate formula, I say, is after all but proximately correct.
It is true that it does not fail by including the growth of
a crystal ; for the successive changes this implies cannot be
called heterogeneous. It is true that the action of a galvanic
battery is not comprised in it ; since here, too, heterogeneity
is not exhibited by the successive changes. It is true that by

PROXIMATE DEFINITION OF LIFE. 71

tins same qualification the motions of the Solar System are
excluded ; as are also those of a watch and a steam-engine.
It is true, moreover, that while, in virtue of their heteroge-
neity, the actions going on in a cloud, in a volcano, in a
glacier, fulfil the definition ; they fall short of it in lacking
definiteness of combination. It is further true that this
definiteness of combination, distinguishes the changes taking
place in an organism during life, from those which commence
at death. And beyond all this it is true that, as well as
serving to mark off, more or less clearly, organic actions from
inorganic actions, each member of the definition serves to
mark off the actions constituting high vitality from those
constituting low vitality ; seeing that life is high in propor-
tion to the number of successive changes occurring between
birth and death ; in proportion to the number of simultaneous
changes ; in proportion to the heterogeneity of the changes ;
in proportion to the combination subsisting among the
changes ; and in proportion to the definiteness of their com-
bination. Nevertheless, answering though it does to so
many requirements, this definition is essentially defective.
It does not convey a complete idea of the thing contem-
plated. The definite combination of heterogeneous changes,
both simultaneous and successive, is a formula which fails to
call up an adequate conception. And it fails from omitting
the most distinctive peculiarity — the peculiarity of which we
have the most familiar experience, and with which our notion
of Life is, more than with any other, associated. It remains
now to supplement the definition by the addition of this
peculiarity.

CHAPTER V.

THE CORRESPONDENCE BETWEEN LIFE AND ITS
CIRCUMSTANCES.

§ 27. We habitually distinguish between a live object
and a dead one, by observing whether a change which we
make in the surrounding conditions, or one which Nature
makes in them, is or is not followed by some perceptible change
in the object. By discovering that certain things shrink when
touched, or fly away when approached, or start when a noise
is made, the child first roughly discriminates between the
living and the not living ; and the man when in doubt
whether an animal he is looking at is dead or not, stirs it
with his stick ; or if it be at a distance, shouts, or throws a
stone at it. Vegetal and animal life are alike primarily
recognized by this process. The tree that puts ont leaves
when the spring brings a change of temperature, the flower
which opens and closes with the rising and setting of the
sun, the plant that droops when the soil is dry, and re-erects
itself when watered, are considered alive because of these in-
duced changes ; in common with the zoophyte which contracts
on the passing of a cloud over the sun, the worm that comes to
the surface when the ground is continuously shaken, and the
hedgehog that rolls itself up when attacked.

Not only, however, do we habitually look for some response
when an external stimulus is applied to a living organism,
but we perceive a fitness in the response. Dead as well as
living things display changes under certain changes of COn-
72

CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. 73

dition : instance, a. lump of carbonate of soda that effervesces
when dropped into sulphuric acid ; a cord that contracts
when wetted ; a piece of bread that turns brown when held
near the fire. But in these cases, we do not see a connexion
between the changes undergone, and the preservation of the
things that undergo them ; or, to avoid any teleological im-
plication— the changes have no apparent relations to future
external events which are sure or likely to take place. In
vital changes, however, such relations are manifest. Light
being necessary to vegetal life, we see in the action of a
plant which, when much shaded, grows towards the unshaded
side, an appropriateness which we should not see did it grow
otherwise. Evidently the proceeding of a spider, which
rushes out when its web is gently shaken and stays within
when the shaking is violent, conduce better to the obtainment
of food and the avoidance of danger than were the}' reversed.
The fact that we feel surprise when, as in the case of a bird fas-
cinated by a snake, the conduct tends towards self-destruction,
at once shows how generally we have observed an adaptation
of living changes to changes in surrounding circumstances.

Note further the kindred truth, rendered so familiar by
infinite repetition that we forget its significance, that there
is invariably, and necessarily, a conformity between the vital
functions of any organism, and the conditions in which it is
placed — between the processes going on inside of it, and the
processes going on outside of it. We know that a fish can-
not live in air, or a man in water. An oak growing in the
ocean, and a seaweed on the top of a hill, are incredible
combinations of ideas. We find that every animal is limited
to a certain range of climate ; every plant to certain zones of
latitude and elevation. Of the marine flora and fauna, each
species is found exclusively between such and such depths.
Some blind creatures flourish only in dark caves ; the limpet
only where it is alternately covered and uncovered by the
tide ; the red-snow alga rarely elsewhere than in the arctic
regions or among alpine peaks.
6

74 THE DATA OF BIOLOGY.

Grouping together the cases first named, in which a parti-
cular change in the circumstances of an organism is followed
by a particular change in it, and the cases last named, in
which the constant actions occurring within an organism im-
ply some constant actions occurring without it ; we see that
in both, the changes or processes displayed by a living body
are specially related to the changes or processes in its en-
vironment. And here we have the needful supplement to
our conception of Life. Adding this all-important charac-
teristic, our conception of Life becomes — The definite com-
bination of heterogeneous changes, both simultaneous and
successive, in corresj)ondence with external co-existences and
sequences. That the full significance of this addition may be
seen, it will be necessary to glance at the correspondence
under some of its leading aspects.*

§ 28. Neglecting minor requirements, the actions going

* Speaking of " the general idea of Kfe,n M. Comte says : " Cette idee sup-
pose, en effet, non-seulcment celle d'un etre organise de maniere a comporter
l'etat vital, mais aussi celle, non moins indispensable, d'un certain ensemble
d'influences exterieure propres a son accomplissement. Une telle harmonie entre
l'etre vivant et le milieu correspondant, caracterise evidemment la condition fon-
damentale de la vie." Commenting on de Blainvillc's definition of life, which he
adopts, he says : — " Cette lumineuse definition ne me parait laisser rien d'impor-
tant a desirer, si ce n'est une indication plusdirecte et plus explicitedecesdeux
conditions fondamentales co-relatives, necessairement inseparables de l'etat vivant,
un organisme determine et un milieu convenable." It is strange that M. Comte
should have thus recognized the necessity of a harmony between an organism and
its environment, as a condition essential to life, and should not have seen that the
continuous maintenance of such inner actions as will counterbalance outer actions,
constitutes life. It is the more strange that he should have been so near this
truth and yet missed it, since, besides his wide range of thought, M. Comte is
often remarkable for his clear intuitions. Lest by saying this, I should deepen a
misconception into which some have fallen, let me take the opportunity of stating,
that though I believe some of M. Comte's minor generalizations to be true and
though I recognize the profundity of many incidental observations he makes, I
by no means accept his system. Those general doctrines in which I agree with
him, are those which he holds in common with sundry other thinkers. With all
those general doctrines which are distinctive of his philosophy, I disagree — with
all those at least that I have definite knowledge of ; for beyond the first half of
his " Course of Positive Philosophy," I know his opinions only by hearsay.

CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. 75

on in a plant pre-suppose a surrounding medium containing
at least carbonic acid and water, together with a due supply
of light and a certain temperature. Within the leaves
carbon is being assimilated and oxygen given off ; without
them, is the gas from which the carbon is abstracted, and the
imponderable agents that aid the abstraction. Be the nature
of the process what it may, it is clear that there are external
elements prone to undergo special re-arrangements under
special conditions. It is clear that the plant in sunshine
presents these conditions and so effects these re-arrange-
ments. And thus it is clear that the changes which consti-
tute the plant's life, are in correspondence with co-existences
in its environment.

If, again, we ask respecting the lowest protozoon, how
it lives ; the answer is, that while on the one hand its sub-
stance is ever undergoing oxidation, it is on the other hand
ever absorbing nutriment ; and that it may continue to exist,
the assimilation must keep pace with, or exceed, the oxidation.
If further we ask under what circumstances these combined
changes are possible ; there is the obvious reply, that the
medium in which the protozoon is placed, must contain oxy-
gen and food — oxygen in such quantity as to produce some
disintegration ; food in such quantity as to permit that dis-
integration to be made good. In other words — the two
antagonistic processes taking place internally, imply the pres-
ence externally of materials having affinities that can give
rise to these processes.

Leaving those lowest animal forms revealed by the mi-
croscope, which simply take in through their surfaces the
nutriment and oxygenated fluids coming in contact with
them, we pass to those somewhat higher forms which have
their tissues partially specialized into assimilative and re-
spiratory. In these we see a correspondence between certain
actions in the digestive sac, and the properties of certain sur-
rounding bodies. That a creature of this order may continue
to live, it is necessary not only that there be masses of sub-

76 THE DATA OF BIOLOGY.

stance in the environment capable of transformation into its
own tissue ; but that the introduction of these masses into its
stomach, shall be followed by the secretion of a solvent fluid
that will reduce them to a fit state for absorption. Special
outer properties must be met by special inner properties.

When, from the process by which food is digested, we
turn to the processes by which it is seized, we perceive the
same general truth. The stinging and contractile power of
a polype's tentacle, correspond to the sensitiveness and
strength of the creatures serving it for prey. Unless that
external change which brings one of these creatures in con-
tact with the tentacle, were quickly followed by those inter-
nal changes which result in the coiling and drawing up of
the tentacle, the polype would die of inanition. The funda-
mental processes of integration and disintegration within it,
would get out of correspondence with the agencies and pro-
cesses without it ; and the life would cease.

Similarly, it may be shown that when the creature be-
comes so large that its tissue cannot be efficiently supplied
with nutriment by mere absorption through its limiting
membranes, or duly oxygenated by contact with the fluid
that bathes its surface, there arises a necessity for a circu-
latory system by which nutriment and oxygen may be dis-
tributed throughout the mass ; and the functions of this sys-
tem, being subsidiary to the two primary functions, form
links in the correspondence between internal and external
actions. The like is obviously true of all those subordinate
functions, secretory and excretory, that facilitate oxidation
and assimilation — functions in which we may trace, both co-
temporaneous changes answering to co-existences in the en-
vironment, and successive changes answering to those changes
of composition, of temperature, of light, of moisture, of pres-
sure, which the environment undergoes.

Ascending from the visceral actions to the muscular and
nervous actions, we find the correspondence displayed in a
manner still more obvious. Every act of locomotion implies

CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. 77

the expenditure of certain internal mechanical forces, adapted
in amounts and directions to balance or out-balance certain
external ones. The recognition of an object is impossible
without a harmony between the changes constituting per-
ception, and particular properties co-existing in the environ-
ment. Escape from enemies supposes motions within the
organism, related in kind and rapidity to motions without it.
Destruction of prey requires a particular combination of sub-
jective actions, fitted in degree and succession to overcome a
group of objective ones. And so with those countless auto-
matic processes exemplified in works on animal instinct.

In the highest order of vital changes, the same fact is
equally manifest. The empirical generalization that guides
the farmer in his rotation of crops, serves to bring his actions
into concord with certain of the actions going on in plants
and soil. The rational deductions of the educated navigator
who calculates his position at sea, constitute a series of mental
acts by which his proceedings are conformed to surrounding
circumstances. Alike in the simplest inferences of the child,
and the most complex ones of the man of science, we find a
correspondence between simultaneous and successive changes
in the organism, and co-existences and sequences in its envi-
ronment.

§ 29. This general formula, which thus includes the lowest
vegetal processes as well as the highest manifestations of hu-
man intelligence, will perhaps call forth some criticisms which
it is desirable here to meet.

It may be thought that there are still a few inorganic ac-
tions included in the definition ; as for example that displayed
oy the mis-named storm-glass. The feathery crystallization
which, on a certain change of temperature, takes place in the
solution contained by this instrument, and which afterwards
dissolves to reappear in new forms under new conditions, may
be held to present simultaneous and successive changes that
are to some extent heterogeneous, that occur with some de-

T8 THE DATA OF BIOLOGY.

finiteness of combination, and. above all, occur in correspond-
ence with external changes. In this case vegetal life is sim-
ulated to a considerable extent ; but it is merely simulated.
The relation between the phenomena occurring in the storm-
glass and in the atmosphere respectively, is really not a cor-
respondence at all, in the proper sense of the word. Outside
there is a certain change ; inside there is a change of atomic
arrangement. Outside there is another certain change ; in-
side there is another change of atomic arrangement. But
subtle as is the dependence of each internal upon each ex-
ternal change, the connexion between them does not, in the
abstract, differ from the connexion between the motion of a
straw and the motion of the wind that disturbs it. In either
case a change produces a change, and there it ends. The
alteration wrought by some environing agency on an inani-
mate object, does not tend to induce in it a secondary altera-
tion, that anticipates some secondary alteration in the en-
vironment. But in every living body there is a tendency
towards secondary alterations of this nature ; and it is in
their production that the correspondence consists. The dif-
ference may be best expressed by symbols. Let A be a
change in the environment ; and B some resulting change
in an inorganic mass. Then A having produced B, the ac-
tion ceases. Though the change A in the environment, is
followed by some consequent change a in it ; no parallel se-
quence in the inorganic mass simultaneously generates in it
some change b that has reference to the change a. Bnt if we
take a living body of the requisite organization, and let the
change A impress on it some change C ; then, while in the
environment A is occasioning a, in the living body C will
be occasioning c : of which a and c will show a certain con-
cord in time, place, or intensity. And while it is in the con-
tinuous production of such concords or correspondences that
Life consists, it is by the continuous production of them that
Life is maintained.

The further criticism that may be expected, concerns cer-

CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. 79

tain verbal imperfections in the definition, which it seems
impossible to avoid. It may be fairly urged that the word
correspondence will not include, without straining, the various
relations to be expressed by it. It may be asked : — How can
the continuous processes of assimilation and respiration, cor-
respond with the co-existence of food and oxygen in the en-
vironment ? or again : — How can the act of secreting some
defensive fluid, correspond with some external danger which
may never occur ? or again : — How can the dynamical phe-
nomena constituting perception, correspond with the statical
phenomena of the solid body perceived ? The only reply to
these questions, is, that we have no word sufficiently general
to comprehend all forms of this relation between the organ-
ism and its medium, and yet sufficiently specific to convey an
adequate idea of the relation ; and that the word correspond-
ence seems the least objectionable. The fact to be expressed
in all cases, is, that certain changes, continuous or discon-
tinuous, in the organism, are connected after such a manner
that, in their amounts, or variations, or periods of occurrence,
or modes of succession, they have a reference to external ac-
tions, constant or serial, actual or potential — a reference such
that a definite relation among any members of the one group,
implies a definite relation among certain members of the
other group ; and the word correspondence appears the best
fitted to express this fact.

§ 30. The presentation of the phenomena under this gen-
eral form, suggests how our definition of Life may be reduced
to its most abstract shape ; and perhaps its best shape. By
regarding the respective elements of the definition as relations ;
we avoid both the circumlocution and the verbal inaccuracy ;
and that we may so regard them with propriety is obvious.
If a creature's rate of assimilation is increased in consequence
of a decrease of temperature in the environment ; it is that
the relation between the food consumed and heat produced, is
so re-adjusted by multiplying both its members, that the

80 THE DATA OF BIOLOGY.

altered relation in the surrounding medium between the
quantity of heat absorbed from, and radiated to, bodies of a
given temperature, is counterbalanced. If a sound or a scent
wafted to it on the breeze, prompts the stag to dart away
from the deer-stalker ; it is that there exists in its neighbour-
hood a relation between a certain sensible property and cer-
tain actions dangerous to the stag, while in its organism
there exists an adapted relation between the impression this
sensible property produces, and the actions by which danger
is escaped. If inquiry has led the chemist to a law enabling
him to tell how much of any one element will combine with
so much of another ; it is that there has been established
in him specific mental relations, which accord with specific
chemical relations in the things around. Seeing, then, that in
all cases we may consider the external phenomena as simply
in relation, and the internal phenomena also as simply in re-
lation ; the broadest and most complete definition of Life will
be — The continuous adjustment of internal relations to ex-
ternal relations*

While it is simpler, this modified formula has the further
advantage of being somewhat more comprehensive. To say
that it includes not only those definite combinations of simul-
taneous and successive changes in an organism, which cor-
respond to co-existences and sequences in the environment,
but also those structural arrangements which enable the or-
ganism to adapt its actions to actions in the environment,
may perhaps be going too far; for though these structural
arrangements present internal relations adjusted to external
relations, yet the continuous adjustment of relations can
scarcely be held to include ajixed adjustment already made.
Clearly, Life, which is made up of dynamiccd phenomena,
cannot be defined in terms that shall at the same time define
the apparatus manifesting it, which presents only statical
phenomena. But wmile this antithesis serves to remind us
that the fundamental distinction between the organism and

* In further elucidation of this general doctrine, see First Principles, § 25.

n

CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. 81

its actions, is as wide as that between Matter and Motion, it
at the same time draws attention to the fact, that if the
structural arrangements of the adult are not properly in-
cluded in the definition, yet the developmental processes by
which those arrangements were established, are included
For that process of evolution during which the organs of the
embryo are fitted to their prospective functions, is from be
ginning to end the gradual or continuous adjustment of in
ternal relations to external relations. Moreover, those struc-
tural modifications of the adult organism, which, under change
of climate, change of occupation, change of food, slowly bring
about some re-arrangement in the organic balance, must simi-
larly be regarded as continuous adjustments of internal re-
lations to external relations. So that not only does the de-
finition, as thus expressed, comprehend all those activities,
bodily and mental, which constitute our ordinary idea of Life ;
but it also comprehends, both those processes of development
by which the organism is brought into general fitness for
these activities, and those after-processes of adaptation by I
which it is specially fitted to its special activities. • — i

Nevertheless, superior as it is in simplicity and comprehen-
siveness, so abstract a formula as this is scarcely fitted for
our present purpose. Reserving its terms for such use as oc-
casion may dictate, it will be best commonly to employ its
more concrete equivalent — to consider the internal relations
as "definite combinations of simultaneous and successive
changes ; " the external relations as " co-existences and se-
quences ; " and the connexion between them as a " corre-
spondence."

CHAPTER VI.

THE DEGREE OF LIFE VARIES AS THE DEGREE OF
CORRESPONDENCE.

§ 31. Already it has been shown respecting each other
qualification included in the foregoing definition, that the life
is high in proportion as that qualification is well fulfilled ;
and it is now to be remarked, that the same thing is especially
true respecting this last qualification — the correspondence be-
tween internal and external relations. It is manifest dj)7'iori,
that since changes in the physical state of the environment, as
also those mechanical actions and those variations of available
food which occur in it, are liable to stop the processes going
on in the organism ; and since the adaptive changes in the
organism have the effects of directly or indirectly counter-
balancing these changes in the environment ; it follows that
the life of the organism will be short or long, low or high,
according to the extent to which changes in the environment
are met by corresponding changes in the organism. Allow-
ing a margin for perturbations, the life will continue only
while the correspondence continues ; the completeness of the
life will be proportionate to the completeness of the corre-
spondence ; and the life will be perfect only when the corre-
spondence is perfect. Not to dwell in general statements,
however, let us contemplate this truth under its concrete
aspects.

§ 32. In life of the lowest order, we find that only the

82

TIIE LIFE VARIES AS THE CORRESPONDENCE. 83

most prevalent coexistences and sequences in the environ-
ment, have any simultaneous and successive changes answer-
ing to them in the organism. A plant's vital processes
display adjustment solely to the continuous coexistence of
certain elements and forces surrounding its roots and leaves ;
and vary only with the variations produced in these ele-
ments and forces by the sun — are unaffected by the countless
mechanical and other changes occurring around ; save when
accidentally arrested by these. The life of a worm is made
up of actions referring almost exclusively to the tangible pro-
perties of adjacent things. All those visible and audible
changes which happen near it, and are connected with other
changes that may presently destroy it, pass unrecognized —
produce in it no adapted changes : its only adjustment of in-
ternal relations to external relations of this order, is seen
when it escapes to the surface on feeling the vibrations pro-
duced by an approaching mole. Adjusted as are the pro-
ceedings of a bird, to a far greater number of coexistences and
sequences in the environment, cognizable by sight, hearing,
scent, and their combinations ; and numerous as are the
dangers it shuns and the needs it fulfils, in virtue of this ex-
tensive correspondence ; it exhibits no such actions as those
by which a human being counterbalances variations in tem-
perature and supply of food, consequent on the seasons. And
when we see the plant eaten, the worm trodden on, the bird
dead from starvation ; we see alike that the death is an arrest
of such correspondence as existed ; that it occurred when
there was some change in the environment to which the or-
ganism made no answering change ; and that thus, both in
shortness and simplicity, the life was incomplete in propor-
tion as the correspondence was incomplete. Progress towards
more prolonged and higher life, evidently implies an ability
to respond to less general coexistences and sequences. Each
step upwards must consist in adding to the previously-adjasted
relations which the organism exhibits, some further relation
parallel to a further relation in the environment. And the

8J: THE DATA OF BIOLOGY.

greater correspondence thus established, must, other things
equal, show itself both in greater complexity of life, and
greater length of life — a truth which will be duly realized on
remembering that enormous mortality which prevails among
lowly-organized creatures, and that gradual increase of lon-
gevity and diminution of fertility which we meet with on as-
cending to creatures of higher and higher development.

It must, however, be remarked, that while length and com-
plexity of life are, to a great extent, associated— while a
more extended correspondence in the successive changes,
commonly implies increased correspondence in the simul-
taneous changes ; yet it is not uniformly so. Between the
two great divisions of life — animal and vegetal — this contrast
by no means holds. A tree may live a thousand years,
though the simultaneous changes going on in it answer only
to the few chemical affinities in the air and the earth, and
though its serial changes answer only to those of day and
night, of the weather and the seasons. A tortoise, which
exhibits in a given time nothing like the number of internal
actions adjusted to external ones, that are exhibited by a dog,
yet lives far longer. The tree by its massive trunk, and the
tortoise by its hard carapace, are saved the necessity of re-
sponding to those many surrounding mechanical actions which
organisms not thus protected must respond to or die ; or
rather — the tree and the tortoise display in their structures,
certain simple statical relations adapted to meet countless
dynamical relations external to them. But notwithstanding
the qualifications suggested by such cases, it needs but to
compare a microscopic fungus with an oak, an animalcule
with a shark, a mouse with a man, to recognize the fact that
this increasing correspondence of its changes with those of
the environment, which characterizes progressing life, ha-
bitually shows itself at the same time in continuity and in
complication.

Even were not the connexion between length of life and
complexity of life thus conspicuous, it would still be true

THE LIFE VARIES AS THE CORRESPONDENCE. 85

that the degree of life varies with the degree of correspond-
ence. For if the lengthened existence of a tree be looked
upon as tantamount to a considerable degree of life ; then it
must be admitted that its lengthened display of correspond-
ences is tantamount to a considerable degree of correspond-
ence. If otherwise it be held, that notwithstanding its much
shorter existence, a dog must rank above a tortoise in degree
of life, because of its superior activity ; then it is implied that
its life is higher, because its simultaneous and successive
changes are more complex and more rapid — because the
correspondence is greater. And since we regard as the high-
est life, that which, like our own, shows great complexity in
the correspondences, great rapidity in the succession of them,
and great length in the series of them ; the equivalence
between degree of life and degree of correspondence, is un-
questionable.

§ 33. In further elucidation of this general truth, and
especially in explanation of the irregularities just referred to,
it requires to be observed, that as the life becomes higher
the environment itself becomes more complex. Though,
literally, the environment means all surrounding space with
the coexistences and sequences contained in it ; yet, practi-
cally, it often means but a small part of this. The environ-
ment of an entozoon, can scarcely be said to extend beyond
the body of the animal in which the entozoon lives. That of
a fresh-water alga is, virtually, limited to the ditch inhab-
ited by the alga. And understanding the term in this re-
stricted sense, we shall see that the superior organisms
inhabit the more complicated environments.

Thus, contrasted with that found on land, the lower life is
that found in the sea ; and it has the simpler environment.
Marine creatures are affected by a smaller number of co-
existences and sequences than terrestrial ones. Being very
nearly of the same specific gravity as the surrounding
medium, they have to contend with less various mechanical

86 THE DATA OF BIOLOGY.

actions. The zoophyte rooted to a stone, and the acalephe
passively borne along in the current, need to undergo no
internal changes such as those by which the caterpillar meets
the varying effects of gravitation, while creeping over and
under the leaves. Again, the sea is liable to none

of those extreme and rapid alterations of temperature which
the air suffers. JS'ight and day produce no appreciable
modifications in it ; and it is comparatively little affected by
the seasons. Thus its contained fauna show no marked cor-
respondences similar to those by which air-breathing crea-
tures counterbalance thermal changes. Further, in
respect to the supply of nutriment the conditions are more
simple. The lower tribes of animals inhabiting the water,
like the plants inhabiting the air, have their food brought to
them. The same current which brings oxygen to the oyster,
also brings it the microscopic organisms on which it
lives : the disintegrating matter and the matter to be inte-
grated, coexist under the simplest relation. It is otherwise
with land animals. The oxygen is everywhere ; but that
which is needed to neutralize its action is not everywhere : it
has to be sought ; and the conditions under which it is to be
obtained are more or less complex. So too with
that liquid by the agency of which the vital processes are
carried on. To marine creatures, water is ever present, and by
the lowest is passively absorbed ; but to most creatures living
on the earth and in the air, it is made available only through
those nervous changes constituting perception, and those
muscular ones by which drinking is effected. Simi-
larly, the contrast might be continued with respect to the
electric and hygrometric variations ; and the greater multi-
plicity of optical and acoustic phenomena with which ter-
restrial life is surrounded. And tracing upwards from the
amphibia the widening extent and complexity which the
environment, as practically considered, assumes — observing
further how increasing heterogeneity in the flora and fauna
of the globe, itself progressively complicates the environment

THE LIFE VARIES AS THE CORRESPONDENCE. 87

of each species of organism — it might finally be shown that
the same general truth is displayed in the history of mankind :
whose advance in civilization has been simultaneous with
their advance from the less varied requirements of the torrid
zone to the more varied requirements of the temperate zone ;
whose chief steps have been made in regions presenting a
complicated physical geography ; and who, in the course of
their progress, have been adding to their physical environ-
ment a social environment that has been growing even more
involved. Thus, speaking generally, it is clear that those re-
lations in the environment to which relations in the organism
must correspond, themselves increase in number and intricacy
as the life assumes a higher form.

§ 3-i. To make yet more manifest the fact, that the degree
of life varies as the degree of correspondence, I may here
point out, that those other distinctions successively noted
when contrasting vital changes with non-vital changes, are
all implied in this last distinction — their correspondence
with external co-existences and sequences. And to this may
be added the supplementary fact, that the increasing fulfil-
ment of those other distinctions which we found to accompany
increasing life, is involved in the increasing fulfilment of this
last distinction. To descend to particulars : — We saw that
living organisms are characterized by successive changes ;
and that as the life becomes higher, the successive changes
become more numerous. "Well, the environment is full of
successive changes, both positive and relative ; and the
greater the correspondence, the greater the number of suc-
cessive changes an organism must display. We saw that life
presents simultaneous changes ; and that the more elevated
it is, the more marked the multiplicity of them. Well,
besides countless phenomena of coexistence in the environ-
ment, there are often many changes occurring in it at the
same moment ; and hence increased correspondence with it,
supposes an increased display of simultaneous changes in the

88 THE DATA OF BIOLOGY.

organism. Similarly with the heterogeneity of the changes.
In the environment the relations are very varied in their
kinds; and hence, as the organic actions come more and more
into correspondence with them, they also must become very
varied in their kinds. So again is it, even with definiteness
of combination. For though the inorganic bodies of wThich
the environment mainly consists, do not present definitely-
combined changes, yet they present definitely-combined
properties ; and thoguh the minor meteorologic variations of
the environment, do not show much definiteness of combina-
tion, yet those resulting from day and night and the seasons
do. Add to which, that as the environment of each organism
comprehends all those other organisms existing within its
sphere of life — as the most important and most numerous
surrounding changes with which each animal has to deal,
are the definitely-combined changes exhibited by other ani-
mals, whether prey or enemies ; it results that definiteness
of combination is a general characteristic of the external
changes with which internal ones have to correspond. Hence,
increase of correspondence involves increased definiteness of
combination. So that throughout, the correspondence of
the internal relations with the external ones, is the essential
thing ; and all the special characteristics of the internal rela-
tions, are but the collateral results of this correspondence.

§ 35. As affording the simplest and most conclusive proof
that the degree of life varies as the degree of correspondence,
it remains to point out that perfect correspondence would be
perfect life. Were there no changes in the environment but
such as the organism had adapted changes to meet ; and were
it never to fail in the efficiency with which it met them ; there
would be eternal existence and universal knowledge. Death
by natural decay, occurs because in old age the relations be-
tween assimilation, oxidation, and genesis of force going on
in the organism, gradually fall out of correspondence with the
relations between oxygen and food and absorption of heat by

THE LIFE VARIES AS THE CORRESPONDENCE. 89

the environment. Death from disease, arises either when the
organism is congenitally defective in its power to balance the
ordinary external actions by the ordinary internal actions, or
when there has taken place some unusual external action to
which there was no answering internal action. Death by
accident, implies some neighbouring mechanical changes of
which the causes are either unobserved from inattention, or
are so intricate that their results cannot be foreseen ; and
consequently certain relations in the organism are not adjusted
to the relations in the environment. Manifestly, if, to every
outer coexistence and sequence by which it was ever in any
degree affected, the organism presented an answering process
or act ; the simultaneous changes would be indefinitely nu-
merous and complex, and the successive ones endless — the
correspondence would be the greatest conceivable, and the
life the highest conceivable, both in degree and in length.

§ 36. Before closing the chapter, it will be useful to com-
pare the definition of Life here set forth, with the defini-
tion of Evolution set forth in First Principles. Living
bodies being bodies which display in the highest degree the
structural changes constituting Evolution ; and Life being
made up of the functional changes that accompany these
structural changes ; we ought to find a certain harmony
between the definitions of Evolution and of Life. Such a
harmony is not wanting.

The first distinction we noted between the kind of change
shown in Life, and other kinds of change, was its serial
character : we saw that vital change is substantially unlike
non-vital change, in being made up of successive changes.
Xow since organic bodies display in so much higher a de-
gree than inorganic bodies, those continuous differentiations
and integrations which constitute Evolution ; and since the
re-distributions of matter thus carried so far in a compara-
tively short period, imply concomitant re-distributions of mo-
tion ; it is clear that in a given time, organic bodies must

90 THE DATA OF BIOLOGY.

undergo changes so comparatively numerous as to render the
successiveness of their changes a marked characteristic. And
it will follow a priori, as we found it to do d posteriori, that
the organisms exhibiting Evolution in the highest degree,
exhibit the longest or the most rapid succession of changes,
or both. Again, it was shown that vital change is

distinguished from non-vital change by being made up of
many simultaneous changes ; and also that creatures possess-
ing high vitality are marked off from those possessing low
vitality, by the far greater number of their simultaneous
changes. Here too there is entire congruity. In First
Principles, § 116, we reached the conclusion, that a force
falling on any aggregate is divided into several forces ; that
when the aggregate consists of parts that are unlike, each
part becomes a centre of unlike differentiations of the inci-
dent force ; and that thus the multiplicity of such differen-
tiations must increase with the multiplicity of the unlike
parts. It follows necessarily, therefore, that organic aggre-
gates, which as a class are distinguished from inorganic
aggregates by the greater number of their unlike parts, must
be also distinguished from them by the greater number of
simultaneous changes they display ; and further that the
higher organic aggregates, having more numerous unlike
parts than the lower, must undergo more numerous simul-
taneous changes. "We next found that the changes
occurring in living bodies, are contrasted with those occurring
in other bodies, as being much more heterogeneous / and that
the changes occurring in the superior living bodies, are
similarly contrasted with those occurring in inferior ones.
Well, heterogeneity of function is the correlate of hetero-
geneity of structure ; and heterogeneity of structure is the
leading distinction between organic and inorganic aggre-
gates, as well as between the more highly organized and the
more lowly organized. By reaction, an incident force must
be rendered multiform in proportion to the multiformity of
the aggregate on which it falls ; and hence those most mul-

THE LIFE VARIES AS THE CORRESPONDENCE. 91

tiform aggregates which display in the highest degree the
phenomena of Evolution structurally considered, must at the
same time be aggregates which display in the highest de-
gree the multiform actions which constitute Evolution
functionally considered. These heterogeneous changes,

exhibited simultaneously and in succession by a living or-
ganism, prove, on further inquiry, to be distinguished by
their combination from certain non-vital changes which
simulate them. Here, too, the parallelism is maintained.
It was shown in § 56 of First Principles, that an essential
characteristic of Evolution is the integration of parts, which
accompanies their differentiation — an integration that is
shown both in the consolidation of each part, and in the
consolidation of all the parts into a whole. Now, manifestly,

combination anions; the changes going; on in different coin-
ed c? o o

bined parts, must be proportionate to the degree of com-
bination among these' parts : the more mutually dependent
the parts, the more mutually-dependent must be their
actions. Hence, animate bodies having greater co-ordin-
ation of parts than inanimate ones, must exhibit greater
co-ordination of changes. And this greater co-ordination of
their changes must not only distinguish organic from inor-
ganic aggregates ; but must, for the same reason, distinguish
higher organisms from lower ones, as we found that it
did. Yet once more, it was pointed out that the

changes constituting Life, differ from other changes in the
d'tiniteness of their combination ; and that a distinction like in
kind, though less in degree, holds between the vital changes
of superior creatures and those of inferior creatures. These,
also, are contrasts in harmony with the contrasts disclosed by
the analysis of Evolution. We saw {First Principles, §§ 54,
55) that during Evolution, there is an increase of definiteness
as '.veil as an increase of heterogeneity. We saw that the
integration accompanying differentiation, has necessarily the
effect of increasing the distinctness with which the parts are
marked off from each other ; and that so, out of the inco-

92 THE DATA OF BIOLOGY.

herent and indefinite, there arises the coherent and definite.
But a coherent whole made up of definite parts definitely
combined, must exhibit more definitely combined changes
than a whole made up of parts that are neither definite in
themselves nor in their combination. Hence, if living bodies
display more than other bodies this structural definiteness,
then, definiteness of combination must be a characteristic of
the changes constituting Life ; and must also distinguish the
vital changes of higher organisms from those of lower organ-
isms. Finally, however, we discovered that all these
peculiarities are subordinate to the one fundamental pecu-
liarity, that vital changes take place in correspondence with
external co-existences and sequences ; and that the highest
possible Life is reached, when there is some inner relation of
actions fitted to meet every outer relation of actions by
which the organism can be affected. But this conception of
the highest possible Life, is in perfect harmony with the con-
ception, before arrived at, of the ultimate limit of Evolution.
When treating of equilibration as exhibited in organic
phenomena {First Principles, §§ 133, 134), it was pointed
out, that the continual tendency is towards the establishment
of a balance between inner and outer changes. It was
shown that " the final structural arrangements must be such
as will meet all the forces acting on the aggregate, by
equivalent antagonistic forces," and that "the maintenance
of such a moving equilibrium " as an organism displays,
" requires the habitual genesis of internal forces correspond-
ing in number, directions, and amounts, to the external
incident forces — as many inner functions, single or com-
bined, as there are single or combined outer actions to be
met." It was shown, too, that the relations among concep-
tions and ideas, are ever in progress towards a better balance
between mental actions and those actions in the environment
to which conduct must be adjusted. So that that main-
tenance of a correspondence between inner and outer rela-
tions, which we have here found to constitute Life, and the

THE LIFE VARIES AS THE CORRESPONDENCE. 93

perfection of which is the perfection of Life, answers com-
pletely to that state of organic moving equilibrium which
we saw arises in the course of Evolution, and tends ever to
become more complete.

There is much significance in this complete parallelism.
That two inquiries starting from different points and carried
on in different ways, should lead to conclusions so entirely
harmonizing with each other, cannot fail further to confirm
these conclusions; if further confirmation of them be needed.

CHAPTER VII.

THE SCOPE OF BIOLOGY.

§ 37. We are now in a position to map ont the boundaries
and divisions of our subject. Grouping together the general
results arrived at in the first three chapters, and joining with
them the results which the last three chapters have brought us
to, we shall be prepared to comprehend the science of Biology
as a whole ; and to see how its truths may best be classified.

In the chapters treating of Organic Matter, the Actions of
Forces on it, and its Reactions on Forces, the generalizations
reached were these : — that organic matter is specially sensi-
tive to surrounding agencies ; that in consequence of the
extreme instability of the compounds it contains, minute dis-
turbances can cause in it large amounts of re-distribution ;
and that during the fall of its unstably-arranged atoms into
stable arrangements, there are given out proportionately
large amounts of motion. We saw that organic matter is so
constituted, that small incident actions are capable of initiat-
ing great reactions— setting up extensive structural modifica-
tions, and liberating large quantities of power. In
the chapters just concluded, the changes of which Life is
made up, were shown to be so adjusted as to balance outer
changes. And the general process of the adjustment we
found resolves itself into this ; that if in the environment
there are any related actions, A and B, by which the or-

94

THE SCOPE OF BIOLOGY. 95

ganism is affected, then if A produces in the organism some
change #, there follows in the organism some change b, fitted
in time, direction, and amount to meet the action B — a
change which is often required to he much larger than its
antecedent. Mark, now, the relation between these

two final results. On the one hand, for the maintenance of
that correspondence between inner and outer actions which
constitutes Life, an organism must be susceptible to small
changes from small external forces (as in sensation), and must
be able to initiate large changes in opposition to large external
forces (as in muscular action). On the other hand, organic
matter is at once extremely sensitive to disturbing agencies
of all kinds, and is capable of suddenly evolving motion in
great amounts. That is to say, the constitution of organic
matter specially adapts it to receive and produce the internal
changes required to balance external changes.

This being the general character of the vital Functions,
and of the Matter in which they are performed, the science
of Biology becomes an account of all the phenomena attend-
ant on the performance of such Functions by such Matter —
an account of all the conditions, concomitants, and conse-
quences, under the Various circumstances fallen into by living
bodies. If all the functional phenomena which living bodies
present, are, as we have concluded, incidents in the main-
tenance of a correspondence between inner and outer ac-
tions ■ and if all the structural phenomena which living
bodies present, are direct or indirect concomitants of func-
tional phenomena ; then the entire Science of Life, must con-
sist in a detailed interpretation of all these functional and
structural phenomena in their relations to the phenomena of
the environment. Immediately or mediately, proximately
or remotely, every trait exhibited by organic bodies, as
distinguished from inorganic bodies, must be referable to
this continuous adjustment between their actions and the
actions going on around them. Such being the extent and
nature of our subject-matter, it may be thus divided.

96 THE DATA OF BIOLOGY.

1. An account of the structural phenomena presented by
organisms. And this subdivides into : —

a. The structural phenomena presented by individual
organisms.

b. The structural phenomena presented by successions
of organisms.

2. An account of the functional phenomena which or-
ganisms present. And this, too, admits of sub-division into : —

a. The functional phenomena of individual organisms.

b. The functional phenomena of. successions of organisms.

3. An account of the actions of Structure on Function,
and the re-actions of Function on Structure. And like the
others, this is divisible into : —

a. The actions and re-actions as exhibited in individual
organisms.

b. The actions and re-actions as exhibited in successions
of organisms.

4. An account of the phenomena attending the production
of successions of organisms : in other words — the phenomena
of Genesis.

There is, indeed, another mode of grouping the facts of
Biology, with which all are familiar. According as they
are facts of animal or vegetal life, they may be classed
under the heads of Zoology and Botany. But this di-
vision, though convenient and indeed necessary for practi-
cal purposes, is one that does not here concern us. Dealing
with organic structures and functions in connexion with
their causes, conditions, concomitants, and consequences,
Biology cannot divide itself into Animal-Biology and Vege-
tal-Biology ; since the same fundamental classes of phe-
nomena are common to both. Eecognizing this familiar
distinction only as much as convenience obliges us to do, let
us now pass on to consider, more in detail, the classification
of biologic phenomena, above set down in its leading outlines.

§ 38. The facts of structure which an individual or-

THE SCOPE OF BIOLOGY. 97

ganism exhibits, are of two chief kinds. In order of con-
spicnousness, though not in order of time, there come first
those ultimate arrangements of parts which characterize the
organism in its mature state — an account of which, commonly
called Anatomy, is more properly called Morphology. And
second, there come those successive modifications through
which the organism passes in its development from the germ
to the adult form — an account of which is called Embryology.

The facts of structure which any succession of individual
organisms exhibits, admit of similar classification. On the
one hand, we have those inner and outer differences of shape,
that are liable to arise between the adult members of suc-
cessive generations descended from a common stock — differ-
ences which, though usually not marked between adjacent
generations, may in course of many generations become great.
And on the other hand, we have those developmental modi-
fications through which such modifications of the descended
forms are reached.

The interpretation of structure, as exhibited in individual
organisms and successions of organisms, is aided by two sub-
sidiary divisions of biologic inquiry, named Comparative
Anatomy (properly Comparative Morphology) and Compara-
tive Embryology. These cannot properly be regarded as in
themselves parts of Biology ; since the facts embraced under
them are not substantive phenomena, but are simply inci-
dental to substantive phenomena. All the facts of structural
Biology are comprehended under the two foregoing sub-
divisions ; and the comparison of these facts as presented
in different classes of organisms, is simply a method of inter-
preting the real relations and dependencies of the facts com-
pared.

Nevertheless, though Comparative Morphology and Com-
parative Embryology do not disclose additional series of con-
crete or special facts, they lead to the establishment of certain
abstract or general facts. By them it is made manifest that
underneath the superficial differences of groups and classes

98 THE DATA OF BIOLOGY.

and types of organisms, there are hidden fundamental simi-
larities ; and that the courses of development in such groups
and classes and types, though in many respects divergent,
are in some essential respects, coincident. The wide truths
thus disclosed, come under the heads of General Morphology
and General Embryology.

By contrasting the structures of organisms, there is also
achieved that grouping of the like and separation of the
unlike, called Classification. First by observation of ex-
ternal characters ; second by observation of internal charac-
ters ; and third by observation of the phases of development ;
it is ascertained what organisms are most similar in all
particulars ; what organisms are like each other in every
important attribute ; what organisms have common primor-
dial characters. Whence there finally results such an ar-
rangement of organisms, that if certain structural attributes
of any one be given, its other structural attributes may be
empirically predicted ; and which prepares the way for that
interpretation of their relations and genesis, which forms an
important part of rational Biology.

§ 39. The second main division of Biology, above de-
scribed as embracing the functional phenomena of organ-
isms, is that which is in part signified by Physiology : the re-
mainder being what we distinguish as Psychology. Both of
these fall into subdivisions that may best be treated sepa-
rately. That part of Physiology which is concerned
with the molecular changes going on in organisms, is known
as Organic Chemistry. An account of the modes in which the
force generated in organisms by chemical change, is trans-
formed into other forces, and made to work the various or-
gans that carry on the functions of Life, comes under the
head of Organic Physics. Psychology, which is
mainly concerned with the adjustment of vital actions to
actions in the environment (in contrast with Physiology,
which is mainly concerned with vital actions apart from

THE SCOPE OF BIOLOGY. 99

actions in the environment) consists of two quite distinct por-
tions. Objective Psychology deals with those functions of the
nervo-muscular apparatus by which such organisms as possess
it, are enabled to adjust inner to outer relations ; and includes
also, the study of the same functions as externally manifested
in conduct. Subjective Psychology deals with the sensations,
perceptions, ideas, emotions, and volitions that are the direct
or indirect concomitants of this visible adjustment of inner
to outer relations — considers these several kinds of conscious-
ness in their genesis, and their connexions of co-existence and
succession. Consciousness under its different modes and
forms, being a subject-matter radically distinct in nature from
the subject-matter of Biology in general ; and the method of
self-analysis, by which alone the laws of dependence among
changes of consciousness can be found, being a method un-
paralleled by anything in the rest of Biology ; we are
obliged to regard Subjective Psychology as a separate study
— not absolutely, of course, but relatively to the mind of each
student. And since it would be very inconvenient to dis-
sociate Objective Psychology from Subjective Psychology,
we are practically compelled to deal with the two as forming
an independent sub-science, to be treated apart from the lower
divisions of Biology.

Obviously, the functional phenomena presented in succes-
sions of organisms, similarly divide into physiological and
psychological. Under the physiological, come the

modifications of bodily actions that arise in the course of
generations, as concomitants of structural modifications ; and
these may be modifications, qualitative or quantitative, in
the molecular changes classed as chemical, or in the organic
actions classed as physical, or in both. Under the

psychological, come the qualitative and quantitative modifica-
tions of instincts, feelings, conceptions, and mental changes
in general, that occur in creatures having more or less
intelligence, when certain of their conditions are changed.
This, like the preceding department of Psychology, has in

100 THE DATA OF BIOLOGY.

the abstract two different aspects — the objective and the sub-
jective. Practically, however, the objective, which deals
with these mental modifications as exhibited in the changing
habits and abilities of successive generations of creatures, is
the only one that admits of scientific investigation ; since the
corresponding alterations in consciousness, cannot be imme-
diately known to any but the subjects of them. Evidently,
convenience requires us to class this part of Psychology along
with the other parts, in a distinct sub-science.
"""Light is thrown on functions, as well as on structures,
by comparing organisms of different kinds. Comparative
Physiology and Comparative Psychology, are the names
given to those collections of facts respecting the homologies
and analogies, bodily and mental, that are brought to light by
this kind of inquiry. These classified observations concern-
ing likenesses and differences of functions, are helpers to
interpret functions in their essential natures and relations.
Hence Comparative Physiology and Comparative Psychology
are names of methods, rather than names of true sub-divisions
of Biology.

Here, however, as before, the comparison of special truths,
besides facilitating their interpretation, brings to light certain
general truths. Contrasting bodily and mental functions as
exhibited in various orders of organisms, shows that there
exists, more or less extensively, a community of processes
and methods. Hence result two groups of abstract propo-
sitions, constituting General Physiology and General Psy-
chology.

§ 40. In these various divisions and sub-divisions of the
first two great departments of Biology, the phenomena of
Structure are considered separately from the phenomena of
Function, so far as separate treatment of them is possible.
The third great department of Biology deals with them in
their necessary connexions. It comprehends the determin-

THE SCOPE OF BIOLOGY. 101

ation of functions by structures, and the determination of
structures by functions. r__

As displayed in individual organisms, the action of struc-
tures on functions is to be studied, not only in the broad and
familiar fact that the general kind of life an organism leads
is necessitated by the main characters of its organization, but
in the more special and less conspicuous fact, that between
members of the same species minor differences of structure lead
to minor differences of power to perform certain kinds of action,
and of tendency to perform such kinds of action. Con-

versely, under the re-actions of function on structure as
displayed in individual organisms, come the facts slewing
that functions, when fulfilled to their normal extents, main-
tain integrity of structure in their respective organs ; and
that within certain limits, the increase of functions is followed
by such structural changes in their respective organs, as en-
ables the organs to discharge better their extra functions.

Inquiry into the action of structure on function as dis-
played in successions of organisms, introduces us to such
phenomena as Mr. Darwin's " Origin of Species " deals with.
In this category come all proofs of the general truth, that
when an individual is enabled by a certain structural pecu-
liarity, to perform better than others of its species some
advantageous action ; and when it bequeaths more or less of
its structural peculiarity to descendants, among whom those
which have it most markedly, are best able to thrive and
propagate ; there arises through this continuous action of
structure on function, a visibly modified type of structure,
having a more or less distinct function. In the cor-

relative class of facts, which come under the category of re-
actions of function on structure as exhibited in successions of
organisms, are to be placed all those modifications of struc-
ture which arise in races, when changes of conditions entail
changes in the balance of their functions. Here is to be
studied the way in which altered function externally necessi-

102 THE DATA OF BIOLOGY.

tated, works, byre-action, altered structure ; and how in succeed-
ing generations, this altered structure may be made continu-
ally more marked by this altered function. Though
logically distinct, these two sub-divisions of biologic inquiry
cannot in practice be carried on apart. A speciality of struc-
ture which leads to an excess of function in any direction,
is, by the perpetual re-action of function, rendered ever more
decided. A speciality of function, by calling forth a corre-
sponding speciality of structure, produces an increasingly
efficient discharge of such function. Whichever of the two
initiates the change, there goes on between them an unceas-
ing action and re-action, producing in them co-ordinate
modifications.

§ 41. The fourth great division of Biology, comprehend-
ing the phenomena of Genesis, may be conveniently separated
into three sub-divisions.

Under the first, comes a description of all the special
modes whereby the multiplication of organisms is carried on :
which modes range themselves under the two chief heads of
sexual and asexual. An account of Sexual Multiplication in-
cludes the various methods by which germs and ova are
fertilized, and by which, after fertilization, they are furnished
with the materials, and maintained in the conditions, needful
for their development. An account of Asexual Multiplica-
tion includes the various methods by which, from the same
fertilized germ or ovum, there are produced many organisms
that are partially or totally independent of each other.

The second of these sub-divisions deals with the phenomena
of Genesis in the abstract. It takes for its subject-matter, such
general questions as — What is the end subserved by the
union of sperm-cell and germ-cell ? Why cannot all multi-
plication be carried on after the asexual method ? What
are the laws of hereditary transmission ? What are the causes
of variation %

The third sub-division is devoted to still more abstract

THE SCOPE OF BIOLOGY. 103

aspects of the phenomena. Recognizing the general facts of
multiplication without reference to their modes or immediate
causes, it concerns itself simply with the different rates of
multiplication in different kinds of organisms, and different
individuals of the same kind. Generalizing the numerous
contrasts and variations of fertility, it seeks a rationale of
them in their relations to other organic phenomena.

§ 42. Such appears to be the natural arrangement of
divisions and sub-divisions which Biology presents, when re-
garded from the highest point of view, as the Science of
Life — the science which has for its subject-matter, the cor-
respondence of organic relations, with the relations amid
which organisms exist. This, however, is a classification of
the parts of Biology when fully developed ; rather than a
classification of the parts of Biology as it now stands.
Several of the sub-divisions above named have no recognized
existence ; and sundry of the others are in quite rudimentary
states. It is therefore impossible now to fill in, even in the
roughest way, more than a part of the outlines here
sketched.

Our course of inquiry being thus in great measure de-
termined by the present state of knowledge, we are com-
pelled to follow an order widely different from this ideal one.
It will be necessary first to give an account of those empiri-
cal generalizations which naturalists and physiologists have
established : arranging them rather with a view to facility
of comprehension than to logical sequence ; and append-
ing to those which admit of it, such deductive interpreta-
tions as First Principles furnish us with. Having done this,
we shall be the better prepared for dealing with the lead-
ing truths of Biology, in connexion with the doctrine of
Evolution.

PART II.

THE INDUCTIONS OF BIOLOGY.

CHAPTER I.

GROWTH.

$ 43. Perhaps the widest and most familiar induction of
Biology, is that organisms grow. While, however, this is a
characteristic so habitually and markedly displayed by plants
and animals, as to be carelessly thought peculiar to them,
it is really not so. Under appropriate conditions, increase of
size takes place in inorganic aggregates, as well as in organic
aggregates. Crystals grow ; and often far more rapidly than
living bodies. Where the requisite materials are supplied in
the requisite forms, growth may be witnessed in non-crystal-
line masses : instance the fungus-like accumulation of
carbon that takes place on the wick of an unsnuffed candle.
On an immensely larger scale, we have growth in geologic
formations : the slow accumulation of deposited sediment into
a stratum, is not distinguishable from growth in its widest
acceptation. And if we go back to the genesis of celestial
bodies, assuming them to have arisen by Evolution, these,
too, must have gradually passed into their concrete shapes
through processes of growth. Growth is indeed a concomi-
tant of Evolution ; and if Evolution of one kind or other is
universal, growth is universal— universal, that is, in the
6ense that all aggregates display it in some way at somo
period.

The essential community of nature between organic
growth and inorganic growth, is, however, most clearly seea

108 THE INDUCTIONS OF BIOLOGY.

on observing that they both result in the same way. The
segregation of different kinds of detritus from each other, aa
well as from the water carrying them, and their aggregation
into distinct strata, is but an instance of a universal tend-
ency towards the union of like units and the parting of un-
like units (First Principles, § 123). The deposit of a crystal
from a solution, is a differentiation of the previously mixed
atoms ; and an integration of one class of atoms into a solid
body, and the other class into a liquid solvent. Is not the
growth of an organism a substantially similar process ?
Around a plant there exist certain elements that are like
the elements which form its substance ; and its increase of
size is effected by continually integrating these surrounding
like elements with itself. Nor does the animal fundament-
ally differ in this respect from the plant or the crystal. Its
food is a portion of the environing matter, that contains somo
compound atoms like some of the compound atoms constitut-
ing its tissues; and either through simple imbibition or
through digestion, the animal eventually integrates with it-
self, units like those of which it is built up, and leaves behind
the unlike units. To prevent misconception, it may

be well to point out that growth, as here defined, must be
distinguished from certain apparent and real augmentations
of bulk which simulate it. Thus, the long, white potato-
shoots thrown out in the dark, are produced at the expense
of the substances which the tuber contains : they illustrato
not the accumulation of organic matter, but simply its re-
arrangement. Certain animal-embryos, again, during their
early stages, increase considerably in size without assimil-
ating any solids from the environment; and they do this
by absorbing the surrounding water. Even in the highest
organisms, as in children, there appears sometimes to occur
a rapid gain in dimensions, that does not truly measure the
added quantity of organic matter ; but is in part due to
ehauges analogous to those just named. Alterations of this

GROWTH. 109

kind must not be confounded with that growth, properly so
called, of which we have here to treat.

The next general fact to be noted respecting organic
growth, is, that it has limits. Here there appears to be a
distinction between organic and inorganic growth ; but this
distinction is by no means definite. Though that aggreoa-
tion of inanimate matter which simple attraction produces,
may go on without end ; yet there appears to be an end to
that more definite kind of aggregation which results from
polar attraction. Different elements and compounds, habitu-
ally form crystals more or less unlike in their sizes ; and each
seems to have a size that is not usually exceeded without a
tendency arising to form new crystals rather than to increase
the old. On looking at the organic kingdom as a

whole, we see that the limits between which growth ranges,
are very wide apart. At the one extreme, we have monads
bo minute as to be rendered but imperfectly visible by micro-
scopes of the highest power ; and at the other extreme, we
have trees of 300 feet high, and animals of 100 feet long.
It is true that though in one sense this contrast may be
legitimately drawn, yet in another sense it may not ; since
these largest organisms are made by the combination of units
that are individually like the smallest. A single plant of the
genus Protococcus, is of the same structure as one of the
many cells united together to form the thallus of some
higher Alga, or the leaf of a phgenogam. Each separate
6hoot of a phaenogam is usually the bearer of many
leaves. And a tree is an assemblage of numerous united
shoots. One of these great teleophytes is thus an ag-
gregate of aggregates of aggregates of units, which sever-
ally resemble protophytes in their sizes and structures;
and a like building up is traceable throughout a consider-
able part of the animal kingdom. Even, however, when
we bear in mind this qualification, and make our com-
parisons between organisms of the same degree of compo

110 THE INDUCTIONS OF BIOLOGY.

sition, we still find the limit of growth to have a great
range. The smallest branched flowering plant is extremely
insignificant by the side of a forest tree; and there is an
enormous difference in bulk between the least and the great-
est mammal. But on comparing members of the same
species, we discover the limit of growth to be much less vari-
able. Among the Protozoa and Protophyta, each kind has a
tolerably constant adult size ; and among the most complex
organisms, the differences between those of the same kind
that have reached maturity, are usually not very great.
The compound plants do, indeed, sometimes present marked
contrasts between stunted and well-grown individuals ; but
the higher animals diverge but inconsiderably from the
average standards of their species.

On surveying the facts with a view of empirically general-
izing the causes of these differences, we are soon made aware
that by variously combining and conflicting with each other,
these causes produce great irregularities of result. It be-
comes manifest that no one of them can be traced to it a
consequences, unqualified by the rest. Hence the several
statements contained in the following paragraphs, must be
taken as subject to mutual modification.

Let us consider first, the connexion between degree of
growth and complexity of structure. This connexion being
involved with many others, becomes apparent only on so
averaging the comparisons, as to eliminate differences among
the rest. Nor does it hold at all where the conditions are
radically dissimilar; as between plants and animals. But
bearing in mind these qualifications, we shall see that
organization has a determining influence on increase of
mass. Of plants the lowest, classed as Thallogens,

usually attain no considerable size. Lichens, Algoe, and Fun-
gi, count among their numbers but few bulky species : the
largest, such as certain Algae found in antartic seas, not
serving greatly to raise the average. Though among
Acrogens there are some, as the Tree-ferns, whiuh attain a

GROWTH. Ill

considerable height, the majority are but of humble growth.
The Endogens, including at one extreme small grasses and
at the other tall palms, show us an average and a maximum
greater than that reached by the Acrogens. And the En-
dogens are exceeded by the Exogens ; among which are
found the monarchs of the vegetal kingdom. Pass-

ing to animals, we meet the fact that the size attained by
Vertebrata is usually much greater than the size attained by
Invertebrate. Of invertebrate animals the smallest, classed
as Protozoa, are also the simplest ; and the largest, be-
longing to the Annulosa and Mollusca, are among the most
complex of their respective types. Of vertebrate animals
we see that the greatest are Mammals ; and that though,
in past epochs, there were reptiles of vast bulk, their bulk
did not equal that of the whale. Between reptiles and
birds, and between land -vertebrates and aquatic vertebrates,
the relation does not hold : the conditions of existence be-
ing in these cases widely different. But among fishes as a
class, and among reptiles as a class, it is observable that,
speaking generally, the larger species are framed on the
higher types. The critical reader, who has men-

tally checked these statements in passing them, has doubtless
already seen that this relation is not a dependence of or-
ganization on growth, but a dependence of growth on or-
ganization. The majority of Exogens are smaller than some
Endogens ; many Endogens are exceeded in size by certain
Acrogens ; and even among Thallogens, the least developed
of plants, there are kinds of a size which many plants of the
highest order do not reach. Similai-ly among animals :
there are plenty of Crustaceans less than Actiniae ; numerous
reptiles are smaller than some fish; the majority of mam-
mals are inferior in bulk to the largest reptiles ; and in the
contrast between a mouse and a well-grown Medusa, we see a
creature that is elevated in the scale of organization, ex-
ceeded in mass by one that is extremely degraded. Clearly
then, it cannot be held that high organization is habitually

112 THE INDUCTIONS OF BIOLOGY.

accompanied by great size. The proposition here illustrated
is the converse one, that great size is habitually accompanied
by high organization. The conspicuous fact that the largest
species of both animals and vegetals belong to the highest
classes ; and that throughout their various sub-classes the
higher usually contain the more bulky forms ; shows this
connexion as clearly as we can expect it to be shown, amid
so many modifying causes and conditions.

The relation between growth and supply of available
nutriment, is too familiar a relation to need proving. There
are, however, some aspects of it that must be contemplated be-
fore its implications can be fully appreciated. Among
plants, which are all constantly in contact with the gaseous,
liquid, and solid matters to be incorporated with their tissues ;
and which, in the same locality, receive not very unlike
amounts of light and heat ; differences in the supplies of
available nutriment, have but a subordinate connexion with
differences of growth. Though in a cluster of herbs spring-
ing up from the seeds let fall by a parent, the greater size of
some than of others is doubtless due to better nutrition,
consequent on accidental advantages ; yet no such inter-
pretation can be given of the contrast in size between these
herbs and an adjacent tree. Other conditions here come into
play : one of the most important probably being, an absence in
the one case, and presence in the other, of an ability to se-
crete such a quantity of ligneous fibre as will produce a stem
capable of supporting a large growth. Among
animals, however, which (excepting some Entozoa) differ
from plants in this, that instead of bathing their surfaces,
the matters they subsist on are dispersed, and have to be
obtained ; the relation between available food and growth,
is shown with more regularity. The Protozoa, living on
microscopic fragments of organic matter contained in the
surrounding water, are unable, during their brief lives, to
accumulate any considerable quantity of nutriment. Polypes
and Mollmcoida, having for food these scarcely visible mem-

GROWTH. 1 18

bers of the animal kingdom, are, though large compared
with their prey, small as measured by other standards : even
when aggregated into groups of many individuals, which
severally catch food for the common weal, they are often so
inconspicuous as readily to be passed over by the unobservant.
And if from this point upwards we survey the successive
grades of animals, it becomes manifest that, in proportion aa
the size is great, the masses of nutriment are either large, or,
what is practically the same thing, are so abundant and so
grouped as that large quantities may be readily taken in.
Though, for example, the greatest of mammals, the arctic
whale, feeds on such comparatively small creatures as the
acalephes and molluscs floating in the seas it inhabits, its
method of gulping in whole shoals of them and filtering
away the accompanjung water, enables it to secure great
quantities of food. We may then with safety say, that,
other things equal, the growth of an animal depends on the
abundance and sizes of the masses of nutriment which its
powers enable it to appropriate. Perhaps it may be

needful to add that, in interpreting this statement, the
number of competitors must be taken into account. Clearly,
not the absolute, but the relative, abundance of fit food is
the point ; and this relative abundance very much depends
on how many individuals are competing for the food. Thus
all who have had experience of fishing in Highland lochs,
know that where the trout are numerous they are small, and
that where they are comparatively large they are compara-
tively few.

What is the relation between growth and expenditure cf
force ? is a question which next presents itself. Though
there is reason to believe such a relation exists, it is not very
readily traced : involved as it is with so many other rela-
tions. Some contrasts, however, ma)T be pointed out, that
appear to give evidence of it. Passing over the vegetal
kingdom, throughout which the expenditure of force is too
small to allow of such a relation being visible ; let us seek in

114 THE INDUCTIONS OF BIOLOGY.

the animal kingdom, some case where classes otherwise
allied, are contrasted in their locomotive activities. Let us
compare birds on the one hand, with reptiles and mammals
3n the other. It is an accepted doctrine that birds are
organized on a type closely allied to the reptilian type, but
superior to it ; and though in many respects the organization
of birds is inferior to that of mammals, yet in other respects,
as in the greater heterogeneity and integration of the skeleton,
the more complex development of the respiratory system,
and the higher temperature of the blood, it may be held
that birds stand above mammals. Hence were growth de-
pendent only on organization, we might infer that the limit
of growth among birds should not be much short of that
among mammals ; and that the bird-type should admit of a
larger growth than the reptile-type. Again, we see no mani-
fest disadvantages under which birds labour in obtaining
food, but from which reptiles and mammals are free. On the
contrary, birds are able to get at food that is fixed beyond
the reach of reptiles and mammals ; and can catch food that
is too swift of movement to be ordinarily caught by reptiles
and mammals. Nevertheless, the limit of growth in birds,
falls far below that reached by reptiles and mammals. With
what other contrast between these classes, is this contrast
connected ? May we not suspect that it is connected with
the contrast between their amounts of locomotive exertion ?
"Whereas mammals (excepting bats, which are small), are
during all their movements supported by solid surfaces or
dense liquids ; and whereas reptiles (excepting the ancient
pterodactyles, which were not very large), are similarly re-
stricted in their spheres of movement ; the majority of birds
move more or less habitually through a rare medium, in which
they cannot support themselves without relatively great
efforts. The conclusion that there exists this inverse

ratio between growth and expenditure of force, is enforced
by the significant fact, that those members of the class Aves,
as the Dinornis and Ejiiornis, which approached in size to

GROWTH. 115

the larger Mammalia and Rcptilia, wore creatures incapable
of flight — creatures which did not expend this excess of
force in locomotion. Further evidence that there is

an antagonism between the increase of bulk and the quantity
of motion evolved by an organism, is supplied by the ge-
neral experience, that human beings and domestic animals,
when overworked while growing, are prevented from attain-
ing the ordinary dimensions.

One other general truth concerning degrees of growth,
must be set down. It is a rule, having exceptions of no
great importance, that large organisms commence their
separate existences as masses of organic matter more or less
considerable in size, and commonly with organizations more or
less advanced; and that throughout each organic sub-kingdom,
there is a certain general, though irregular, relation between
the initial and the final bulks. Yegetals exhibit this

relation much less clearly and constantly than animals. Yet
though, among the plants that begin life as minute spores,
there are some which, under their special conditions, grow to
considerable sizes, the immense majority of them remain
small. While, conversely, the great Endogens and Exogens,
when thrown off from their parents, have already the formed
organs of young plants, to which are attached large stores of
highly nutritive matter. That is to say, where the young
plant consists merely of a centre of development, the ultimate
growth is commonly insignificant ; but where the growth
is to become great, there exists to start with, a well-developed
embryo and a stock of assimilable matter. Through-

out the animal kingdom, this relation is tolerably regular.
Save among classes that escape the ordinary requirements of
animal life, small germs or eggs do not give rise to bulky
creatures. Where great bulk is to be reached, the young
proceeds from an egg of considerable bulk, or is born of con-
siderable bulk ready-organized and partially active. In the
class fishes, for instance, a certain average proportion obtains
between the sizes of the ova and the sizes of the adult indi

116

THE INDUCTIONS OF BIOLOGT.

dividuals ; and among the highest fishes, as sharks, the
eggs are comparatively few and comparatively large. Rep-
tiles ha^e eggs that are smaller in number, and relatively
greater in mass, than those of fishes ; and throughout this
class, too, there is a general ratio between the bulk of the egg
and the bulk of the adult creature. As a group, birds show
us a further limitation in the number of their eggs, and a
further increase in their relative sizes ; and from the minute
eggs of the humming-bird up to the immense ones of the
Epiomis, holding several quarts, we see that, speaking ge-
nerally, the greater the eggs, the greater the birds. Finally,
among mammals (omitting the marsupials) the young are
born, not only of comparatively large sizes, but with ad-
vanced organizations ; and throughout this sub-division of
the vertebrata, as throughout the others, there is a mani-
fest connexion between the sizes at birth and the sizes at
maturity. As having a kindred meaning, there

must finally be noted the fact, that the young of these
highest animals, besides starting in life with bodies of
considerable sizes, almost fully organized, are, during sub-
sequent periods of greater or less length, supplied with nutri-
ment— in birds by feeding, and in mammals by suckling and
afterwards by feeding. That is to say, beyond the mass and
organization directly bequeathed, a bird or mammal obtains
a further large mass at but little cost to itself.

Were an exhaustive treatment of the topic intended, it
would be needful to give a paragraph to each of the many
incidental circumstances by which growth may be aided or
restricted. Such facts as that an entozoon is limited by the
size of the creature, or even the organ, in which it thrives ;
that an epizoon, though getting abundant nutriment with-
out appreciable exertion, is restricted to that small bulk at
which it escapes ready detection by the animal it infests ;
that sometimes, as in the weazel, smallness is a condition to
successful pursuit of the animals preyed upon ; and that at
other times, the advantage of resembling certain other crea-

GROWTH. 117

tures, and so deceiving enemies or prey, becomes an indirect
cause of restricted size. But the present purpose is simply
to set down those most general relations between growth and
other organic phenomena, which induction leads us to.
Having done this, let us go on to inquire whether these
general relations can be deductively established.

§ 4-1. That there must exist a certain dependence of
growth on organization, may be shown a priori. When we
consider the phenomena of Life, either by themselves or in
their relations to surrounding phenomena, we see that, other
things equal, the larger the aggregate the greater is the
needful complexity of structure.

In plants, even of the highest type, there is a com-
paratively small mutual dependence of parts : a gathered
flower-bud will unfold and flourish for days, if its stem be
immersed in water ; and a shoot cut off from its parent-tree
and stuck in the ground, will grow. The respective parts
having vital activities that are not widely unlike, it is pos-
sible for great bulk to be reached without that structural
complexity required for combining the actions of parts.
Even here, however, we see that for the attainment of great
bulk, there requires such a degree of organization as shall
co-ordinate the functions of roots and branches — we see
that such a size as is reached by trees, is not possible
without an efficient vascular system enabling the remote
organs to utilize each other's products. And we see that
such a co-existence of large growth with low organization,
as occurs in seme of the marine Algce, occurs where the
conditions of existence do not necessitate any considerable
mutual dependence of parts — where the near approach of the-
plant to its medium in specific gravity, precludes the need of
a well -developed stem, and where all the materials of growth
being derived from the water by each portion of the thallus,
there requires no apparatus for transferring materials from
port to part. Among animals which, with but few

118

THE INDUCTIONS OF BIOLOOr.

exceptions, are, by the conditions of their existence, required
to take in nutriment through one specialized part of the
body, it is clear that there must be a means whereby other
parts of the body, to be supported by this nutriment, must
have it conveyed to them. It is clear that for an equally
efficient maintenance of their nutrition, the parts of a larg6
mass must have a more elaborate propelling and conducting
apparatus ; and that in proportion as these parts undergo
greater waste, a yet higher development of the vascular
system is necessitated. Similarly with the pre-requisites to
those mechanical motions which animals are required to
perform. The parts of a mass cannot be made to move, and
have their movements so co-ordinated as to produce locomo-
tive and other actions, without certain structural arrange-
ments ; and, other things equal, a given amount of such
activity requires more involved structural arrangements in a
large mass than in a small one. There must at least be a
co-ordinating apparatus presenting greater contrasts in its
central and peripheral parts.

The qualified dependence of growth on organization, is
equally implied when we study it in Connexion with that
adjustment of inner to outer relations which constitutes Life.
In plants this is not conspicuous, because the adjustment of
inner to outer relations is but small. Still, it is visible in tie
fact that the condition on which only a plant can grow to a
great size, is, that it shall, by the development of a massive
trunk, present inner relations of forces fitted to counter-
balance those outer relations of forces, which tend continually
and occasionally to overthrow it ; and this formation of a
core of regularly- arranged woody fibres, is an advance in
organization. Throughout the animal kingdom, this

connexion of phenomena is manifest. To obtain materials for
growth ; to avoid injuries, which interfere with growth ; and
to escape those enemies which bring growth to a sudden end ;
implies in the organism, the means of fitting its movements
to meet numerous external co-existences and sequences —

GROWTH. 119

implies such various structural arrangements as shall make
possible these variously-adapted actions. It cannot be
questioned that, everything else remaining constant, a more
complex animal, capable of adjusting its conduct to a greater
number of surrounding contingences, will be the better able
to secure food and evade damage, and so to increase bulk.
And evidently, without any qualification, we may say that a
large animal, living under such complex conditions of exist-
ence as everywhere obtain, is not possible without compara-
tively high organization.

While, then, this relation is traversed and obscured by
sundry other relations, it cannot but exist. Deductively we
see that it must be modified, as inductively we saw that it is
modified, by the circumstances amid which each kind of or-
ganism is placed ; but that it is always a factor in determin-
ing the result.

§ 45. That growth is, ceeteris paribus, dependent on the sup-
ply of assimilable matter, is a proposition so continually illus-
trated by special experience, as well as so obvious from general
experience, that it would scarcely need stating, were it not re-
quisite to notice the qualifications with which it must be taken.

The materials which each organism requires for building
itself up, are not of one kind, but of several kinds. As a
vehicle for transferring matter through their structures, all
organisms require water as well as solid constituents ; and how-
ever abundant the solid constituents, there can be no growth
in the absence of water. Among the solids supplied, there
must be a proportion ranging within certain limits. A
plant round which carbonic acid, water, and ammonia exist
in the right quantities, may yet be arrested in its growth by
a deficiency of silica. The total absence of lime from its
food, may stop the formation of a mammal's skeleton : thus
dwarfing, if not eventually destroying, the mammal ; and
this, no matter what quantities of other needful colloids and
crystalloids are furnished.

120 THE INDUCTIONS OF BIOLOGY.

Again, the truth that, other things equal, growth varic3
according to the supply of nutriment, has to be qualified by
the condition, that the supply shall not exceed the ability to
appropriate it. In the vegetal kingdom, the assimilating
surface being external, and admitting of rapid expansion by
the formation of new roots, shoots, and leaves, the effect of
this limitation is not conspicuous : by artificially supplying
plants with those materials which they have usually the most
difficulty in obtaining, we can greatly facilitate their growth ;
and so can produce striking differences of size in the same
species. Even here, however, the effect is confined within
the limits of the ability to appropriate ; since in the absence
of that solar light and heat, by the help of which the chief
appropriation is carried on, the additional materials of
growth are useless. In the animal kingdom this

restriction is rigorous. The absorbent surface being, in the
great majority of cases, internal ; having a comparatively
small area, which cannot be greatly enlarged without re-
construction of the whole body ; and being in connexion
with a vascular system, which must also be re-constructed
before any considerable increase of nutriment can be made
available ; it is clear that beyond a certain point, very soon
reached, increase of nutriment will not cause increase of
growth. On the contrary, if the quantity of nutriment
taken in, is greatly beyond the absorbent power, the excess,
becoming an obstacle to the regular working of the organism,
may retard growth rather than advance it.

While then it is certain, a priori, that there cannot be
growth in the absence of such substances as those of which
an organism consists ; and while it is equally certain that the
amount of growth must primarily be governed by the supply
of these substances ; it is not less certain that extra supply
will not produce extra growth, beyond a point very soon
reached. Deduction shows to be necessary, as induction
makes familiar, the truths that, the value of food for purposes
of growth depends not on the quantity of the various

GROWTH.

121

organizable materials it contains, but on the quantity of
the material most needed ; that given a right proportion of
materials, the pre-existing structure of the organism limits
their availability ; and that the higher the structure, the
sooner is this limit reached.

§ 46. But why should the growth of every organism be
finally arrested ? Though the rate of increase may, in each
case, be necessarily restricted within a narrow range of varia-
tion— though the increment that is possible in a given time,
cannot exceed a certain amount ; yet why should the incre-
ments decrease, and finally become insensible ? Why should
not all organisms, when supplied with sufficient materials,
continue to grow as long as they live ? To find an answer
to this question, we must first revert to the nature and
functions of organic matter.

In the first three chapters of Part I., it was shown that
plants and animals mainly consist of substances in states of
unstable equilibrium — substances which have been raised to
this unstable equilibrium by the expenditure of the forces we
know as solar radiations, and which give out these forces in
other forms, on falling into states of stable equilibrium.
Leaving out the water, which serves as a vehicle for these
materials and a medium for their changes ; and excluding
those mineral matters that play either passive or subsidiary
parts ; organisms are built up of compounds which are stores
of force. Those complex colloids and crystalloids which, as
united together, form organized bodies, are the same colloids
and crystalloids which give out, on their decomposition, the
forces expended by organized bodies. Thus these

nitrogeneous and carbonaceous substances, being at once
the materials for organic growth and the sources of organic
force ; it results that as much of them as is used up for the
genesis of force, is taken away from the means of growth ;
and as much as is economized by diminishing the genesis of
force, is available for growth. Given that limited quantity
9

122 1HE INDUCTIONS OF BIOLOGY.

of nutritive matter which the pre-existing structure of nz\
organism enables it to absorb ; and it is a necessary corollary
from the persistence of force, that the matter accumulated as
growth, cannot exceed that surplus which remains unde-
composed, after the production of the required amounts ol
sensible and insensible motion. This, which would

be rigorously true under all conditions, if exactly the sams
substances were used in exactly the same proportions, for the
production of force and for the formation of tissue, requires,
however, to be taken with the qualification, that some of the
force-evolving substances are not constituents of tissue ; and
that thus, there may be a genesis of force which is not at the
expense of potential growth. But since organisms (or at
least animal organisms, with which we are here chiefly
concerned,) have a certain power of selective absorption,
which, partially in an individual and more completely in a
race, adapts the proportions of the substances absorbed to the
needs of the system ; then if a certain habitual expenditure
of force, leads to a certain habitual absorption of force-
evolving matters that are not available for growth ; and if,
were there less need for such matters, the ability to absorb
matters available for growth would be increased to an equi-
valent extent ; it follows that the antagonism described, does,
m the long run, hold even without this qualification. Hence,
growth is substantially equivalent to the absorbed nutriment,
minus the nutriment used up in action.

This, however, is no answer to the question — why has
individual growth a limit ? The antagonism described, does
not manifestly account for the fact, that in every domestic
animal the increments of growth bear continually decreasing
ratios to the mass, and finally come to an end. Nevertheless,
it is demonstrable that the excess of absorbed over expended
nutriment, must, other things equal, become less as the size of
the animal becomes greater. In similarly-shaped bodies,

the masses vary as the cubes of the dimensions ; whereas the
strengths vary as the squares of the dimensions. See here

gho-vvth. 123

the solution of the problem. Supposing a creature which a
year ago was one foot high, has now become two feet high,
while it is unchanged in proportions and structure ; what are
the necessary concomitant changes that have taken place in
it ? It is eight times as heavy ; that is to say, it has to re-
sist eight times the strain which gravitation puts on its
structure ; and in producing, as well as in arresting, every
one of its movements, it has to overcome eight times the
inertia. Meanwhile, the muscles and. bones have sever-
ally increased their contractile and resisting powers in pro-
portion to the areas of their transverse sections ; and hence
are severally but four times as strong as they were. Thus,
while the creature has doubled in height, and while its ability
to overcome forces has quadrupled, the forces it has to overcome
have grown eight times as great. Hence, to raise its body
through a given space, its muscles have to be contracted with
twice the intensity, at a double cost of matter expended. This
necessity will be seen still more clearly if we leave out the
motor apparatus, and consider only the forces required and
the means of supplying them. For since, in similar bodies,
the areas vary as the squares of the dimensions, and the
masses vary as the cubes ; it follows that the absorbing sur-
face has become four times as great, while the weight to be
moved by the matter absorbed has become eight times as
great. If then, a year ago, the absorbing surface could take
up twice as much nutriment as was needed for expenditure,
thus leaving one-half for growth, it is now able only just to
meet expenditure, and can provide nothing for growth. How-
ever great the excess of assimilation over waste, may be dur-
ing the early life of an active organism, we see that because
a series of numbers increasing as the cubes, overtakes a series
increasing as the squares, even though starting from a much
smaller number, there must be reached, if the organism lives
long enough, a point at which the surplus assimilation is
brought down to nothing — a point at which expenditure ba-
lances nutrition — a state of moving equilibrium. This.

124 THE INDUCTIONS OF BIOLOGY.

however, though the chief, is not the sole, varying relation be-
tween degrees of growth and amounts of expended force. There
are two more ; one of which conspires with the last, while
the other conflicts with it. Consider in the first place, the
cost at which nutriment is distributed through the body, and
effete matters removed from it. Each increment of growth
being added at the periphery of the organism, the force ex-
pended in the transfer of matter must increase in a rapid
progression — a progression more rapid than that of the mass.
Bat as the dynamic expense of distribution is small compared
with the dynamic value of the materials distributed, this item
in the calculation is unimportant. Now consider, in the
second place, the changing proportion between production
and loss of heat. In similar organisms, the quantities of heat
generated by similar actions going on throughout their sub-
stance, must increase as the masses, or as the cubes of the
dimensions. Meanwhile, the surfaces from which loss of heat
by radiation takes place, increase only as the squares of the
dimensions. Though the loss of heat does not therefore in-
crease only as the squares of the dimensions, it certainly in-
creases at a smaller rate than the cubes. And to the extent
that augmentation of mass results in a greater retention of
heat, it effects an economization of force. This advantage is
not, however, so important as at first appears. Organic heat
is a concomitant of organic action, and is so abundantly pro-
duced during action, that the loss of it is then of no conse-
quence : indeed the loss is often not rapid enough to keep
the supply from rising to an inconvenient excess. It is only
in respect of that maintenance of heat which is needful during
quiescence, that large organisms have an advantage over
email ones in this relatively diminished loss. Thus these two
(subsidiary relations between degrees of growth and amounts
of expended force, being in antagonism with each other, we
may conclude that their differential result does not greatly
modify the result of the chief relation previously set forth.
Any one who proceeds to test this deduction, will find some

GROWTH. 126

seeming incongruities between it and certain facts inductively
established. Lest these should mislead him, it will be well
to explain them. Throughout the vegetal kingdom,

he may remark that there is no limit of growth except what
death entails. Passing over a large proportion of plants
which never exceed a comparatively small size, because they
wholly or partially die down at the end of the year ; and
pointing to trees that annually send forth new shoots, even
when their trunks are hollowed out by decay ; he may ask —
How does growth happen here to be unlimited ? The answer
is, that plants are only accumulators ; they are in no apprecia-
ble degree expenders. As they do not undergo a waste which
increases as the cubes of the dimensions, while assimilation
increases as their squares ; there is no reason why their
growth should be arrested by the equilibration of assimilation
and waste. Again, should he look among animals for an

exact correspondence between the decreasing increments of
growth as ascertained by observation and as determined by de-
duction, he will not find it. And there are sufficient reasons
why the correspondence cannot be more than approximate.
Besides the fact above noted, that there are other varying
relations which complicate the chief one, he must bear in
mind that the bodies compared are not truly similar : the
proportions of trunk to limbs and trunk to head, vary con-
siderably. The comparison is still more seriously vitiated by
the inconstant ratio between the constituents of which the
body is composed. In the flesh of adult mammalia, water
forms from 68 to 71 per cent., organic substance from 24 to
28 per cent., and inorganic substance from 3 to 5 per cent.;
whereas in the foetal state, the water amounts to 87 per cent.,
and the solid organic constituents to only 1 1 per cent. Clearly
this change from a state in which the force- evolving matter
forms one tenth of the whole, to a state in which it forms two
and a half tenths, must greatly interfere with the parallelism
between the actual and the theoretical progression. Yet

another difficulty may come under his notice. The crocodile

126 THE INDUCTIONS OF BIOLOGY.

is said to grow as long as it lives ; and there appears reason
to think that some predaceous fishes, such as the pike, do
the same. That these animals of comparatively high organ-
ization, have no definite limits of growth, is, however, an ex-
ceptional fact due to the exceptional non-fulfilment of those
conditions which entail limitation. What kind of life does
a crocodile lead ? It is a cold-blooded, or almost cold-
blooded, creature ; that is, it expends very little for the main-
tenance of heat. It is habitually inert: not chasing prey, but
lying in wait for it ; and undergoes considerable exertion
only during its occasional brief contests with prey. Such
other exertion as is, at intervals, needful for moving from
place to place, is rendered small by the small difference
between the animal's specific gravity and that of water.
Thus the crocodile expends in muscular action, an amount of
force that is insignificant compared with the force commonly
expended by land-animals. Hence its habitual assimilation
is diminished much less than usual by habitual waste ; and
beginning with an excessive disproportion between the two,
it is quite possible for the one never quite to lose its advance
over the other while life continues. On looking closer into
such cases as this and that of the pike, which is similarly
cold-blooded, similarly lies in wait, and is similarly able to
obtain larger and larger kinds of prey as it increases in size ;
we discover a further reason for this absence of a definite
limit. The mechanical causes necessitating a limit, are here
only partially in action. For a creature living in a medium
of nearly the same density as its bod}'', has not constantly to
overcome that gravitative force which is the chief resistance
to be met by terrestrial animals : it has not to expend for
this purpose, a muscular power that is large at the outset, and
increases as the cubes of its dimensions. The only force in-
creasing as the cubes of its dimensions, which it has thus to
overcome, is the inertia of its parts. The exceptional con-
tinuance of growth observed in creatures so circumstanced, ia
therefore perfectly explicable.

GROWTH. 127

§ 47. Obviously this antagonism between accumulation and
expenditure, must be a leading cause of the contrasts in size
between allied organisms that are in many respects similarly
conditioned. The life followed by each kind of animal, is
one involving a certain average amount of exertion for the
obtainment of a given amount of nutriment — an exertion,
part of which goes to the gathering or catching of food, part
to the tearing and mastication of it, and part to the after-
processes requisite for separating the nutritive atoms — an
exertion which therefore varies according as the food is abund-
ant or scarce, fixed or moving, according as it is mechani-
cally easy or difficult to deal with when secured, and accord-
ing as it is, or is not, readily soluble. Hence, while among
animals of the same species having the same mode of life,
there will be a tolerably constant ratio between accumulation
and expenditure, and therefore a tolerably constant limit of
growth ; there is every reason to expect that different species,
following different modes of life, will have unlike ratios be-
tween accumulation and expenditure, and therefore unlike
limits of growth.

Though the facts as inductively established, show a general
harmony with this deduction, we cannot usually trace this
harmony in any specific way ; since the conflicting and con-
spiring causes which affect growth are so numerous. The
only contrast which seems fairly to the point, is the before-
named one between the vertebrates which fly, and the most
nearly-allied vertebrates which do not fly : the differences
in degrees of organization and relations to food, being not such
as seriously to affect the comparison. If it be admitted that
birds habitually expend more force than mammals and rep-
tiles, then it will follow a priori, that, other things being
tolerably equal, they should have a lower limit of growth
than mammals and reptiles ; and this we know to be the fact
a posteriori.

§ 18. One of the chief causes, if not the chief cause, of

128 THE INDUCTIONS OF BIOLOGY.

the differences between the sizes of organisms, has yet to be
considered. We are introduced to it by pushing the above
inquiry a little further. Small animals have been shown to
possess an advantage over large ones, in the greater ratio
which, other things equal, assimilation bears to expenditure:
and we have seen that hence, small animals in becoming
large ones, gradually lose that surplus of assimilative power
which they had, and eventually cannot assimilate more than
is required to balance waste. But how come these animals
while young and small, to have surplus assimilative powers ?
Have all animals equal surplus of assimilative powers ?
And if not, how far do differences between the surpluses de-
termine differences between the limits of growth? We
shall find in the answers to these questions, the interpretation
of many marked contrasts in growth that are not due to any
of the causes above assigned. For example, an ox immensely
exceeds a sheep in mass. Yet the two live from generation
to generation in the same fields, eat the same grass and tur-
nips, obtain these aliments with the same small expenditure
of force, and differ scarcely at all in their degrees of organiz-
ation. Whence arises, then, their striking unlikeness of bulk ?

We noted when studying the phenomena of growth in-
ductively, that organisms of the larger and higher types, com-
mence their separate existences, as masses of organic matter
having tolerable magnitudes. Speaking generally, we saw
that throughout each organic sub-kingdom, the acquire-
ment of great bulk occurs only where the incipient bulk
and organization are considerable ; and that they are the
more considerable in proportion to the complexity of the life
which the organism is to lead.

The deductive interpretation of this induction may best be
commenced by an analogy. A street orange- vendor makes
but a trifling profit on each transaction ; and unless more
than ordinarily fortunate, he is unable to realize during
the day a larger amount than will meet his wants : leav-
ing him to start on the mcrrow in the same condition as

GROAVTFI. 129

before. The trade of the huxter in ounces of tea and half-
pounds of sugar, is one similarly entailing much labour for
small returns. Beginning with a capital of a few pounds, it
is impossible for him to have a shop large enough, or goods
sufficiently abundant and various, to permit an extensive
business : he must be content with the half-pence and pence
which he makes by little sales to poor people ; and if, avoid-
ing bad debts, he is able by strict economy to accumulate
anything, it can be but a trifle. A large retail trader is
obliged to lay out much money in fitting up an adequate
establishment ; he must invest a still greater sum in stock ;
and he must have a further floating capital to meet the
charges that fall due before his returns come in. Setting
out, however, with means enough for these purposes, he is
able to make numerous and comparatively large sales ; and
so to get greater and more numerous increments of profit.
Similarly, to get returns in thousands, merchants and manu-
facturers must make their investments in tens of thousands.
In brief, the rate at which a man's wealth accumulates, is
measured by the surplus of income over expenditure ; and
this, save in exceptionably favourable cases, is determined by
the capital with which he begins business. Now ap-

plying the analogy, we may trace in the transactions of an
organism, the same three ultimate elements. There is the
expenditure required for the obtainment and digestion of
food ; there is the gross return in the shape of nutriment as-
similated, or fit for assimilation ; and there is the difference
between this gross return of nutriment and the nutriment
that was used up in the labour of securing it — a difference
which may be a profit or a loss. Clearly, however, a surplus
implies that the force expended is less than the force latent
in the assimilated food. Clearly, too, the increment of
growth is limited to the amount of this surplus of income
over expenditure ; so that large growth implies both that the
excess of nutrition over waste shall be relatively considerable,
and that the waste and nutrition shall be on extensive scales.

130 THE INDUCTIONS OF BIOLOGY.

And clearly, the ability of an organism to expend largely and
assimilate largely, so as to make a large surplus, presupposes
a large physiological capital, in the shape of organic matter
more or less complete in its structural arrangements.

Throughout the vegetal kingdom, the illustrations of this
truth are not conspicuous and regular : the obvious reason
being, that since plants are accumulators and in so small a
degree expenders, the premises of the above argument are
but very partially fulfilled. The food of plants (excepting
Fungi and certain parasites) being in a great measure the
same for all, and bathing all so that it can be absorbed with-
out effort, their vital processes result almost entirely in profit.
Once fairly rooted in a fit place, a plant may thus from the
outset add its entire returns to capital ; and may soon be able
to carry on its processes on a large scale, though it does not
at first do so. When, however, plants are expenders, namely,
during their germination and first stages of growth, their
degrees of growth are determined by their amounts of vital
capital. It is because the young tree commences life with a
ready- formed embryo and store of food sufficient to last for
some time, that it is enabled to strike root and lift its head
above the surrounding herbage. Throughout the

animal kingdom, however, the necessity of this relation is
everywhere obvious. The small carnivore preying on small
herbivores, can increase in size only by small increments : its
organization unfitting it to digest larger creatures, even if it
ran kill them, it cannot profit by amounts of nutriment ex-
ceeding a narrow limit; and its possible increments of growth
being small to set out with, and rapidly decreasing, must
come to an end before any considerable size is attained.
Manifestly the young lion, born of tolerable bulk, suckled un-
til much bigger, and fed until half- grown, is enabled by the
power and organization which he thus gets gratis, to catch
and kill animals of size enough to give him the large supply
of nutriment needed to meet his large expenditure, and yet
leave a large surplus for growth. Thus then is explained

GROWTH. 131

the above-named contrast between the ox and the sheep. A
calf and a lamb commence their physiological transactions on
widely different scales ; their first increments of growth are
similarly contrasted in their amounts ; and the two diminish-
ing series of such increments, end at similarly-contrasted
limits.

§ 49. Such are the several conditions by which the phe-
nomena of growth are governed. Conspiring and conflicting
in endless different ways and degrees, they in every case
qualify more or less differently each other's effects. Hence
it happens that we are obliged to state each generalization as
true on the average, or to make the proviso — other things
equal.

Understood, in this qualified form, our conclusions are
these. First, that growth being an integration with the
organism, of such environing matters as are of like nature
with the matters composing the organism, its growth is de-
pendent on the available supply of such matters : this is alike
a truth established by experience, and an inference from the
truth given in our forms of thought (First Principles, § 67).
Second, that the available supply of assimilable matter being
the same, and other conditions not dissimilar, the degree of
growth varies according to the surplus of nutrition over ex-
penditure— a generalization which is illustrated in some of
the broader contrasts between different divisions of organ-
isms, and is a direct corollary from the persistence of force.
Third, that in the same organism, the surplus of nutrition
over expenditure is a variable quantity ; and that growth is
unlimited or has a definite limit, according as the surplus
docs or does not progressively decrease. This proposition we
found on the one hand exemplified by the unceasing growth
of organisms that do not expend force ; by the growth, slowlv
diminishing but never completely ceasing, of organisms that
expend comparatively little force ; and by the definitely
limited growth of organisms that expend much force ; and

132 THE INDUCTIONS OF BIOLOGY.

on the other hand, we found it to follow from a certain rela
tive increase of expenditure that necessarily accompanies in
crease of bulk, and to be therefore an indirect corollary from
the persistence of force. Fourth, that among organisms
which are large expenders of force, the size ultimately at-
tained is, other things equal, determined by the initial size :
in proof of which conclusion we have abundant facts, as well,
as the a priori necessity that the sum-totals of analogous
diminishing series, must depend upon the amounts of their
initial terms. Fifth, that where the likeness of other cir-
cumstances permits a comparison, the possible extent of
growth depends on the degree of organization : an inference
testified to by the larger forms among the various divisions
and sub-divisions of organisms; and inferable a priori from
the conditions of existence.

CHAPTER II.

DEVELOPMENT*

§ 50. Certain general aspects of Development may "be

studied apart from any examination of internal structures.

These fundamental contrasts between the modes of arrange-
rs

ment of parts, originating, as they do, the leading external
distinctions among the various forms of organization, will be
best dealt with at the outset. If all organisms have arisen
by Evolution, it is of course not to be expected that such
several modes of development can be absolutely demarcated :
we may be sure of finding them united by transitional modes.
But premising that a classification of modes can but approx-
imately represent the facts, we shall find our general con-
ceptions of Development aided by one.

Development is primarily central. All organic forms of
which the entire history is known, set out with a symmetri-
cal arrangement of parts round a centre. In organisms of
the lowest grade, no other mode of arrangement is ever
definitely established; and in the highest organisms, central
development, though subordinate to another mode of de-
velopment, continues to be habitually shown in the changes of

* In ordinary speech, Development is often used as synonymous with Growth.
It hence seems needful to say, that Development as here and hereafter used,
means increase of structure, and not increase of bulk. It may be added, that the
word Evolution, comprehending Growth as well as Development, is to be reserved
foi occasions when both are implied

134 THE INDUCTIONS OF BIOLOGY.

minute structure. Let us glance at these propositions in the
concrete. Leaving out those Rhizopods which are

wholly structureless, every plant and animal in its earliest
stage, consists of a spherical sac, full of liquid containing
organic matter, in which is suspended a nucleated cell, more
or less distinct from the rest ; and the first changes that
occur in the germ thus constituted, are changes that take
place round centres produced by division of the original
centre. From this type of structure, the simplest organisms
do not depart ; or depart in no definite or conspicuous ways.
Among plants, the Uredo and the several tribes of Protococci
permanently maintain such a central distribution ; while
among animals, it is permanently maintained by crea-
tures like the Gregarina, and in a different manner by the
Amceba, Actiaophrys, and their allies. In larger organisms,
made up chiefly of units that are analogous in structure to
these simplest organisms, the formation of units ever continues
to take place round points or' nuclei ; though the arrangement
of these units into groups and wholes may proceed after
another method.

Central development may be distinguished into unicentral
and multicentral ; according as the product of the original
germ, develops symmetrically round one centre, or develops
without subordination to one centre — develops, that is, in
subordination to many centres. Unicentral de-

velopment, as displayed not in the formation of single cells
but in the formation of aggregates, is not common. The
animal kingdom shows it only in the small group named
Thalassicollce : inert, spherical masses of jelly, with scarcely
any organization, which are found floating in southern seas.
It is feebly represented in the vegetal kingdom by the Vol-
vox ylobator. On the other hand, multicentral devel-

opment, or development round insubordinate centres, is va-
riously exemplified in both divisions of the organic world. It
is exemplified in two distinct ways, according as the insubor-
dination among the centres of development is partial or totaJ

DEVELOPMENT. 135

"We may most conveniently consider it under the heads hence
arising.

Total insubordination among the centres of develccinert,
is shown where the units or cells, as fast as the}r are severally
formed, part company and lead independent lives. This, in
the vegetal kingdom, habitually occurs among the Proto-
phyta; and in the animal kingdom, among the Proto-
zoa. Partial insubordination is seen in those
somewhat advanced organisms, that consist of units which,
though they have not separated, have so little mutual depend-
ence that the aggregate they form is irregular. Among
plants, the Thallogens very generally exemplify this mode of
development. Lichens, spreading with flat or corrugated
edges in this or that direction, as the conditions determine,
have no manifest co-ordination of parts. In the Algce, the
Nostocs similarly show us an unsymmetrical structure. Of
Fungi, the sessile and creeping kinds display no further
dependence of one part on another, than is implied by their
cohesion. And even in such better-organized plants as the
Marchantia, the general arrangement shows no reference to a
directive centre. Among animals, many of the Sponges may
be cited as being thus devoid of that co-ordination implied
by symmetry: the Amoeba-like units composing them, though
they have some subordination to local centres, have no subor-
dination to a general centre. To distinguish that
kind of development in which the whole product of a germ
coheres in one mass, from that kind of development in which
it does not, Professor Huxley has introduced the words " con-
tinuous " and " discontinuous ;" and these seem the best fitted
for the purpose. Multicentral development, then, is divisible
into continuous and discontinuous.

From central development we pass insensibly to that higher
kind of development for which axial seems the most appro-
priate name. A tendency towards this is vaguely manifested
almost eveiy where. The great majority even of Protop/ryta
anil P> otozoa have different longitudinal and transverse di-

136 THE INDUCTIONS OF BIOLOGY.

mensions — have an obscure if not a distinct axial otructum
The originally cellular units out of which higher organisme
are mainly built up, usually pass into shapes that are subordi-
nated to lines rather than to points. And in the higher organ-
isms, considered as wholes, an arrangement of parts in rela-
tion to an axis is distinct and nearly universal. We see it in
the superior orders of Thallogens ; and in all the Acrogens,
Endogens, and Exogens. With few exceptions the Ccelente-
rata clearly exhibit it ; it is traceable, though less conspicu-
ously, throughout the Mollusea; and the Annulosa and
Vertebrata uniformly show it with perfect definiteness.

This kind of development, like the first kind, is of two
orders. The whole germ-product may arrange itself round
a single axis, or it may arrange itself round many axes ; the
structure may be uniaxial or multiaxial. Each division of
the organic kingdom furnishes examples of both these or-
ders. In such Fungi as exhibit axial development at
all, we commonly see development round a single axis. Some
of the Alga;, as the common tangle, show us this arrange-
ment. And of the higher plants, many Endogens and
small Exogens are uniaxial. Of animals, the advanced are
without exception in this category. There is no known ver-
tebrate in which the whole of the germ- product is not subor-
dinated to a single axis. In the more fully-organized Annu-
losa, the like is almost universal ; as it is also in the superior
orders of Mollusea. Multiaxial development occurs
in most of the plants we are familiar with — every branch of
a shrub or tree being an independent axis. But while in the
vegetal kingdom, multiaxial development prevails among the
highest types; in the animal kingdom, it prevails only among
the lowest types. It is extremely general, if not universal,
among the Ccelenterata ; it is characteristic of the Mollus-
coida ; among Molluscs the compound Ascidians exhibit it ;
and it is seen, though under another form, in the inferior
Annulosa.

Development that is axial, like development that is centraL

DEVELOPMENT. 137

may be either continuous or discontinuous : the parts having
different axes may continue united, or they may separate.
Instances of each alternative are supplied by both plants
and animals. Continuous, multiaxial development, is

that which plants usually display ; and need not be illustrated
Further than by reference to every garden. As cases of it in
animals may be named, all the compound Hijdrozoa and Ac-
tinozoa; and such molluscous forms as the BotrylUdie. Of

multiaxial development that is discontinuous, a familiar
instance among plants exists in the common strawberry.
This sends out over the neighbouring surface, long slender
shoots, bearing at their extremities buds that presently strike
roots, and become new individuals ; and these by and by lose
their connexions with the original axis. Other plants there
are that produce certain specialized buds called bulbils, which
separating themselves and falling to the ground, grow into
independent plants. Among animals the fresh- water polype
very clearly shows this mode of development : the young
polypes, budding out from its surface, severally arrange
their parts around distinct axes, and eventually detaching
themselves, lead separate lives, and produce other polypes
after the same fashion. By some of the lower Annulosa, this
multiplication of axes from an original axis, is carried on after
a different manner : the string of segments spontaneously
divides ; and after further growth, division recurs in one or
both of the halves. And in the Aphides, we have a still fur-
ther modification of this process.

Grouping together its several modes as above delineated,
we see that

Central
Development is \ or
Axial

10

Unicentral

or

r Continuous

Multicentral ■

or

I

L Discontinuous

Uniaxial

or i

r Continuous

Multiaxial '

or

I

^ Discontinuous

lo3 THE INDUCTIONS OF BIOLOGY.

Any one adequately acquainted with the facts, may readily
raise objections to this arrangement. He may name forma
which do not obviously come under any of these heads. He may
point to plants that are for a time multicentral, but after-
wards develop axially. And from lower types of animals, he
may choose many in which the continuous and discontinuous
modes are both displayed. But, as already hinted, an ar-
rangement free from such anomalies must be impossible, if the
various orders of organization have arisen by Evolution. The
one above sketched out, is to be regarded as only a rough
grouping of the facts, which helps us to a conception of them
in their totality ; and so regarded, it will be of service when
we come to treat of Individuality and Reproduction.

§ 51. From these most general external aspects of organic
development, let us now turn to its internal and more special
aspects. When treating of Evolution as a universal process
of things, a rude outline of the course of structural changes in
organisms was given (First Principles, §§ 43, 55, 56). Here,
however, it will be proper to describe these changes more fully.

The bud of any common plant in its earliest stage, consists
of a small hemispherical or sub-conical projection. While
it increases most rapidly at the apex, this presently deve-
lops on one side of its base, a smaller projection of like general
shape with itself. Here is the rudiment of a leaf ; which pre-
sently spreads more or less round the base of the central
hemisphere or main axis. At the same time that the central
hemisphere rises higher, this lateral prominence, also in-
creasing, gives rise to subordinate prominences or lobes.
These are the rudiments of stipules, where the leaves are
stipulated. Meanwhile, towards the other side of the main
axis, and somewhat higher up, another lateral prominence
arising, marks the origin of a second leaf. By the time that
the first leaf has produced another pair of lobes, and the
second leaf has produced its primary pair, the central hemi-
sphere, still increasing at its apex, exhibits the rudiment of a

DEVELOPMENT. 1-39

third leaf. Similarly throughout. While the g( rm of each
succeeding leaf thus arises, the germs of the previous leaves,
in the order of their priority, are changing their rude nodu-
lated shapes into flattened-out expansions ; which slowly put
on those sharp outlines they show when unfolded. Thna
from that extremely indefinite figure, a rounded lump, giving
off from time to time lateral lumps, which severally becoming
symmetrically lobed, gradually assume specific and involved
forms, we pass little by little to that comparatively complex
tiling — a leaf- bearing shoot. Internally, a bud under-

goes analogous changes. The layer of substance which forms
the surface of the hemisphere, and in which these metamor-
phoses commence, consists of a transparent, irregularly-aggre-
gated mass of cells and centres of growth, not formed into a
tissue. Especially is this the case at the apex, where the
vital activity is the greatest. Here the primitive cellular
mass passes without any line of demarcation into the tissues
that are developing from it. While, by continued cell-multi-
plication this la}rer increases, and doing so most rapidly al
the apex thrusts outwards its lateral portions, these begin to
exhibit differentiations. " Gradually," says Schleiden, " se-
parate masses of cells, with a distinct and definite outline,
appear in this chaos, and they cease to partake of the process
of growth going on. At first the epidermis is separated,
then the vascular bundles, later the parenchyma." Similarly
with the lateral buds whence leaves arise. In the, at first, un-
organized mass of cells constituting the rudimentary leaf,
there are formed vascular bundles which eventually become
the veins of the leaf; and gradually there appear also, though
La ways that have not been specified, the parenchyma and the
epithelium. Nor do we fail to find an essentially

parallel tet of changes, when we trace the histories of the in-
dividual cells. While the tissues they compose are separ-
ating, the cells are growing step by step more unlike.
Some become flat, some polyhedral, some cylindrical, some
prismatic, some spindle-shnped. These develop spiral fibres

140 THE INDUCTIONS OF BIOLOGY.

in their interiors ; and those, net-works of fibres. Here a
number of cells unite together to form a tube; and there
they become solid by the internal deposition of woody or other
matter. Through such changes, too numerous and involved
to be here detailed, the originally uniform cells go on diverg-
ing and re-diverging, until there are produced various forms
that seem to have very little in common.

The arm of a man makes its first appearance in as simple
a way as does the shoot of a plant. According to Bischoff, it
buds-out from the side of the embryo, as a little tongue-shaped
projection, presenting no differences of parts ; and it might
serve for the rudiment of some one of the various other organs
that also arise as buds. Continuing to lengthen, it presently
becomes somewhat enlarged at its end ; and is then described as
a pedicle bearing a flattened, round-edged lump. This lump is
the representative of the future hand ; and the pedicle, of the
future arm. By and by, at the edges of this flattened lump,
there appear four clefts, dividing from each other the buds of
the future fingers ; and the hand as a whole grows a littl 3
more distinguishable from the arm. Up to this time, th3
pedicle has remained one continuous piece ; but it now begins
to show a bend at its centre, which indicates the division into
arm and forearm. The distinctions thus rudely indicated,
gradually increase : the fingers elongate and become jointed ;
and the proportions of all the parts, originally very un-
like those of the complete limb, slowly approximate to
them. During its bud-like stage, the rudimentary

arm is nothing but a Homogeneous mass of simple cells, with-
out any arrangement. By the diverse changes they gradually
undergo, these cells are transformed into bones, muscles,
blood-vessels, and nerves. The extreme softness and delicacy
of this primary cellular tissue, renders it difficult to trace the
initial stages of these differentiations. In consequence of the
colour of their contents, the blood-vessels are the first parw to
become visible. Afterwards the cartilaginous parts, wHeh
are the bases of the future bones, become marked out by the

DEVELOPMENT. HI

denser aggregation of their constituent cells, and the produc-
tion between these of a hyaline substance which unites them
into a translucent mass. When first perceptible, the muscles
are gelatinous, pale, yellowish, transparent, and indistinguish-
able from their tendons. The various other tissues of which
the arm cons'sts, beginning with very faintly-marked differ-
ences, become day by day more definite in their outlines and
appearances. In like manner, the units composing

f.hese tissues, severally assume increasingly-specific characters.
The fibres of muscle, at first made visible in the midst of
their gelatinous matrix only by immersion in alcohol, grow
more numerous and distinct ; and by and by they begin to
exhibit transverse stripes. The bone-cells put on by degrees
tneir curioua structure of branching canals. And so in their
respective ways with the units of skin ana the rest.

Thus in each of the organic sub-kingdoms, we see this
change from an incoherent, indefinite homogeneity, to a
coherent, definite heterogeneity, illustrated in a quadruple
way. The originally -like units or cells, become unlike in
various ways, and in ways more numerous and marked as the
development goes on. The several tissues which these
several classes of cells form by aggregation, grow little by
little distinct from each other ; and little by little put on
those structural complexities, that arise from differentiations
among their component units. In the shoot, as in the limb,
the external form, originally very simple, and having much
in common with countless simple forms, organic and in-
organic, gradually acquires an increasing complexity, and an
increasing unlikeness to other forms. And meanwhile, the
remaining parts of the organism to which the shoot or limb
belongs, having been severally assuming structures divergent
from each other and from that of this particular shoot or
limb, there has arisen a greater heterogeneity in the organ-
Ism as a whole.

$ 52. One of the most remarkable inductions of embry-

142 THE INDUCTIONS OF BIOLOGY.

ology. comes next in order. Yon Baer found that in its
earliest stage, every organism has the greatest number of
characters in common with all other organisms in their
earliest stages ; that at a stage somewhat later, its structure
is like the structures displayed at corresponding phases by a
less extensive multitude of organisms ; that at each sub-
sequent stage, traits are acquired which successively distin-
guish the developing embryo from groups of embryos that it
previously resembled — thus step by step diminishing the
group of embryos which it still resembles ; and that thus the
class of similar forms, is finally narrowed to the species of
which it is a member. This abstract proposition will per-
haps not be fully realized by the general reader. It will be
best to re-state it in a concrete shape. The germ

out of which a human being is evolved, differs in no visible
respect from the germ out of which every animal and plant is
evolved. The first conspicuous structural change undergone
by this human germ, is one characterizing the germs of
animals only — differentiates them from the germs of plants.
The next distinction established, is a distinction exhibited by
all Vertebrata; but never exhibited by Annulosa, Mollutca, or
Ccelenterata. Instead of continuing to resemble, as it now
does, the rudiments of all fishes, reptiles, birds, and mammals ;
this rudiment of a man, assumes a structure that is seen onlv
in the rudiments of mammals. Later, the embryo undergoes
changes which exclude it from the group of implacental
mammals ; and prove that it belongs to the group of placental
mammals. Later still, it grows unlike tlie embryos of those
placental mammals distinguished as ungulate or hoofed ; and
continues to resemble only the unguiculate or clawed. .By
and by, it ceases to be like any foetuses but those of the cpad-
rumana ; and eventually the foetuses of only the 3 lgher
quadrumana are simulated. Lastly, at birth, the ('nfaut,
belonging to whichever human race it may do, is struci urally
very much like the infants of all other human race; ; and
only afterwards acquires those various minor peculiarities of

DEVELOPMENT. 14^

form that distinguish the variety of man to which it be-
longs.

The generalization here expressed and illustrated, must
not be confounded with an erroneous semblance of it that has
obtained considerable currency. An impression has been~~
given by those who have popularized the statements of em-
In yologists, that during its development, each higher organ-
ism passes through stages in which it resembles the adult
forms of lower organisms — that the embryo of a man is at
one time like a fish, and at another time like a reptile. This
is not the fact. The fact established is, that up to a certain
point, the embryos of a man and a fish continue similar, and
that then differences begin to appear and increase — the one
embryo approaching more and more towards the form of a
fish ; the other diverging from it more and more. And so
with the resemblances to the more advanced types. Suppos-
ing the germs of all kinds of organisms to be simultaneously
developing, we may say that all members of the vast mul-
titude take their first steps in the same direction ; that' at the
second step one-half of this vast multitude diverges from the
other half, and thereafter follows a different course of deve-
lopment ; that the immense assemblage contained in either
of these divisions, very soon again shows a tendency to take
two or more routes of development ; that each of the two or
more minor assemblages thus resulting, shows for a time but
small divergences among its members, but presently again
divides into groups which separate ever more widely as they
progress ; and so on, until each organism, when nearly com-
plete, is accompanied in its further modifications only by
organisms of the same species ; and last of all, assumes the
peculiarities which distinguish it as an individual — diverges
to a slight extent to the organisms it is most like. The

reader must also be cautioned against accepting this general-
ization as exact. The likenesses thus successively displayed
are not precise but approximate. Only leading characteris-
tics are the same : not all the details. It is as though in

144 THE INDUCTIONS OF BIOLOGY.

one of the diverging groups just described, each kind of
organism, though having a general direction of development
like that of the others it is for a time travelling with, shows
from the first a tendency to leave the general route — a tend-
ency which presently becomes strongly marked. Making
all requisite qualifications, however, these resemblances re-
main conspicuous ; and the fact that they follow each other
in the way described, is a fact of great significance.

§ 53. This comparison between the course of development
in any creature, and the course of development in all other
creatures — this arrival at the conclusion that the course of
development in each, at first the same as in all others, be-
comes stage by stage differentiated from the courses of all
others, brings us within view of an allied conclusion. If we
contemplate the successive stages passed through by any
higher organism, and observe the relation between it and its
environment at each of these stages ; we shall see that this re-
lation is modified in a way analogous to that in which the
relation between the organism and its environment is modi-
fied, as we advance from the lowest to the highest grades.
Along with the progressing differentiation of each organism
from others, we find a progressing differentiation of it
from its environment ; like that progressing differentiation
from the environment which we meet with in the ascending
forms of life. Let us first glance at the way in which the
ascending forms of life exhibit this progressing differentiation
from the environment.

In the first place, it is illustrated in structure. Ad-
vance from the homogeneous to the heterogeneous, itself in-
volves an increasing distinction from the inorganic world.
In the lowest Protozoa we have a simplicity approaching
to that of air, water, or earth ; and the ascent to organisms
of greater and greater complexity of structure, is an ascent to
organisms that are in that respect more strongly contrasted
with the structureless environment. Inform, again,

DEVELOPMENT. 143

we see the same fact. An ordinary characteristic of inor-
ganic matter is its indefiniteness of form ; and this is also a
characteristic of the lower organisms, as compared with the
higher. Speaking generally, plants are less definite than
animals, both in shape and size — admit of greater modifica-
tions from variations of position and nutrition. Among ani-
mals, the simplest Rhizopods are not only structureless bat
amorphous : the form is never specific, and is constantly
changing. Of the organisms resulting from the aggregation
of such creatures, we see that while some, as the Forammi-
fera, assume a certain definiteness of form, in their shells at
least ; others, as the Sponges, are very irregular. The Zoo-
phytes and the Polyzoa are compound organisms, most of
which have a mode of growth not more determinate than that
of plants. But among the higher animals, we find not
only that the mature shape of each species is very definite,
but that the individuals of each species differ very little in
size. A parallel increase of contrast is seen in chemi-

cal composition. With but few exceptions, and those only
partial ones, the lowest animal and vegetal forms are inhabit-
ants of the water ; and water is almost their sole constituent.
Desiccated Protophyta and Protozoa shrink into mere dust ;
and among the Acalephes, we find but a few grains of solid
matter to a pound of water. The higher aquatic plants, in
common with the higher aquatic animals, possessing as they
do increased tenacity of substance, also contain a greater pro-
portion of the organic elements ; and so are chemically more
unlike their medium. And when we pass to the superior
classes of organisms — land-plants and land-animals — we find
that, chemically considered, they have little in common either
with the earth on which they stand or the air which sur-
rounds them. In specific gravity too, we may note
the like truth. The very simplest forms, in common with
the spores and gemmules of higher ones, arc as nearly as may
he of the same specific gravity as the water in which they
Boat ; and though it cannot be said that anion jj aquatic

146' THE INDUCTIONS OF BIOLOGY.

creatures, superior specific gravity is a standard of general
superiority, yet we may fairly say that vhe superior orders oi
them, when divested of the appliances by which their specific
gravity is regulated, differ more from water in their relative
weight than do the lowest. In terrestrial organisms, tli8
contrast becomes extremely marked. Trees and plants, in
common with insects, reptiles, mammals, birds, are all of a
specific gravity considerably less than that of the earth and
immensely greater than that of the air. Yet further,

we see the law similarly fulfilled in respect of temperature.
Plants generate but extremely small quantities of heat, which
are to be detected only by very delicate experiments ; and
practically they may be considered as having the same tem-
perature as their environment. The temperature of aquatic
animals is very little above that of the surrounding water :
that of the invertebrata being mostly less than a degree above
it, and that of fishes not exceeding it by more than two or
three degrees ; save in the case of some large red-blooded
fishes, as the tunny, which exceed it in temperature by nearly
ten degrees. Among insects, the range is from two to ten
degrees above that of the air : the excess varying according
to their activity. The heat of reptiles is from four to fifteen
degrees more than the heat of their medium. While mam •
mals and birds maintain a heat which continues almost un-
affected by external variations, and is often greater than that
of the air by seventy, eighty, ninety, and even a hundred
degrees. Once more, in greater self-mobility a pro-

gressive differentiation is traceable. The especial character*
istic by which we distinguish dead matter is its inertness :
some form of independent motion is our most general test of
life. Passing over the indefinite border-land between the
animal and vegetal kingdoms, we may roughly class plants
as organisms which, while they exhibit that species of motion
implied in growth, are not only devoid of locomotive power,
but with some unimportant exceptions are devoid of the
power of moving their parts in relation to each other ; and

DEVELOPMENT. 147

thus arc less differentiated from the inorganic world than
animals. Though in those microscopic Protophyta and Pro-
tozoa inhabiting the water — the spores of algoe, the gemmules
of sponges, and the infusoria generally — we see locomotion
produced by ciliary action ; yet this locomotion, while rapid
relatively to the size of the creatures, is absolutely slow. Of
the Ccelentcrata, a great part are either permanently rooted or
habitually stationary ; and so have scarcely any self-mobility
but that implied in the relative movements of parts ; while
the rest, of which the common jelly-fish will serve as a sam-
ple, have mostly but little ability to move themselves through
the water. Among tne nigher aquatic Invertebrate!, — cuttle-
fishes and lobsters, for instance, — there is a very considerable
power of locomotion ; and the aquatic Vertebrata are, con-
sidered as a class, much more active in their movements than
the other inhabitants of the water. But it is only when we
come to air-breathing creatures, that we find the vital charac
teristic of self-mobility manifested in the highest degree.
Flying insects, mammals, birds, travel with a velocity far
exceeding that attained by any of the lower classes of ani-
mals ; and so are more strongly contrasted with their inert
environment. Thus, on contemplating the various

grades of organisms in their ascending order, we find them
more and more distinguished from their inanimate media, in
structure, in form, in chemical composition, in specific gravity,
in temperature, in self-mobility. It is true that this general-
ization does not hold with complete regularity. Organisms
which are in some respects the most strongly contrasted with
the environing inorganic world, are in other respects less so
than inferior organisms. As a class, mammals are higher
than birds ; and yet they are of lower temperature, and have
smaller powers of locomotion. The stationary oyster is of
higher organization than the free-swimming medusa ; and
the cold-blooded and less heterogeneous fish, is quicker in its
movements than the warm-blooded and more heterogeneous
sloth. But the admission that the several aspects undrr

148 THE INDUCTIONS OF BIOLOGY.

which this increasing contrast shows itself, bear variable
ratios to each other, does not conflict with the general truth,
that as we ascend in the hierarchy of organisms, we meet with
not only an increasing differentiation of parts, but also an
increasing: differentiation from the surrounding medium in
sundry other physical attributes. It would seem that this
peculiarity has some necessary connexion with superior
vital manifestations. One of those lowly gelatinous forms,
so transparent and colourless as to be with difficulty dis-
tinguished from the water it floats in, is not more like its
medium in chemical, mechanical, optical, thermal, and other
properties, than it is in the passivity with which, it sub-
mits to all the influences and actions brought to bear upon
it ; while the mammal does not more widely differ from
inanimate things in these properties, than it does in the ac-
tivity with which it meets surrounding changes by compens-
ating changes in itself. And between these two extremes,
we shall observe a constant ratio between these two kinds of
contrast. Whence we may say, that in proportion as an
organism is physically like its environment, does it remain a
passive partaker of the changes going on in its environment ;
while in proportion as it is endowed with powers of counter-
acting such changes, it exhibits greater uulikeness to its en-
vironment.*

If now, from this same point of view, we consider the rela-
tion borne to its environment by any superior organism in
its successive stages, we find an analogous series of. con-
trasts. Of course in respect of degrees of structure, the
parallelism is complete. The difference, at first small, be-
tween the comparatively structureless germ and the com-
paratively structureless inorganic world, becomes necessarily
greater, step by step, as the differentiations of the germ be-
come more numerous and definite. How of form
the like holds, is equally manifest. The sphere, which is

• This paragraph originally formed part of a review-article on " Transcenden-
tal Physiology," published in ] 857

DEYI.l.OrMKXT. 149

the point of departure common to all organisms, is the most
generalized of figures ; and one that is, under various circum-
stances, assumed by inorganic matter. While the incij)ient
organism is spherical, it is not only like many particular in-
organic masses ; but it is like the rest, in the sense that it has
the shape which would result, were all their irregularities
averaged. But as it develops, it loses all likeness to inor-
ganic objects in the environment ; and eventually becomes
distinct even from ail organic elects in its environ-
ment. In specific gravity, the alteration, though not
very marked, is still in the same direction. Development
being habitually accompanied by a relative decrease in the
quantity of water, and an increase in the quantity of consti-
tuents that are heavier than water, there results a small aug-
mentation of relative weight. In power of maintain-
ing a temperature above that of surrounding things, the
differentiation from the environment that accompanies deve-
lopment, is marked. All ova are absolutely dependent for
their heat on external sources. Like inorganic bodies, they
gain or lose heat according as neighbouring bodies are colder
or hotter. The mammalian young is, during its uterine life,
dependent on the maternal heat ; and at birth has but a par-*
tial power of making good the loss by radiation. But as it
advances in development, it gains an ability to maintain a
constant temperature above that of surrounding things : so
becoming markedly unlike all surrounding things, save or-
ganisms of allied nature. Lastly, in self- mobility this
increasing contrast is not less decided. Save in a few aber-
rant tribes, chiefly parasitic, we find the general fact to be,
that the locomotive power, totally absent or very small at the
outset, increases with the advance towards maturity? The
more highly developed the organism becomes, the stronger
grows the contrast between its activity and the inertness of
the objects amid which it moves.

Thus we may say that the development of an individual
organism, is at the same time a differentiation of its parts

lf>0 THE INDUCTIONS OF BIOLOGY.

from each, other, and a differentiation of the consolidated
whole from the environment ; and that in the last as in the
first respect, there is a general analogy between the progres-
sion of an individual organism, and the progression from the
lowest orders of organisms to the highest orders. It

may be remarked that some kinship seems to exist between
these generalizations and the doctrine of Schelling, that Life
is the tendency to individuation. For evidently, in becom-
ing more distinct from each other, and from their environ-
ment, organisms acquire more marked individualities. As
far as I can gather from outlines of his philosophy, however,
it appears that Schelling entertained this conception in a
general and transcendental sense, rather than in a special and
scientific one.

§ 54. The deductive interpretations of these general facts
of development, in so far as they are at present possible, must
be postponed until we arrive at the fourth and fifth divisions of
this work ; which will be chiefly occupied with them. There
are, however, one or two general aspects of these inductions,
^ which maybe here most conveniently dealt with deductively.

The general law of development as displayed in organisms,
is readily shown to be necessary, if the initial and terminal
stages are such as we know them to be. Grant that each
organism is at the outset homogeneous, and that when com-
plete it is relatively heterogeneous ; and of necessity it fol-
lows that development is a change from the homogeneous
to the heterogeneous — a change during which there must be
gone through all the infinitesimal gradations of heterogeneity
that lie between these extremes. If, again, there is at first
indefiifiteness, and at last definiteness, the transition cannot
but be from the one to the other of these, through all intermedi-
ate degrees of definiteness. Further, if the parts, originally
incoherent or uncombined, eventually become relatively co-
herent or combined ; there must be a continuous increase of
coherence or combination. Ilence the general truth thai

DEVELOPMENT. 151

development is a change from incoherent, indefinite homo-
geneity, to coherent, definite heterogeneity, becomes a self-
evident one, when observation has shown us the state in
which organisms begin, and the state in which they end.

Just in the same way that the growth of an entire organ-
ism, is carried on by abstracting from the environment
substances like those composing the organism ; so the pro-
duction of each organ within the organism, is carried on by
abstracting from the substances contained in the organism,
those required by this particular organ. Each organ at the
expense of the organism as a whole, integrates with itself
certain special kinds and proportions of the matters circulat-
ing around it ; in the same way that the organism as a
whole, integrates with itself certain special kinds and propor-
tions of matters at the expense of the environment as a
whole. So that the organs are qualitatively differentiated
from each other, in a way analogous to that by which the en-
tire organism is qualitatively differentiated from things
around it. Evidently this selective assimilation

illustrates the general truth, demonstrable a priori, that like
units tend to segregate. It illustrates, moreover, the further
aspect of this general truth, that the pre-existence of a mass
of certain units, produces, probably by polar attraction, a
tendency for diffused units of the same kind to aggregate
with this mass, rather than elsewhere. It has been shown of
particular salts, A and B, co-existing in a solution not suf-
ficiently concentrated to crystallize, that if a crystal of the salt
A be put in o the solution, it will increase by uniting with itself
the dissolved atoms of the salt A ; and that similarly, though
there otherwise takes place no deposition of the salt B, yet if
a crystal of the salt B is placed in the solution, it will exercise
a coercive force on the diffused atoms of this salt, and grow at
their expense. No doubt much organic assimilation occurs
in the same way. Particular parts of the organism are com-
posed of special units, or have the function of secretin"
special units, which are ever present in them in large quan-

152 THE INDUCTIONS OF BIOLOGY.

tities. The fluids circulating through the body contain
special units of this same order. And these diffused units
are continually being deposited along with the groups of like
units that already exist. How purely physical are the causes
of this selective assimilation, is, indeed, conclusively shown
"by the fact, that abnormal constituents of the blood are
segregrated in the same way. Cancer-cells having begun to
be deposited at a particular place, continue to be deposited at
that place. Tubercular matter, making its appearance at
particular points, collects more and more round those points.
And similarly in numerous pustular diseases. Where

the component units of an organ, or some of them, do not
exist as such in the circulating fluids, but are formed out of
elements or compounds that exist separately in the circulat-
ing fluids ; it is clear that the process of differential assimil-
ation is of a more complex kind. Still, however, it seems
not impossible that it is carried on in an analogous way. If
there be an aggregate of compound atoms, each of which
contains the constituents A, B, C ; and if round this aggre-
gate the constituents A and B and' C are diffused in uncom-
bined states ; it may be suspected that the coercive polar force
of these aggregated compound atoms A, B, C, may not only
bring into union with themselves adjacent compound atoms
A, B, C, but may cause the adjacent constituents A and B
and C to unite into such compound atoms, and then aggre-
gate with the mass. Should this be so, the process of differ-
ential assimilation, which plays so important a part in
organic development, will not be difficult to understand. At
present, however, chemical inquiry appears to have furnished
no evidence either for or against such an hypothesis.

CHAPTER III.

FUNCTION.

§ 55. Does Structure originate Function, or docs Func-
tion originate Structure ? is a question about which there has
been disagreement. Using the word Function in its widest
signification, as the totality of all vital actions, the question
amounts to this — does Life produce Organization, or does
Organization produce Life ? ^

To answer this question is not easy, since we habitually
find the two so associated that neither seems possible without
the other ; and they appear uniformly to increase and
decrease together. If it be said that the arrangement of or-
ganic substances in particular forms, cannot be the ultimate
cause of vital changes, which must depend on the properties
of such substances ; it may be replied that, in the absence of
structural arrangements, the forces evolved cannot be so
directed and combined as to secure that correspondence
between inner and outer actions which constitutes Life.
Again, to the allegation that the vital activity of every germ
whence an organism arises, is obviously antecedent to the
development of its structures ; there is the answer that such
germ is not absolutely structureless, but consists of a mass of
cells, containing a cell that differs from the rest, and initiates
the developmental changes. There is, however, one

fact implying that Function must be regarded as taking pre-
cedence of Structure. Of the lowest Ehizopods, which pre-
11

154 THE INDUCTIONS ^F BIOLOGY.

sont no distinctions of parts, and nevertheless feed and
grow and move about, Prof. Huxley has remarked that they
exhibit Life without Organization. The perpetual changes of
form which alone distinguish one of these creatures from an
inanimate fragment, are no doubt totally irregular and un-
directed. Still they do, through an average of accidents,
subserve the creatures' nutrition ; and they do imply an ex-
penditure of force that in some way depends on the consump-
tion of nutriment. They do, therefore, though in the rudest
way, display a vital adjustment of internal to external relations.

§ 56. Function falls into divisions of several kinds, ac-
cording to our point of view. Let us take these divisions in
the order of their simplicity.

Under Function in its widest sense, are included both the
statical and the dynamical distributions of force which an
organism opposes to the forces brought to bear on it. In a
tree, the woody core of trunk and branches, and in an animal,
the skeleton, internal or external, may be regarded as pas-
sively resisting the gravity and momentum which tend
habitually or occasionally to derange the requisite relations
between the organism and its environment ; and since they
resist these forces simply by their cohesion, their functions
may be classed as statical. Conversely, the leaves and sap-
vessels in a tree, and those organs which in an animal
similarly carry on nutrition and circulation, as well as those
which generate and direct muscular motion, must be con-
sidered as dynamical in their actions. From another
point of view, Function is divisible into the accumulation of
force (latent in food) ; the expenditure of force (latent in the
tissues and certain matters absorbed by them) ; and the
transfer of force (latent in the prepared nutriment or blood)
from the parts which accumulate to the parts which expend.
In plants we see little beyond the first of these : expenditure
being inappreciable, and transfer required only to facilitate

FUNCTION. 155

accumulation. In animals, the function of accumulation
comprehends those processes by which the materials contain-
ing latent force are taken in, digested, and separated from
other materials ; the function of transfer comprehends those
processes by which these materials, and such others as are
needful to liberate the forces they contain, are conveyed
throughout the organism ; and the function of expenditure
comprehends those processes by which the forces are liberated
from these materials, and transformed into properly co-ordin-
ated motions. Each of these three most general
divisions, includes several more special divisions. The accu-
mulation of force may be separated into alimentation and
aeration ; of which the first is again separable into the
various acts gone through between prehension of food and
the transformation of part of it into blood. By the transfer
of force is to be understood what we call circulation; if the
meaniu": of circulation be extended to embrace the duties of
both the vascular system and the lymphatics. Under the
head of expenditure of force, come nervous actions and mus-
cular actions : though not absolutely co-extensive with ex-
penditure, these are almost so. Lastly, there are the
subsidiary functions which do not properly fall within any
of these general functions, but subserve them by removing
the obstacles to their performance : those, namely, of ex-
cretion and exhalation, whereby waste products are got
rid of. Again, disregarding their purposes and
considering them analytically, the general physiologist may
consider functions in their widest sense as the correlatives of
tissues — the actions of epidemic tissue, cartilaginous tissue,
elastic tissue, connective tissue, osseous tissue, muscular
tissue, nervous tissue, glandular tissue. Once more,
plrysiology in its concrete interpretations, recognizes special
functions as the ends of special organs — regards the teeth as
having the office of mastication ; the heart as an apparatus
to propel blood ; this gland as fitted to produce one requisite

156 THE [EDUCTIONS OF BIOLOGY.

secretion and that to produce another ; each muscle as the
agent of a particular motion ; each nerve as the vehicle of a
special sensation or a special motor impulse.

It is clear that dealing with Biology only in its larger
aspects, specialities of function do not concern us ; except in
so far as they serve to illustrate, or to qualify, its general-
ities

§ 57. The first induction to be here set down, is a
familiar and obvious one : the induction, namely, that com-
plexity of function, is the correlative of complexity of struc-
ture. The leading aspects of this truth must be briefly noted.

Where there are no distinctions of structure, there are no
distinctions of function. One of the Rhizopods above
instanced as exhibiting life without organization, will serve
as an illustration. From the outside of this creature,
which has not even a limiting membrane, there are protruded
numerous thread-like processes. Originating from any point
of the surface, each of these may contract again and disap-
pear ; or it may touch some fragment of nutriment, which it
draws with it, when contracting, into the general mass — thus
serving as hand and mouth ; or it may come in contact with
its fellow-processes at a distance from the body, and become
confluent with them ; or it may attach itself to an adjacent
fixed object, and help by its contraction to draw the body
into a new position. In brief, this structureless speck of
animated jelly, is at once all stomach, all skin, all mouth, all
limb, and doubtless, too, all lung. In organisms

having a fixed distribution of parts, there is a concomitant
fixed distribution of actions. Among plants we see that
when, instead of a uniform tissue like that of the Algce,
everywhere devoted to the same process of assimilation,
there arise, as in the Exogens, root and stem and leaves,
there arise correspondingly unlike processes. Still more con-
spicuously among animals, do there result varieties of function
when the originally homogeneous mass is replaced by hetero-

FUNCTION. 157

geneous organs; since both singly and by their combinations,
do modified parts generate modified changes. Up to

the highest organic types, this dependence continues mani-
fest ; and it may be traced not only under this most general
form, but also under the more special form, that in animals
having one set of functions developed to more than usual
heterogeneity, there is a correspondingly heterogeneous ap-
paratus devoted to them. Thus among birds, which have
more varied locomotive powers than mammals, the limbs are
more widely differentiated ; while mammals, which rise to
more numerous and more involved adjustments of inner to
outer relations than birds, have more complex nervous
systems.

§ 58. It is a generalization almost equally obvious with
the last, that functions, like structures, arise by progressive
differentiations. Just as an organ is first an indefinite rudi-
ment, having nothing but some most general characteristic
in common with the form it is ultimately to take ; so a
function begins as a kind of action that is like the kind of
action it will eventually become, only in a very vague way.
And in functional development, as in structural development,
the leading trait thus early manifested, is followed success-
ively by traits of less and less importance This holds
equally throughout the ascending grades of organisms, and
throughout the stages of each organism. Let us look at
cases : confining our attention to animals, in which func-
tional development is better displayed than in plants

The first differentiation established, separates the two
fundamentally- opposed functions above named — the accumu-
lation of force and the expenditure of force. Passing over
the, (Protozoa among which, however, such tribes as present
fixed distributions of parts show us substantially the same
thing), and commencing with the lowest Coelentcrata, where
definite tissues make their first appearance, we observe that
the onlv marked functional distinction is between the endo-

15^ THfl IXTTUCTTONS OF RIOT.OCt.

derm, which absorbs nutriment, and the ectoderm, which, i»y
its own contractions and those of the tentacles it bears, pro-
duces motion. That the functions of accumulation and ex-
penditure are here very incompletely distinguished, may be
admitted without affecting the position that this -is the first
specialization which begins to appear. These two

most genei'al and most radically-opposed functions, become,
in the Pohjzoa, much more clearly marked-off from each
other ; at the same time that each of them becomes partially
divided into subordinate functions. The endoderm. and
ectoderm are no longer merely the inner and outer walls of
the same simple sac into which the food is drawn ; but the
endoderm forms a true alimentary canal, separated from the
ectoderm by a peri- visceral cavity, containing the nutritive
matters absorbed from the food. That is to say, the function
of accumulating force is exercised by a part distinctly divided
from the part mainly occupied in expending force : the
space between them, full of absorbed nutriment, effecting in
a vague way that transfer of force which, at a higher stage of
evolution, becomes a third leading function. Meanwhile, the
endoderm no longer discharges the accumulative function
in the same way throughout its whole extent ; but its differ-
ent portions, oesophagus, stomach and intestine, perform
different portions of this function. And instead of a con-
tractility uniformly diffused through the ectoderm, there
have arisen in it, some parts which have the office of con-
tracting (muscles), and some parts which have the office of
making them contract (nerves and ganglia). As we

pass upwards, the transfer of force, hitherto effected quite
incidentally, comes to have a special organ. In the ascidian
molluscs, circulation is produced by a muscular tube, open at
both ends, which, by a wave of contraction passing along it,
sends out at one end the nutrient fluid drawn in at the
other ; and which, having thus propelled the fluid for a time
in one direction, reverses its movement and propels it in the
opposite direction. By such means does this rudimentary

FUNCTION. 159

heart generate alternating currents in the crude and dilute
nutriment occupying the peri-visceral cavity. How the func-
tion of transferring force, thus vaguely indicated in these in-
ferior forms, comes afterwards to be the definitely-separated
office of a complicated apparatus made up of many parts, each
of which has a particular portion of the general duty, need
not be described. It is sufficiently manifest that this General
function becomes more clearly marked-off from the others,
at the same time that it becomes itself Darted into subordinate
tunctions

In a developing emDrvo, tne functions or more strictly
the structures whicn are to perform tnem, arise in the same
general order. A like primarv distinction very early ap-
pears between the endoderm and the ectoderm — the part
which has the office of accumulating force, and the part out
jf which grow those organs that are the great expenders of
force Between these two there presently becomes visible
the rudiment of that vascular system, which has to fulfil the
intermediate duty of transferring force. Of these three
general functions, that of accumulating force is carried on
fi-om the outset: the endoderm, even while yet incompletely
differentiated from the ectoderm, absorbs nutritive matters
from the subjacent yelk. The tr?,nsfer of force is also to
some extent effected by the rudimentary vascular system, as
soon as its central cavity and attached vessels are sketched
out But the expenditure of force (in the higher animals at
least) is not appreciably displayed by the ectodermic struc-
tures that are afterwards to be mainly devoted to it : there
is no sphere for the actions of these parts. Similarly

with the chief subdivisions of these fundamental functions.
If we look at those discharged by the ectoderm, potentially
if not actually, we see that the distinction first established
separates the office of transforming other force into mechani
cal motion, from the office of liberating the force to be so
transformed — in the midst of the part out of which the mus-
cular system is to be developed, there is marked-out the

160 THE INDUCTIONS OF BIOLOGY.

rudiment of the nervous system. This indication of struc-
tures which are to share between them the general duty oi
expending force, is soon followed by changes that foreshadow
further specializations of this general duty. In the incipient
nervous system, there begins to arise that contrast betweeu
the cerebral mass and the spinal cord, which, in the main,
answers to the division of nervous actions into directive
and executive ; and at the same time, the appearance of
vertebral laminre foreshadows the separation of the osseous
system, which has to resist the strains of muscular action,
from the muscular system, which, in generating motion, en-
tails these strains. Simultaneously there have been going
on similar actual and potential specializations in the functions
of accumulating force and transferring force. And through-
out all subsequent phases, the method is substantially the
same.

This progress from general, indefinite, and simple kinds
of action, to special, definite, and complex kinds of action,
has been aptly termed by Milne-Edwards, the " physio-
logical division of labour." Perhaps no metaphor can more
truly express the nature of this advance from vital activity
in its lowest forms to vital activity in its highest forms.
And probably the general reader cannot in any other way
obtain so clear a conception of functional development in
organisms, as he can by tracing out functional development in
societies : noting how there first comes a distinction between
the governing class and the governed class ; how while in
the governing class there slowly grow up such differences of
duby as the civil, military, and ecclesiastical, there arise in
the governed class, fundamentally industrial differences like
those between agriculturists and artizans ; and how there is
a continual multiplication of such specialized occupations,
and specialized shares of each occupation.

§ 59. Fully to understand this change from homogeneity
to heterogeneity of function, which accompanies the change

FUNCTION. 161

from homogeneity to heterogeneity of structure, it is needful
to contemplate it under a converse aspect. Standing alone,
the above exposition conveys both an inadequate and an
erroneous idea. The divisions and subdivisions of function,
becoming definite as they become multiplied, do not lei.d to
a more and more complete independence of functions ; as
they would do were the process nothing beyond that just de-
scribed ; but by a simultaneous process they are rendered
more mutually dependent. While in one respect they are
separating from each other, they are in another respect com-
bining with each other. At the same time that they are
bein^ differentiated, they are also being integrated. Some
illustrations will make this plain.

In animals which display little beyond the primary dif-
ferentiation of functions, the activity of that part which
absoi'bs nutriment or accumulates force, is not immediately
bound up with the activity of that part which, in producing
motion, expends force. In the higher animals, however, the
performance of the alimentary functions depends on the per-
formance of various muscular and nervous functions. Masti-
cation and swallowing are nervo-muscular acts ; the ryth-
mical contractions of the stomach and the allied vermicular
motions of the intestines, result from the stimulation of cer-
tain muscular coats by the nerve- fibres distributed through
them ; the secretion of the several digestive fluids by their
respective glands, is due to nervous excitation of them ; and
digestion, besides requiring these special aids, is not properly
performed in the absence of a continuous discharge of energy
from the great nervous centres. Again, the function

of transferring nutriment or latent force, from part to part,
though at first not closely connected with the other functions,
eventually becomes so. The short contractile tube which
propels backwards and forwards the crude dilute blood con-
tained in the perivisceral cavity of an inferior mollusc, is
neither structurally nor functionally much entangled with
the creature's other organs. But on passing upwards through

162 THE INDUCTIONS OV BIOLOGY

the higher molluscs, in which this simple tube is replaced
Ly a system of branched tubas, that deliver their contents
through their open ends into the tissues at distant parts ;
and on coming to those advanced types of animals which
have closed arterial and venous systems, ramifying minutely
in every corner of ever}' organ ; we find that the vascular
apparatus, while it has become structurally interwoven
with the whole body, has become unable to fulfil its
office without the help of offices that are quite separated from
its own. The heart is now a complex pump, worked by
powerful muscles that are excited by a local nervous system ;
and the general nervous system also, takes a share in regu-
lating the contractions both of the heart and of all the
arteries. On the due discharge of the respiratory function,
too, the function of circulation is directly dependent : if the
aeration of the blood is impeded, the vascular activity is
lowered ; and arrest of the one very soon causes stoppage of
the other. Similarly with the duties of the nervo-

muscular system. Animals of low organization, in which
the differentiation and integration of the vital actions have
not been carried far, will move about for a considerable time
after being eviscerated, or deprived of those appliances by
which force is accumulated and transferred. But animals of
high organization are instantly killed by the removal of
these appliances, and even by the injury of minor parts of
them : a dog's movements are suddenly brought to an end, by
cutting one of the main canals along which the materials
that evolve movements are conveyed. Thus while

in well-developed creatures the distinction of functions is
very marked, the combination of functions is very close.
From instant to instant, the aeration of blood implies that,
certain respiratory muscles are being made to contract by
certain nerves; and that the heart is duly propelling the
blood to be aerated. From instant to instant digestion pro-
ceeds only on condition that there is a supply of aerated blood,
and a due current of nervous energy through the digestive

FUNCTION. .103

organs. That the heart may act, it must from instant to in-
stant be excited by discharges from certain ganglia ; and
the discharges from these ganglia are made possible, only by
the conveyance to them, from instant to instant, of the
blood which ttifj heart propels.

It is not easy to find an adequate expression for this double
re-distribution of functions. It is not easy to realize a trans-
formation through which the functions thus become in one
sense separated and in another sense combined, or even in-
terfused. Here, however, as before, an analogy drawn from
social organization helps us. If we observe how the increas-
ing division of labour in societies, is accompanied by a closer
co-operation ; and how the agencies of different social actions,
while becoming in one respect more distinct, become in an-
other respect more minutely ramified through each other ;
we shall understand better the increasing physiological co-
operation that accompanies increasing physiological division
of labour. Note, for example, that while local

divisions and classes of the community have been grow-
ing unlike in their several occupations, the carrying on of
their several occupations has been growing dependent on
♦.he due activity of that vast organization by which sus-
tenance is collected and diffused. During the early stages
of social development, every small group of people, and often
every family, obtained separately its own necessaries; but
now, for each necessary, and for each superfluity, there ex-
ists a combined body of wholesale and retail distributors,
which brings its branched channels of supply within reach
of all. While each citizen is pursuing a business that does not
immediately aim at the satisfaction of his personal wants, his
personal wants are satisfied by a general agency that brings
from all places commodities for him and his fellow-citizens
— an agency which could not cease its special duties for a few
days, without bringing to an end his own special duties and
those of most others. Consider, again, how each

of these differentiated functions is everywhere pervaded by

164 THE INDUCTIONS OF BIOLOGY.

certaiD otlicr differentiated functions. Merchants, manu-
facturers, wholesale distributors of their several species, to-
gether with lawyers, bankers, &c, all employ clerks. In
clerks we have a specialized class dispersed through various
other classes ; and having its function fused with the differ-
ent functions of these various other classes. Similarly
commercial travellers, though having in one sense a
separate occupation, have in another sense an occupation
forming part of each of the many occupations which it
aids. As it is here with the sociological division

of labour, so is it with the physiological division of la-
bour above described. Just as we see in an advanced com-
munity, that while the magisterial, the clerical, the medical,
the legal, the manufacturing, and the commercial activities,
have grown distinct, theyJiave yet their agencies mingled
together in every locality ; so in a developed organism, we
see that while the general functions of circulation, secretion,
absorption, excretion, contraction, excitation, &c, have be-
come differentiated, yet through the ramifications of the sys-
tems apportioned to them, they are closely combined with
each other in every organ.

§ 60. The physiological division of labour, is usually not
carried so far as wholly to destroy the primary physiological
community of labour. As in societies the adaptation of special
classes to special duties, does not entirely disable these classes
from performing each others' duties on an emergency ; so in
organisms, tissues and structures that have become fitted to
the particular offices they have ordinarily to discharge, often
remain partially able to discharge other offices. It has been
pointed out by Dr Carpenter, that " in cases where the differ
ent functions are highly specialized, the general structure
retains, more or less, the primitive community of function
which originally characterized it." A few instances will
bring home this generalization.

The roots and leaves of plants are widely differenti-

FUNCTION. 18a

ated in their functions : by the roots, water and mineral
substances are absorbed ; while the leaves take in. and de-
compose, carbonic acid. Nevertheless, leaves retain a con-
siderable power of absorbing water ; and in what are popu-
larly called " air-plants," the absorption of water is wholly
carried on by them and by the stems. Conversely, the under-
ground parts can partially assume the functions of leaves :
the exposed tuber of a potato develops chlorophyll on its
surface, and in other cases, roots, properly so called, do the
like. In trees, the trunks, which have in great measure
ceased to produce buds, recommence producing them if the
branches are cut off; and under such circumstances the
roots, though not in the habit of developing leaf-bearing
organs, send up numerous suckers. Much more

various examples of vicarious function may be found among
animals. Starting with the extreme case of the common
hydra, which can live when the duties of skin and stomach
have been interchanged by turning it inside out, we find in
all grades, even up to the highest, that absorbent and excret-
ing organs can partially supply each others' places. Among
well-organized animals, the taking in of nutriment is ef-
fected exclusively by an internal membrane ; but the external
membrane is not wholly without the power to take in nutri-
ment : when food cannot be swallowed, life may be pro-
longed by immersing the body in nutritive fluids. The ex-
cretion of carbonic acid and absorption of oxygen, are mainly
performed by the lungs, in creatures which have lungs ; but
in such creatures there continues a certain amount of cutane-
ous respiration, and in soft-skinned batrachians like the frog,
this cutaneous respiration is important. Again, when the
kidneys are not discharging their duties, a notable quantity
of urea is got rid of by perspiration. Other

instances are supplied by the higher functions. In man,
the limbs, which among lower vertebrates are almost wholly
organs of locomotion, are specialized into organs of locomo-
tion and organs of manipulation. Nevertheless, the human

166

THE INDUCTIONS OF I IOLOGY.

arms and legs do, when needful, fulfil, to some extent, each
others' offices. JSot only in childhood and old age are the
arms used for purposes of support, but on occasions of emerg-
ency, as when mountaineering, they are so used by men in full
vigour. And that legs are to a considerable degree capable
of performing the duties of arms, is proved by the great
amount of manipulatory skill reached by them when the
arms are absent. Among the perceptions, too, there are ex-
amples of partial substitution. The deaf Dr Kitto described
himself as having become excessively sensitive to vibrations
propagated through the body ; and as so having gained the
power of perceiving, through his general sensations, those
neighbouring concussions of which the ears ordinarily give
notice. Blind people make hearing perform, in part, the
office of vision. Instead of identifying the positions and
sizes of neighbouring objects by the reflection of light from
their surfaces, they do this in a rude way by the reflection
of sound from their, surfaces.

We see, as we might expect to see, that this power of per-
forming more general functions, is great in proportion as
the parts have been but little adapted to their special func-
tions. In the hydra, where complete transposition of functions
is possible, the histological differentiation that has been estab-
lished, is extremely slight, or even inappreciable. Those parts
of plants which show so considerable a power of discharging
each others' offices, are not widely unlike in their minute
structures. And the tissues that in animals are to some
extent mutually vicarious, are tissues in which the original
cellular composition is still conspicuous. But we do not find
evidence that the muscular, nervous, or osseous tissues are
able in any degree to perform those processes which the
less differentiated tissues perform. Nor have we any
proof that nerve can partially fulfil the duty of muscle,
or muscle that of nerve. "We must say, therefore, that
the ability to resume the primordial community of function

FUNCTION. 167

varies inversely as the established specialization of function ;
and that it disappears when the specialization of function
becomes great.

§ GL. Something approaching to a priori reasons may be
given for the conclusions thus reached a posteriori. They
must be accepted for as much as they seem worth.

It may be argued that on the hypothesis of Evolution,
Life necessarily comes before organization. On this hypo-
thesis, organic matter in a state of homogeneous aggregation,
must precede organic matter in a state of heterogeneous ag-
gregation. But since the passing from a structureless state
to a structured state, is itself a vital process, it follows that
vital activity must have existed while there was yet no
structure : structure could not else arise. That

function takes precedence of structure, seems also implied in
the definition of Life. If Life consists of inner actions so
adjusted as to balance outer actions — if the actions are the
substance of Life, while the adjustment of them constitutes
its form; then, may we not say that the actions to be formed
must come before that which forms them — that the continu-
ous change which is the basis of function, must come before
the structure which brings function into shape ? Or

again, since throughout all phases of Life up to the highest,
every advance is the effecting of some better adjustment of
inner to outer actions; and since the accompanying new com-
plexity of structure is simply a means of making possible
this better adjustment ; it follows that function is from
beginning to end the determining cause of structure. ]Not
only is this manifestly true where the modification of struc-
ture arises by reaction from modification of function ; but it
is also true where a modification of structure otherwise pro-
duced, apparently initiates a modification of function. For
it is only when such so-called spontaneous modification of
structure subserves some advantageous action, that it is per-

per-

168 THE INDUCTIONS DF BIOLOGY.

manently established : if it is a structural modification that
hajypens to facilitate the vital activities, "natural selection"
retains and increases it ; but if not, it disappears.

The connexion which we noted between heterogeneity
of structure and heterogeneity of function — a connexion
made so familiar by experience as to appear scarcely worth
specifying — is clearly a necessary one. It follows from the
general truth that in proportion to the heterogeneity of any
aggregate, is the heterogeneity it will produce in any inci-
dent force (First Principles, § 116). The force continually
liberated in the organism by decomposition, is here the inci-
dent force ; the functions are the variously modified forms
produced in its divisions by the organs they pass through ;
and the more multiform the organs the more multiform must
be the differentiations of the force passing through them.

It follows obviously from this, that if structure progresses
from the homogeneous, indefinite, and incoherent, to the
heterogeneous, definite, and coherent, so too must function.
If the number of different parts in an aggregate must deter-
mine the number of differentiations produced in the forces
passing through it — if the distinctness of these parts from each
other, must involve distinctness in their reactions, and there-
fore distinctness between the divisions of the differentiated
furce ; there cannot but be a complete parallelism between
the development of structure and the development of func-
tion. If structure advances from the simple and general to
the complex and special, function must do the same.

CHAPTER IV.

WASTE AND REPAIR.

§ 62. Throughout the vegetal kingdom, the processes of
SYaste and Repair are comparatively insignificant in their
amounts. Though plants, and especially certain parts of
thera, do, in the absence of light or under particular con-
ditions, give out carbonic acid ; yet this carbonic acid,
assuming it to indicate consumption of tissue, indicates but a
small consumption. Of course if there is little waste, there
can be but little repair — that is, little of the interstitial repair
which restores the integrity of parts worn by functional acti-
vity. Nor, indeed, is there displayed by plants in any con-
siderable degree, if at all, that other species of repair which
consists in the restoration of lost or injured organs. Torn
leaves and the shoots that are shortened by the pruner, do
not reproduce their missing parts ; and though when the
branch of a tree is cut off close to the trunk, the place is in
the course of years covered over, it is not by any reparative
action in the wounded surface, but by the lateral growth of
the adjacent bark. Hence, without saying that Waste and
Repair do not go on at all in plants, we may fitly pass them
Dver as of no importance.

There are but slight indications of waste in those lower

orders of animals which, by their comparative inactivitv,

Bhow themselves least removed from vegetal life. Actinia

k»pt in an aquarium, do not appreciably diminish in bulk

12

170 THE INDUCTIONS OF BIOLOGY.

from prolonged abstinence. Even fish, though, much more
active than most other aquatic creatures, appear to undergo
but little loss of substance when kept unfed during con-
siderable periods. .Reptiles, too, maintaining no great
temperature, and passing their lives mostly in a state of
torpor, suffer but little diminution of mass by waste. When,
however, we turn to those higher orders of animals which
are active and hot-blooded, we see that waste is rapid :
producing when unchecked, a notable decrease in bulk
and weight, ending very shortly in death. Besides

finding that waste is inconsiderable in creatures that pro-
duce but little insensible and sensible motion, and that it
becomes conspicuous in creatures that produce much insen-
sible and sensible motion ; we find that in the same crea-
tures there is most waste when most motion is generated.
This is clearly proved by hybernating animals. " Va-
lentin found that the waking marmot excreted in the average
75 times more carbonic acid, and inhaled 41 times more
oxygen than the same animal in the most complete state of
hybernation. The stages between waking and most pro-
found hybernation yielded intermediate figures. A waking
hedgehog yielded about 20" 5 times more carbonic acid, and
consumed 18*4 times more oxygen than one in the state of hy-
bernation." If we take these quantities of absorbed oxygen
and excreted carbonic acid, as indicating something like the
relative amounts of consumed organic substance, we see
that there is a striking contrast between the waste ac-
companying the ordinary state of activity, and the waste
accompanying complete quiescence and reduced temperature.
This difference is still more definitely shown by the fact,
that the mean daily loss from starvation in rabbits and
guinea-pigs, bears to that from hybernation, the proportion
of 183 : 1. Among men and domestic animals, the relation
between degree of waste and amount of expended force,
though one respecting which there is little doubt, is lesa
distinctly demonstrable ; since waste is not allowed to go on

WASTE AND REPAIR. 171

rtninterfered with. "We have however in the lingering lives of
invalids who are able to take scarcely any nutriment, but
are kept warm and still, an illustration of the extent to
which waste diminishes as the expenditure of force declines.

Besides the connexion between the waste of the organism
as a whole, and the production of sensible and insensible
motion by the organism as a whole ; there is a traceable
connexion between the waste of special parts and the activi-
ties of such special parts. Experiments have shown that " the
starving pigeon daily consumes in the average 40 times
more muscular substance than the marmot in the state of
torpor, and only 11 times more fat, 33 times more of the
tissue of the alimentary canal, 183 times more liver, 15
times more lung, 5 times more skin." That is to s&y, in
the hybernating animal the parts least consumed are the
almost totally quiescent motor-organs, and the part most
consumed is the hydro-carbonaceous deposit serving as a
store of force ; whereas in the pigeon, similarly unsupplied
with food but awake and active, the greatest loss takes place
in the motor-organs. The relation between special

activity and special waste, is illustrated too in the daily
experiences of all : not indeed in the measurable decrease of
the active parts in bulk or weight, for this we have no means
of ascertaining ; but in the diminished ability of such parts
to perform their functions. That legs exerted for many hours
in walking, and arms long strained in rowing, lose their
powers — that eyes become enfeebled by reading or writing
without intermission — that concentrated attention unbroken
by rest, so prostrates the brain as to incapacitate it for think-
ing; are familiar truths. And though we have no direct
evidence to this effect, there is little danger in concluding that
muscles exercised until they ache or become stiff, and nerves
of sense rendered weary or obtuse by work, are organs so
much wasted by action as to be partially incompetent.

Repair is everywhere and alwa}^s making up for waste
Though the two processes vary in their relative rates, both

172 THE INDUCTIONS OF BIOLOGY

are constantly going on. Though during the active, waking
state of an animal, waste is in excess of repair, yet repair is
in progress ; and though during sleep, repair is in excess of
waste, yet some waste is necessitated by the carrying on of
certain never-ceasing functions. The organs of these never-
ceasing functions furnish, indeed, the most conclusive proofs
of the simultaneity of repair and waste. Day and night the
heart never stops beating, but only varies in the rapidity
and vigour of its beats ; and hence the loss of substance
which its contractions from moment to moment entail, must
from moment to moment be made good. Day and night
the lungs dilate and collapse ; and the muscles which make
them do this, must therefore be ever kept in a state of integ-
rity by a repair which keeps pace with waste, or which
alternately falls behind and gets in advance of it to a very
slight extent.

On a survey of the facts, we see, as we might expect to
see, that repair is most rapid when activity is most reduced.
Assuming that the organs which absorb and circulate nutri-
ment are in proper order, the restoration of the organism
to a state of integrity, after the disintegration consequent
on expenditure of force, is proportionate to the diminution
in expenditure of force. Thus we all know that those
who are in health, feel the greatest return of vigour after
profound sleep — after complete cessation of motion. "We
know that a night during which the quiescence, bodily
and mental, has been less decided, is usually not followed by
that spontaneous overflow of energy that indicates a high
state of efficiency throughout the organism. "We know,
again, that long- continued recumbency, even with wakeful-
ness (providing the wakefulness is not the result of disorder),
h followed by a certain renewal of strength ; though a re-
newal less than that which would have followed the greater
inactivity of slumber. We know, too, that when exhausted
by labour, sitting brings a partial return of vigour. And
we also know that after the violent exertion of running

WASTE AND RErAIR 173

a lapse into the less violent exertion of walking, results in
a gradual disappearance of that prostration which the run-
ning produced. This series of illustrations conclusively
proves that the rebuilding of the organism is ever making
up for the pulling down of it caused by action ; and that the
effect of this rebuilding becomes manifest, in proportion as
the pulling down is less rapid. From each digested meal,
there is every few hours absorbed into the mass of prepared
nutriment circulating through the body, a fresh supply of
the needful organic compounds ; and from the blood thus
occasionally re-enriched, the organs through which it passes
are ever taking up materials to replace the materials used up
in the discharge of functions. During activity, the reinte-
gration falls in arrear of the disintegration ; until, as a conse-
quence, there presently comes a general state of functional
languor ; ending, at length, in a quiescence which permits the
reintegration to exceed the disintegration, and restore the
parts to their state of integrity. Here, as wherever there
are antagonistic actions, we see rhythmical divergences on
opposite sides of the medium state — changes which equilibrate
each other by their alternate excesses. (First Principles,
§§ 96, 133.)

Illustrations are not wanting of special repair, that is
similarly ever in progress, and similarly has intervals during
which it falls below waste and rises above it. Every one
knows that a muscle, or a set of muscles, continuously strain-
ed, as by holding out a weignt at arm's length, soon loses its
power ; and that it recovers its power more or less fully after
a short rest. The several organs of special sensation yield
us like experiences : strong tastes, powerful odours, and loud
sounds, temporarily unfit the nerves impressed by them, for
appreciating faint tastes, odours, or sounds ; but these inca-
pacities are remedied by brief intervals of repose. Vision
still better illustrates this simultaneity of waste and repair
Looking at the sun so affects the eye that, for a short time,
it cannot perceive the ordinarv contrasts of light and shade.

174 THE INDUCTIONS OF BIOLOGY.

After gazing at a bright light of a particular colour, we see
on turning the eyes to adjacent objects, an image of the
complementary colour; showing that the retina has, for the
moment, lost the power to feel small amounts of those rays
which have strongly affected it. Such inabilities disappear
in a few seconds or a few minutes, according to circumstances.
And here, indeed, we are introduced to a conclusive proof
that special repair is ever neutralizing special waste. For
the rapidity with which the eyes recover their sensitiveness,
varies with the reparative power of the individual. In youth,
the visual apparatus is so quickly restored to its state of in-
tegrity, that many of these photogenes, as they are called,
cannot be perceived. When sitting on the far side of a room,
and gazing out of the window against a light sky, a person
who is debilitated by disease or advancing years, perceives,
on transferring the gaze to the adjacent wall, a momentary
negative image of the window — the sash-bars appearing light
and the squares dark ; but a young and healthy person has
no such experience. With a rich blood and vigorous circu-
lation, the repair of the visual nerves after impressions of
moderate intensity, is nearly instantaneous.

Function carried to excess, may produce waste so great,
that repair cannot make up for it during the ordinary
daily periods of rest ; and there may result incapacities of
the overtaxed organs, lasting for considerable periods. We
know that eyes strained by long-continued minute work, lose
their power for months or years : perhaps suffering an injury
which they never wholly recover. Brains, too, are often so
unduly worked that permanent relaxation fails to restore
them to vigour. Even of the motor organs the like holds.
The most frequent cause of what is called " wasting palsy,'*'
or atrophy of the muscles, is habitual excess of exertion : the
proof being, that the disease occurs most frequently among
those engaged in laborious handicrafts, and usually attacks
first the muscles that have been most worked.

There has yet to be noticed another kind of repair ; — that

WASTE AND REPAIR. 175

namely, by which injured or lost parts are restored. Among
the Hydrozoa it is common for any portion of the body to re-
produce the rest ; even though the rest to be so reproduced
is the greater part of the whole. In the more highly-organ-
ized Actinozoa, the half of an individual will grow into a
complete individual. Some of the lower Annelids, as the
Nais, may be cut into thirty or forty pieces, and each piece will
eventually become a perfect animal. As we ascend to higher
forms, we find this reparative power much diminished, though
still considerable. The reproduction of a lost claw by a
lobster or crab, is a familiar instance. Some of the inferior
Vertebrate also, as lizards, can develop new limbs or new
tails, in place of those that have been cut off; and can even
do this several times over, though with decreasing complete-
ness. The highest animals, however, thus repair themselves
to but a very small extent. Mammals and birds do it only
in the healing of wounds ; and very often but imperfectly
even in this. For in muscular and glandular organs, the
tissues destroyed are not properly reproduced, but are re-
placed by tissue of an irregular kind, which serves to hold
the parts together. So that the power of reproducing lost parts
is greatest where the organization is lowest ; and almost dis-
appears where the organization is highest. And though we
cannot say that between these extremes there is a constant in-
verse relation between reparative power and degree of organ-
ization; yet we may say that there is some approach to
euch a relation.

§ 63. There is a very obvious and complete harmony be-
tween the first of the above inductions, and the deduction
that follows immediately from first principles. "We have
already seen (§ 23) " that whatever amount of power an
organism expends in any shape, is the correlate and equi-
valent of a power that was taken into it from without."
Motion, sensible or insensible, generated by an organism, ia
insensible motion which was absorbed in producing certain

176 THE INDUCTIONS OF BIOLOGY.

chemical compounds appropriated by the organism under
the form of food. As much power as was required to raise
the elements of these complex atoms to their state of unsta-
ble equilibrium, is given out in their falls to a state of stable
equilibrium ; and having fallen to a state of stable equilib-
rium, they can give out no further power, but have to be
got rid of as inert and useless. It is an inevitable corollary
" from the persistence of force, that each portion of mechanical
or other energy which an organism exerts, implies the trans-
formation of as much organic matter as contained this
energy in a latent state ; " and that this organic matter in
yielding up its latent energy, loses its value for the purposes
of life, and becomes waste matter needing to be excreted.
The loss of these complex unstable substances must hence be
proportionate to the quantity of expended force. Here then
is the rationale of certain general facts lately indicated.
Plants do not waste to any considerable degree, for the obvi-
ous reason that the sensible and insensible motions they
generate are inconsiderable. Between the small waste, small
activity, and low temperature of the inferior animals, the rela-
tion is similarly one admitting of a priori establishment. Con-
versety, the rapid waste of energetic, hot-blooded animals
might be foreseen with equal certainty. And not less mani-
festly necessary is the variation in waste which, in the same
organism, attends the variation in the heat and mechanical
motion produced.

Between the activity of a special part and the waste of
that part, a like relation may be deductively inferred ; though,
it cannot be inferred that this relation is equally defi-
nite. Were the activity of every organ quite independent
of the activities of other organs, we might expect to trace
out this relation distinctly ; but since one part of the force
which any organ expends, is derived from materials brought
to it by the blood from moment to moment in quantities
varying with the demand, and since another part of the
force which suoh organ expends, comes to it in the shape of

WASTE AND REPAIR. 1 1 (

nervous discharges from distant organs ; it is clear that spe-
cial waste and general waste are too much entangled to
admit of a definite relation being established between special
waste and special activity. We may fairly say, however,
that this relation is quite as manifest as we can reasonably
anticipate.

§ 64. Deductive interpretation of the phenomena of He-
pair, is by no means so easy. The tendency displayed by an
animal organism, as well as by each of its organs, to return
to a state of integrity by the assimilation of new matter,
when it has undergone the waste consequent on activity, is a
tendency which is not manifestly deducible from first princi-
ples ; though it appears to be in harmony with them. If
in the blood there existed ready-formed units exactly like in
kind to those of which each organ consists, the sorting of these
units, ending in the union of each kind with already existing
groups of the same kind, would be merely a good example of
Differentiation and Integration [First Principles, § 123). It
would be analogous to the process by which, from a mixed
solution of salts, there are deposited segregated masses of
these salts, in the shape of different crystals. But as already
said (§ 54), though the selective assimilation by which the
repair of organs is effected, no doubt results in part from an
action of this kind, which is consequent on the persistence of
force (First Principles, § 129), the facts cannot be thus wholly
accounted for ; since organs are in part made up of units
that do not exist as such in the circulating fluidu. The pro-
cess becomes comprehensible however, if it be shown that, as
suggested in § 54, groups of compound units have a certain
power of moulding adjacent fit materials into units of their
own form. Let us see whether there is not reason to think
such a power exists.

" The poison of small-pox or of scarlatina," remarks Mr.
Paget, " being once added to the blood, presently affects the
composition of the whole : the disease pursues its course,

178 THE INDUCTIONS OF BIOLOGY.

and, if recovery ensue, the blood will seem to have returned
to its previous condition : yet it is not as it was before ; for
now the same poison may be added to it with impunity."
* * * " The change once effected, may be maintained
through life. And herein seems to be a proof of the assimil-
ative force in the blood ; for there seems no other mode of
explaining these cases than by admitting that the altered
particles have the power of assimilating to themselves all
those by which they are being replaced : in other words, all
the blood that is formed after such a disease deviates from
the natural composition, so far as to acquire the peculiarity
engendered by the disease : it is formed according to the
altered model." Now if the compound molecules of the
blood, or of an organism considered in the aggregate, have
the power of moulding into their own type, the matters
which they absorb as nutriment ; and if, as Mr Paget
points out, they have the power when their type has been
changed by disease, of moulding all materials afterwards
received into the modified type ; may we not reasonably
suspect that the more or less specialized molecules of each
organ, have, in like manner, the power of moulding the
materials which the blood brings to them, into similarly
specialized molecules ? The one conclusion seems to be a
corollarv from the other. Such a power cannot be claimed
for the component units of the blood, without being con-
ceded to the component units of every tissue. Indeed the
assertion of this power is little more than an assertion of the
fact, that organs composed of specialized units are capable
of resuming their structural integrity, after they have been
wasted by function. For if they do this, they must do it by
forming from the materials brought to them, certain special-
ized units like in kind to those of which they are composed ,
and to say that they do this, is to say that their component
units have the power of moulding fit materials into othei
units of the same order.

The repair of a wasted tissue may therefore be considered

WASTE AND REPAIR. 179

as duo to forces analogous to those by which a crystal repro*
duces its lost apex, when placed in a solution like that from
which it was formed. In either case, a mass of units of a
given kind, shows a power of integrating with itself diffused
units of the same kind : the only difference being, that the
organic mass of units arranges the diffused units into special
compound forms, before integrating them with itself. In
the case of the crystal, this reintegration is ascribed to
polarity — a power of whose nature we know nothing. What-
ever be its nature, however, it appears probable that the
power by which organs repair themselves from the nutritive
matters circulating through them, is of the same order.

§ 65. That other kind of repair which shows itself in the
regeneration of lost members, is comprehensible only as an
effect of actions like those just referred to. The ability of
an organism to recompletc itself when one of its parts has
been cut off, is of the same order as the ability of an injured
crystal to recomplete itself. In either case, the newty-assimi-
lated matter is so deposited as to restore the original outline.
And if in the case of the crystal, we say that the whole
aggregate exerts over its parts, a force which constrains the
newly-integrated atoms to take a certain definite form ; we
must in the case of the organism, assume an analogous force.
This is, in truth, not an hypothesis : it is nothing more than
a generalized expression of the facts. If when the leg of a
lizard has been amputated, there presently buds out the germ
of a new one, which, passing through phases of development
like those of the original leg, eventually assumes a like shape
and structure ; we assert nothing more than what we see,
when we assert that the organism as a whole exercises such
power over the newly- forming limb, as makes it a repetition
of its predecessor, if a leg is reproduced where there was a
leg, and a tail where there was a tail ; we have no alternative
but to conclude that the aggregate forces of the body, con-
trol the formative processes going on in each part. And on

ISO THE INDUCTIONS OF BIOLOGY.

contemplating these facts in connexion with various kindred
ones, there is suggested the hypothesis, that the form of each
species of organism is determined by a peculiarity in the con-
stitution of its units — that these have a special structure in
which they tend to arrange themselves ; just as have the
simpler units of inorganic matter. Let us glance at the evi-
dences which more especially thrust this conclusion upon us.

A fragment of a Begonia-leaf, imbedded in fit soil and kept
at an appropriate temperature, will develop a young Bego-
nia ; aud so small is the fragment which is thus capable of
originating a complete plant, that something like a hundred
plants might be produced from a single leaf. The friend to
whom I owe this observation, tells me that various succulent
plants have like powers of multiplication. Illustrating a
similar power among animals, we have the often-cited exper-
iments of Trembley on the common polype. Each of the
four pieces into which one of these creatures was cut, grew
into a perfect individual. In each of these again, bisection
and tri-section effected a like result. And so with their
segments, similarly produced, until as man}'- as fifty polypes
had resulted from the original one. Bodies when cut off
regenerated heads ; heads regenerated bodies ; and when a
polype had been divided into as many pieces as was practica-
ble, nearly every piece survived and became a complete
animal. What, now, is the implication ? We

cannot say that in each portion of a Begonia-leaf, and in
every fragment of a Hydra's body, there exists a ready-
formed model of the entire organism. Even were there
warrant for the now abandoned doctrine, that the germ of
every organism contains the perfect organism in miniature, it
still could not be contended that each considerable part of the
perfect organism resulting from such a germ, contains another
such miniature. Indeed the one hypothesis obviously nega-
tives the other. We have therefore no alternative but to
say, that the living particles composing one of these frag-
ments, have an innate tendency to arrange themselves into

WASTE AND REPAIR. 181

the shape of the organism to which they belong. We must
infer that a plant or animal of any species, is made np of
special units, in all of which there dwells the intrinsic apti-
tude to aggregate into the form of that species : jast as in the
atoms of a salt, there dwells the intrinsic aptitude to crystal-
lize in a particular way. It seems difficult to conceive that
this can be so ; but we see that it is so. Groups of units
taken from an organism (providing they are of a certain
bulk and not much differentiated into special structures) have
this power of re-arranging themselves; and we are thus
compelled to recognize the tendency to assume the specific
form, as inherent in all parts of the organism. Mani-

festly too, if we are thus to interpret the reproduction
of an organism from one of its amorphous fragments,
we must thus interpret the reproduction of any minor
portion of an organism by the remainder. When in place
of its lost claw, a lobster puts forth from the same spot a
cellular mass, which, while increasing in bulk, assumes the
form and structure of the original claw ; we can have no
hesitation in ascribing this result to a play of forces like
that which moulds the materials contained in a piece of
Begonia-leaf into the shape of a young Begonia. In the one
case as in the other, the vitalized molecules composing the
tissues, show their proclivity towards a particular arrange-
ment ; and whether such proclivity is exhibited in repro-
ducing the entire form, or in completing it when rendered
imperfect, matters not.

For this property there is no fit term. If we accept the
word polarity, as a name for the force by which inorganic
units are aggregated into a form peculiar to them ; we may
apply this word to the analogous force displayed by organic
units. But, as above admitted, polarity, as ascribed to atoms,
is but a name for something of which we are ignorant— a
name for a hypothetical property which as much needs ex-
planation as that which it is used to explain. Nevertheless,
in default of another word, we must employ this : taking

182 THE INDUCTIONS OF BIOLOGY.

care, however, to restrict its meaning. If we simply substi-
tute the term polarity, for the circuitous expression — the
power which certain units have of arranging themselves
into a special form, we may, without assuming anything
more than is proved, use the term organic polarity or po-
larity of the organic units, to signify the proximate cause
of the ability which organisms display of reproducing lost
parts.

§ 66. As we shall have frequent occasion hereafter to refer
to these units, which possess the property of arranging
themselves into the special structures of the organisms
to which they belong ; it will be well here to ask what
these units are, and by what name they may be most fitly
called.

On the one hand, it cannot be in those proximate chemical
compounds composing organic bodies, that this specific polar-
ity dwells. It cannot be that the atoms of albumen, or fibrine,
or gelatine, or the hypothetical protein- substance, possess
this power of aggregating into specific shapes ; for in
such case, there would be nothing to account for the unlike-
nesses of different organisms. Millions of species of plants
and animals, more or less contrasted in their structures,
are all mainly built up of these complex atoms. But if the
polarities of these atoms determined the forms of the or-
ganisms they composed, the occurrence of such endlessly
varied forms would be inexplicable. Hence, what we may
call the chemical units, are clearly not the possessors of this
property.

On the other hand, this property cannot reside in what
may be roughly distinguished as the morphological units. The
germ of every organism is a microscopic cell. It is by
multiplication of cells that all the early developmental changes
are effected. The various tissues which successively arise
in the unfolding organism, are primarily cellular ; and in
many of them the formation of cells continues to be, through-

WASTE AND REPAIR. 1£3

out life, the process by which repair is carried on. But
though cells are so generally the ultimate visible components
of organisms, that they may with some show of reason be
called the morphological units ; yet, as they are not uni-
versal, we cannot say that this tendency to aggregate into
specified forms dwells in them. Finding that in many
cases a fibrous tissue arises out of a structureless blastema,
without cell- formation ; and finding that there are creatures,
such as Rhizopods, which are not cellular, but nevertheless
exhibit vital activities, and perpetuate in their progeny
certain specific distinctions ; we are forbidden to ascribe to
cells this peculiar power of arrangement. Nor, indeed,
were cells universal, would such an hypothesis be acceptable ;
since the formation of a cell is, to some extent a manifesta-
tion of this same peculiar power.

If, then, this organic polarity can be possessed neither bj
the chemical units nor the morphological units, we must
conceive it as possessed by certain intermediate units, which
we may term physiological. There seems no alternative but
to suppose, that the chemical units combine into units
immensely more complex than themselves, complex as they
are ; and that in each organism, the physiological units
produced by this further compounding of highly compound
atoms, have a more or less distinctive character. AVe must
conclude that in each case, some slight difference of com-
position in these units, leading to some slight difference in
their mutual play of forces, produces a difference in the form
which the aggregate of them assumes.

The facts contained in this chapter, form but a small part
of the evidence which thrusts this assumption upon us. We
shall hereafter find various reasons for inferring that such
physiological units exist, and that to their specific properties,
more or less unlike in each plant and animal, various organio
phenomena are due.

CHAPTER V.
ADAPTATION.

§ 67. In plants, waste and repair being scarcely appre
ciable, there are not likely to arise appreciable changes in the
proportions of already- formed parts. The only divergences
from the average structure of a species, which we may expect
particular conditions to produce, are those producible by the
action of these conditions on parts in course of formation ;
and such divergences we do find. We know that a tree
which, standing alone in an exposed position, has a short
and thick stem, has a tall and slender stem when it grows
in a wood ; and that its branches then take a different inclin-
ation. AVe know that potato-sprouts which, on reaching
the light, develop into foliage, will, in the absence of
light, grow to a length of several feet without foliage.
And every in-door plant furnishes proof, that shoots and
leaves, by habitually turning themselves to the light, exhibit
a certain adaptation — an adaptation due, as we must suppose,
to the special effects of the special conditions on the still grow-
ing parts. In animals, however, besides analogous
structural changes wrought during the period of growth,
by subjection to circumstances unlike the ordinary circum-
stances ; there are structural changes similarly wrought,
after maturity has been reached. Organs that have
arrived at their full size, possess a certain modifiability ;
bo that whiln the organism as a whole, retains pretty

ADAPTATION. 185

nearly the same bulk, the proportions of its parts may bo
considerably varied. Their variations, here treated of under
the title Adaptation, depend on specialities of individual
action. We saw in the last chapter, that the actions of or-
ganisms entail re-actions on them ; and that specialities of
action entail specialities of re-action. Here it remains to be
pointed out, that the special actions and re-actions do not end
with temporary changes, but work permanent changes.

If, in an adult animal, the waste and repair in all parts
were exactly balanced — if each organ daily gained by
nutrition, exactly as much as it lost daily by the discharge of
its function — if excess of function were followed only by sucn
excess of nutrition as balanced the extra waste ; it is clear
that there would occur no change in the relative sizes of
organs. But there is no such exact balance. If the excess
of function, and consequent excess of waste, is moderate, it is
not simply compensated by repair, but more than compensated
— there is a certain increase of bulk. This is true to some
degree of the organism as a whole, when the organism is
framed for activity. A considerable waste giving considerable
power of assimilation, is more favourable to accumulation of
tissue, than is quiescence with its conrparatively feeble assimi-
lation : whence results a certain adaptation of the whole
organism to its requirements. But it is more especially true
of the parts of an organism in relation to each other. The
illustrations fall into several groups. The growth

of muscles exercised to an unusual degree, is a matter of com-
mon observation. In the often-cited blacksmith's arm, the
dancer's legs, and the jockey's crural adductors, we have
marked examples of a modifiability which almost every one
has to some extent experienced. It is needless to multi-
ply proofs. The occurrence of changes in the struc-
ture of the skin, where the skin is exposed to a stress of
function, is also familiar. That thickening of the epidermis
on a labourer's palm, results from continual pressure and
friction, is certain : those who have not before exerted theii
13

18() TIfE INDUCTIONS OF BIOLOGY.

hands, find that su<fh an exercise as rowing, soon begins to
produce a like thickening. This relation of cause and effect
is still better shown by the marked indurations at the ends of
a violinist's fingers. Even in mucous membrane, which
ordinarily is not subject to mechanical forces of any intensity,
similar modifications are possible : witness the callosity of
the gums which arises in those who have lost their teeth, and
have to masticate without teeth. The vascular"!

system furnishes good instances of the increased growth J
that follows increased function- When, because of some |
permanent obstruction to the circulation, the. heart has to
exert a greater contractile force on the mass of blood which it
propels at each pulsation into the arteries, and when there re-
sults the laboured action known as palpitation ; there usually
occurs dilatation, or hypertrophy, or a mixture of the two :
the dilatation, which is a yielding of the heart's structure
under the increased strain, implying a failure to meet the
emergency ; but the hypertrophy, which consists in a thick-
ening of the heart's muscular walls, being an adaptation of it
to the additional effort required. Again, when an aneurism
in some considerable artery has been obliterated, either arti-
ficially or by a natural inflammatory process ; and when this
artery has consequently ceased to be a channel for the blood ;
some of the adjacent arteries which anastomose with it,
become enlarged, so as to carry the needful quantity of blood
to the parts supplied. Though we have no direct

proof of analogous modifications in nervous structures ; yet
indirect proof is given by the greater efficiency that fol-
lows greater activity. This is manifested alike in the
senses and the intellect. The palate may be cultivated in-
to extreme sensitiveness, as in professional tea-tasters. An
orchestral conductor gains by continual practice, an unusually
great ability to discriminate differences of sound. And in
the finger-reading 0f the blind, we have evidence that the
I sense of touch may be brought by exercise to a far higher
capability than is ordinaiy. The increase of power which

ADAPTATION. 187

habitual exertion gives to mental faculties, needs no illustra-
tion : every person of ed ucation has personal experience
of it. Even from the osseous structures, evidence

may be drawn. The bones of men accustomed to great mus-
cular action, are more massive and have more strongly
marked processes for the attachment of muscles, than the
bones of men who lead sedentary lives ; and a like contrast
holds between the bones of wild and tame animals of the
same species. Adaptations of another order, in which there
is a qualitative rather than a quantitative modification, arise
after certain accidents to which the skeleton is liable. When
the hip-joint has been dislocated, and long delay has made it
impossible to restore the parts to their proper places, the
head of the thigh-bone, imbedded in the surrounding muscles,
becomes fixed in its new position by attachments of fibrous
tissue, which afford support enough to permit a halting walk.
But the most remarkable modification of this order occurs in
ununited fractures. "False joints " are often formed — ■
joints which rudely simulate the hinge structure or the ball-
and-socket structure, according as the muscles tend to pro-
duce a motion of flexion and extension or a motion of rota-
tion. In the one case, according to Rokitansky, the two ends
of the broken bone become smooth and covered with perios-
teum and fibrous tissue, and are attached by ligaments that
allow a certain backward and forward motion; and in the
other case, the ends, similarly clothed with the appropriate
membranes, become the one convex and the other concave,
are inclosed in a capsule, and are even occasionally supplied
with synovial fluid !

The general truth that extra function is followed by extra
growth, must be supplemented__by_the equally general truth,
that bej^jidLaUimitJ_u^anyi^Qon reached, very little, if any,
further modification can be produced. The experiences from
which we draw the~~one inductionTlhrust the other upon us.
After a time, no training makes the pugilist or the athlete
any stronger. The adult gymnast at last acquires the powci

L88 THE INDUCTIONS OF BIOLOGY.

to perform certain difficult feats • but certain more difficult
feats, no additional practice enables him to perform. Years of
discipline give the singer a pa1 'cular loudness and range of
voice, beyond which further discipline does not give greater
loudness or wider range : on the contrary, increased vocal ex-
ercise, causing a waste in excess of repair, is often followed
by decrease of power. In the perceptions we sec

similar limits. The culture which exalts the susceptibility of
the ear to the intervals and harmonies of notes, will not
turn a bad ear into a good one. Life-long effort fails to
make this artist a correct draftsman, or that a fine colourist :
each does better than he did at first, but each fulls short of
the power attained by some other artists. Nor is

this truth less clearly illustrated among the more complex
mental powers. Each man has a mathematical faculty, a
poetical faculty, or an oratorical faculty, which special educa-
tion improves to a certain extent. But unless he is. unusually
endowed in one of these directions, no amount of education
will make him a first-rate mathematician, a first-rate poet, or
a first-rate orator. Thus the general fact appears to

be, that Avhile in each individual, certain changes in the
proportions of parts, may be caused by variations of function,
the congenital structure of each individual puts a limit to
the modifiability of every part. Nor is this true of

individuals only : it holds, in a sense, of species. Leaving
open the question whether, in indefinite time, indefinite modi-
fication may not be produced ; experience proves that within
assigned times, the changes wrought in races of organisms
by changes of conditions fall within narrow limits. We see,
for instance, that though by discipline, aided by selective
breeding, one variety of horse has had its locomotive power
increased considerably beyond the locomotive powers of other
varieties ; yet that further increase takes place, if at all, at an
inappreciable rate. The different kinds of dogs, too, in
which different forms and capacities have been established,
lo not show aptitudes for diverging in the same directions «i1

ADAPTATION.

189

considerable rates. In domestic animals generally, certain
accessions of intelligence have been produced by culture ; but
accessions beyond these are inconspicuous. It seems that
in each species of organism, there is a margin for functional
oscillations on all sides of a mean state, and a consequent
margin of structural variations ; that it is possible rapidly to
push functional and structural changes towards the extreme
of this margin in any direction, both in an individual and
in a race ; but that to push these changes further in any
direction, and so to alter the organism as to bring its mean
state up to the extreme of the margin in that direction, is a
comparatively slow process.*

We have also to note that the limited increase of size pro-
duced in any organ by a limited increase of its function, is
not maintained unless the increase of function is permanent.
A mature man or other animal, led by circumstances into
exerting particular members in unusual degrees, and acquir-
ing extra size and power in these members, begins to lose
such extra size and power on ceasing to exert these members;
and eventually lapses more or less nearly into the original
state. Legs strengthened by a pedestrian tour, become weak
again after a prolonged return to sedentary life. The
acquired ability to perform feats of skill, disappears in course
of time, if the performance of them is given up. For compara-
tive failure in executing a piece of music, in playing a game
at chess, or in anything requiring special culture, the being
out of practice is a reason of which every one recognizes the
validity. It is observable, too, that the rapidity and com-
pleteness with which an artificial power is lost, is proportionate
to the shortness of the cultivation which evoked it. One who
has for many years persevered in habits which exercise
special muscles or special faculties of mind, retains the extra

* Here, as in sundry places throughout this chapter, the necessities of the argu-
ment have obliged me to forestall myself, by assuming the conclusion reached in a
subsequent chapter, that modifications of structure produced by modifications of
function, are transmitted to offspring.

190 THE INDUCTIONS OF BIOLOGY.

capacity produced, to a very considerable degree, even after a
long period of desistance ; but one who has persevered in such
habits for but a short time, has, at the end of a like period,
scarcely any of the facility he had gained. Here,

too, as before, successions of organisms present an analogous
fact. A species in which domestication, continued through
many generations, has organized certain peculiarities ; and
which afterwards, escaping domestic discipline, returns to
something like its original habits ; soon loses, in great mea-
sure, such peculiarities. Though it is not true, as alleged,
that it resumes completely the ctructure it had before domes-
tication ; yet it approximates to that structure. The Dingo,
or wild dog of Australia, is one of the instances given
of this ; and the wild horse of South America is another.
Mankind, too, supplies us with instances. In the Austra-
lian bush, and in the backwoods of America, the Anglo-
Saxon race, in which civilization has developed the higher
feelings to a considerable degree, rapidly lapses into compara-
tive barbarism : adopting the moral code, and sometimes the
habits, of savages.

§ 68. It is important to reach, if possible, some rationale
of these general truths — especially of the last two. A right
understanding of these laws of organic modification, underlies
a right understanding of the great question of species.
While, as before hinted (§ 40), the action of structure on
function, is one of the factors in that process of differentiation
by which unlike forms of plants and animals are produced,
the re-action of function on structure, is another factor.
Hence, it is well worth while inquiring how far these induc-
tions are deductively interpretable.

The first of them is the most difficult to deal with. Why
an organ exerted somewhat beyond its wont, should presently
grow, and thus meet increase of demand by increase of sup-
ply, is not obvious. We know, indeed, (First Principles,
§§ 96, 133,) that of necessity, the rhythmical changes pro-

ADAPTATION. 191

duced by antagonist organic actions, cannot any of them bo
carried to an excess in one direction, without there being
produced an equivalent excess in the opposite direction. It
is a corollary from the persistence of force, that any deviation
effected by a disturbing cause, acting on some member of a
moving equilibrium, must (unless it altogether destroys the
moving equilibrium) be eventually followed by a compensating
deviation. Hence, that excess of repair should succeed ex-
cess of waste, is to be expected. But how happens the mean
state of the organ to be changed ? If daily extra waste
naturally brings about daily extra repair, only to an equiva-
lent extent, the mean state of the organ should remain con-
stant. How then comes the organ to augment in size and
power ?

Such answer to this question as we may hope to find, must
be looked for in the effects wrought on the organism as a
whole, by increased function in one of its parts. For since
the discharge of its function by any part, is possible only on
condition that those various other functions on which its own
is immediately dependent, are also discharged ; it follows
that excess in its function presupposes some excess in their
functions. Additional work given to a muscle, implies ad-
ditional work given to the branch arteries which bring it
blood, and additional work, smaller in proportion, to the
arteries from which these branch arteries come. Similarly,
the smaller and larger veins which take away the blood, as
well as the absorbents which carry off effete products, must
have more to do. And yet further, on the nervous centres
which excite the muscle, a certain extra duty must fall. But
excess of waste will entail excess of repair, in these parts as
well as in the muscle. The several appliances by which the
nutrition and excitation of an organ are carried on, must ulso
be influenced by this rhythm of action and re-action ; and
therefore, after losing more than usual by the destructive
process, they must gain more than usual by the constructive
process. But temporarily-increased efficiency in these ap-

192 THE INDUCTIONS OF BIOLOGY.

pliances by which blood and nervous force are brought to an
organ, will cause extra assimilation in the organ, beyond
that required to balance its extra expenditure. Regarding
the functions as constituting a moving equilibrium, we may
say, that divergence of any function in the direction of in-
crease, causes the functions with which it is bound up to
diverge in the same direction ; that these again cause the
functions which they are bound up with, also to diverge in
the same direction ; and that these divergences of the con-
nected functions, allow the specially-affected function to be
carried further in this direction than it could otherwise be
— further than the perturbing force could carry it if it had a
fixed basis.

It must be admitted that this is but a vague explanation.
Among actions so involved as these, we can scarcely expect
to do more than dimly discern a harmony with first princi-
ples. That the facts are to be interpreted in some such way,
may, however, be inferred from the circumstance that an
extra supply of blood continues for some time to be sent to
an organ that has been unusually exercised ; and that when
unusual exercise is long continued, a permanent increase of
vascularity results.

15 6-3. Answers to the questions — Why do these adaptive
modifications in an individual animal, soon reach a limit?
and why, in the descendants of "such animal, similarly condi-
tioned, is this limit very slowly extended ? — are to be found
in the same direction as was the answer to the last question.
And here the connexion of cause and consequence is much
more manifest.

Since the function of any organ is dependent on the func-
tions of the organs which supply it with materials and forces;
and since the functions of these subsidiary organs are de-
pendent on the functions of organs which supply them wi< h
materials and forces; it follows that before any great extra
power of discharging its function, can be gained by a

ADAPTATION. 193

specially- exercised organ, a considerable extra power must
be gained by a series of immediately-subservient organs, and
Borne extra power by a secondary series of remotely-sub-
servient organs. Thus there are required numerous and
wide-spread modifications. Before the artery which feeds a
hard-worked muscle, can permanently furnish a large ad-
ditional quantity of blood, it must increase in diameter and
contractile power ; and that its increase of diameter and con-
tractile power may be of use, the main artery from which it
diverges, must also be so far modified as to bring this addi-
tional quantity of blood to the branch artery. Similarly
with the veins ; similarly with the absorbents ; similarly
with the nerves. And when we ask what these subsidiary
changes imply, we are forced to conclude that there must be
an analogous group of more numerous changes, ramifying
throughout the system. The growth of the arteries prima-
rily and secondarily implicated, cannot go to any extent,
without growth in the minor blood-vessels on which their
nutrition depends ; while their greater contractile power in-
volves enlargement of the nerves which excite them, and
some modification of that part of the spinal cord whence
these nerves proceed. Thus, without tracing the like remote
alterations implied by extra growth of the veins, absorbents,
and other agencies, it is manifest that a large amount of re-
building must be done throughout the organism, before any
organ of importance can be permanently increased in size
and power to a great extent. Hence, though such extra
growth in any part as does not necessitate considerable
changes throughout the rest of the organism, may rapidly
take place ; a further growth in this part, requiring a re-
modelling of numerous parts remotely and slightly affected,
must take place but slowly.

\Ve have before found our conceptions of vital processes
made clearer by studying analogous social processes. In
societies there is a mutual dependence of functions, essentially
like that which exists in organisms; and there is also an

L94 THE INDUCTIONS OF BIOLOGY.

essentially like re-action of functions on structures. From tLe
laws of adaptive modification in societies, we may therefore
hope to get a clue to the laws of adaptive modification in
organisms. Let us suppose, then, that a society has arrived
at a state of equilibrium like that of a mature animal — a
state not like our own, in which growth and structural de-
velopment are rapidly going on ; but a state of settled
balance among the functional powers of the various classes
and industrial bodies, and a consequent fixity in the relative
sizes of such classes and bodies. Further, let us suppose
that in a society thus balanced, there occurs something which
throws an unusual demand on some one industry — say an
unusual demand for ships (which we will assume to be built
of iron) in consequence of a competing mercantile nation
having been prostrated by famine or pestilence. The imme-
diate result of this additional demand for iron ships, is the
employment of more workmen, and the purchase of more iron,
by the ship-builders ; and when, presently, the demand con-
tinuing, the builders find their premises and machinery in-
sufficient, they enlarge them. If the extra requirement
persists, the high interest and high wages bring such extra
capital and labour into the business, as are needed for new
ship-building establishments. But such extra capital and
labour do not come quickly ; since, in a balanced community,
not increasing in population and wealth, labour and capital
have to be drawn from other industries, where they are
already yielding the ordinary returns. Let us now go a
step further. Suppose that this iron-ship-building industry,
having enlarged as much as the available capital and labour
permit, is still unequal to the demand ; what limits its im-
mediate further growth ? The lack of iron. By the hypo-
thesis, the iron-producing industry, like all the other indus-
tries throughout the community, yields only as much iron as
is habitually required for all the purposes to which iron is
applied : ship-building being only one. If, then, extra iron
id required for ship-building, the first effect is to withdraw

ADAPTATION 195

part of the iron habitually consumed for other purposes, and
lo raise the price of iron. Presently, the iron-makers feel
this change, and their stocks dwindle. As, however, tho
quantity of iron required for ship-building, forms but a small
part of the total quantity required for all purposes ; the ex-
tra demand on the iron-makers, can be nothing like so great
in proportion as is the extra demand on the ship- builders.
Whence it follows, that there will be much less tendency to
an immediate enlargement of the iron-producing industry —
the extra quantity will for some time be obtained by working
extra hours. Nevertheless, if, as fast as more iron can be
thus supplied, the ship-building industry goes on growing
— if, consequently, the iron-makers experience a permanently-
increased demand, and out of their greater profits get higher
interest on capital, as well as pay higher wages ; there will
eventually be an abstraction of capital and labour from other
industries, to enlarge the iron-producing industry : new blast-
furnaces, new rolling-mills, new cottages for workmen, will
be erected. But obviously, the inertia of capital and labour
to be overcome, before the iron-producing industry can grow
by a decrease of some other industries, will prevent its growth
from taking place until long after the increased ship-build-
ing industry has demanded it ; and meanwhile, the growth
of the ship-building industry must be limited by the
deficiency of iron. A remoter restraint of the same nature,
meets us if we go a step further — a restraint which can
be overcome, only in a still longer time. For the manu-
facture of iron depends on the supply of coal. The pro-
duction of coal being previously in equilibrium with the
consumption ; and the consumption of coal for the manu-
factuie of iron, being but a small part of the total con-
sumption ; it follows that a considerable extension of the iron
manufacture, when it at length takes place, will cause but a
comparatively small additional demand on the coal-owners and
coal-miners — a demand which will not, for a long period, suf-
fice to cause enlargement of the coal- trade, by drawing capital

196 THE INDUCTIONS OF BIOLOGY.

and labour from other investments and occupations. And
until the permanent extra demand for coal, has become great
enough to draw from other investments and occupations, suf-
ficient capital and labour to sink new mines, the increasing
production of iron must be restricted by the scarcity of coal ;
and the multiplication of ship-yards and ship-builders,
must be checked by the want of iron. Thus, in a com-
munity which has reached a state of moving equilibrium,
though any one industry directly affected by an additional
demand, may rapidly undergo a small extra growth ;
yet a growth beyond this, requiring, as it does, the build-
ing-up of subservient industries, less directly and strongly
affected, as well as the partial wwbuilding of other industries,
can take place only with comparative slowness. And a
still further growth, requiring structural modifications of
industries still more distantly affected, must take place still
more slowly.

Returning from this analogy, we realize more clearly the
truth, that any considerable member of an animal organism,
cannot be greatly enlarged without some general re-organiza-
tion. Besides a building-up of the primary, secondary, and
tertiary groups of subservient parts, there must be an un-
building of sundry non-subservient parts ; — or at any rate,
there must be permanently established, a lower nutrition of
6uch non-subservient parts. For it must be remembered that
in a mature animal, or one which has reached a balance
between assimilation and expenditure, there cannot be an in-
crease in the nutrition of some organs, without a decrease in
the nutrition of others ; and an organic establishment of the
increase, implies an organic establishment of the decrease —
implies more or less change in the processes and structures
throughout the entire system. And here, in-

, deed, is disclosed one reason why growing animals under-
go adaptations so much more readily than adult ones. For
while there is surplus nutrition, it is possible for specially-ex-
ercijed parts to be specially enlarged, without any positive

ADAPTATION. 197

deduction from other parts. There is required only that
negative deduction, shown in the diminished growth of other
parts.

§ 70. Pursuing the argument further, we reach an ex-
planation of the third general truth ; namely, that organisms,
and species of organisms, which, under new conditions, have
undergone adaptive modifications, soon return to something
like their original structures, when restored to their original
conditions. Seeing, as we have done, how excess of action
and excess of nutrition in any part of an organism, must
affect action and nutrition in subservient parts, and
these again in other parts, until the re-action has divided
and subdivided itself throughout the organism, affecting
in decreasing degrees the more and more numerous parts
more and more remotely implicated ; we see that the
consequent changes in the parts remotely implicated, consti-
tuting the great mass of the organism, must be extremely
slow. Hence, if the need for the adaptive modification
ceases, before the great mass of the organism has been much
altered in its structure by these ramified but minute re-ac-
tions; we shall have a condition in which the specially-
modified part, is not in equilibrium with the rest. All the
i-emotely-affected organs, as yet but little changed, will, in the
absence of the perturbing cause, resume very nearly their
previous actions. The parts that depend on them, will
consequently by and by do the same. Until at length, by a
reversal of the adaptive process, the organ at first affected will
be brought back almost to its original state. Recon-

sidering the above-drawn analogy between an organism and
society, will enable us better to realize this necessity. If, in
the case supposed, the extra demand for iron ships, after
causing the erection of some additional ship-yards and the
drawing of iron from other manufactures, were to cease ;
the old dimensions of the ship-building trade would be
quickly returned to: discharged workmen would seek fresh

198 THE INDUCTIONS OF BIOLOGY.

occupations, and the new yards would be devoted to othei
uses. But if the increased need for ships lasted long
enough, and became great enough, to cause a flow of capital
and labour from other industries into the iron-manufacture, a
falling off in the demand for ships, would much less rapidly
entail a dwindling of the ship-building industry. For iron
being now produced in greater quantity, a diminished con-
sumption of it for ships, would cause a fall in its price, and
a consequent fall in the cost of ships : thus enabling the
ship-builders to meet the competition which we may sup-
pose led to a decrease in the orders they received. And since,
when new blast-furnaces and rolling-mills, &c, had been built
with capital drawn from other industries, its transference
back into other industries, would involve great loss ; the
owners, rather than transfer it, would accept unusually low in-
terest ; and an excess of iron would continue to be produced ;
resulting in an undue cheapness of ships, and a maintenance
of the ship-building industry at a size beyond the need.
Eventually, however, if the number of ships required still
diminished, the pioduction of iron in excess would become
very unremunerative : some of the blast-furnaces would be
blown out ; and as much of the capital and labour as remained
available, would be re-distributed among other occupations.
Without repeating the steps of the argument, it will be clear
that were the enlargement of the ship-building industry
great enough, and did it last long enough, to cause an in-
crease in the number of coal-mines ; the ship-building in-
dustry would be still better able to maintain itself under
adverse circumstances ; but that it would, though at a more
distant period, end by sinking down to the needful dimensions.
Thus our conclusions are : — First, that if the extra activity
and growth of a particular industry, has lasted long enough
onlv to remodel the proximately- affected industries ; it will
dwindle away again after a moderate period, if the need for
it disappears. Second, that an enormous period must be re-
quired before the re-actions produced by an enlarged industry

ADAPTATION. 199

can cause a re-construction of the whole society, and before
the countless re-distributions of capital and labour, can again
reach a state of equilibrium. And third, that only when
such a new state of equilibrium is eventually reached, can the
adaptive modification become a permanent one. How,

in animal organisms, the like argument will hold, needs not
be pointed out. The reader will readily follow the parallel.

That organic types should be comparatively stable^ might
be anticipated on the hypothesis of Evolution. If we assume,
as we must according to this hypothesis, that the structure
of any organism is a product of the almost infinite series of
actions and re-actions to which all ancestral organisms have
been exposed ; we shall see that any unusual actions and re-
actions brought to bear on an individual, can have but
an infinitesimal effect in permanently changing the structure
of the organism as a whole. The new set of forces, com-
pounded with all the antecedent sets of forces, can but inap-
preciably modify that moving equilibrium of functions which
all these antecedent sets of forces have established. Though
there may result a considerable perturbation of certain func-
tions— a considerable divergence from their ordinary rhythms;
yet the general centre of equilibrium cannot be sensibly
changed. On the removal of the perturbing cause, the pre-
vious balance will be quickly restored : the effect of the new
forces being almost obliterated by the enormous aggregate of
forces which the previous balance expresses.

§ 71. As thus understood, the phenomena of adaptation
full into harmony with first principles. The inference that
organic types are fixed, because the deviations from them
which can be produced within assignable periods, are relatively
small ; and because, when a force producing deviation ceases,
there is a return to something like the original state ; proves to
be an invalid inference. Without assuming fixity of species,
we find good reasons for anticipating that kind and degree of
stability which is observed. We find grounds for concluding,

200 THE INDUCTIONS OF BIOLOGY.

a priori, that an adaptive change of structure, will soon reach
a point beyond which further adaptation will be slow ; for
concluding that when the modifying cause has been but
a short time in action, the modification generated, will be
evanescent ; for concluding that a modifying cause acting
even for many generations, will do but little towards per-
manently altering the organic equilibrium of a race ;
and for concluding that on the cessations of such cause, its
eifects will become unapparent in the course of a few gener-
ations.

CHAPTER VI.
INDIVIDUALITY.

§ 72. What is an individual ? is a question which many
readers will think it easy to answer. Yet it is a question
that has led to much controversy among Zoologists and
Botanists ; and no quite satisfactory reply to it seems possi-
ble. As applied to a man, or to any one of the higher
animals, which are all sharply-defined and independent, the
word individual has a clear meaning ; though even hero,
when we turn from average cases to exceptional cases —
as a calf with two heads and two pairs of fore-limbs — we
find ourselves in doubt whether to predicate one individuality
or two. But when we extend our range of observation to
the organic world at large, we find that difficulties allied to
this exceptional one, meet us everywhere under every variety
of form.

Each uniaxial plant may perhaps fairly be regarded as a
distinct individual ; though there are botanists who do not
make even this admission. What, however, are we to say of
a raultiaxial plant ? It is, indeed, usual to speak of a tree
with its many branches and shoots, as singular ; but strong
reasons may be urged for considering it as plural. Every
one of its axes has a more or less independent life, and when
cut off and planted, may grow into the likeness of its parent;
ov by grafting and budding, parts of this tree may be
developed upon another tree, and there manifest their
14

202 THE INDUCTIONS OF BIOLOGY.

specific peculiarities. Shall we regard all the growing axes
thus resulting from slips and grafts and buds, as parts of one
individual, or as distinct individuals ? If a strawberry-plant
sends out runners carrying buds at their ends, which strike
root and grow into independent plants, that separate from
the original one by decay of the runners, must we not say
that they possess separate individualities ; and yet if we do
this, are we not at a loss to say when their separate individu-
alities were established, unless we admit that each bud was
from the beginning an individual ? Commenting on such
perplexities, Schleiden says — " Much has been written and
disputed concerning the conception of the individual, with-
out, however, elucidating the subject, principally owing to
the misconception that still exists as to the origin of the con-
ception. Now the individual is no conception, but the mere
subjective comprehension of an actual object, presented to us
under some given specific conception, and on this latter it
alone depends whether the object is or is not an individual.
Under the specific conception of the solar system, ours is an
individual : in relation to the specific conception of a planet-
ary body, it is an aggregate of many individuals." * * * "I
think, however, that looking at the indubitable facts
already mentioned, and the relations treated of in the course of
these considerations, it will appear most advantageous and
most useful, in a scientific point of view, to consider the
vegetable cell as the general type of the plant (simple plant
of the first order). Under this conception, Protococcus and
other plants consisting of only one cell, and the spore and
pollen- granule, will appear as individuals. Such individuals
may, however, again, with a partial renunciation of their in-
dividual independence, combine under definite laws into
definite forms (somewhat as the individual animals do in the
globe of the Volvox globator*). These again appear empiri-
cally as individual beings, under a conception of a species

« It is now generally agreed thai the Volvox globator is a plant.

INDIVIDUALITY.

203

(simple plants of the second order) derived from the form of
the normal connexion of the elementary individuals. But
we cannot stop here, since nature herself combines these in-
dividuals, under a definite form, into larger associations,
whence we draw the third conception of the plant, from a
connexion, as it were, of the second power (compound plants
— plants of the third order).' The simple plant proceeding
from the combination of the elementary individuals is then
termed a bud (gemma), in the composition of plants of the
third order."

The animal kingdom presents still greater difficulties.
When, from sundry points on the body of a common polype,
there bud-out young polypes, which, after acquiring mouths
and tentacles and closing up the communications between
their stomachs and the stomach of the parent, finally separate
from the parent ; we may with propriety regard them as dis-
tinct individuals. But when, in the allied compound Hydro-
zoa, we find that these young polypes continue permanently
connected with the parent ; and when, by this continuous
budding-out, there is presently produced a tree-like aggre-
gation, having a common alimentary canal into which the
digestive cavity of each polype opens; it is no longer so
clear that these little sacs furnished with mouths and tenta-
cles, are severally to be regarded as distinct individuals. We
cannot deny a certain individuality to the polypedom. And
on discovering that some of the buds, instead of unfolding in
the same manner as the rest, are transformed into capsules
in which eggs are developed — on discovering that certain of
the incipient polypes thus become wholly dependent on the
aggregate for their nutrition, and discharge functions which
have nothing to do with their own maintenance, we have
still clearer proof that the individualities of the members are
partially merged in the individuality of the group. Other
organisms belonging to the same order, display still more
decidedly this transition from simple individualities to a com-
plex individuality. In the Diplujes there is a special modifi-

^04 THE INDUCTIONS OF BIOLOGY.

cation of one or more members of the polypcdom into a
swimming apparatus, which, by its rhythmical contractions,
propels itself through the water, drawing the polypedom after
it. And in the more differentiated Physalin, various organs
result from the metamorphosis of parts that are the honio-
logues of individual polypes. In this last instance, the in-
dividuality of the aggregate is so predominant, that the
individualities of the members are practically lost. This

combination of individualities in such way as to produce a
composite individual, meets us in other forms among the
ascidian molluscs. While in some of these, as in the
Clavelina, the animals associated are but little subordinated
to the community they form ; in others, as in the Botryllidce,
they are so fused into a rounded mass, as to present the
appearance of a single animal with several mouths and
stomachs.

On the hypothesis of Evolution, perplexities of this nature
are just such as we might anticipate. If Life in general, com-
menced with minute and simple forms, like those out of
which all individual organisms, however complex, now
originate ; and if the transitions from these primordial units
to organisms made up of groups of such units, and to higher
organisms made up of groups of such groups, took place by
degrees ; it is clear that individualities of the first and
simplest order, would merge gradually in those of a larger
and more complex order, and these again in others of an
order having still greater bulk and organization ; and that
hence it would be impossible to say where the lower indivi-
dualities ceased, and the higher individualities commenced.

§ 73. To meet these difficulties, it has been proposed that
the whole product of a single fertilized germ, shall be re-
garded as a single individual : whether such whole product
be organized into one mass, or whether it be organized into
many masses, that are partially or completely separate. It
is urged that whether the development of the fertilized germ

INDIVIDUALITY. 205

bo continuous or discontinuous (§ 50) is a matter of secondary
importance ; that the totality of living tissue to which the
fertilized germ gives rise in any one case, is the equivalent
of the totality to which it gives rise in any other case ; and
that we must recognize this equivalence, whether such totality
of living tissue takes a concrete or a discrete arrangement.
In pursuance of this view, a zoological individual is consti-
tuted either by any such single animal as a mammal or bird,
which may properly claim the title of a zoon, or by any such
group of animals as the numerous Medusa that have been
developed from the same egg, which are to be severally dis-
tinguished as zooids.

Admitting it to be very desirable that there should be
words for expressing these relations and this equivalence, it
may still be objected, that to apply the word individual to a
number of separate living bod ies, is inconvenien t : conn ictingso
much, as it does, with the ordinary conception which this word
suggests. It seems a questionable use of language to say that
the countless masses of Anacharts Alsinastrum, which, within
these few years, have grown up in our rivers, canals, and
ponds, are all parts of one individual ; and yet as this plant
does not seed in England, these countless masses, having
arisen by discontinuous development, must be so regarded, if
we accept the above definition.

It may be contended, too, that while it does violence to
our established way of thinking, this mode of interpreting
the facts is not without its difficulties — smaller, perhaps,
than those it escapes, but still considerable. Something
seems to be gained by restricting the application of the title
individual, to organisms which, being in all respects fully
developed, possess the power of producing their kind after
the ordinary sexual method; and denying this title to those
incomplete organisms which have not this power. But the
definition does not really establish this distinction for us. On
the one hand, Ave have cases in which, as in the working bee,
the whole of the germ-product is aggregated into a single

206 THE INDUCTIONS OF BIOLOGY.

organism ; and yet, though an individual according to the
definition, this organism has no power of reproducing its
kind. On the other hand, we have cases like that of the
perfect Aphides, where the organism is but an infinitesimal
part of the germ-product ; and yet has that completeness
required for sexual reproduction. Moreover, if we

adopt the proposed view, we find ourselves committed to the
anomalous position, that among many orders of animals, there
are no concrete individuals at all. If the individual is consti-
tuted by the whole germ-product, whether continuously or
discontinuously developed, then, not only must individuality
be denied to each of the imperfect Aphides, but also to
each of the perfect males and females ; since no one of
them is more than a minute fraction of the total germ-
product. And yet further, it might be urged with
some show of reason, that if the conception of individuality
involves the conception of completeness ; then, an organism
which possesses an independent power of reproducing itself,
being more complete than an organism in which this power
is dependent on the aid of another organism, is more in-
dividual.

§ 74. There is, indeed, as already implied, no definition
of individuality that is unobjectionable. All we can do is to
make the best practicable compromise.

As applied either to an animate or an inanimate object,
the word individual ordinarily connotes union among the
parts of the object, and separateness from other objects.
This fundamental element in the conception of individuality,
we cannot with propriety ignore in the biological application
of the word. That which we call an individual plant or animal,
must, therefore, be some concrete whole, and not a discrete
whole. If, however, we say that each concrete

living whole is to be regarded as an individual, we are still
met by the question — What constitutes a concrete living
whole ? A young organism arising by internal or externa]

INDIVIDUALITY. 207

gemmation from a parent organism, passes gradually from a
state in which it is an indistinguishable part of the parent
organism, to a state in which it is a separate organism of like
structure with the parent. At what stage does it become an
individual ? And if its individuality be conceded only when
it completely separates from the parent, must we deny in-
dividuality to all organisms thus produced, which permanently
retain their connexions with their parents ? Or again, what
must we say of the Hcctocotylus, which is an arm of the
Cuttle-fish that undergoes a special development, and then
detaching itself, lives independently for a considerable
period ? And what must we say of that larval Echinus,
which is left to move about awhile after being robbed of its
viscera by the young Echinus developed within it ?

To answer such questions, we must revert to the definition
of Life. The distinction between individual in its biological
6ense, and individual in its more general sense, must consist
in the manifestation of Life, properly so called. Life we
have seen to be, " the definite combination of heterogeneous
changes, both simultaneous and successive, in correspondence
with external co-existences and sequences." Hence, a biolo-
gical individual is any concrete whole having a structuro
which enables it, when placed in appropriate conditions, to
continuously adjust its internal relations' to external relations,
so as to maintain the equilibrium of its functions. In

pursuance of this conception, we must consider as individuals,
all those wholly or partially independent organized masses,
which arise by multicentral and multiaxial development that
is either continuous or discontinuous (§ 50). We must
accord the title to each separate aphis, each polype of a
polypedom, each bud or shoot of a flowering plant, whether
it detaches itself as a bulbil or remains attached as a branch.

By thus interpreting the facts, we do not, indeed, avoid all
anomalies. While, among flowering plants, the power of in-
dependent growth and development, is usually possessed only
by shoots or axes ; yet, in some cases, as in that of the Begonia-

208 THE INDUCTIONS OF BIOLOGY.

leaf awhile since mentioned, the appendage of an axis, or even
a small fragment of such appendage, is capable of initiating
and carrying on the functions of life ; and in other cases, as
shown by M. Naudin in the Droscra intermedia, young
plants are occasionally developed from the surfaces of leaves,
while still connected with the parent plant. Nor among
forms like the compound Hydrozoa, does the definition
enable us to decide where the line is to be drawn between
the individuality of the group and the individualities of the
members — merging into each other, as these do, in different
degrees. But, as before said, such difficulties must necessa-
rily present themselves, if organic forms have arisen by in-
sensible gradations. We must be content with a course
which commits us to the smallest number of incongruities ;
and this course is, to consider as an individual, any centre or
axis that is capable of independently carrying on that con-
tinuous adjustment of inner to outer relations which consti-
tutes Life.

CHAPTER VII.
GENESIS.

§ 75. Ha\ing concluded what constitutes an individual,
we are in a position to deal with the multiplication of in-
dividuals. For this, the title Genesis is here chosen, as being
the most comprehensive title — the least specialized in its
meaning. By some biologists, Generation has been used to
signify one method of multiplication, and Reproduction to
signify another method ; and each of these words has been
thus rendered in some degree unfit to signify multiplication
in general.

Here the reader is indirectly introduced to the fact, that
the production of new organisms is carried on in fundament-
ally unlike ways. Up to quite recent times, it was believed,
even by naturalists, that all the various processes of multipli-
cation observable in different kinds of organisms, have one
essential character in common : it was supposed that in every
species, the successive generations arc alike. It has now been
proved, however, that in plants, and in numerous animals, the
successive generations are not alike ; that from one generation
there proceeds another whose members differ more or less
in structure from their parents ; that these produce others
like themselves, or like their parents, or like neither ; but
that eventually, the original form re-appears. Instead of
there being, as in the cases most familiar to us, a constant
recurrence of the same form, there is a cyclical recurrence of

210 THE INDUCTIONS OF BIOLOGY.

the same form. These two distinct processes of multiplication,
may be aptly termed homogenesis and heterogenesis* Under
these heads let us consider them more closely.

The kind of genesis, once supposed to be universal, in
which the successive generations are alike, is always sexual
genesis ; or, as it has been otherwise called — gamogenesis. In
every species of organism which multiplies by homogenesis,
each generation consists of males and females ; and from the
fertilized germs they produce, the next generation of similar
males and females arises. This method of propagation is
further distinguished by the peculiarity, that each fertilized
germ gives rise to but one individual — the product of de-
velopment is always organized round one axis, and not round
several axes. .Between the different kinds of homo-

genesis, the most marked contrast, and the only one which
need here detain us, is that between the oviparous and the
viviparous. The oviparous kind is that in which the fertil-
ized germ is detached from the parent, before it has
undergone any considerable development. The viviparous
kind is that in which development is considerably advanced,
or almost completed, before final detachment takes place.
This distinction is, however, not a sharply- denned one: there
are transitions between the oviparous and the viviparous
processes. In ovo-viviparous genesis, thei*e is an internal
incubation ; and though the young are in this case finally
detached from the parent in the shape of eggs, they do not
leave the parent's body until after they have assumed
something like the parental form. Looking

around, we find that homogenesis is universal among the
Vertebrata : there is no known vertebrate animal but what
arises from a fertilized germ, and unites into its single indi-
viduality the whole products of this fertilized germ. In

* Unfortunately the word heierc genesis, has been already used as a synoiiymt
for " spontaneous generation." Save by those few who believe in " sponteueoua
generation," however, little objection will be felt to using the word in a seaac
that seems much more appropriate.

GE3NESIS. 211

the mammals or highest Vertebrata, this homogenesis is in
every case viviparous ; in birds it is uniformly oviparous ;
and in reptiles and fishes, it is always essentially oviparous,
though there are cases, of the kind above referred to, in
which viviparity is simulated. Passing to the Invertebrate,
we find oviparous homogenesis universal among the Arach-
nida (except the Scorpions, which are ovo-viviparous) ;
universal among the higher Crustacea, but not among
the lower ; extremely general, though not universal, among
Insects ; and universal among the higher Mollusca, though
not among the lower. Along with extreme inferiority among
animals, we find homogenesis to be the exception rather
than the rule ; and in the vegetal kingdom, there appear to
be no cases, save those of a few aberrant parasites like the
Rafflesiacca;, in which the centre or axis which arises from a
fertilized germ, becomes the immediate producer of fertilized
germs.

Where propagation is carried on by heterogenesis, or is
characterized by unlikeness of the successive generations,
there is always asexual genesis with occasionally-recurring
sexual genesis ; in other words — agamogenesis interrupted
more or less frequently by gamogencsis. If we set out with
a generation of perfect males and females ; then, from their
ova or seeds, there arise individuals that are neither males
nor females, but that produce the next generation from
buds. By this method of multiplication, many individuals
originate from a single fertilized germ : the product of
development is organized round more than one centre or
axis. The simplest form of heterogenesis is that

seen in uniaxial plants. If, as we find ourselves obliged to
do, we regard each separate shoot or axis of growth, as a dis-
tinct individual ; then, in uniaxial plants, the successive in-
dividuals are not represented by the series A, A, A, A, &c,
like those resulting from homogenesis ; but they are repre-
sented by the series A, B, A, B, A, B, &c. For in plants
which were before classed as uniaxial (§ 50), and which may

212 THE INDUCTIONS OF BIOLOGY.

be conveniently so distinguished from other plants, the axis
which shoots up from the seed, and substantially constitutes
the plant, does not itself flower and bear seed ; but gives lateral
origin to flowering, or seed -bearing, axes. Though in uni-
axial plants, the fructifying apparatus appears to be at the end
of the primary, vertical axis ; yet dissection shows that,
morphologically considered, each fructifying axis is usually
an offspring from the primary axis. There arises from the seed,
a sexless individual, from which spring by gemmation, in-
dividuals having reproductive organs ; and from these there
result fertilized germs or seeds, that give rise to sexless
individuals. That is to say, gamogenesis and agamogenesis
alternate : the peculiarity being, that the sexual individu-
als arise from the sexless ones by continuous development.
The Salpce show us an allied form of heterogenesis in
the animal kingdom. Individuals developed from fertilized
ova, instead of themselves producing fertilized ova, produce,
by gemmation, strings of individuals ; from which fertilized
ova again originate. In multiaxial plants, we have

a succession of generations represented by the series A, B,
B, B, &c, A, B, B, B, &c. Supposing A to be a flowering
axis, or sexual individual ; then, from any fertilized germ it
casts off, there grows up a sexless individual, B ; from this
there bud-out other sexless individuals, B ; and so on for
generations more or less numerous ; until at length, from
some of these sexless individuals, there bud-out seed-bearing
individuals of the original form A. Branched herbs,
shrubs, and trees, exhibit this form of heterogenesis : the
successive generations of sexless individuals thus produced,
being in most cases continuously developed, or aggregated
into a compound individual ; but being in some cases dis-
continuously developed. Among animals, a kind of hetero-
genesis represented by the same succession of letters, occurs
in such compound polypes as the Sertularia; and in
those of the Hydrozoa which assume alternately the poly-
poid form, and the form of the Medusa : the chief differences

GENESIS. 213

presented by these groups, arising from the fact that the
successive generations of sexless individuals produced by
budding, are in some cases continuously developed, and in
others discontinuously developed ; and from the fact that, in
some cases, the sexual individuals give off their fertilized
germs while still growing on the parent-polypedom, but in
other cases, not until after leaving the parent-polypedom and
undergoing further development. Where, as in all

the foregoing kinds of agamogenesis, the new individuals
bud-out, not from any specialized reproductive organs, but
from unspecialized parts of the parent ; the process has been
named, by Prof. Owen, metagenesis. In most instances, the
individuals thus produced, grow from the outsides of the
parents — the metagenesis is external. But there is also a
kind of metagenesis which we may distinguish as internal.
Certain entozoa of the genus Distoma, exhibit it. From the
egg of a Distoma, there results a rudely-formed creature
known to naturalists as the " King's-yellow worm." Gradu-
ally as this increases in size, the greater part of its inner
substance is transformed into young animals called Cercarice
(which are the larva3 of Distomata) ; until at length, it
becomes little more than a living sac, full of living offspring.
In the Distoma pacijica, the brood of young animals thus
arising by internal gemmation, are not Cercarice, but are of
tbe same form as their parent : themselves becoming the
producers of Cercarice after the same manner, at a subsequent
period. So that sometimes the succession of forms is repre-
sented by the series A, B, A, B, &c. ; and sometimes by the
series A, B, B, A, B, B, &c. Both cases, however, exemplify
internal metagenesis, in contrast with the several kinds of
external metagenesis described above. That agamo-

genesis which is carried on in a reproductive organ — either
a true ovarium or the homologue of one — has been called, by
Prof. Owen, parthenogenesis. In his work published under
tbis title, he embraced those cases in which the buds arising
in the pseud- ovarium, are not ova in the full sense of the

214: THE INDUCTIONS OF BIOLOGY.

Word ; but rather, as they have since been called by Prof.
Huxley, pseud-ova. Yon Siebold and other naturalists, have
hence applied the term parthenogenesis to a narrower class
cf cases. Perhaps it would be best to distinguish this
process, which is intermediate between metagenesis anr1
parthenogenesis, by the term pseudo-parthenogenesis. It
is the process familiarly exemplified in the Aphides.
Here, from the fertilized eggs laid by perfect females, there
grow up imperfect females, in the pseud-ovaria of which
there are developed pseud-ova ; and these, rapidly assuming
the organization of other imperfect females, are born vivi-
parously. From this second generation of imperfect females,
there by and by arises, in the same manner, a third genera-
tion, of the same kind ; and so on for many generations : the
series being thus symbolized by the letters A, B, B, B, B,
B, &c, A. Pespecting this kind of heterogenesis, it should
be added, that in animals, as in plants, the number of genera-
tions of sexless individuals produced before the re-appearance
of sexual ones, is indefinite ; both in the sense that in the
same species it may go on to a greater or less extent accord-
ing to circumstances, and in the sense that among the genera-
tions of individuals proceeding from the same fertilized germ,
a recurrence of sexual individuals takes place earlier in some
of the diverging lines of multiplication than in others. In
trees we see that on some branches, flower-bearing axes arise
while other branches are still producing only leaf-bearing
axes ; and in the successive generations of Aphides, a parallel
truth has been observed. Lastly has to be set down,

that form of heterogenesis in which, along with gamogenesis,
there occurs a form of agamogenesis exactly like it, save in tho
absence of fecundation. This is called true parthenogenesis —
reproduction carried on by virgin mothers, which are in all
respects like other mothers. In the silk-worm-moths
this parthenogenesis is exceptional, rather than ordinary :
usually the eggs of these insects are fertilized ; but if they
are not, they are still laid, and some of them produce larva).
In certain Lepidoptcra, however, of the groups Psychidce. and

GENESIS.

!lo

Tiiicidfc, parthenogenesis appears to be a normal process —
indeed, so far as is known, the only process ; for of some
species the males have never been found.

A general conception of the relations among the different
modes of Genesis, thus briefly described, will be best given
by the following tabular statement.

Homogencsis, which is Gamogenesis -

Genesis is-

' Oviparous

or
Ovo-viviparouo

or
w Viviparous

. HetcrogenesiSj'vvliich is

f Gamogenesis
alternating
with
Agamogenesis

' Parthenogenesis

or
Pseudo-parthenogenesir
or r Internal

Metagenesis 1 or

[External

This, like all other classifications of such phenomena, pre-
sents anomalies. It may be justly objected, that the processes
here grouped under the head agamogenesis, are the same as
those before grouped under the head of discontinuous develop-
ment (§ 50) : thus making development and genesis partially
coincident. Doubtless it seems awkward that what are from
one point of view considered as structural changes, are from
another point of view considered as modes of multiplication.*

* Prof. Huxley avoids this difficulty by making every kind of Genesis a mode
of development. His classification, which suggested the one given above, is at

follows : —

'Continuous

Development

( Growth

( Metamorphosis

Discontinuous \

I Agamogenesis {

/ Metagenesis

' Gamogenesis

( Parthenogenesis

21G THE INDUCTIONS OF BIOLOGY.

There is, hoAvever, nothing for us but a choice of imperfec-
tions. We cannot by any logical dichotomies, accurately
express relations which, in Nature, graduate into each other
insensibly. Neither the above, nor any other scheme, can do
more than give an approximate idea of the truth.

§ 76. Genesis under every form, is a process of negative
or positive disintegration ; and is thus essentially opposed to
that process of integration, which is one element of individual
evolution. Negative disintegration occurs in those cases
where, as among the compound Hydrozoa, there is a con-
tinuous development of new individuals by budding from the
bodies of older individuals ; and where the older individuals
are thus prevented from growing to a greater size, or reach-
ing a higher degree of integration. Positive disintegration
occurs in those cases of agamogenesis where the formation
of new individuals is discontinuous, and in all cases of gamo-
genesis. The degrees of disintegration are various. At
the one extreme, the parent organism is completely broken
up, or dissolved into new individuals ; and at the other
extreme, the new individual forms but a small deduction
from the parent organism. Protozoa and Protophyta, show
us that form of disintegration called spontaneous fission :
two or four individuals being produced by the splitting-up
of the original one. The Volcox and the Hydrodidyon,
are plants which, having developed broods of young plants
within themselves, give them exit by bursting ; and among
animals, the one lately referred to, which arises from the
Distoma egg, entirely loses its individuality in the individ-
ualities of the numerous Distonia-larYXs with which it be-
comes filled. Speaking generally, the degree oi
disintegration becomes less marked, as we approach the higher
organic forms. Plants of advanced types throw off from
themselves, whether by gamogenesis or agamogenesis, parts
that are relatively small ; and among the higher animals,
there is no case in which the parent individuality is habitually

GENESIS. 217

lost, in the production of new individualities. To the

last, however, there is of necessity a greater or less disinte-
gration. The seeds and pollen-grains of a flowering plant,
are disintegrated portions of tissue ; as are also the ova and
spermatozoa of animals. And whether the fertilized germs
carry away from their parents small or large quantities of
nutriment, these quantities of nutriment in all cases involve
further negative or positive disintegrations of the parents.

New individuals that result from agamogenesis, usually do
not separate from the parent-individuals, until they have
undergone considerable development, if not complete develop-
ment. The agamogenetic offspring of those lowest organisms
which develop centrally, do not, of course, pass beyond cen-
tral structure ; but the agamogenetic offspring of organisms
that develop axially, commonly assume an axial structure
before they become independent. The vegetal kingdom shows
us this in the advanced organization of detached bulbils, and
of buds that root themselves before separating. Of animals,
the Hydrozoa, the Trematoda, the Salpce, and the Aphides,
present us with different kinds of agamogenesis, in all of
which the new individuals are organized to a considerable
extent before being cast off. This rule is not without excep-
tions, however. The winter-eggs of the Plitmatella, developed
in an unspecialized part of the bod)'-, present us with a case
of metagenesis, in which centres of development, instead of
axes, are detached ; and in the above-described parthenogene-
sis of moths and bees, such centres are detached from an
ovarium.

When produced by gamogenesis, the new individuals be-
come independent of the parents while in the shape of centres
of development, rather than axes of development ; and this
even where the reverse is apparently the case. The fertilized
germs of those inferior plants which are central, or multicen-
tral, in their development, are of course thrown off as centres.
In the higher plants, of the two elements that go to the form-
ation of the fertilized germ, the pollen-cell is absolutely
15

218 THE INDUCTIONS OF BIOLOGY.

separated from the parent-plant under the shape of a centre :
and the embryo-cell, though not absolutely separated from
the parent, is still no longer subordinate to the organizing
forces of the parent. So that when, the embryo- cell having
been fertilized by matter from the pollen-tube, the develop-
ment commences, it proceeds without parental control :
the new individual, though remaining physically united
with the old individual, becomes structurally and functionally
separate while still only a centre of development ; and takes
on its axial form by processes of its own — the old individual
doing no more than supply materials. Through-

out the animal kingdom, the new individuals produced by
gamogenesis, are obviously separated in the shape of centres
of development wherever the reproduction is oviparous . the
only conspicuous variation being in the quantity of nutritive
matter bequeathed by the parent to the new centre of de-
velopment, at the time of its separation. And though, where
the reproduction is viviparous, the process appears to be
different, and in one sense is so ; yet, intrinsically, it is the
same. For in these cases, the new individual really detaches
itself from the parent while still only a centre of develop-
ment ; but instead of being finally cast off in this state, it is
re-attached, and supplied with nutriment until it assumes a
more or less complete axial structure.

§ 77. Under all its various forms, the essential act in gamo-
genesis, is the union of two centres or cells, produced by
different parent organisms : the sperm-cell being the male
product, and the germ-cell the female. There are very
many modes and modifications of modes in which these
cells are produced ; very many modes and modifications of
modes by which they are brought into contact ; and very
many modes and modifications of modes by which the result-
ing fertilized germs have secured to them the fit conditions
for their development. But passing over these many diver-
gent and re-divergent kinds of sexual multiplication, which

GENESIS. 219

t would take too much space here to specify, the one uni-
versal peculiarity which it concerns us to remark, is, this co-
alescence of a detached portion of one organism, with a more
or less detached portion of another.

Such protophytes as the Palmellce and the Dcstnidicm,
which are sometimes distinguished as unicellular plants, show
us a coalescence, not of detached portions of two organisms,
but of two entire organisms : in the Palmellce, conjugation is
a complete fusion of the individuals ; and in the Dcsmidiece,
the entire contents of the individuals unite to form the germ-
mass. Where, as among the Confervce, we have aggregated
cells whose individualities are scarcely at all subordinate to
that of the aggregate, the gamogenetic act is effected by the
union of the contained granules of two adjacent cells. In
Spirogyra, it is not adjacent cells in the same thread which
thus combine ; but cells of one thread with those of another.
As we ascend to plants of high organization, we find that;
the two reproductive elements become quite distinct in
their characters ; and further, that they arise in different
organs set apart for their production : the arrangements
being such, that the sperm-cells of one plant combine with
the germ -cells of another.

There is reason to think that, among the lowest Protozoa,
a fusion of two individualities, analogous to that which occurs
in the conjugation of certain Algce, is the process from which
results the gerni of a new series of individuals. But in
animals formed by the aggregation of units that are homolo-
gous with Protozoa, the sperm-cells and germ-cells are differ-
entiated. And even in these humble forms, where there is no
differentiation of sexes, we have good evidence that, as in all
higher forms, the union is not between sperm-cells and germ-
cells that have arisen in the same individual ; but between
those that have arisen in different individuals.

The marvellous phenomena initiated by the meeting of
sperm-cell and germ-cell, naturall)' suggest the conception of
some quite special and peculiar properties possessed by thcoe

t

220 THE INDUCTIONS OF BIOLOGY.

cells. It seems obvious that this mysterious power which
they display, of originating a new and complex organism,
distinguishes them in the broadest way from portions of organio
substance in general. Nevertheless, the more we study the
evidence, the more is this assumption shaken — the more are
we led towards the conclusion, that these cells have not
been made by some unusual elaboration, fundamentally
different from all other cells. The first fact which

points to this modified conclusion, is the fact recently dwelt
upon (§ 68), that in many plants and inferior animals, a
small fragment of tissue that is but little differentiated, is
capable of developing into the form of the organism from
which it was taken. Conclusive proof obliged us to admit,
that the component units of organisms, have inherent powers
of arranging themselves into the forms of the organisms to
which they belong. And if to these component units, which
we distinguished as physiological, such powers must be con-
ceded— if, under fit conditions, and when not much specialized,
they manifest such powers in a way as marked as that in
which the contents of sperm-cells and germ-cells manifest
them ; then, it becomes clear that the properties of sperm-
cells and germ-cells are not so peculiar as we are apt to
assume. Again, the organs for preparing sperm-

cells and germ-cells, have none of the speciality of struc-
ture which might be looked for, did sperm-cells and germ-
cells need endowing with properties essentially unlike
those of all other organic agents. On the contrary, these
reproductive centres proceed from tissues that are character-
ized by their low organization. In plants, for example, it is
not appendages that have acquired considerable structure,
which produce the fructifying particles : these arise at the
extremities of the axes, where the degree of structure is the
least. The embryo-cells are formed in the undifferentiated
part of the cambium-layer ; the pollen-grains are formed at
the little-differentiated extremities of the stamens ; and both
&re homologous with simple epithelium- cells. Among manv

GXMSSI8. 221

inferior animals devoid of special reproductive organs, such
as the Hydra, the ova and spermatozoa originate in the
layer of indifferent tissue that lies between the endoderm
and the ectoderm ; that is, they consist of portions of the
least specialized substance. And in the higher animals,
these same generative agents appear to be merely modified
epithelium-cells — cells not remarkable for their complexity
of structure, but rather for their simplicit}>\ If, by

way of demurrer to this view, it is asked why other epithe-
lium-cells do not exhibit like properties ; there are two replies.
The first is, that other epithelium-cells are usually so far
changed to fit them to their special functions, that they are
unfitted for assuming the reproductive function. The second
reply is, that in some cases, where the epithelium- cells are
but very little specialized, they do exhibit the like properties :
not, indeed, by uniting with other epithelium-cells to produce
new germs, but by producing new germs without such union.
I learn from Dr Hooker, that the Begonia phyllomaniaca
habitually develops young plants from the scales of its stem
and leaves — nay, that many young plants are developed by a
single scale. The epithelium-cells composing one of these
scales, swell, here and there, into large globular cells ; form
chlorophyll in their interiors ; shoot out rudimentary axes ;
and then, by spontaneous constrictions, cut themselves off;
drop to the ground ; and grow into Begonias. It appears,
too, that in a succulent English plant, the Malaxis paludosa,
a like process occurs : the self-detached celk being, in this
case, produced by the surfaces of the leaves. Thus,

there is no warrant for the assumption that sperm-cells and
germ-cells possess powers fundamentally unlike those of
other cells. The inference to which the facts point, is, that
they differ from the rest, mainly in not having undergone
modifications such as those by which the rest are adapted to
particular functions. They are cells that have departed but
little from the original and most general type. Or, in the
words suggested by a friend, it is not that they are peculiar!)

222 THE INDUCTIONS OF BIOLOGY.

specialized, but rather that they are unspecialized : such
specializations as some of them exhibit in the shape of loco-
motive appliances, &c, being interpretable not as intrinsic,
but as extrinsic, modifications, that have reference to nothing
beyond certain mechanical requirements. Sundry

facts tend likewise to show, that there does not exist the pro-
found distinction which we are apt to assume, between the
male and female reproductive elements. In the common
polype, sperm-cells and germ-cells are developed in the same
layer of indifferent tissue ; and in Tethya, one of the sponges,
Prof. Huxley has observed that they occur mingled together
in the general parenchyma. The pollen-grains and embryo-
cells of plants, arise in adjacent parts of the cambium-layer ;
and from a description of a monstrosity in the Passion-flower,
recently given by Mr Salter to the Linnncan Society, it ap-
pears, both that ovule3 may, in their general structure,
graduate into anthers, and that they may produce pollen in
their interiors. All which evidence is in perfect harmony
with the foregoing conclusion ; since, if sperm-cells and
germ-cells have natures not essentially unlike those of un-
specialized cells in general, their natures cannot be essen-
tially unlike each other.

The next general fact to be noted, is, that these cells
whose union constitutes the essential act of gamogenesis, are
cells in which the developmental changes have come to a
close — cells which, however favourably circumstanced in
respect of nutrition, are incapable of further evolution.
Though they are not, as many cells are, unfitted for growth
and metamorphosis by being highly specialized; yet they
have lost the power of growth and metamorphosis. They
have severally reached a state of equilibrium. And while
the internal balance of forces prevents a continuance of con-
structive changes, it is readily overthrown by external
destructive forces. For it uniformly happens that sperm-
cells aud germ-cells which are not brought in contact, disap-
pear. In a plant, the embryo-cell, if not fertilized, is

GENESIS. 223

absorbed or dissipated, while the ovule aborts; and the un-
impregnated ovum eventually decomposes.

Such being the characters of these cells, and such being
their fates if kept apart, we have now to observe what hap-
pens when they are united. For a long time, the immediate
sequence of their contact was not ascertained. This is at
length, however, decided. It has been shown that in plants,
the extremity of the elongated pollen-cell applies itself to tho
surface of the embryo-sac, but does not enter the embryo-
sac. In animals, however, the process is different. Careful
observers agi'ee, that the spermatozoon passes through the
limiting membrane of the ovum. The result in both cases is
presumed to be a mixture of the contents of the two
cells. The evidence goes to show that in plants, matter
passes by osmose from the pollen-cell into the embryo-
cell ; and that in animals, the substance contained in the
spermatozoon becomes mingled with the substance contained
in the ovum, either by simple diffusion or by cell-multiplica-
tion. But the important fact which it chiefly con-
cerns us to notice, is, that on the union of these reproductive
elements, there begins, either at once or on the return of
favourable conditions, a new series of developmental changes.
The state of equilibrium at which each of them had arrived,
is destroyed by their mutual influence ; and the constructive
changes which had come to a close, recommence : a process
of cell-multiplication is set up ; and the resulting cells pre-
sently begin to aggregate into the rudiment of a new
organism.

Thus, passing over the variable concomitants of ganio-
genesis, and confining our attention to what is constant in it,
we see : — that there is habitually, if not universally, a fusion
of two portions of organic substance, which are either them-
selves distinct individuals, or are thrown off by distinct
individuals ; that these portions of organic substance, which
are severally distinguished by their low degree of special-
ization, have arrived at states of structural quiescence or

224 THE INDUCTIONS OF BIOLOGY.

equilibrium ; that if they are not united, this equilibrium
ends in dissolution ; but that by the mixture of them, thie
equilibrium is destroyed, and a new evolution initiated.

§ 78. What are the conditions under which Genesis takes
place ? How does it happen that some organisms multiply
by homogenesis, and others by heterogenesis ? Why is it
that where agamogenesis prevails, it is usually from time to
time interrupted by gamogenesis ? These are questions of
extreme interest ; but questions to which decisive answers
cannot yet be given. In the existing state of Biology, we
must be content if we can learn the direction in which
answers lie. A survey of the facts, discloses certain correla-
tions which, if not universal, are too general to be without
significance.

Where the multiplication of individuals is carried on by
heterogenesis, we find, in numerous cases, that agamogenesis
continues as long a3 the forces which result in growth, are
greatly in excess of the antagonistic forces. While conversely,
we find that the recurrence of gamogenesis, takes place when
the conditions are no longer so favourable to growth. In
like manner, where there is homogenetic multiplication, new
individuals are usually not formed while the preceding in-
dividuals are still rapidly growing — that is, while the forces
producing growth exceed the opposing forces to a great extent,-
but the formation of new individuals begins when nutrition
is nearly equalled by expenditure. To specify all the facts
uhat seem to warrant these inductions, would take more space
than can be here spared. A few of them must suffice.

The relation between fructification and innutrition, among
plants, was long ago asserted by a German biologist — by
Wolff, I am told. When, some years ago, I met with the
assertion, I was not acquainted with the evidence on which it
rested. Since that time, however, I have, when occasion
favoured, examined into the facts for myself. The result has
been a conviction, strengthened by every further inquiry,

GENESIS.

225

that such a relation exists. Uniaxial plants begin to

produce their lateral, flowering axes, only after the main
axis has developed the great mass of its leaves, and is show-
ing its diminished nutrition by smaller leaves, or shorter
internodes, or both. In multiaxial plants, two, three, or
more generations of leaf-bearing axes, or sexless individuals,
are produced before any seed-bearing individuals show them-
selves. When, after this first stage of rapid growth and
agamogenetic multiplication, some gamogenetic individuals
arise, they do so where the nutrition is least ; — not on the
main axis, or on the secondary axes, or even on the tertiary
axes ; but on axes that are the most removed from the
channels which supply nutriment. Again, a flowering axis
is commonly less bulky than the others : either much
shorter, or, if long, much thinner, xind further, it is an
axis of which the terminal internodes are undeveloped : the
foliar organs, which instead of becoming leaves become sepals,
and petals, and stamens, follow each other in close succession,
instead of being separated bj7 portions of the still-growing
axis. Another group of evidences meets us, when

we observe the variations of fruit-bearing that accompany
variations of nutrition, in the plant regarded as a whole,
besides finding, as above, that gamogenesis commences only
when the luxuriance of early growth has been somewhat
checked, by the extension of the remoter parts of the plant to
some distance from the roots ; we find that gamogenesis is
induced at an earlier stage than usual, by checking the nutri-
tion Trees are made to fruit while still quite small, by
cutting their roots, or putting them in pots ; and luxuriant
branches which have had the flow of sap into them diminished,
Dy what gardeners call " ringing," begin to produce flower-
shoots instead of leaf- shoots. Moreover, it is to be remarked
that trees which, by flowering early in the year, seem to
show a direct relation between gamogenesis and increasing
nutrition, really do the reverse ; for in such trees, the flower-
buds are formed in the autumn — that structure which deter-

226 THE INDUCTIONS OF BIOLOGY.

mines these buds into sexual individuals, is given when the
nutrition is declining. Conversely, very high nutri-

tion in plants, prevents, or arrests, gamogenesis. It is
notorious that unusual richness of soil, or too large a
quantity of manure, results in a continuous production of
leaf-bearing, or sexless, shoots. Besides being prevented
from producing sexual individuals, by excessive nutrition,
plants are, by excessive nutrition, made to change the sexual
individuals they were about to produce, into sexless ones.
This arrest of gamogenesis may be seen in various stages.
The familiar instance of flowers made barren by the trans-
formation of their stamens into petals, shows us the lowest
degree of this reversed metamorphosis. Where the petals
and stamens are partially changed into green leaves, the
return from the gamogenetic structure towards the agamo-
genetic structure, is more marked ; and it is still more
marked when, as occasionally happens in luxuriantly-growing
plants, new flowering axes, and even leaf-bearing axes, grow
out of the centres of flowers.* The anatomical

* Among various examples of this which I have observed, some of the most
remarkable were among Foxgloves, growing in great numbers and of large size,
in a wood between "Whatstandwell Bridge and Crich, in Derbyshire. In one case,
the lowest flower on the stem, contained, in place of a pistil, a shoot or spike of
flower-buds, similar in structure to the embryo-buds of the main spike. 1
counted seventeen buds on it ; of which the first had three stamens, but was other-
wise normal ; the second had three ; the third, four ; the fourth, four ; &c.
Another plant, having more varied monstrosities, evinced excess of nutrition with
equal clearness. The following are the notes I took of its structure : — 1st, or
lowest flower on the stem, very large ; calyx containing eight divisions, one
partly transformed into a corolla, and another transformed into a small bud with
bract (this bud consisted of a five-cleft calyx, four sessile anthers, a pistil, and a
rudimentary corolla) ; the corolla of the main flower, which was complete, con-
tained six stamens, three of them hearing anthers, two others being flattened and
coloured, and one rudimentary ; there was no pistil, but, in place of it, a large
bud, consisting of a three-cleft calyx, of which two divisions were tinted at the
ends, an imperfect corolla, marked internally with the usual purple spots and
hairs, three anthers sessile on this mal-formed corolla, a pistil, a seed-vessei with
ovules, and, growing to it, another bud of which the structure was indistinct.
2r1 flower, large ; calyx of seven divisions, one being transformed into a bud

GENESIS.

227

structure of the sexual axis, affords corroborative evidence :
giving very much the impression, as it does, of an aborted
sexless axis. Besides lacking those internodes which the
leaf- bearing axis commonly possesses, the flowering axis
differs by the absence of rudimentary lateral axes. In a leaf-
bearing axis, the axil of every leaf usually contains a small
bud, which may or may not develop into a lateral axis;
but though the petals of a flower are homologous with leaves,
they do not bear homologous buds at their bases. Ordinarily,
too, the foliar appendages of sexual axes, are much smaller
than those of sexless ones — the stamens and pistils especially,
which are the last formed, being extremely dwarfed ; and
there is even reason for thinking that the absence of chloro-
phyll from the parts of fructification, is a fact of like mean-
ing. Moreover, the formation of the seed-vessel appears
to be a direct consequence of arrested nutrition. If a
gloved- finger be taken to represent a growing shoot,
(the finger standing for the core of the shoot, and the
glove for the cambium-layer, in which the process of
growth takes place) ; and if it be supposed that there is a
diminished supply of material for growth ; then, it seems
a fair inference, that growth will first cease at the apex of
the cambium-layer, represented b}r the end of the glove-
finger ; and supposing growth to continue in those parts
of the cambium-layer that are nearer to the supply of nutri-
ment, their further longitudinal extension will lead to the
formation of a cavity at the extremity of the shoot, like that
which results in a glove-finger when the finger is partially
withdrawn and the glove sticks to its end. "Whence it seems,

with bract, but much smaller than the other ; corolla large but cleft along the top ;
six stamens with anthers, pistil, and seed-vessel. 3rd flower, large; six-cleft
calyx, cleft corolla, with six stamens, pistil, and seed-vessel, with a second pistil
half unfolded at its apex. 4th flower, large ; divided along the top, six stamens.
5th flower, large; corolla divided into three parts, six stamens. 6th flower,
large ; corolla cleft, calyx six- cleft, the rest of the flower normal. 7th, and all sue-
ooecliiig flowers, normal.

22S THE INDUCTIONS OF BIOLOGY.

both that this introversion of the carnbium-layor may be
considered as due to failing nutrition, and that the ovules
growing from its introverted surface (which would have been
its outer surface but for the defective nutrition) are extremely
aborted homologues of external appendages — either leaves
or Literal axes : the essential organs of fructification thus
arising where the defective nutrition has reached its extreme.*
To all which let us not forget to add, that the sperm -cells and
germ-cells are formed at the very ends of the organs of fruc-
tification.

Those kinds of animals which multiply by heterogenesis,
present us with a parallel relation between the recurrence of
gamogenesis and the recurrence of conditions unfavourable to
growth — at least, this is shown where experiments have
thrown light on the connexion of cause and effect ;
namely, among the Aphides. These creatures, hatched from
eggs in the spring, multiply by agamogenesis throughout
the summer. When the weather becomes cold, and plants
no longer afford abundant sap, perfect males and females
are produced ; and from gamogenesis there result fertilized
ova. But now observe that beyond this evidence, wo
have much more conclusive evidence. For it has been shown,
both that the rapidity of the agamogenesis is proportionate
to the warmth and nutrition, and that if the temperature and

« It appears that botanists do not agree respecting the homologies of tho
ovules: some thinking that they are rudimentary foliar organs, and others that
they are rudimentary axial organs. Possibly the dispute will prove a bootless
one ; since there seems evidence that ovules may be transformed into either ono
or the other. Mr Salter's paper, lately referred to, shows that they may
graduate into stamens, which are foliar organs ; and the case of the Foxglove,
which I have described above, shows that they may develop into flower-ouds,
which are axial organs. I would venture to suggest, that the conflicting evidence
can be reconciled, only by regarding ovules as the homologues of lateral append-
ages ; and considering a lateral appendage as composed of a leaf, plus a rudiment-
ary axis, either of which may abort. This is the view which seems countenanced
by development ; since, in its first stage, a lateral bud, whence a lateral append-
age arises, 6hows no division into rudimentary leaf and rudimentary axis ; and
it is to the lateral bud in this first stage, that the seed-bud or ovule is horoo-

GENESIS. 220

supply of food bo artificially maintained, the agamogenesis
continues through the winter. Nay more — it not only, under
these conditions, continues through one winter, but it has
been known to continue for four successive years : some
forty or fifty sexless generations being thus produced. And
those who have investigated the matter, see no reason to
doubt the indefinite continuance of this agamogenetic mul-
tiplication, so long as the external requirements are duly
met. Evidence of another kind, which points very

distinctly to the same conclusion, is furnished by the hetero-
genesis of the Daphnia — a small crustacean commonly known
as the "Water-flea, which inhabits ponds and ditches. From
the nature of its habitat, this little creature is exposed to very
variable conditions. Besides being frozen up in winter, the
small bodies of water in which it lives, are often unduly
heated by the summer sun, or dried up by continued drought.
The circumstances favourable to the Daphnia' s life and
growth, being thus liable to interruptions which, in our cli-
mate, have a regular irregularity of recurrence ; we may, in
conformity with the hypothesis, expect to find both that the
gamogenesis recurs along with evidence of declining nutri-
tion, and that its recurrence is very variable. This we do
find. From Mr Lubbock's paper on the Daphnia in the
" Philosophical Transactions " for 1857, and from further
information which he has been good enough to furnish me,
the following general facts are deducible : — First, that in
each ovarium, along with the rudiments of agamic eggs, or
eggs which, if developed, produce young by true partheno-
genesis, there usually, if not alwaj^s, exists the rudiment of
un ephippial egg ; which, from sundry evidences, is inferred
to be a sexual or gamic egg. Second, that according to cir-
cumstances, either agamogenesis or gamogenesis takes place ;
but that if the agamic eggs develop, the rudimentary gamic
egg disappears, or becomes absorbed ; and conversely, if the
gamic egg develops, the agamic eggs disappear, or are ab-
sorbed by it. Third, that the brood of agamic eggs contained

2u0 THE INDUCTIONS OF BIOLOGY.

in each ovarium, amounts, under favourable circumstances,
to as many as eight or nine ; while of the gamic eggs, only
one at a time is produced in each ovarium, and occasionally
one of the ovaria produces none : whence it follows, that as
the gamic egg is not more than twice the bulk of the agamic
egg, the quantity of matter contained in an agamic brood, is
four times, and occasionally even eight time3, as great as
that contained in a gamic bi'ood. Thus the quantity of
nutriment expended in gamogenesis during a given period
(making allowance for that which goes to the formation of
the ephippium), is far less than that expended in agamogenesis
during a like period. Seeing, then, this constant preparation
for either gamic or agamic genesis, in a creature liable to
such irregular variations of nutrition ; and seeing that the
agamogenesis implies by its amount, a large excess of nutri-
tion, while the gamogenesis implies by its amount, a small
excess of nutrition ; we can scarcely doubt that the one or
the other mode of multiplication occurs, according as the
external conditions are or are not favourable to nutrition.

Passing now to animals which multiply by homogenesis —
animals in which the whole product of a fertilized germ ag-
gregates round a single centre or axis, instead of round many
centres or axes ; we see, as before, that so long as the con-
ditions allow rapid increase in the mass of this germ-product,
the formation of new individuals by gamogenesis does not
take place. Speaking generally, we find that only when
growth is declining in relative rapidity, do perfect sperm-
cells and germ-cells begin to appear; and that the fullest
activity of the reproductive function, arises as growth ceases
— speaking generally, we must say, because, though tlria
relation is tolerably definite in the highest orders of animala
which multiply by gamogenesis, it is less definite in the lower
orders. This admission does not militate against the hypo-
thesis, as it seems to do ; for the indefiniteness of the relation
occurs where the limit of growth is comparatively indefinite.
Wo «aw (§ 4G) that among active, hot-blooded creatures,

GENESIS. 231

Rich as mammals and birds, the inevitable balancing of
assimilation by expenditure, establishes, for each species, an
almost uniform adult size ; - and among creatures of these
kinds, (birds especially, in which this restrictive effect of
expenditure is most conspicuous), the connexion between
cessation of growth and commencement of reproduction, is
distinct. But we also saw (§ 46) that where, as in the Cro-
codile and the Pike, the conditions and habits of life are such,
that expenditui*e does not overtake assimilation as the size
increases, there is no precise limit of growth ; and in creatures
thus circumstanced, we may naturally look for a compara-
tively indeterminate relation between declining growth and
commencing reproduction.* There is, indeed, among

fishes, at least one case which appears very anomalous. The
male parr, or young of the male salmon, a fish of four or five
inches in length, is said to produce milt. Having, at this
early stage of its growth, not one hundredth of the weight
of a full-grown salmon, how does its production of milt
consist with the alleged general law ? The answer must be
in a great measure hypothetical. If the salmon is (as it
appears in its young state) a species of fresh-water trout,
that has contracted the habit of annually migrating to the
sea, where it finds a food on which it thrives — if the original
size of this species was not much greater than that of the
parr (which is nearly as large as some varieties of lake-trout
and river-trout) — and if the limit of growth in the trout
tribe is very indefinite, as we know it to be ; then we
may reasonably infer, that the parr has nearly the adult
form and size of this species of trout, before it acquired
its migratory habit ; and that this production of milt, is,

• I owe to Mr Lubbock an important confirmation of tbis view. After stat-
ing Lis belief, that between Crustaceans and Insects, there exists a physiological
relation analogous to that which exists between watcr-vertebrata and land-verte-
brata; he pointed out to me, that while among Insects, there is a definite limit
of growth, and an accompanying definite commencement of reproduction, among
Crustaceans, where growth has no definite limit, there is no definite relation
between the commencement of reproduction and the decrease or arrest of growth

232 THE INDUCTIONS OF BIOLOGY.

in such, case, a concomitant of the incipient decline of
growth naturally arising in the species, when living under
the conditions of its remote ancestors. If this be admitted,
the immense subsequent growth of the parr into the salmon,
must be regarded as due to a suddenly -increased facility in
obtaining food — a facility which removes to a great distance
the limit at which assimilation is balanced by expenditure ;
and which has the effect, analogous to that produced in
plants, of arresting the incipient reproductive process, and
causing a resumption of growth. A confirmation of this
view may be drawn from the fact, that when the parr, after
its first migration to the sea, returns to fresh water, having
increased in a few months from a couple of ounces to five or
six pounds, it no longer shows any fitness for propagation :
the grilse, or immature salmon, does not produce milt or
spawn. But without citing further illustrations, or

attempting to meet further difficulties, it has, I think, been
made sufficiently clear, that some such connexion as that al-
leged, exists. Traversed, as is this relation between commence-
ment of sexual reproduction and declining rate of growth, by
various other relations, it is quite as manifest as we can
expect it to be.

The general law to which both homogenesis and hetero-
genesis conform, thus appears to be, that the products of a
fertilized germ go on accumulating by simple growth, so long
as the forces whence growth results are greatly in excess of
the antagonist forces ; but that when diminution of the one
set of forces, or increase of the other, causes a considerable
decline in this excess, and an approach towards equilibrium,
fertilized germs are again produced. Whether the germ-
product be organized round one axis, or round the many
uxes that arise by agamogenesis — whether the development
be continuous or discontinuous ; matters not. "Whether, as
in concrete organisms like the higher animals, this approach
to equilibrium results from that disproportionate increase of
expenditure entailed by increase of size; or whether, as in

GEXKSIS. 233

partially and wholly discrete organisms, like most plants and
many inferior animals, this approach to equilibrium results
from absolute or relative decline of nutrition ; matters not.
In any case, the recurrence of gamogenesis is associated with
u more or less marked decrease in thte excess of tissue-pro-
ducing power. We cannot say, indeed, that a do*
ciease in this excess always results in gamogenesis ; for wo
have evidence to the contrary, in the fact that some organ-
isms multiply for an indefinite period by agamogenesis only.
Thus, the weeping willow, which has been propagated through-
out Europe, does not seed in Europe ; and yet, as the weep-
ing willow, by its large size and the multiplication of
generation upon generation of lateral axes, presents the same
causes of local innutrition as other trees, we cannot ascribe
the absence of sexual axes to the continued predominance of
nutrition. Among animals, too, the anomalous case of the
Tineidce, a group of moths in which parthenogenetic mul-
tiplication goes on- for generation after generation, shows us
that gamogenesis does not necessarily result from an approxi-
mate balance of assimilation by expenditure. What we must
say, is, that an approach towards equilibrium between the
forces which cause growth and the forces which oppose
growth, is the chief condition to the recurrence of gamo-
genesis ; but that there are other unknown conditions, in the
absence of which this approach to equilibrium is not followed
by gamogenesis.

§ 79. The above induction is an approximate answer to
the question — When does gamogenesis recur ? but not to the
question which was propounded — Why does gamogenesis re-
cur?— Why cannot multiplication be carried on in all cases,
as it is in many cases, by agamogenesis ? As already said,
biologic science is not yet advanced enough to reply. Mean-
while, the evidence above brought together, suggests a cer-
tain hypothetical answer, which it may be well to set down.

Seeing as we do, on the one hand, that gamogenesis recuxa
16

234 THE INDUCTIONS OF BIOLOGY.

only in individuals that are approaching towards a state of
organic equilibrium ; and seeing, on the other hand, as we
do, that the sperm-cells and germ-cells thrown off by such
individuals, are cells in which developmental changes have
ended in quiescence, but in which, after their union, there
arises a process of active cell- formation ; we may suspect
that the approach towards a state of general equilibrium in
such gamogenetic indiviluals, is accompanied by an approach
towards molecular equilibrium in them ; and that the need
for this union of sperm-cell and germ-cell, is the need for
overthrowing this equilibrium, and re-establishing active mole-
cular change in the detached germ — a result which is pro-
bably effected by mixing the slightly different physiological
units of slightly different individuals. The several argu-
ments that may be brought in support of this view, cannot
be satisfactorily set forth until after the topics of Heredity
and Variation have been dealt with. Leaving it for the pre-
sent, I propose hereafter to reconsider thfs question, in con-
nexion with sundry others that are raised by the phenomena
of Genesis.

Before ending the chapter, however, it may be well to note
the relations between these different modes of multiplication,
and the conditions of existence under which they are respect-
ively habitual. While the explanation of the teleologist is
untrue, it is often an obverse to the truth ; for though, on the
hypothesis of Evolution, it is clear that things are not
arranged thus or thus for the securing of special ends, it is
also clear, that arrangements which do secure these special
ends, tend continually to establish themselves — are establish-
ed by their fulfilment of these ends. Besides insuring a
structural fitness between each kind of organism and its cir-
cumstances, the working of " natural selection " also insures
a fitness between the mode and rate of multiplication of each
kind of organism and its circumstances. We may, therefore,
without any teleological implication, consider the fitness of

GENESIS. 236

homogenesis and heterogenesis to the needs of the different
classes of organisms which exhibit them.

One of the facts to be observed, is, that heterogenesis pre-
vails among organisms of which the food, though abundant
compared with their expenditure, is dispersed in such a way
that it cannot be appropriated in a wholesale manner. Pro-
topliyta, subsisting on diffused gases and decaying organic
matter in a state of minute subdivision ; and Protozoa, to
which food comes in the shape of extremely small floating
particles ; are enabled by their rapid agamogenetic multipli-
cation, to obtain materials for growth, better than they would
do did they not thus continually divide and disperse in pur-
suit of it. The higher plants, having for nutriment the car-
bonic acid of the air and certain mineral components of the
soil, show us modes of multiplication adapted to the fullest
utilization of these substances. A herb, with but little power
of forming the woody-fibre requisite to make a stem that can
support wide-spreacling branches, after producing a few sex-
less axes, produces sexual ones ; and maintains its race better
by the consequent early dispersion of seeds, than by a further
production of sexless axes. But a tree, able to lift its suc-
cessive generations of sexless axes high into the air, where
each axis gets carbonic acid and light almost as freely as if it
grew by itself, may with advantage go on budding-out sex-
less axes year after year; since it thereby increases its sub-
sequent power of budding-out sexual axes. Meanwhile, it
may advantageously transform into seed-bearers, those axes
which, in consequence of their less direct access to materials
absorbed by the roots, are failing in their nutrition ; for in
doing this, it is throwing-off from a point at which sus-
tenance is deficient, a migrating group of germs that may
find sustenance elsewhere. The heterogenesis displayed by
animals of the Coelenterate type, has evidently a like utility.
A polype, feeding on minute annelids and crustaceans, which,
flitting through the water, come in contact with its tentacles,'

236 THE INDUCTIONS OF BIOLOGY.

and limited to that quantity of prey which chance brings
within its grasp ; buds out young polypes which, either as a
colony or as dispersed individuals, spread their tentacles
through a larger space of water than the parent alone can ;
and by producing them, the parent better insures the continu-
ance of its species, than it would do if it went on slowly grow-
ing until its nutrition was nearly balanced by its waste, and
then multiplied by gamogenesis. Similarly with the Aphis.
Living on sap sucked through its proboscis from tender shoots
and leaves, and able thus to take in but a very small quan-
tity in a given time, this creature's race is more likely to
be preserved by a rapid asexual propagation of small indi-
viduals, which disperse themselves over a wide but nowhere
rich area of nutrition, than it would be did the individual
growth continue so as to produce large individuals multiply-
ing sexually. While at the same time we see, that when
autumnal cold and diminishing supply of sap, put a check to
growth, the recurrence of gamogenesis, and production of
fertilized ova that remain dormant through the winter, is
more favourable to the preservation of the race, than would be
a further continuance of agamogenesis. On the

other hand, it is obvious that among the higher animals,
living on food which, though dispersed, is more or less
aggregated into large masses, this alternation of gamic and
agamic reproduction ceases to be useful. The development
of the germ- product into a single organism of considerable
bulk, is in many cases a condition without which these large
masses of nutriment could not be appropriated ; and here thu
formation of many individuals instead of one, would be fatal.
But we still see the beneficial results of the general law — the
postponement of gamogenesis until the rate of growth begins
to decline. For so long as the rate of growth continues
rapid, it is a proof that the organism gets food with great
facility — that expenditure is not such as seriously to check
accumulation ; and that the size reached is as yet not disad-
vantageous— or rather, indeed, that it is advantageous. But

GENESIS. l2'Sl

when the rate of growth is much decreased by the compara-
tively rapid increase of expenditure — when the excess of
assimilative power is diminishing in such a way as to indi-
cate its approaching disappearance ; it becomes needful for
the maintenance of the species, that this excess shall be
turned to the production of new individuals ; since, did
growth continue until this excess disappeared through the
complete balancing of assimilation and expenditura, the pro-
duction of new individuals would be either impossible or fatal
to the parent. And it is clear that " natural selection " will
continually tend to determine the period at which gamo-
genesis commences, in such a way as most favours the main-
tenance of the race.

Here, too, may fitly be pointed out the fact, that, by
"natural selection," there will in every case be produced, the
most advantageous proportion of males and females. If the
conditions of life are such as to render a greater or less in-
equality of the sexes beneficial to the species, in respect
either of the number of the offspring, or the character of the
offspring ; then, those varieties of the species which, from any
cause, approach more than other varieties towards thL
beneficial degree of inequality, will be apt to supplant other
varieties. And conversely, where equality in the number of
males and females is beneficial, the equilibrium will be main-
tained by the dying out of such varieties as produce offspring
among which the sexes are not balanced.

CHAPTER VIII.

HEREDITY.

{$ 80. Already, in the last two chapters, the law of heredi-
tary transmission has been tacitly assumed ; as, indeed, it
unavoidably is in all such discussions. Understood in its
entirety, the law is, that each plant or animal produces
others of like kind with itself: the likeness of kind consist-
ing, not so much in the repetition of individual traits, as in
the assumption of the same general structure. This truth has
been rendered so familiar by daily illustration, as almost to
have lost its significance. That wheat produces wheat — that
existing oxen have descended from ancestral oxen — that every
unfolding organism eventually takes the form of the class,
order, />enus, and species from which it sprang ; is a fact
which, by force of repetition, has acquired in our minds
almost the aspect of a necessity. It is in this, however,
that Heredity is principally displayed : the phenomena com-
monly referred to it, being quite subordinate manifestations.
And, as thus understood, Heredity is universal. The various
instances of heterogenesis lately contemplated, seem, indeed,
to be at variance with this assertion. But they are not
really so. Though the recurrence of like forms, is, in these in-
stances, not direct but cyclical, still, the like forms do recur ;
and when taken together, the group of forms produced during
one of the cycles, is as much like the groups produced in pre-
ceding cycles, as the single individual arising by homo-
genesis, is like ancestral individuals.

HEREDITY. 239

"While, however, the general truth that organisms of a
given type uniformly descend from organisms of the same
type, is so well established by infinite illustrations, as to have
assumed the character of an axiom ; it is not universally
admitted that non-typical peculiarities are inherited. While
the botanist would be so incredulous if told that a plant oi
one class had produced a plant of another class, or that from
seeds belonging to one order- individuals belonging to another
order had grown, that he would deem it needless to examine
the evidence ; and while the zoologist would treat with con-
tempt the assertion, that from the egg of a fish a reptile had
arisen, or that an implacental mammal had borne a pla-
cental mammal, or that an unguiculate quadruped had sprung
from an ungulate quadruped, or even that from individuals
of one species offspring of an allied species had proceeded ;
yet there are botanists and zoologists who do not consider it
certain, that the minor specialities of organization are trans-
mitted from one generation to another. Some naturalists
seem to entertain a vague belief, that the law of Heredity
applies only to main characters of structure, and not to de-
tails ; or, at any rate, that though it applies to such details
as i onstitute differences of species, it does not apply to
smaller details. The circumstance that the tendency to re-
petition, is in a slight degree qualified by the tendency to
variation (which, as we shall hereafter see, is but an indirect
result of the tendency to repetition), leads some to doubt,
whether Heredity is unlimited. A careful weighing of the
evidence, however, and a due allowance for the influences by
which the minuter manifestations of Heredity are obscured
will remove the grounds for this scepticism.

First in order of importance, comes the fact, that not only
are there' uniformly transmitted from an organism to its
offspring, those traits of structure which distinguish the class,
order, genus, and species ; but also those which distinguish
the variety. We have numerous cases, among both plants
and animals, where, b}- natural or artificial conditions, there

240 THE INDUCTIONS OF BIOLOGY.

have been produced divergent modifications of the same
species ; and abundant proof exists that the members of any
one sub-species, habitually transmit their distinctive pecu-
liarities to their descendants. Agriculturists and
gardeners can furnish unquestionable illustrations. Several
varieties of wheat are known ; of which each reproduces
itself. Since its introduction into England, there have been
formed from the potato, a number of sub-species: some of them
differing greatly in their forms, sizes, qualities, and periods
of ripening. Of peas, also, the like may be said. And the
case of the cabbage-tribe, is often cited as showing the per-
manent establishment of races that have diverged widely
from a common stock. Among fruits and flowers, the multi-
plication of kinds, and the continuance of each kind with
certainty by agamogenesis, and to some extent by gamo-
genesis, might be exemplified without end. From all
sides evidence may be gathered showing a like persistence of
varieties in each species of animal. We have our distinct
breeds of sheep, our distinct breeds of cattle, our distinct
breeds of horses : each breed maintaining its characteristics.
The several sorts of dogs, which, if we accept the physiolo
gical test, we must consider as all of one species, show us in
a marked manner the hereditary transmission of small differ-
ences— each sort, when kept pure, reproducing itself not
only in size, form, colour, and quality of hair, but also in
disposition and speciality of intelligence. Rabbits, too, have
their permanently-established races. And in the Isle of Man,
we have a tail-less kind of cat. Even* in the absence
of other evidence, that which ethnology furnishes would
suffice. Grant them to be derived from one stock, and the
varieties of man yield proof upon proof that non-specific
traits of structure are bequeathed from generation to gener-
ation. Or grant only that there is evidence of their deriva-
tion from several stocks, and we still have, between races de-
scended from a common stock, distinctions which prove the
inheritance of minor peculiarities. Besides seeing that

HEREDITY. 24:1

negroes continue to produce negroes, copper-coloured men to
produce men of a copper colour, and the fair-skinned races
to perpetuate their fair skins — besides seeing that the broad-
faced and flat-nosed Calmuck begets children with broad faces
and flat noses, while the Jew bequeaths to his offspring the
features which have so long characterized Jews ; we see that
those small unlikenesses which distinguish more nearly-allied
varieties of men, are maintained from generation to generation.
In Germany, the ordinary shape of skull is appreciably differ-
ent from that common in Britain : near akin though the
Germans are to the British. The average Italian face con-
tinues to be unlike the faces of northern nations. The French
character is now, as it was centuries ago, contrasted in sundry
respects with the characters of neighbouring peoples. Nay,
even between races so closely allied as the Scotch Celts, the
Welch Celts, and the Irish Celts, appreciable differences of
form and nature have become established.

That sub-species and sub-sub-species, thus exemplify that
same general law of inheritance which shows itself in the per-
petuation of ordinal, generic, and specific peculiarities ; is
strong reason for the belief that this general law is unlimited
in its application. In addition to the warrant which this be-
lief derives from evidence of this kind, it has also the support
of still more special evidence. Numerous illustrations of He-
redity are yielded by experiment, and by direct observation of
successive generations. They are divisible into two classes.
In the one class come cases where congenital peculiarities,
not traceable to any obvious causes, are bequeathed to de-
scendants. In the other class come cases where the peculiar-
ities thus bequeathed are not congenital, but have resulted
from changes of functions during the lives of the individuals
bequeathing them. "We will consider first the cases that
come in the first class.

§ 81. Note at the outset the character of the chief testi-
mony. Excluding those inductions that have been so fully

242 THE INDUCTIONS OF BIOLOGY.

verified as to rank with exact science, there are no inductions
so trustworthy as those which have undergone the mercantile
test. When we have thousands of men whose profit or loss
depends on the truth of the inferences they draw from simple
and perpetualty- repeated observations ; and when we find
that the inference arrived at, and handed down from genera-
tion to generation of these deeply-interested observers, has
become an unshakable conviction ; we may accept it without
hesitation. In breeders of animals we have such a class, led
by such experiences, and entertaining such a conviction — the
conviction that minor peculiarities of organization are in-
herited as well as major peculiarities. Hence the immense
prices given for successful racers, bulls of superior forms,
sheep that have certain desired peculiarities. Hence the
careful record of pedigrees of high-bred horses and sporting
dogs. Hence the care taken to avoid intermixture with in-
ferior stocks. Citing the highest authorities respecting the
effects of breeding from animals having certain superiorities,
with the view of propagating those superiorities, Mr Darwin
writes : — " Youatt, who was probably better acquainted with
the works of agriculturists than almost any other individual,
and who was himself a very good judge of an animal, speaks
of the principle of selection as ' that which enables the agri-
culturist not only to modify the character of his flock, but to
change it altogether. It is the magician's wand, by means of
which he may summon into life whatever form and mould he
pleases.' " Lord Somerville, speaking of what breeders have
done for sheep, says : — " It would seem that they had chalked
upon a wall a form perfect in itself and then given it exist-
en oe." That most skilful breeder, Sir John Sebright, used to
say, with respect to pigeons, that "he would produce any
given feather in three years, but it would take him six years
to obtain head and beak." In all which statements the
tacit assertion is, that individual traits are bequeathed
from generation to generation ; and that when they are
not brought into conflict with opposite traits, they may be

HEREDITY. 243

so perpetuated and increased as to become permanent dis-
tinctions.

Of special instances, there are many besides that of the oft
en -cited Otter-breed of sheep, descended from a single short
legged lamb, and that of the six-fingered Gratio Kelleia, who
transmitted his peculiarity in different degrees, to several of
his children and to some of his grandchildren. In a paper con.
tributed to the Edinburgh New Philosophical Journal for July
1863, Dr Struthers gives several cases of hereditary digital
variations. Esther P — , who had six fingers on one hand, be-
queathed this malformation, along some lines of her descend-
ants, fcr two, three, and four generations. A — S — inherited
an exha digit on each hand and each foot from his father;
and C — G — , who also had six fingers and six toes, had an aunt
and a grandmother similarly formed. A collection of evidence
has been made by Mr Sedgwick, and published by him in the
Medico- Chirurgical Review for April and for July 1863, in
two articles on " The Influence of Sex in limiting Hereditary
Transmission." From these articles are selected the following
cases and authorities : — Augustin Duforet, a pastry-cook of
Douai, who had but two instead of three phalanges to all his
fingers and toes, inherited this malformation from his grand-
father and father, and had it in common with an uncle and
numerous cousins. An account has been given by Dr Lepine,
of a man with only three fingers on each hand and four toes
on each foot, and whose grandfather and son exhibited the
like anomaly. Bechet describes Victoire Barre as a woman
who, like her father and sister, had but one developed finger
on each hand, and but two toes on each foot, and whose mon-
strosity re-appeared in two daughters. And there is a case
where the absence of two distal phalanges on the hands was
traced for two generations. The various recorded instances
in which there has been transmission from one generation to
another, of webbed-fingers, of webbed-toes, of hare-lip, of
congenital luxation of the thigh, of absent patella?, of
club-foot, &c, would occupy more space than can here bo

24:4: THE INDUCTIONS OF BIOLOGY.

spared. Defects in the organs of sense are also not

un frequently inherited. Four sisters, their mother, and
grandmother, are described by Duval as similarly affected by
cataract. Prosper Lucas details an example of hereditary am-
aurosis affecting the females of a family for three generations.
Duval, Graffe, Dufon, and others testify to like cases coming
under their observation.* Deafness, too, is occasionally trans-
mitted from parent to child. There are deaf-mutes whose
imperfections have been derived from ancestors; and mal-
formations of the external ears have also been perpetuated in
offspring. Of transmitted peculiarities of the skin

and its appendages, many illustrations have been noted. One
is that of a family remarkable for enormous black eyebrows ;
another that of a family in which every member had a lock of
hair of a lighter colour than the rest on the top of the head ;
and there are also instances of congenital baldness being
hereditary. Entire absence of teeth, absence of particular,
teeth, and anomalous arrangements of teeth, are recorded as
traits that have descended to children. And we have evidence
that soundness and unsoundness of teeth are transmissible.

The inheritance of such diseases as gout, consumption, and
insanity, is universally admitted. Among the less-common
diseases of which the descent from one generation to another
has been observed, are, ichthyosis, leprosy, pityriasis, sebace-
ous tumours, plica polonica, dipsomania, somnambulism, cata-
lepsy, epilepsy, asthma, apoplexy, elephantiasis. General
nervousness displayed by parents, almost always re-appears
in their children. Even a bias towards suicide appears to
be sometimes hereditary.

§ 82. To prove the transmission of those structural pecu-
liarities that have resulted from functional peculiarities, is,

* While this chapter is passing through the press, I learn from Mr. White
Cooper, that not only are near sight, long sight, dull sight, and squinting,
hereditary ; but that a peculiarity of vision confined to one eye, is frequently
transmitted — re-appearing in the same eye in offspring.

TIER EDITY.

245

for several reasons, comparatively difficult. Changes pro-
duced in the sizes of parts by changes in their amounts of
action, are mostly unobtrusive. A muscle that has increased
in bulk, is so obscured by natural or artificial clothing, that un-
less the alteration is extreme it passes without remark. Such
nervous developments as are possible in the course of a single
life, cannot be seen externally. Visceral modifications of a
normal kind, are observable but obscurely, or not at all. And
if the changes of structure worked in individuals by changes
in their habits, are thus difficult to trace ; still more difficult
to trace must be the transmission of them — further hidden,
as this is, by the influence of other individuals that are often
otherwise modified by other habits. Moreover, such special-
ities of structure as are due to specialities of function, are
usually entangled with specialities of structure that are, or
may be, due to selection, natural or artificial. In the majority
of cases, it is impossible to say that a structural peculiarity
which seems to have arisen in offspring from a functional
peculiarity in the parent, is wholly independent of some
congenital peculiarity of structure in the parent, which in-
duced this functional peculiarity. We are restricted to
cases with which natural or artificial selection can have had
nothing to do ; and such cases are difficult to find. Some,
however, may here be noted.

A species of plant that has been transferred from one soil
or climate to another, frequently undergoes what botanists
call " a change of habit " — a change which, without affecting
its specific characters, is yet conspicuous. In its new locality,
the species is distinguished by leaves that are much larger,
or much smaller, or differently shaped, or more fleshy ; or
instead of being, as before, comparatively smooth, it becomes
hairy; or its stem becomes woody instead of being herbaceous;
or its branches, no longer growing upwards, assume a droop-
ing character. Now these " changes of habit" are clearly de-
termined by functional changes. Occurring, as they do, in
many individuals that have undergone the same transportation,

246

THE INDUCTIONS OF BIOLOGY.

they cannot be classed as " spontaneous variations." They
are modifications of structure, consequent on modifications of
function, that have been produced by modifications in the
actions of external forces. And as these modifications re-ap-
pear in succeeding generations, we have, in them, examples
of functionally-established variations that are hereditarily
transmitted. Further evidence is supplied by what

are called " sports " in plants. These are of two kinds — the
gamogenetic and the agamogenetic. The gamogenetic may
be ascribed wholly to " spontaneous variations ;" or if they are
partly due to the inheritance of structural changes that are
produced by functional changes, this cannot be proved. But
where the individuals displaying the variations arise by
agamogenesi3, the reverse is the case : spontaneous variation
is out of the question ; and the only possible interpretation is
deviation of structure caused by deviation of function. A
new axis which buds out from a parent-axis, assumes an un-
like character — gives off lobed leaves in place of single leaves,
or has an otherwise different mode of growth. This change
of structure implies change in the developmental actions
which produced the new bud — change, that is, in the actions
going on in the parent shoot — functional change. And
since the modified structure thus impressed on the new shoot
by modified function, is transmitted by it to all the shoots
it bears ; we are obliged to regard the case as one of acquired
modification that has become hereditary.

Evidence of analogous changes in animals, is difficult to
disentangle. Only among domesticated animals, have we any
opportunity of tracing the effects of altered habits ; and here,
in nearly all cases, artificial selection has obscured the results.
Still, there are some facts which seem to the point. Mr
Darwin, while ascribing almost wholly to " natural selection "
the production of those modifications which eventuate in
differences of species, nevertheless admits the effects of use and
disuse. He says — " I find in the domestic duck that the bones
of the wing weigh less and the bones of the leg more, in pro-

HEREDITY. 247

portion to the whole skeleton, than do the same hones in the
wild duck ; and I presume that this change may be safely
attributed to the domestic duck flying much less, and walking
more, than its wild parent. The great and inherited develop-
ment of the udders in cows and goats in countries where they
are habitually milked, in comparison with the state of these
or grans in other countries, is another instance of the effect of
use. Not a single domestic animal can be named which has
not in some country drooping ears ; and the view suggested by
some authors, that the drooping is due to the disuse of the
muscles of the ear, from the animals not being much alarmed
by danger, seems probable." Again — " The eyes of moles and
of some burrowing rodents are rudimentary in size, and in
some cases are quite covered up by skin and fur. This state
of the eyes is probably due to gradual reduction from disuse,
but aided perhaps by natural selection." * * * " It is well
known that several animals, belonging to the most differ-
ent classes, which inhabit the caves of Styria and of Kentucky,
are blind. In some of the crabs the footstalk of the eye re-
mains, though the eye is gone ; the stand for the telescope is
there, though the telescope with its glasses has been lost. As
it is difficult to imagine that eyes, though useless, could be in
any way injurious to animals living in darkness, I attribute
their loss wholly to disuse." The direct inheritance of an ac-
quired peculiarity is sometimes observable. Mr Lewes gives
a case. He " had a puppy taken from its mother at six weeks
old, who, although never taught, 'to beg' (an accomplishment
his mother had been taught), spontaneously took to begging
for everything he wanted when about seven or eight months
old : he would beg for food, beg to be let out of the room,
nnd one day was found opposite a rabbit hutch begging for
rabbits." Instances are on record, too, of sporting dogs which
spontaneously adopted in the field, certain modes of behaviour
which their parents had learnt.

But the best examples of inherited modifications produced
by modifications of function, occur in the human race. To no

248 THE INDUCTIONS OF BIOLOGY.

other cause can be ascribed the rapid metamorphoses under-
gone by the British races when placed in new conditions. It
is notorious that, in the United States, the descendants of the
immigrant Irish lose their Celtic aspect, and become Ameri-
canized. This cannot be ascribed to intermarriage with
Americans ; since the feeling with which Irish are regard-
ed by Americans, prevents any considerable amount of inter-
marriage. Equally marked is the case of the immigrant
Germans, who, though they keep themselves very much
apart, rapidly assume the prevailing type. To say that
" spontaneous variation " increased by natural selection, can
have produced this effect, is going too far. Races so numer-
ous, cannot have been supplanted in the course of two or
three generations by varieties springing from them. Hence
there is no escape from the conclusion, that physical and so-
cial conditions have here wrought modifications of function
and structure, which offspring have inherited and increased.
Similarly with special cases. In the Cyclopaedia of Practical
Medicine, Yol. II. p. 419, Dr Brown states that he "has in
many instances observed in the case of individuals whose
complexion and general appearance has been modified by re-
sidence in hot climates, that children born to them subse-
quently to such residence, have resembled them rather in
their acquired than primaiy mien."

Some special modifications of organs caused by special
changes in their functions, may also be noted. That large
hands are inherited by men and women whose ancestors
led laborious lives ; and that men and women whose descent,
for many generations, has been from those unused to manual
labour, commonly have small hands ; are established opinions.
It seems very unlikely that in the absence of any such con-
nexion, the size of the hand should thus have come to be
generally regarded as some index of extraction. That there
exists a like relation between habitual use of the feet and large-
ness of the feet, we have strong evidence in the customs of the
Chinese. The torturing practice of artificially arresting the

HEREDITY. 249

growth of the feet, could never have become established among
the ladies of China, had they not found abundant proof
that a small foot was significant of superior rank — that is
of a luxurious life — that is of a life without bodily
labour. There is some evidence, too, that modifica«

tions of the eyes, caused by particular uses of the eyes, are
inherited. Short sight appears to be uncommon in rural
populations ; but it is frequent among classes of people who
use their eyes much for reading and writing ; and in these
classes, short sight is often congenital. Still more marked is
this relation in Germany. There, the educated classes are no-
toriously studious ; and judging from the numbers of young
Germans who wear spectacles, there is reason to think that
congenital myopia is very frequent among them.

Some of the best illustrations of functional heredity, are
furnished by the mental characteristics of human races. Cer-
tain powers which mankind have gained in the course of civil-
ization, cannot, I think, be accounted for, without admitting
the inheritance of acquired modifications. The musical faculty
is one of these. To say that " natural selection" has developed
it, by preserving the most musically endowed, seems an in-
adequate explanation. Even now that the development and
prevalence of the faculty have made music an occupation by
which the most musical can get sustenance and bring up
families ; it is very questionable whether, taking the musical
life as a whole, it has any advantage over others in the
struggle for existence and multiplication. Still more if we
look back to those eaidy stages through which the faculty must
have passed, before definite perception of melody was arrived
at, we fail to see how those possessing the rudimental faculty
in a somewhat greater degree than the rest, woftld thereby be
enabled the better to maintain themselves and their children.
If so, there is no explanation but that the habitual association
of certain cadences of human speech with certain emotions,
has slowly established in the race an organized and inherited
oonnexion between such cadences and such emotions ; that tho
17

250 THE INDUCTIONS OF BIOLOGY.

combination of such cadences, more or less idealized, which
constitutes melody, has all along had a meaning in the average
mind, only because of the meaning which cadences had acquired
in the average mind ; and that by the continual hearing and
practice of melody, there has been gained and transmitted an
increasing musical sensibility. Confirmation of this

view may be drawn from individual cases. Grant that among
a people endowed with musical faculty to a certain degree,
spontaneous variation will occasionally produce men possessing
it in a higher degree ; it cannot be granted that spontaneous
variation accounts for the frequent production, by such highly-
endowed men, of men still more highly endowed. On the
average, the offspring of marriage with others not similarly
endowed, will be less distinguished rather than more distin-
guished. The most that can be expected is, that this unusual
amount of faculty shall re-appear in the next generation undi-
minished. How then shall we explain cases like those of Bach,
Mozart, and Beethoven, who were all sons of men having un-
usual musical powers, but who greatly excelled their fathers
in their musical powers ? What shall we say to the facts,
that Haydn was the son of the organist, that Hummel was
born to a music master, and that Weber's father was a dis-
tinguished violinist? .The occurrence of so many cases in
one nation, within a short period of time, cannot rationally
be ascribed to the coincidence of " spontaneous variations." It
can be ascribed to nothing but inherited developments of
structure, caused by augmentations of function.

But the clearest proof that structural alterations caused by
alterations of function, are inherited, occurs when the alter-
ations are morbid. " Certain modes of living engender gout ; "
and gout is transmissible. It is well known that in persons pre-
viously healthy, consumption may be produced by unfavourable
conditions of life — by bad and insufficient food ; by foul, damp,
unventilated habitations ; and even by long-continued anxiety.
It is still more notorious that the consumptive diathesis is
conveyed from parent to child. Unless, then, a distinction

HEREDITY. 251

be assumed between constitutional consumption and con-
sumption induced by unwholesome conditions — unless it bo
asserted that consumption of unknown origin is transmiss-
ible, while functionally-produced consumption is not ; it
must be admitted that those changes of structure from which
the consumptive diathesis results, may be caused in parents
by changes of function, and may be inherited by their chil-
dren. Most striking of all, however, is the fact lately
brought to light, that functional disorders artificially estab-
lished, may be conveyed to offspring. Some few years since
M. Brown-Sequard, in the course of inquiries into the nature
and causes of epilepsy, hit on a method by which epilepsy
could be originated. Guinea-pigs were the creatures on
which, chiefly, he experimented ; and eventually, he disco-
vered the remarkable fact, that the young of these epileptic
guinea-pigs were epileptic : the functionally-established
epilepsy in the parents, became constitutional epilepsy in the
offspring. Here we have an instance which, standing even
alone, decides the question. We have a special form of nervous
action, not caused by any natural variation of structure that
had arisen spontaneously in the organism, but one caused
by a certain incidence of external forces. We have this
special form of nervous action becoming confirmed by re-
petition : the fits are more and more easily induced — there is
established the epileptic habit. That is to say, the connected
nervous actions constituting a fit, produce in the nervous
system such changes of structure, that subsequent connected
nervous actions of like kind, follow one another with increased
readiness. And that this epileptic habit is inherited, proves
conclusively that these structural modifications worked by
functional modifications, are impressed on the whole organism
in such way as to affect the reproductive centres, and cause
them to unfold into organisms that exhibit like modifications.
Evidence nearly allied to this, and scarcely less significant,
is furnished by that transmission of general nervousness, no-
ticed in the last section. Nervousness is especially common

252 THE INDUCTIONS OF BIOLOOT.

among classes of people who tax their brains much. Among
these classes, we daily see this constitutional modification
produced by excess of function, in men whose progenitors
wrere not nervous ; and the children of such men habitually
inherit more or less of the modification.

. § 83. Two modified manifestations of Heredity remain to be
noticed. The one is the re-ajjpearance in offspring, of traits
not borne by the parents, but borne by the grandparents or by
remoter ancestors. The other is the limitation of Heredity by
sex — the restriction of certain transmitted peculiarities to
offspring of the same sex as the parent possessing these
peculiarities.

Atavism, which is the name given to the recurrence of
ancestral traits, is proved by many and varied facts. In the
picture-galleries of old families, and on the monumental
brasses in the adjacent churches, are often seen types of
feature that are still, from time to time, repeated in members of
these families. It is matter of common remark that some con-
stitutional diseases, such as gout and insanity, after missing a
generation, will show themselves in the next. Dr Struthers,
in his above-quoted paper on " Variation in the Number of
Fingers and Toes, and of the Phalanges, in Man," gives cases
of malformations that were common to grandparent and
grandchild, but of which the parent had no trace. M. Girou
(as quoted by Mr Sedgwick) says — " One is often surprised
to see lambs black, or spotted with black, born of ewes and
rams with white wool, but if one takes the trouble to go
back to the origin of this phenomenon, it is found in the an-
cestors." Instances still more remarkable, in which the re-
moteness of the ancestors copied is very great, are given by
Mr Darwin. He points out that in crosses between varieties
of the pigoon, there will sometimes re-appear the plumage of
the original rock-pigeon, from which these varieties descend-
ed ; and he instances the faint zebra-like markings occasion
ally traceable in lorses, as having probably a like meaning

HEREDITY. 253

The limitation of Heredity by sex, cannot yet be regarded
as established. While in many cases it seems clearly mani-
fested ; it is in other cases manifested to a very small degree,
if at all. In Mr Sedgwick's essays, already named, will be
found evidence implying that there exists some such tendency
to limitation, which does or does not show itself distinctly,
according to the nature of the organic modification to be
conveyed. But more facts must be collected before any
positive conclusion can be reached.

§ 8-1. A positive explanation of Heredity is not to be expected
inthepresent state of Biology. We can look for nothing beyond
a simplification of the problem ; and a reduction of it to the
same category with certain other problems which also admit
of hypothetical solution only. If an hypothesis which certain
other wide-spread phenomena have already thrust upon us,
can be shown to render the phenomena of Heredity more in-
telligible than the}r at present seem, we shall have reason to
entertain it. The applicability of any method of interpreta-
tion to two different but allied classes of facts, is evidence of
its truth.

The power which organisms display of reproducing lost
parts, we saw to be inexplicable except on the assumption
that the units of which any organism is built have an innate
tendency to arrange themselves into the shape of that organ-
ism (§ 65). We inferred that these units must be the pos-
sessors of special polarities, resulting from their special struc-
tures ; and that by the mutual play of their polarities they are
compelled to take the form of the species to which they belong.
And the instance of the Begonia phyllomaniaca left us no
escape from the admission that the ability thus to arrange
themselves, is latent in the units contained in every undiffer-
entiated cell. Quite in harmony with this conclusion,
are certain implications since noticed, respecting the characters
of sperm-cells and germ-cells. We saw sundry reasons for
rejecting the supposition that these are highly-specialized cells

254 THE INDUCTIONS OF BIOLOGY.

and for accepting the opposite supposition, that they are cells
differing from others rather in being unspecialized. And here
the assumption to which we seem driven by the ensemble of
the evidence, is, that sperm-cells and germ-cells are essentially
nothing more than vehicles, in which are contained small
groups of the physiological units in a fit state for obeying their
proclivity towards the structural arrangement of the species
they belong to.

Thus the phenomena of Heredity are seen to assimilate
with other phenomena ; and the assumption which these
other phenomena thrust on us, appears to be equally
thrust on us by the phenomena of Heredity. We must con-
clude that the likeness of any organism to either parent, is
conveyed by the special tendencies of the physiological units
derived from that parent. In the fertilized germ we have
two groups of physiological units, slightly different in their
structures. These slightly-different units, severally multiply
at the expense of the nutriment supplied to the unfolding germ
— each kind moulding this nutriment into units of its own
type. Throughout the process of evolution, the two kinds of
units, mainly agreeing in their polarities and in the form
which they tend to build themselves into, but having m:\ior
differences, work in unison to produce an organism of the
species from which they were derived, but work in antago asm
to produce copies of their respective pa rent- organisms. And
hence ultimately results, an organism in which traits of the
one are mixed with traits of the other.

If the likeness of offspring to parents is thus determined, it
becomes manifest, a priori, that besides the transmission of
generic and specific peculiarities, there will be a transmis-
sion of those individual peculiarities which, arising without
assignable causes, are classed as " spontaneous." For if the
assumption of a special arrangement o^ parts by an organism,
is due to the pi'oclivity of its physiological units towards
that arrangement ; then the assumption of an arrangement
of parts slightly different from that of the species; unplios

HEREDITY. 255

physiological units slightly unlike those of the species ; and
these slightly- unlike physiological units, communicated
through the medium of sperm-cell or germ-cell, will tend, in
the offspring, to build themselves into a structure similarly
diverging from the average of the species.

It is not equally manifest, a priori, however, that on this hy-
pothesis, alterations of structure caused by alterations of func-
tion, must be transmitted to offspring. It is not obvious that
change in the form of a part, caused by changed action, in-
volves such change in the physiological units throughout the
organism, that these, when groups of them are thrown off in
the shape of reproductive centres, will unfold into organisms
that have this part similarly changed in form. Indeed, when
treating of Adaptation (§ 69), we saw that an organ modified
by increase or decrease of function, can but slowly so re-act
on the system at large, as to bring about those correlative
changes required to produce a new equilibrium ; and yet only
when such new equilibrium has been established, 'can we ex-
pect it to he fully expressed in the modified physiological units
of which the organism is built — only then can we count
on a complete transfer of the modification to descendants.
Nevertheless, that changes of structure caused by changes
of action, must also be transmitted, however obscurely, from
one generation to another, appears to be a deduction from
first principles — or if not a specific deduction, still, a general
implication. For if an organism A, has, by any peculiar
habit or condition of life, been modified into the form A, it
follows inevitably, that all the functions of A', reproductive
function included, must be in some degree different from the
functions of A. An organism being a combination of
rhythmically-acting parts in moving equilibrium, it is im-
possible to alter the action and structure of any one part,
without causing alterations of action and structure in all the
rest; just as no member of the Solar System could be modi-
fied in motion or mass, without producing re-arrangementa
throughout the whole Solar System. And if the organism A

256 THE INDUCTIONS OF BIOLOGY.

when changed to A', must be changed in all its functions :
then the offspring of A' cannot be the same as they would
have been had it retained the form A. It involves a denial
of the persistence of force to say that A may be changed
into A', and may yet beget offspring exactly like those it
would have begotten had it not been so changed. That the
change in the offspring must, other things equal, be in the
same direction as the change in the parent, we may dimly see
is implied by the fact, that the change propagated throughout
the parental system is a change towards a new state of
equilibrium — a change tending to bring the actions of all
organs, reproductive included, into harmony with these new
actions. Or, bringing the question to its ultimate and
simplest form, we may say that as, on the one hand, phy-
siological units will, because of their special polarities, build
themselves into an organism of a special structure ; so. on
the other hand, if the structure of this organism is modified
by modified function, it will impress some corresponding
modification on the structures and polarities of its units. The
units and the aggregate must act and re-act on each other.
The forces exercised by each unit on the aggregate and by
the aggregate on each unit, must ever tend towards a balance.
If nothing prevents, the units will mould the aggregate into
a form in equilibrium with their pre-existing polarities. If.
contrariwise, the aggregate is made by incident actions to
take a new form, its forces must tend to re-mould the units
into harmony with this new form. And to say that the
physiological units are in any degree so re- moulded as to bring
their polar forces towards equilibrium with the forces of the
modified aggregate, is to say that when separated in the
shape of reproductive centres, these units will tend to build
themselves up into an aggregate modified in the same di-
rection.

CHAPTER IX.
VARIATION.

§ 85 Equally conspicuous with the truth that every organ-
ism bears a general likeness to its parents, is the truth that
no organism is exactly like either parent. Though similar
to both in generic and specific traits, and usually, too, in those
traits which distinguish the variety, it diverges in numer-
ous traits of minor importance. No two plants are indistin-
guishable ; and no two animals are without differences.
Variation is co-extensive with Heredity.

The degrees of variation have a wide range. There are
deviations so small as to be not easily detected ; and there
are deviations great enough to be called monstrosities. In
plants, we may pass from cases of slight alteration in the
shape or texture of a leaf, to cases where, instead of a flower
with its calyx above the seed-vessel, there is produced a flower
with its calyx below the seed-vessel ; and while in one
animal, there arises a scarcely noticeable unlikeness in the
length or colour of the hair, in another, an organ is absent,
or a supernumerary organ appears. Though small variations
are by far the most general, yet variations of considerable
magnitude are not uncommon ; and even those variations
constituted by additions or suppressions of parts, are not so
rare as to be excluded from the list of causes by which
organic forms are changed. Cattle without horns are fre-
quent. Of sheep there are horned breeds and breeds that

268 THE INDUCTIONS OF BIOLOGY.

have lost their horns. At one time, there existed in Scot-
land a race of pigs with solid feet instead of cleft feet. In
pigeons, according to Mr Darwin, " the number of the cau-
dal and sacral vertebrae vary ; as does the number of the
ribs, together with their relative breadth and tha presence of
processes."

That variations both small and large which arise without
any specific assignable cause, tend to become hereditary, was
shown in the last chapter. Indeed the evidence which proves
Heredity in its smaller manifestations, is the same evidence
which proves Variation ; since it is only when there occur vari-
ations, that the inheritance of anything beyond the structural
peculiarities of the species, can be proved. It remains here,
however, to be observed, that the transmission of variations
is itself variable ; and that it varies both in the direction of
decrease and in the direction of increase. An individual trait
of one parent, may be so counteracted by the influence of the
other parent, that it may not appear in the offspring ; or not
being so counteracted, the offspring may possess it, perhaps
in an equal degree or perhaps in a less degree ; or the off-
spring may exhibit the trait in even a still higher degree.
Of the illustrations of this, one must suffice. I quote it from
the essay by Dr Struthers, referred to in the last chapter.

" The great-great-grandmother, Esther P (who mar-
ried A L ), had a sixth little finger on one hand. Of

their eighteen children (twelve daughters and six sons), oniy
one (Charles) is known to have had digital variety. We
have the history of .the descendants of three of the sons,
Andrew, Charles, and James.

" (1.) Andrew L had two sons, Thomas and Andrew ;

and Thomas had two sons all without digital variety. Here
we have three successive generations without the variety
possessed by the great- grandmother showing itself.

"(2.) James L , who was normal, had two sons and

seven daughters, also normal. One of the daughters became
Mrs J (one of the informants), and had three daughters

VARIATION. 259

and five sons, all normal except one of the sons, James J ,

now net. 17, who had six fingers on each hand. * * *

" In tliis branch of the descendants of Esther, we see it
passing over two generations and reappearing in one member
of the third generation, and now on both hands.

" (3.) Charles L , the only child of Esther who had

digital variety, had six fingers on each hand. He had three
eons, James, Thomas, and John, all of whom were born with
six fingers on each hand, while John has also a sixth toe on
one foot. He had also five other sons and four daughters,
all of whom were normal.

" (a.) Of the normal children of this, the third generation,
the five sons had twelve sons and twelve daughters, and the
four daughters have had four sons and four daughters, being
the fourth generation, all of whom were normal. A fifth
generation in this sub-group consists as yet of only two boys
and two girls, who are also normal.

" In this sub-branch, we see the variety of the first gener-
ation present in the second, passing over the third and
fourth, and also the fifth as far as it has yet gone.

" (b.) James had three sons and two daughters, who are
normal.

" (c.) Thomas had four sons and five daughters, who are
normal ; and has two grandsons, also normal.

" In this sub-branch of the descent, we see the variety of
the first generation, showing itself in the second and third,
and passing over the fourth, and (as far as it yet exists)
the fifth generation.

" (d.) John L — (one of the informants) had six fingers,
the additional finger being attached on the outer side, as in
the case of his brothors Jame3 and Thomas. All of them
had the additional digits removed. John has also a sixth
toe on one foot, situated on the outer side. The fiftn and
sixth toes have a common proximal phalanx, and a common
integument invests the middle and distal phalanges, each
having a separate nail.

<J60 THE INDUCTIONS OF BIOLOGY.

" John L has a son who is normal, and a daughter

Jane, who was born with six fingers on each hand and six toea
on each foot. The sixth fingers were removed. The sixth
toes are not wrapped with the fifth as in her father's case,
but are distinct from them. The son has a son and daughter,
who, like himself, are normal.

" In this, the most interesting sub-branch of the descent,
we see digital increase, which appeared in the first generation
on one limb, appearing in the second on two limbs, the
hands ; in the third on three limbs, the hands and one foot ;
in the fourth on all the four limbs. There is as yet no fifth
generation in uninterrupted transmission of the variety.
The variety does not yet occur in any number of the fifth
generation of Esther's descendants, which consists, as yet,
only of three boys and one girl, whose parents were normal,
and of two boys and two girls, whose grandparents were
normal. It is not known whether in the case of the great-
great-grandmother, Esther P , the variety was original

or inherited."*

§ 86. Where there i8 great uniformity among the mem-
bers of a species, the divergences of offspring from the
average type, are usually small ; but where, among the
members of a species, considerable unlikenesses have once
been established, unlikenesses among the offspring are fre-
quent and great. Wild plants growing in their natural
habitats, are uniform over large areas, and maintain from
generation to generation like structures ; but when cultiva-
tion has caused appreciable differences among the members
}f any species of plant, extensive and numerous deviations
are apt to arise. Similarly, between wild and domesticated

* This remarkable case appears to militate against the conclusion, drawn some
few pages back, that the increase of a peculiarity by coincidence of " spontaneous
variations " in successive generations, is very improbable ; and that the special
superiorities of musical composers cannot have thus arisen. The reply is, that
the extreme frequency of the occurrence among so narrow a class as that of
musical composers, forbids the interpretation „hus suggested.

VARIATION. 261

animals of the same species, we see the contrast, that though
the homogeneous wild race maintains its type with great per-
sistence, the comparatively heterogeneous domestic race fre-
quently produces individuals more unlike the average type
than the parents are.

Though unlikeness among progenitors is one antecedent
cf variation, it is by no means the sole antecedent. Were
it so, the young ones successively born to the same parents
would be alike. If any peculiarity in a new organism
were a direct resultant of the structural differences between the
two organisms which produced it ; then all subsequent new
organisms produced by these two, would show the same pecu-
liarity. But we know that the successive offspring have differ-
ent peculiarities : no two of them are ever exactly alike.

One cause of such structural variation in progeny, 18
functional variation in parents. Proof of this is given by
the fact that, among the progeny of the same parents, there is
more difference between those begotten under different con-
stitutional states, than between those begotten under the
same constitutional state. It is notorious that twins are
more nearly alike than children borne in succession. The
functional conditions of the parents being the same for twins,
but not the same for their brothers and sisters (all other ante-
cedents being constant) ; we have no choice but to admit that
variations in the functional conditions of the parents, are the
antecedents of those greater unlikenesses which their brothera
and sisters exhibit.

Some other antecedent remains, however. The parents
being the same, and their constitutional states the same, va-
riation, more or less marked, still manifests itself. Plants
grown from seeds out of one pod, and animals produced at
one birth, are not alike ; and sometimes differ considerably.
In a litter of pigs or of kittens, we rarely see uniformity of
markings ; and occasionally, there are important structural
contrasts. I have myself recently been shown a litter of
Newfoundland puppies, some of which had four digits to

262 THE INDUCTIONS OF BIOLOGY.

their feet, while in others, there was present on each hind- foot)
what is called the " dew-claw " — a rudimentary fifth digit.

Thus, induction points to three causes of variation, all in
action together. We have heterogeneity among progenitors,
which, did it act uniformly and alone in generating, by composi-
tion of forces, new deviations, would impress such new devia-
tions to the same extent on all offspring of the same parents ;
which it does not. We have functional variation in the pa-
rents, which, acting either alone or in combination with the pre-
ceding cause, would entail like variations on all young ones
simultaneously produced ; which it does not. And there is
consequently some third cause of variation, yet to be found,
which acts along with the structural and functional variations
of ancestors and parents.

§ 87 Already, in the last section, there has been implied
some. relation between variation and the action of external
conditions. The above-cited contrast, between the uniformity
of wild species and the multiformity of the same species
when cultivated or domesticated, thrusts this truth upon us.
.Respecting the variations of plants, Mr Darwin remarks
that " ' sports ' are extremely rare under nature, but far from
rare undei cultivation." Others who have studied the matter
assert, that if a species of plant which, up to a certain time,
has maintained great uniformity, once has its constitution
thoroughly disturbed, it will go on varying indefinitely.
Though, in consequence of the remoteness of the periods at
which they were domesticated, there is a lack of positive
proof that our extremely variable domestic animals have be-
come variable under the changed conditions implied by do-
mestication, having been previously constant ; yet competent
judges do not doubt that this has been the case.

Now the constitutional disturbance which precedes varia-
tion, can be nothing else than an overthrowing of the pre-
established equilibrium of functions. Transferring a plant
from forest lands to a ploughed field or a manured garden, ia

VARIATION. 203

altering the balance of forces to which it has been hitherto
subject ; by supplying it with different proportions of the
assimilable matters it requires, and taking away some of the
positive impediments to its growth which competing wild
plants before offered. An animal taken from woods or plains,
where it lived on wild food of its own procuring, and placed
under restraint, while artificially supplied with food not quite
like what it had before, is an animal subject to new outer ac-
tions, to which its inner actions must be re-adjusted. From
the general law of equilibration we found it to follow, that
" the maintenance of such a moving equilibrium " as an or-
ganism displays, " requires the habitual genesis of internal
forces corresponding in number, directions, and amounts, tc
the external incident forces — as many inner functions,
single or combined, as there are single or combined outer ac
tions to be met " (First Principles, % 133) ; and more recently
(§ 27), we have seen that Life itself is "the definite combin-
ation of heterogeneous changes, both simultaneous and suc-
cessive, in correspondence with external co-existences and
sequences." Necessarily, therefore, an organism exposed to a
permanent change in the arrangement of outer forces, must
undergo a permanent change in the arrangement of inner
forces. The old equilibrium must be destroyed ; and a new
equilibrium must be established. There must be func-
tional perturbations, ending in a re-adjusted balance of
functions.

If, then, change of conditions is the only known cause by
which the original homogeneity of a species is destroyed ;
and if change of conditions can affect an organism only by
altering its functions ; it follows that alteration of func-
tions is the only known internal cause to which the com-
mencement of variation can be ascribed. That such minoi
functional changes as parents undergo from year to year, are
influential on the offspring, we have seen to be proved by
the greater unlikeness that exists between children born to
the same parents at different times, than exists between

264 THE INDUCTIONS OF BIOLOGY.

twins. And here we seem forced to conclude, thai the larger
functional variations produced by greater external changes,
are the initiators of those structural variations which, when
once commenced in a species, lead by their combinations and
antagonisms to multiform results. Whether they are or
are not the direct initiators, they must still be the indirect
initiators.

§ 88. That they are not in all cases, or even in most cases,
the direct initiators, is clear. Were they so, those unlike-
nesses which exist between plants that grow from seeds out
of the same seed-vessel, or between animals belonging to the
same litter, would be inexplicable. Here, all the antecedents,
structural and functional, appear to be alike for each of the
new organisms. Any deviations caused by structural con-
trasts or functional disturbances in the parents, must be
equally shared in by all simultaneously-produced offspring.
Hence, an explanation of the variations arising under such
conditions, has still to be sought.

These are the variations termed " spontaneous." Not that
those who apply to them this word or some equivalent, mean
to imply that they are uncaused. Mr Darwin expressly
guards himself against such an interpretation. He says : —
" I have hitherto sometimes spoken as if the variations — so
common and multiform in organic beings under domestica-
tion, and in a lesser degree in those in a state of nature — had
been due to chance. This, of course, is a wholly incorrect
expression, but it serves to acknowledge plainly our ignorance
of the cause of each particular variation." Not only, how-
ever, do I hold, in common with Mr Darwin, that there must
be some cause for these apparently-spontaneous variations ;
but it seems to me that a definite cause is assignable. I
think it may be shown that unlikenesses must necessarily
arise between the new individuals simultaneously produced
by the same parents. Instead of the occurrence of such

VARIATION. 2Go

variations being inexplicable, we shall presently see that the
absence of them would be inexplicable.

In any series of dependent changes, a small initial difference
ofren works a marked difference in the results. The mode in
which a particular breaker bursts on the beach, may determine
whetherthe seed of some foreign plant which it bears, is oris not
stranded — may cause the presence or absence of this plant from
the Flora of the land; and may so affect, for millions of years, in
countless ways, the living creatures throughout the land. A
single touch, by introducing into the body some morbid mat-
ter, may set up an immensely-involved set of functional dis-
turbances and structural alterations. The whole tenor of a life
may be changed by a word of advice ; or a glance may
determine an action which alters thoughts, feelings, and
deeds throughout a long series of years. In those still more
involved combinations of changes which societies exhibit,
this truth is still more conspicuous. A hair's-breadth differ-
ence in the direction of some soldier's musket at the battle of
Areola, by killing Napoleon, might have changed events
throughout Europe : though the social organization in each
European country, would have been now very much what it
is, yet in countless details it would have been different.

Illustrations like these, with which pages might be filled,
prepare us for the conclusion, that organisms produced by
the same parents, at the 3ame time, must be more or less
differentiated both by insensible initial differences, and by
slight differences in the conditions to which they are subject
during their evolution. We need not, however, rest with
assuming such initial differences : the necessity of them i&
demonstrable. The individual germ-cells which, in succes-
sion or simultaneously, are separated from the same parent,
can never be exactly alike ; nor can the sperm-cells which
lertilize them. When treating of the instability of the
homogeneous (First Principles, § 109), we saw that no two
]iarts of any aggregate, can be similarly conditioned with

IS

266

THE INDUCTIONS OF BIOLOGY.

respect to incident forces ; and that being subject to forces
that are more or less unlike, they must become more or less
unlike. Hence, no two ova in an ovarum or ovules in a
seed-vessel— no two spermatozoa or pollen-cells, can be
identical. Whether or not there arise other contrasts, there
are certain to arise quantitative contrasts ; since the process
of nutrition cannot be absolutely alike for all. The repro-
ductive centres must begin to differentiate from the very
outset. Such being the necessities of the case, what

will happen on any successive or simultaneous fertilizations ?
There will inevitably result more or less unlikeness between
the combined parental influences in every instance. Quan-
titative differences among the sperm-cells and among the
germ-cells, will insure this. Grant that the number of
physiological units contained in any one reproductive cell, can
rarely if ever be exactly equal to the number contained
in any other, ripened at the same time or at a different time ;
and it follows that among the fertilized germs produced by
the same parents, the physiological units derived from each
parent will bear a different numerical ratio to each other in
every case. If now the parents are constitutionally alike,
that is, alike in the polarities of their physiological units,
the variation in the ratio between the physiological units
they severally bequeath to the fertilized germs, cannot cause
unlikenesses among the offspring. But if otherwise, no two
of the offspring can be alike. In every case, the small initial
difference in the proportions of the slightly-unlike units,
will lead, during evolution, to a continual multiplication of
differences : the insensible divergence at the outset, will gener-
ate sensible divergences at the conclusion. Possi-
bly some may hence infer, that though, in such case, the
offspring must differ somewhat from each other and from
both parents ; yet that in every one of them there must
result a homogeneous mixture of the traits of the two parents.
A little consideration shows that the reverse is inferable. If,
throughout the process of development, the physiological

VARIATION. 2G7

emits derived from each parent, preserved the same ratio to
each other in all parts of the growing organism, each organ
would show as much as every other, the influence of either
parent. But we know, a priori, that no such uniform dis-
tribution is possible. It has been shown (First Principles,
§ 123), that in any mixed aggregate of units, segregation
must inevitably go on. Incident forces will tend ever to
cause separation of the two orders of units from each other —
will integrate groups of the one order in one place, and
groups of the other order in another place. Hence there
must arise, not a homogeneous mean between the two
parents ; but a mixture of organs, some of which mainly
follow the one parent and some the other. And this is the
kind of mixture which observation shows us.

Still it may be fairly objected, that however the attributes
of the two parents are variously mixed in their several
offspring, they must in all the offspring fall between the
extremes displayed in the parents. In no characteristic
could one of the young exceed both parents, were there no
cause of " spontaneous variation " but the one alleged. Evi-
dently, then, there is a cause yet unfound.

§ 89. Thus far we have contemplated the process under
its simplest aspect. While we have assumed the two parents
to be somewhat unlike, we have assumed that each parent
has a homogeneous constitution — is built up of physiologi-
cal units that are exactly alike. But in no case can such a
homogeneity exist. Each parent had parents that were more
or less contrasted — each parent inherited at least two orders
of physiological units, not quite identical. Here then wc
have a further cause of variation. The sperm-cells or germ-
cells which any organism produces, will differ from each
other not quantitatively only, but qualitatively. Of the
slightly-unlike physiological units bequeathed to an organism,
its reproductive cells cannot habitually contain the same pro-
portions ; and we may expect the proportions to vary not

2G8

THE INDUCTIONS OF BIOLOGV.

slightly but greatly. Just as, during the evolution of an or*
ganism, the physiological units derived from the two parenta
tend to segregate, and produce likeness to the male parent in
this feature and to the female parent in that ; so, during the
formation of reproductive cells by such organism, there will
arise in one cell a predominance of the physiological units
derived from one parent, and in another cell a predominance
of the physiological units derived from the other parent. The
instability of the homogeneous forbids us to assume an even
distribution of the two orders of units in all the reproductive
cells. And inequalities once arising among them, must tend
ever to become more marked ; since, wherever units of a
given order have begun to segregate, the process of differenti-
ation and integration tends to segregate them more and more.
Thus, then, every fertilized germ, besides containing different
amounts of the two parental influences, will contain different
kinds of influences — this having received a marked impress
from one maternal or paternal ancestor, and that from an-
other.

Here, then, we have a clue to the multiplied variations, and
sometimes extreme variations, that arise in races which have
once begun to vary. Amid countless different combinations
of units derived from parents, and through them from ances-
tors, immediate and remote — amid the various conflicts in
*heir slightly-different polarities, opposing and conspiring
with each other in all ways and degrees ; there will from
time to time arise special proportions causing special devi-
ations. From the general law of probabilities it is inferable,
that while these involved influences, derived from many pro-
genitors, must, on the average of cases, obscure and partially
neutralize one another ; there must occasionally result such
combinations of them as will produce considerable divergences
from average structures ; and at rare intervals, such com-
binations as will produce very marked divergences. There is
thus a correspondence between the inferable results, and the
results as habitually witnessed.

VARIATION. 2G9

§ 90. Still there remains a difficulty. It may be said that
admitting functional change to be the initiator of variation
— granting that the physiological units of an organism,
modified by long subjection to new conditions, will tend to be-
come modified in such wav as to cause change of structure in
offspring ; .yet there will still be no cause of ihe supposed
heterogeneity among the physiological units of different in-
dividuals. There seems validity in the objection, that as all
the members of a species whose circumstances have been al-
tered, will be affected in the same manner, the results, when
they begin to show themselves in descendants, will show them-
selves in the same manner : not multiform variations will
arise, but deviations all in one,direction.

The reply is simple. The members of a species thus cir-
cumstanced, will not be similarly affected. In the absence of
absolute uniformity among them, the functional changes
caused in them will be more or less dissimilar. Just as men
of slightly- unlike dispositions behave in quite opposite ways
under the same circumstances ; or just as men of slightly-
unlike constitutions get diverse disorders from the same
cause, and are diversely acted on by the same medicine ; so,
the insensibly-differentiated members of a species whose con-
ditions have been changed, may at once begin to undergo
various kinds of functional changes. As we have already
seen, small initial contrasts may lead to large terminal con-
trasts. The intenser cold of the climate into which a species
has migrated, may cause in one individual increased con-
sumption of food, to balance the greater loss of heat ; while
in another individual, the new requirement 7 nay be met by a
thicker growth of fur. Or, when meeting with the new foods
which the new region furnishes, mere accident may deter-
mine one member of the species to begin with one kind and
another member with another kind ; and hence may arise
established habits in these respective members and their
descendants. Now when the functional divergences thus set
up in sundry families of a species, have lasted long enough

270 THE INDUCTIONS OF BIOLOOV.

to affect their constitutions profoundly, and to modify sorno
what the physiological units thrown off in their reproductive
cells, the divergences produced by these in offspring, will be
of diverse kinds. And the original homogeneity of constitu-
tion having been thus destroyed, variation may go on with
increasing facility. There will result a heterogeneous mix-
ture of modifications of structure, caused by modifications of
function ; and of still more numerous correlated modifica-
tions, indirectly so caused. By natural selection of the most
divergent forms, the unlikenesses of parents will grow more
marked, and the limits of variation wider. Until at length
the divergences of constitutions and modes of life, become
great enough to lead to segregation of the varieties.

§ 91. That variations must occur, and that they must ever
tend, both directly and indirectly, towards adaptive modifica-
tions, are conclusions deducible from first principles; apart
from any detailed interpretations like the above. That the
state of homogeneity is an unstable state, we have found to
be a universal truth. Each species must pass from the uni-
form into the more or less multiform, unless the incidence of
external forces is exactly the same for all its members ; which
it never can be. Through the process of differentiation and
integration, which of necessity brings together, or keeps to-
gether, like individuals, and separates unlike ones from them,
there must nevertheless be maintained a tolerably uniform
species ; so long as there continues a tolerably uniform, set of
conditions in which it may exist. But if the conditions
change, either absolutely by some disturbance of the habitat,
or relatively by spread of the species into other habitats, then
the divergent individuals that result, must be segregated
by the divergent sets of conditions into distinct varieties
(First Principles, § 126). When, instead of contemplating
a species in the aggregate, we confine our attention to a
single member and its descendants, we see it to be a corollary
from the general law of equilibration, that the moving equili-

VARIATION. 271

brium constituted by the vital actions in each member of
this family, must remain constant so long as the external ac-
tions to which they correspond remain constant ; and that if
the external actions are changed, the disturbed balance of
internal changes, if not overthrown, cannot cease undergoing
modification until the internal changes are again in equili-
brium with the external actions : corresponding structural
alterations having arisen.

Or passing from these derivative laws to the ultimate law,
we see that Variation is necessitated by the persistence of force.
The members of a species inhabiting any area, cannot be subject
to like aggregates of forces over the whole of that area. And
if, in different parts of the area, different kinds or amounts or
combinations of forces act on them, they cannot but become
different in themselves and in their progeny. To say otherwise,
is to say that differences in the forces will not produce differ-
ences in the effects ; which is to deny the persistence of force.

Whence it is also manifest, that there can be no variation
of structure, but what is directly or indirectly consequent on
variation of function. On the one hand, organisms in com-
plete equilibrium with their conditions, cannot be changed
except by change in their conditions ; since, to assert other-
wise, is to assert that there can be an effect without a cause ;
which is to deny the persistence of force. On the other hand,
any change of conditions can affect an organism only by
changing the actions going on in it — only by altering its func-
tions. The alterations of functions being necessarily towards
a re- establishment of the equilibrium, (for if not, the equili-
brium must be destroyed and the life cease, either in the in-
dividual or in descendants,) it follows that the structural alter-
ations directly caused, are adaptations ; and that the correlated
structural alterations indirectly caused, are the concomitants of
adaptations. Hence, though, by the intercourse of organisms
that have been functionally, and structurally modified in dif-
ferent directions, there may result organisms that deviate in
compound ways which appear unrelated to external condi-

272 THE INDUCTIONS OF BIOLOGY.

tions, the deviations of such organisms must still be regarded
as indirect results of functional adaptations. We must say
that in all cases, adaptive change of function is the primary
and ever-acting cause of that change of structure which con-
stitutes variation ; and that the variation which appears to
be " spontaneous," is derivative and secondary.

CHAPTER X.

GEXESJS, HEREDITY, AND VARIATION.

$ 92. A question raised, and hypothetically answered, in
§§ 78 and 79, was there postponed until we had dealt with the
topics of Heredity and Variation. Let us now resume the
consideration of this question, in connexion with sundry
others which the facts suggest.

After contemplating the several methods by which the
multiplication of organisms is carried on — after ranging
ihem under the two heads of Homogenesis, in which the suc-
cessive generations are similarly produced, and Heterogenesis,
in which they are dissimilarly produced — after observing
that Homogenesis is always sexual genesis, while Heteroge-
nesis is asexual genesis with occasionally-recurring sexual
genesis ; we came to the questions — why is it that some or-
ganisms multiply in the one way, and some in the other ?
and why is it that where agamogenesis prevails, it is usually,
from time to time, interrupted by gamogenesis ? In seeking
an answer to this question, we inquired whether there are,
common to both Homogenesis and Heterogenesis, any condi-
tions under which alone sperm-cells and germ-cells arise and
are united, for the production of new organisms ; and we
reached the conclusion that, in all cases, they arise only
when there is an approach to equilibrium between the forces
which produce growth and the forces which oppose growth.
This answer to the question — when does gamogenesis recur i'

274 THE INDUCTIONS OF BIOLOGY.

still left unanswered tlie question — xdiy does gamogenetfia
recur ? And to this the reply suggested was, that the ap-
proach towards general equilibrium in organisms, "is ac-
companied by an approach towards molecular equilibrium in
them ; and that the need for this union of spe7'm-cell and
germ-cell, is the need for overthrowing this equilibrium, and
re-establishing active molecular change in the detached germ
— a result which is probably effected by mixing the slightly-
different physiological units of slightly-different individuals."
This is the hypothesis which we have now to consider. Let
us first look at the evidences which certain inorganic pheno-
mena furnish.

The molecules of any aggregate which have not a balanced
arrangement, inevitably tend towards a balanced arrangement.
As before mentioned (First Principles, § 103) amorphous
wrought iron, when subject to continuous jar, begins to arrange
itself into crystals — its atoms assume a condition of polai
equilibrium. The particles of unannealed glass, which are so
unstably arranged that slight disturbing forces make them
separate into small groups, take advantage of that greater
freedom of movement given by a raised temperature, to ad-
just themselves into a state of relative rest. During any
such re-arrangement, the aggregate exercises a coercive force
over its units. Just as in a growing crystal, the atoms suc-
cessively assimilated from the solution, are made by the al-
ready-ciystallized atoms to take a certain form, and even to
re-complete that form when it is broken ; so in any mass of
unstably-arranged atoms that passes into a stable arrangement,
each atom conforms to the forces exercised on it by all the
other atoms. This is a corollary from the general law of
equilibration. We saw (First Principles, % 130) that every
change is towards equilibrium ; and that change can never
cease until equilibrium is reached. Organisms, above

ill other aggregates, conspicuously display this progressive
equilibration ; because their units are of such kinds, and so
conditioned, as to admit of easy re-arrangement. Those

GENESIS, HEREDITY, AND VARIATION. 275

extremely active changes which go on during the early
btages of evolution, imply an immense excess of the mole-
cular forces over those antagonist forces which the aggregate
exercises on the molecules. While this excess continues, it
is expended in growth, development, and function — expendi-
ture for any of these purposes, being proof that part of the
force embodied in molecular tensions, remaias unbalanced.
Eventually, however, this excess diminishes. Either, as in
organisms which do not expend much force, decrease of assi-
milation leads to its decline ; or, as in organisms which ex-
pend much force, it is counterbalanced by the rapidly-increas-
ing re-actions of the aggregate (§ 46). The cessation of
growth, when followed, as in some organisms, by death, im-
plies the arrival at an equilibrium between the molecular
forces, and those forces which the aggregate opposes to them.
When, as in other organisms, growth ends in the establish-
ment of a moving equilibrium, there is implied such a de-
creased preponderance of the molecular forces, as leaves no
surplus beyond that which is used up in functions. The de-
clining functional activity, characteristic of advancing life,
expresses a further decline in this surplus. And when all
vital movements come to an end, the implication is, that
the actions of the units on the aggregate and the re-
actions of the aggregate on the units, are completely bal-
anced. Hence, while a state of rapid growth indi-
cates such a play of forces among the units of an aggregate,
as will produce active re-distribution ; tha diminution and
arrest of growth, shows that the units have fallen into such
relative positions that re-distribution is no longer so facile.
When, therefore, we see that gamogenesis recurs only when
growth is decreasing, or has come to an end, we must say
that it recurs only when the organic units are approxima-
ting to equilibrium — only when their mutual restraints pre-
vent them from readily changing their arrangements in obe-
dience to incident forces.

That units of like forms can be built up into a more stabU'

276 THE INDUCTIONS OF BIOLOGY.

aggregate than units of slightly unlike forms, is tolerably
manifest, a, priori. And we have facts which prove that mixing
allied but somewhat different units, docs lead to comparative in-
stability. Most metallic alloys exemplify this truth. Com-
mon solder, which is a mixture of lead and tin, melts at a much
lower temperature than either lead or tin. The compound of
lead, tin, and bismuth, called " fusible metal," becomes fluid
at the temperature of boiling water ; while the temperatures
at which lead, tin, and bismuth become fluid, are, respectively,
G12°, 442°, and 497°, F. Still more remarkable is the illustra-
tion furnished by potassium and sodium. These metals are
very near akin in all respects — in their specific gravities, their
atomic weights, their chemical affinities, and the properties
of their compounds. That is to say, all the evidences unite to
shosv that their units, though not identical, have a close resem-
blance. What now happens when the}' are mixed ? Potassium
alone melts at 136°, sodium alone melts at 190°, but the alloy of
potassium and sodium, is liquid at the ordinary temperature of
the air. Observe the meaning of these facts, expressed in
general terms. The maintenance of a solid form by any group
of units, implies among them an arrangement so stable, that
it cannot be overthrown by the incident forces. Whereas the
assumption of a liquid form, implies that the incident forces
suffice to destroy the arrangement of the units. In the one
case, the thermal undulations fail to dislocate the parts ; while
in the other case, the parts are so dislocated by the thermal
undulations, that they fall into total disorder — a disorder
admitting of easy re-arrangement into any other order. For
the liquid state is a state in which the units become so far free
from mutual restraints, that incident forces can change their
relative positions very readily. Thus we have reason to
conclude, that an aggregate of units which, though in the
main similar to each other, have minor differences, must be
more unstable than an aggregate of homogeneous units : the
one will yield to disturbing forces which the other successfully
resists.

GENESIS, HEREDITY, AND VARIATION. 277

Now though the colloidal atoms of which organisms are
mainly built, are themselves highly composite ; and though
the ph}-siological units compounded out of these colloidal
atoms, must have structures far more involved ; yet it must
happen with such units, as with simple units, that those
which have exactl}r like forms, will admit of arrangement into
a more stable aggregate than those which have slightly-
unlike forms. Among units of this order, as among units
of a simpler order, imperfect similarity must entail imperfect
polar balance, and consequent diminished ability to withstand
disturbing forces. Hence, given two organisms which, by
diminished nutrition or increased expenditure, are being ar-
rested in their growths — given in each an approaching
equilibrium between the forces of the units and the forces of
the aggregate — given, that is, such a comparatively-balanced
state among the units, that re- arrangement of them by inci-
dent forces is no longer so easy ; and it will follow that by
imiting a group of units from the one organism with a group
of slightly-different units from the other, the tendency to-
wards equilibrium will be diminished, and the mixed units
will be rendered more modifiable in their arrangements by
the forces acting on them : they will be so far freed as to be-
come again capable of that re-distribution which constitutes
evolution. This view of the matter is in harmony

with the results of observation on the initial stages of develop-
ment. Some pages back, it was asserted that sperm-cell and
germ-cell severally arrive, before their union, at a condition
of equilibrium. Though approximately true, this is not liter-
ally true. I learn from Dr "W. II. Ransom, who has investi-
gated the question with great care, that the unfertilized ovum
continues, for a time, to undergo changes similar to those which
the fertilized ovum undergoes; butthat these changes, becoming
languid and incomplete, are finally arrested by decomposition.
Here we find what might be expected. In the first place, an
organism which develops germ-cells, is not in a state of mole-
cular equilibrium, but in a state of approach to such cquili-

278 THE INDUCTIONS OF BIOLOGY.

brmm. Hence, a group of physiological units cast off from it,
will not be wholly without a tendency to undergo the struc-
tural re-arrangements which we call development ; but will
have this tendency unduly restrained by partially-balanced
polarities. In the second place, undue restraint of the phy-
siological units, while it renders them as wholes less-easil)r
altered in their relative positions by incident forces, thereby
also renders them more liable to be individually decomposed
by incident forces : the same thermal undulations which, if
the physiological units are comparatively free, will aid their
re-arrangement by giving them still greater freedom, will, if
they are comparatively fixed, begin to change the arrange-
ments of their components — will decompose them. In the
third place, their decomposition will be prevented as well as
their re-distribution facilitated, by such disturbance of their
polarities as we have seen must result from mixing with them
the slightly-unlike units of another organism.

And now let us test this hypothesis, by seeing what power
it gives us of interpreting established inductions.

§ 93. The majority of plants being hermaphrodites, it has,
until quite recently, been supposed that the ovules of each
flower are fertilized by pollen from the anthers of the same
flower. Mr Darwin, however, has shown that the arrange-
ments are generally such as to prevent this : either the ovules
and the pollen are not ripe simultaneously, or obstacles pre-
vent access of the one to the other. At the same time, he has
shown that there exist arrangements, often of a remarkable
kind, which facilitate the transfer of pollen by insects from the
stamens of one flower to the pistil of another. Simi-

larly, it has been found that among the lower animals, herraa-
phrodism does not usually involve the production of fertile
germs, by the union of sperm-cells and germ-cells developed
in the same individual ; but that the reproductive centres of
one individual are united with those of another, to produce
fertile germs. Either, as in the Pyrosoma, the Perophora, and

GENESIS, HEREDITY, AND VARIATION. 279

in mnnv higher molluscs, the ova an J spermatozoa are ma-
fared at different times ; or, as in annelids, they are prevented
by their relative positions from coining in contact.

Remembering the fact that among the higher classes of
organisms, fertilization is always effected by combining the
sperm-cell of one individual with the germ-cell of another ;
and joining with it the fact that among hermaphrodite organ-
isms, the germ-cells developed in any individual, are usually
not fertilized by sperm-cells developed in the same individual ;
we see reason for thinking that the essential thing in fertiliz-
ation, is the union of specially-fitted portions of different or-
ganisms. If fertilization depended on the peculiar pi'operties
of sperm-cell and germ-cell, as such ; then, in hermaphrodite
organisms, it would be a matter of indifference whether the
united sperm-cells and germ-cells were those of the same in-
dividual, or those of different individuals. But the circum-
stance that there exist in such organisms, elaborate ap-
pliances for mutual fertilization, shows that unlikeness of
derivation in the united reproductive centres, is the deside-
ratum. Now this is just what the foregoing hj'pothesis
implies. If, as was concluded, fertilization has for its object
the disturbance of that approximate equilibrium existing
among the physiological units separated from an adult organ-
ism ; and if, as we saw reason to think, this object is effected
by mixture with the slightly-different physiological units of
another organism ; then, we at the same time see reason to
think, that this object will not be effected by mixture with
physiological units belonging to the same organism. Thus,
the hypothesis leads us to expect such provisions as we find
?xist.

§ 94. But here a difficulty presents itself. These proposi-
tions seem to involve the conclusion, that self-fertilization is
impossible. It apparently follows from them, that a group of
physiological units from one part of an organism, ought to
have no power of altering the state of approaching balance in

280 THE INDUCTIONS OF BIOLOGY.

a group from another part of it. Yet self-fertilization does
occur. Though the ovules of one plant, are generally fer-
tilized by pollen from another plant of the same kind ; yet
they may be, some of them, fertilized by the pollen of the same
plant. And though, among hermaphrodite animals, self-fer-
tilization is usually negatived by structural or functional ar-
rangements ; yet in certain Entozoa, there appear to be special
provisions by which the sperm-cells and germ-cells of the same
individual may be united, when not previously united with
those of another individual. Certainly, at first sight, these
facts do not consist with the above supposition. Neverthe-
less, there is a satisfactory solution of them.

In the last chapter, when considering the variations that
may result in offspring from the combination of unlike
parental constitutions, it was pointed out that in an unfolding
organism, composed of slightly-different physiological units
derived from slightly-different parents, there cannot be main-
tained an even distribution of the two orders of units. We
saw that the instability of the homogeneous, negatives the
uniform blending of them ; and that, by the process of differ-
entiation and integration, they must be more or less separated ;
so that in one part of the body the influence of one pai'ent will
predominate, and in another part of the body the influence of
the other parent : an inference which harmonizes with daily
observation. And we also saw, that the sperm-cells or germ-
. cells produced by such an organism, must, in virtue of these
same laws, be more or less unlike one another. It was shown
that through segregation, some 01 t,ne sperm-cells or germ-
cells will get an excess of the physiological units derived
from one side, and some of them an excess of those derived
from the other side : a cause which accounts for the unlikenesses
among offspring simultaneously produced. Now from this
segregation of the different orders of physiological units, in-
herited from different parents and lines of ancestry, there
arises the possibility of self-fertilization in hermaphrodite
organisms. If the physiological units contained in the sperm-

GENESIS, HEREDITY, AND VARIATION. 281

colls and germ-cells of the same flower, are not quite homo-
geneous— if in some of the ovules the physiological units
derived from the one parent greatly predominate, and in some
of the ovules those derived from the other parent ; and if the
like is true of the pollen-cells ; then, some of the ovules may
be nearly as much contrasted with some of the pollen-cells, in
Ihe characters of their contained units, as were the ovules and
pollen-cells of the parents from which the plant proceeded.
Jietween part of the sperm-cells and part of the germ-cells, the
community of nature will be such that fertilization will not
result from their union ; but between some of them, the
differences of constitution will be such that their union
will produce the requisite molecular instability. The facts,
so far as they are known, seem in harmony with this deduction.
Self-fertilization in flowers, when it takes place, is not so
efficient as mutual fertilization. Though some of the ovules
produce seeds, yet more of them than usual are abortive.
From which, indeed, results the establishment of varieties that
have structures favourable to mutual fertilization; since, being
more prolific, these have, other things equal, greater chances
in the " struggle for existence."

Further evidence is at hand in support of this interpreta-
tion. There is reason to believe that self-fertilization, which
at the best is comparatively inefficient, loses all efficiency in
course of time. After giving an account of the provisions for
an occasional, or a frequent, or a constant crossing between
flowers ; and after quoting Prof. Huxley to the effect that
among hermaphrodite animals, there is no case in which " tbo
occasional influence of a distinct individual can be shown to
be physically impossible ; " Mr Darwin writes — " from these
several considerations and from the many special facts which
I have collected, but which I am not here able to give, I am
strongly inclined to suspect that, both in the vegetable and
animal kingdoms, an occasional intercross with a distinct in-
dividual is a law of nature. * * * in none, as I suspect,
can self-fertilization go on for perpetuity." This conclusion,
19

282 THE INDUCTIONS OF BIOLOGY.

based wholly on observed facts, is just the conclusion to -which
the foregoing argument points. That necessary action and
the re-action between the parts of an organism and the
organism as a whole — that power of the aggregate to re-mould
tiie units, which is the correlative of the power of the units to
build up into such an aggregate ; implies that any differences
existing between the units inherited by an organism, must
gradually diminish. Being subject in common to the total
lorces of the organism, they will in common be modified to-
wards congruity with these forces; and therefore towards
likeness with each other. If, then, in a self- fertilizing organism
and its self-fertilizing descendants, such contrasts as origin-
ally existed among the physiological units, are progressive-
ly obliterated — if, consequently, there can no longer be a
segregation of different physiological units in different sperm-
cells and germ-cells ; self-fertilization will become impossible :
step by step the feitility will diminish, and the series will
finally die out.

And now observe, in confirmation of this view, that self-
fertilization is limited to organisms in which an approximate
equilibrium among the organic forces, is not long maintained.
While growth is actively going on, and the physiological units
are subject to a continually-changing distribution of forces,
no decided assimilation of the units can be expected : like
forces acting on the unlike units, will tend to segregate them,
so long as continuance of evolution permits further segrega-
tion ; and only when further segregation cannot go on, will
the like forces tend to assimilate the units. Hence, where
there is no prolonged maintenance of an approximate organic
balance, self-fertilization may be possible for some gener-
ations ; but it will be impossible in organisms distinguished
by a sustained moving equilibrium.

§ 95. The interpretation which it affords of sundry pheno-
mena familiar to breeders of animais, adds probability to the
hypothesis. Mr Darwin has collected a large " body of facte,

GENESIS, HEREDITY, AXP VARIATION. 283

showing, in accordance with the almost universal belief ol
breeders, that with animals and plants a cross between different
varieties, or between individuals of the same variety but ot
another strain, gives vigour and fertility to the offspring ; and
on the other hand, that close interbreeding diminishes vigour
and fertility," — a conclusion harmonizing with the current
belief respecting family-intermarriages in the human race.
Have we not here a solution of these facts ? Relations must, on
the average of cases, be individuals whose physiological units
are more nearly alike than usual. Animals of different
varieties must be those whose physiological units are more
unlike than usual. In the one case, the unlikeness of the
units may frequently be insufficient to produce fertilization ;
or, if sufficient to produce fertilization, not sufficient to produce
that active molecular change required for vigorous develop-
ment. In the other case, both fertilization and vigorous
development will be made probable.

Nor are we without a cause for theirregular manifestation ot
these general tendencies. The mixed physiological units com-
posing any organism, being, as we have seen, more or less se-
gregated in the reproductive centres it throws off; there may
arise various results, according to the degrees of difference
among the units, and the degrees in which the units are segre-
gated. Of two cousins who have married, the common grand-
parents may have had either similar or dissimilar constitu-
tions; and if their constitutions were dissimilar, the probability
that their married grandchildren will have offspring will be
greater than if their constitutions were similar. Or the
brothers and sisters from whom these cousins descended, in-
stead of severally inheriting the constitutions of their parents
in tolerably equal degrees, may have severally inherited them
in very different degrees : in which last case, intermarriages
among the grandchildren will be less likely to prova infertile.
Or the brothers and sisters from whom these cousins de-
scended, may severally have married persons very like, or
very unlike, themselves ; and from this cause there may

284 THE INDUCTIONS OF BIOLOGY.

have resulted, either an undue likeness, or a due unlike-
ness, between the married cousins. These several causes,
conspiring and conflicting in endless ways and degrees, will
work multiform effects. Moreover, differences of segrega-
tion will make the reproductive centres produced by the
same nearly-related organisms, vary considerably in their
amounts of unlikeness ; and therefore, supposing their amounts
of unlikeness great enough to cause fertilization, this fertiliza-
tion will be effective in various degrees. Hence it may happen
that among offspring of nearly-related parents, there may be
some in which the want of vigour is not marked, and others in
which there is decided want of vigour. So that we are alike
shown why in-and-in breeding tends to diminish both fertility
and vigour ; and why the effect cannot be a uniform effect, but
only an average effect.

§ 96. While, if the foregoing arguments are valid, gamo-
genesis has for its main end, the initiation of a new develop-
ment by the overthrowof that approximate equilibrium arrived
at among the molecules of the parent-organisms ; a further end
appears to be subserved by it. Those inferior organisms
which habitually multiply by agamogenesis, have conditions
of life that are simple and uniform ; while those organisms
that have highly-complex and variable conditions of life,
habitually multiply by gamogenesis. Now if a species has
complex and variable conditions of life, its members must be
severally exposed to sets of conditions that are slightly
different : the aggregates of incident forces cannot be alike
for all the scattered individuals. Hence, as functional
deviation must ever be inducing structural deviation, each
individual throughout the area occupied, tends to become
fitted for the particular habits which its particular conditions
necessitate ; and in so far, emfitted for the average habits
proper to the species. But these undue specializations are
continually checked by gamogenesis. As Mr Darwin remarks
— " intercrossing plays a very important part in nature in

GENESIS, HEREDITY, AND VARIATION. 285

keeping the individuals of the same species, or of the variety,
true and uniform in character :" the idiosyncratic divergence
obliterate each other. Gamogenesis, then, is a means of
turning to positive advantage, the individual differentiations
which, in its absence, would result in positive disadvantage.
Were it not that individuals are ever being made unlike each
other by their unlike conditions, there would not arise among
them those contrasts of molecular constitution, which we have
seen to be needful for producing the fertilized germs of new
individuals. And were not these individual differentiations
ever being mutually cancelled, they would end in a fatal
narrowness of adaptation.

This truth will be most clearly seen if we reduce it to its
purely abstract form, thus : — Suppose a quite homogeneous
species, placed in quite homogeneous conditions ; and suppose
the constitutions of all its members in complete concord with
their absolutely-uniform and constant conditions; what must
happen ? The species, individually and collectively, is in a
state of perfect moving equilibrium. All disturbing forces
have been eliminated. There remains no force which can, in
any way, change the state of this moving equilibrium ; either
in the species as a whole or in its members. But we have
seen (First Principles, § 133) that a moving equilibrium is but.
a transition towards complete equilibration, or death. The
absence of differential or un-equilibrated. forces among the
members of a species, is the absence of all forces that can
cause changes in the conditions of its members — is the ab-
sence of all forces which can initiate new organisms. To sav,
as above, that complete molecular homogeneity existing
among the members of a species, must render impossible that
mutual molecular disturbance which constitutes fertilization,
is but another way of saying, that the actions and re-actions
of each organism, being in perfect balance with the actions
and re-actions of the environment upon it, there remains in
each organism, no force by which it differs from any other
— no force which any other does not meet with an exactly

286

THE INDUCTIONS Of BIOLOGY.

equal force — no force which can set up a new evo'ution
among the units of any other.

And so we reach the remarkable conclusion, that the life of
a species, like the life of an individual, is maintained by tho
unequal and ever- varying actions of incident forces on its
different parts. An individual homogeneous throughout, and
having its substance everywhere continuously subject to like
actions, could undergo none of those changes which life con-
sists of; and similarly, an absolutely- uniform species, having all
its members exposed to identical influences, would be deprived
of that initiator of change which maintains its existence as
a species. Just as, in each organism, incident forces constantly
produce divergences from the mean state in various directions,
which are constantly balanced by opposite divergences indi-
rectly produced by other incident forces ; and just as the
combination of rhythmical functions thus maintained, consti-
tutes the life of the organism ; so, in a species, there is, through
gamogenesis, a perpetual neutralization of those contrary de-
viations from the mean state, which are caused in its different
parts by different sets of incident forces ; and it is similarly
by the rhythmical production and compensation of these con-
trary deviations, that the species continues to live. The
moving equilibrium in a species, like the moving equilibrium
in an individual, would rapidly end in complete equilibration,
or death, were not its continually- dissipated forces continually
re-supplied from without. Besides owing to the external
world, those energies which, from moment to moment, keep
up the lives of its individual members ; every species owes
to certain more indirect actions of the external world, those
energies which enable it to perpetuate itself in successive
generations.

§ 97. What evidence still remains, may be conveniently
woven up along with a recapitulation of the argument pursued
through the last three chapters. Let us contemplate the facts
in their synthetic order.

GENESIS, HEREDITY, AND VARIATION. 287

Tnat compounding and re-compounding through which we
pass from the simplest inorganic substances to the most cora»
plex organic substances, has several concomitants. Each
Buccessi ve stage of composition, presents us with atoms that are
severally larger or more integrated, that are severally more
heterogeneous, that are severally more unstable, and that are
more numerous in their kinds (First Principles, § 111). And
when we come to the substances of which living bodies are
formed, we find ourselves among multiplied, divergent groups
and sub-groups of compounds, the units of which are large,
heterogeneous, and unstable, in high degrees. There is no
reason to assume that this process ends with the formation of
those complex colloids which characterize organic matter. A
more probable assumption is, that out of the complex colloidal
atoms, there are evolved, by a still further integration, atoms
that are still more heterogeneous, and of kinds that are still
more multitudinous. What must be their properties ? Al-
ready the colloidal atoms are extremely unstable — capable
of being variously modified in their characters by very slight
incident forces ; and already the complexity of their polarities
prevents them from readily falling into those positions of
polar equilibrium which result in crystallization. Now the
organic atoms composed of these colloidal atoms, must be simi-
larly characterized in far higher degrees. Far more numerous
must be the minute changes that can be wrought in them by
minute external forces ; far more free must they remain for a
long time to obey forces tending to re-distribute them ; and
far greater must be the number of their kinds.

Setting out with these physiological units, the existence of
which various organic phenomena compel us to recognize, and
the production of which the general law of Evolution thus
leads us to anticipate ; we get an insight into the phenomena
of Genesis, Heredity, and Variation. If each organism is built
of certain of these highly-plastic units peculiar to its species
— units which slowly work towards an equilibrium of their
complex polarities, in producing an aggregate of the specific

288 THE INDUCTIONS OF BIOLOGY.

structure, and which are at the same time slowly modifiable
by the re-actions of this aggregate — we see why the mul-
tiplication of organisms proceeds in the several ways, and
with the various results, which naturalists have observed.

Heredity, as shown not only in the repetition of the specific
structure, but in the repetition of ancestral deviations from it,
becomes a matter of course ; and it falls into unison with the
fact that, in various simple organisms, lost parts can be re-
placed, and that, in still simpler organisms, a fragment can
develop into a whole.

While an aggregate of physiological units continues to
grow, by the assimilation of matter which it moulds into
other units of like type ; and while it continues to undergo
changes of structure ; no equilibrium can be arrived at between
the whole and its parts. Under these conditions, then, an
un-differentiated portion of the aggregate — a group of phy-
siological units not bound up into a specialized tissue — will
be able to arrange itself into the structure peculiar to the
species ; and will so arrange itself, if freed from controlling
forces, and placed in fit conditions of nutrition and temper-
ature. Hence the continuance of agamogenesis in little- differ-
entiated organisms, so long as assimilation continues to be
greatly in excess of expenditure.

But let growth be checked and development approach its
completion — let the units of the aggregate be severally exposed
to an almost constant distribution of forces ; and they must
begin to equilibrate themselves. Arranged as they will
gradually be, into comparatively stable attitudes in relation
to each other, their mobility will diminish ; and groups of
them, partially or wholly detached, will no longer readily re-
arrange themselves into the specific form. Agamogenesis will
be no longer possible ; or, if possible, will be no longer easy.
When we remember that the force which keeps the Earth
in its orbit, is the gravitation of each particle in the Earth
towards every one of the group of particles existing 91,000,000
of miles off; we cannot reasonably doubt, that each unit in

GENESIS, HEREDITY, AND VARIATION. 289

an organism, acts, by its polar forces, on all the other units,
and is re-acted on by them. When, too, we learn that
glass has its molecular constitution changed by light, and
that substances so rigid and stable as metals, have their
atoms re-arranged by forces radiated in the dark from
adjacent objects ; we are obliged to conclude that the ex-
cessively-unstable units of which organisms are built, must be
sensitive in a transcendant degree, to all the forces pervading
the organisms composed of them — must be tending ever to
re-adjust, not only their relative positions, but their molecular
structures, into equilibrium, with these forces. Hence, if ag-
gregates of the same species are differently conditioned, and
re-act differently on their component units, their component
units will be rendered somewhat different ; and they will
become the more different the more widely the re •actions
of the aggregates upon them differ, and the greater the num-
ber of generations through which these different re-actions of
the aggregates upon them are continued.

If, then, unlikenesses of function among individuals of the
same species, produce unlikenesses between the physiological
units of one individual and those of another ; it becomes com
prehensible that when groups of units derived from two indi
viduals are united, the group formed will be more unstable
than either of the groups was before their union : the mixed
units will be less able to resist those re-distributing forces
which cause evolution ; and may so have restored to them,
the capacity for development which they had lost.

This view harmonizes with the conclusion which we saw
reason to draw, that fertilization does not depend on any
intrinsic peculiarities of sperm-cells and germ-cells ; but
depends on their derivation from different individuals. It
explains the fact that nearly -related individuals are less
likely to have offspring than others ; and that their offspring,
when they have them, are frequently feeble. And it gives
us a key to the converse fact, that the crossing of varieties
results in unusual fertility and vigour.

290 THE INDUCTIONS OF BIOLOGY.

Bearing- in mind that the slightly-different orders of phy-
siological units which an organism inherits from its parents,
are subject to the same set of forces ; and that when the
organism is fully developed, this set of forces, becoming con-
stant, tends slowly to re-mould the two orders of units into
the same form ; we see how it happens that self-fertilization
becomes impossible in the higher organisms, while it remains
possible in the lower organisms. In long-lived creatures that
have tolerably-definite limits of growth, this assimilation of
the somewhat-unlike physiological units, is liable to go on to
an appreciable extent ; whereas _in organisms which do not
continuously subject their component units to constant forces,
there will be much less of this assimilation. And where the
assimilation is not considerable, the segregation of mixed
units, may cause the sperm-cells and germ-cells developed in
the same individual, to be sufficiently different to produce, by
their union, fertile germs ; and several generations of self-
fertilizing descendants may succeed one another, before the
two orders of units have had their unlikenesses so far diminish-
ed, that they will no longer do this. The same principles
explain for us the variable results of union between nearly-
related organisms. According to the contrasts among the
physiological units they inherit from parents and ancestors ;
according to the unlike proportions of the contrasted units
which they severally inherit ; and according to the degrees
of segregation of such units in different sperm-cells and
germ-cells ; it may happen that two kindred individuals will
produce the ordinary number of offspring, or will produce
none ; or will at one time be fertile and at another not ; or
will at one time have offspring of tolerable strength, and at
another time feeble offspring.

To the like causes are also ascribable the phenomena of
Variation. These are unobtrusive while the tolerably-uni-
form conditions of a species maintain tolerable uniformity
among the physiological units of its members ; but they
become obtrusive when differences of conditions, entailing

GENESIS, HEREDITY, AND VARIATION. 291

considerable functional differences, have entailed decided dif-
ferences among the physiological units ; and when the differ-
ent ph}'siologicul units, differently mingled in every individual,
come to be variously segregated and variously combined.

Did space permit, it might be shown that this hypothesis
is a key to many further facts — to the fact that mixed races
are comparatively plastic under new conditions ; to the fact
that pure races show predominant influences when crossed
with mixed races ; to the fact that while mixed breeds are
often of larger growth, pure breeds are the more hardy —
have functions less-easily thrown out of balance. But with-
out further argument, it will, I think, be admitted, that the
power of this hypothesis to explain so many phenomena, and
to bring under a common bond phenomena that seem so little
allied, is strong evidence of its truth. And such evidence
gains greatly in strength on observing that this hypothesis
brings the facts of Genesis, Heredity, and Variation into har-
mony with first principles. When we see that these plastic
phvsiological units, which we find ourselves obliged to assume,
are just such more integrated, more heterogeneous, more un-
stable, and more multiform atoms, as would result from con-
tinuance of the steps through which organic matter is reached — ■
when we see that the differentiations of them assumed to oc-
cur in differently- conditioned aggregates, and the equilibra-
tions of them assumed to occur in aggregates which maintain
constant conditions, are but corollaries from those universal
principles implied by the persistence of force — when we see
that the maintenance of life in the successive generations of a
species, becomes a consequence of the continual incidence of
new forces on the species, to replace the forces that are ever
being rhythmically equilibrated in the propagation of the
species — and when we thus see that these apparently-excep-
tional phenomena displayed in the multiplication of organic
beings, fall into their places as results of the general laws of
Evolution ; we have weighty reasons for entertaining the
hypothesis which affords us this interpretation.

CHAPTER XL

CLASSIFICATION.

§ 98. That orderly arrangement of objects called Classi-
fication, has two purposes ; which, though not absolutely dis-
tinct, are distinct in great part. It may be employed to
facilitate identification ; or it may be employed to organize
our knowledge. If a librarian places his books in the alpha-
betical succession of the author's names, he places them in
such way that any particular book may easily be found ; but
not in such way that books of a given nature stand together.
When, conversely, he makes a distribution of books accord-
ing to their subjects, he neglects various superficial similari-
ties and distinctions, and groups them according to certain
primary and secondaiy and tertiary attributes, which sever-
ally imply many other attributes — groups them so that any
one volume being inspected, the general characters of all the
neighbouring volumes may be inferred. He puts together
in one great division, all works on History ; in another all
Biographical works ; in another all works that treat of
Science ; in another Voyages and Travels ; and so on. Each
of his great groups he separates into sub-groups ; as when
hf puts diiferent kinds of pure Literature, under the heads
of Fiction, Poetry, and the Drama. In some cases he
makes sub-sub-groups ; as when, having divided his Scientific
treatises into abstract and concrete, putting in the one Logic
and Mathematics, and in the other Physics, Astronomy, Ge-

CLASSIFICATION. 293

ology, Chemistry, Physiology, &c. ; he goes on to sub divide
his books on Physics, into those which treat of Mechanical
Motion, those which treat of Heat, those which treat of Light,
of Electricity, of Magnetism.

Between these two modes of classification, note the essen-
tial distinctions. Arrangement according to any single con-
spicuous attribute is comparatively easy, and is the first that
suggests itself : a child may place books in the order of thc'ii
sizes, or according to the st}'les of their bindings. But ar-
rangement according to combinations of attributes, which,
though fundamental, are not conspicuous, requires analysis \
and does not suggest itself till analysis has made some pro-
gress. Even when aided by the information which the author
gives on his title page, it requires considerable knowledge to
classify rightly an essay on Polarization ; and in the absence
of a title page, it requires much more knowledge. Again,
classification by a single attribute, which the objects possess
in different degrees, may be more or less serial, or linear.
Books may be put in the order of their dates, in single file ;
or if they are grouped as works in one volume, works in two
volumes, works in three volumes, &c, the groups may be
placed in an ascending succession. But groups severally
formed of things distinguished by some common attribute
which implies man}' other attributes, do not admit of serial
arrangement. You cannot rationally say, either that His-
torical Works should come before Scientific Works, or Scien-
tific Works before Historical Works ; nor of the sub-divi-
?i >ns of creative Literature, into Fiction, Poetry, and the
Drama, can you give a good reason why any one should take
precedence of the others.

Hence this grouping of the like and separation of the un-
like, which constitutes Classification, can reach its complete
form only by slow steps. We saw (First Principles, § 36)
that, other things equal, the relations among phenomena are
recognized in the order of their conspicuousness ; and that,
nner things equal, they arc recognized in ihe order of their

294 THE INDUCTIONS CF BIOLOGY.

simplicity. The first classifications are sure, therefore, to be
groupings of objects that resemble each other in external or
easily-perceived attributes, and attributes that are not of com-
plex characters. Those likenesses among things which are
due to their possession in common of simple obvious properties,
may or may not coexist with further likenesses among them.
AYhen geometrical figures are classed as curvilinear and
rectilinear, or when the rectilinear are divided into trilateral,
quadrilateral, &c, the distinctions made, connote varioiis
other distinctions, with which they are necessarily bound
up ; but if liquids be classed according to their visible cha-
racters— if water, alcohol, sulphuret of carbon, &c, be
grouped as colourless and transparent, we have things placed
together which are unlike in their essential natures. Thus,
where the objects classed have numerous attributes, the pro-
babilities are, that the early classifications, based on simple
and manifest attributes, unite under the same head many
objects that have no resemblances in the majority of their
attributes. As the knowledge of objects increases, it be-
comes possible to make groups of which the members have
more numerous properties in common ; and to ascertain what
property, or combination of properties, is most characteristic
of each group. And the classification eventually arrived at,
is one in which the segregation has been carried so fur, that
the objects integrated in each group have more attributes in
common with one another, than they have in common with
any excluded objects ; one in which the groups of such groups
are integrated on the same principle ; and one in which the
degrees of differentiation and integration are proportioned to
the degrees of intrinsic unlikeness and likeness. And the
ultimate classification, while it serves most completely to
identify the things, serves also to express the greatest amount
of knowledge concerning the things — enables us to predicate
the greatest number of facts concerning each thing ; and by
so doing proves that it expresses the most precise corre-
spondence between our conceptions and the realities.

CLASSIFICATION. 295

§ 99. Biological classifications illustrate well these phases,
ill rough which classifications in general necessarily pass
In early attempts to arrange organic beings in some sjs-
tematic manner, we see at first, a guidance by conspicuous
and simple characters, and a tendency towards arrangement
in linear order. In successively later attempts, we see
more regard paid to combinations of characters which are
essential but often inconspicuous ; and a gradual abandon-
ment of a linear arrangement for an arrangement in di-
vergent groups and re-divergent sub-groups.

In the popular mind, plants are still classed under the
heads of Trees, Shrubs, and Herbs ; and this serial classing
according to the single attribute of magnitude, swayed the
earliest observers. They would have thought it absurd to
call a bamboo, thirty feet high, a kind of grass ; and would
have been incredulous if told that the Hart's-tongue should
be placed in the same great division with the Tree-ferns
The zoological classifications that were current before Na-
tural History became a science, had divisions similarly super-
ficial and simple. Beasts, Birds, Fishes, and Creeping-things,
are names of groups marked off from one another by con-
spicuous differences of appearance and modes of life — crea-
tures that walk and run, creatures that fly, creatures that live
in the water, creatures that crawl. And these groups were
thought of in the order of their importance.

The first arrangements made by naturalists were based
either on single characters, or on very simple combinations
of characters. Describing plant-classifications, Lindley
Bays : — " Rivinus invented, in 1690, a system depend-
ing upon the formation of the corolla ; Kamel, in 1693,
upon the fruit alone ; Magnol, in 1720, on the calyx and
corolla ; and finally, Linnaeus, in 1731, on variations in the
stamens and pistil." In this last system, which has been for
so long current as a means of identification, simple external
attributes are still depended on ; and an arrangement, in
great measure serial, is based on the degrees in which thebc

296 rilE INDUCTIONS OF BIOLOGY.

attributes are possessed. In 1703, some tLirty years before
the time of Linnoeus, our countryman Ray had sketched the
outlines of a more advanced system. He said that —

Plants are either

Flowerless, or

Flowering ; and these are
Dicotyledones, or
Monocotyledones.
Among the minor groups which he placed under these
general heads, " were Fungi, Mosses, Ferns, Composites,
CichoraceaB Umbellifers, Papilionaceous plants, Conifers, La-
biates, &c, under other names, but with limits not very dif-
ferent from those now assigned to them." Being much in
advance of his age, Ray's ideas remained dormant until the
time of Jussieu ; by whom they were developed into what
has become known as the Natural System. Passing through
various modifications in the hands of successive botanists,
the Natural System has now taken the following form ; which
I copy (adding the alliances to the classes) from Prof.
Lindley 's Vegetable Kingdom.*

* From this table I have omitted the class RMzogcm, which other botanists
do not agree with Lindley in regarding as a separate class. The plants respect-
ing which there has arisen this difference of opinion, are certain flowering
plants, which grow parasitically on the roots of trees. The reasons assigned bv
Endlicher and Lindley, for erecting them into a separate group of Phaenogams,
are, that in place of true leaves they have only cellular scales ; that the stem is
an amorphous fungous mass, imperfectly supplied with spiral vessels ; ana :n:it
they are without chlorophyll. Mr Griffith and Dr Hooker, however, have gr < u
preponderating reasons why they should be restored to the class Exogens. It
seems here worth remarking, that certain zoological facts suggest an explanation
of these anomalous botanical facts; and confirm the conclusion reached by Dr
Hooker and Mr Griffith. It very commonly happens that animal-parasites arc
aberrant forms of the types to which they belong ; and, by analogy, we may not
unieasonably expect to find among parasitic plants, the most aberrant forms of
vegetal types. More than this is true. The kind of aberration which we see in the
one case, we see in the other ; and in both cases, the meaning of the aberration is
manifest. In such Epizoa as the Lernece, the Crustacean type is disguised by the
almost entire loss of the limbs and organs of sense, by the simplification of the
digestive apparatus, and by the great development of the reproductive system;

CLASSIFICATION.

297

Asexual, or Flower less Plants.

{Algales
Fungales
Lichenalee
_ , , ,. . . , . , rMuscalea

Stems and leaves distinguishable II. Acbogens < Lycopodalea

^Filicales

Sexual, or Flowering Plants.

(Glumales
Arales
Palmalos

J Hydra] ea
Narcissalea
Amomales
Orchidales
Xyridales
Juncales
Liliales
LAlisinales

IV. DlCTTOGENS.

Wood of stem youngest in centre ;
cotyledon single.

Leaves parallel-veined, permanent ;
wood confused

Leaves net -veined, deciduous ;
wood, when perennial, arranged
in a circle with a central pith

Wood of stem youngest at circum-
ference, always concentric ; coty-
ledons two or more.

Seeds quite naked

V. Gtmnogens.

'Diclinous

Keeds enclosed in seed-vessels

VL Exogens

Hypogynous

Perigynous

Epigynous

{Amen tales
Urtieales
Euphorbialos
&c. Ac.
rViolales
J Cistales
I Malvaies
*• &e. Ac.
fFicoidales
J Daphnales
| Rosales
*■ &c. Ac.

{Campanalea
Mvrtales
Cactales
Ac. Ac.

Here, linear arrangement has disappeared : there is a
breaking up into groups and sub-groups and sub-sub-groups,
which do not admit of being placed in serial order, but only
in divergent and re-divergent order. Were there space to
exhibit the way in which the Alliances are subdivided into
Orders, and these into Genera, and these into Species ; the

the parts no longer needed, abort, and those parts develop which favour the
preservation of the race. Similarly in the Rhizogens, the abortive development
of the leaves, the absence of chloropnyll, and the imperfect supply of spiral
vessels, are changes towards a structure fit for a plant which lives on the juices
absorbed from another plant; while the rapid and great development of the
fructifying organs, are correlative changes advantageous to a plant, the seeds of
which have but small chances of rooting themselves. And just the same reason
that exists for the production of immensely numerous but extremely small eggs
by Entozoa, exists for the production by Rhizogens^ of seeds that are grcul in
uuniber and almost spore-like in size.
20

298 THE INDUCTIONS OF BIOLOGY.

same principle of co-ordination would, be still further mani-
fested. On studying the definitions of these primary, se-
condary, and tertiary classes, it will be found, that the
largest are marked off from each other by some attribute
which connotes sundry other attributes ; that each of the
smaller classes comprehended in one of these largest classes,
is marked off in a similar way from the smaller classes
bound up with it ; and that so, each successively smaller
class, has an increased number of co-existing attributes.

§ 100. Zoological classification has had. a parallel history.
The first attempt which we need notice, to arrange animals
in such a way as to display their affinities, is that of Lin-
naeus. He grouped them thus :* —

Cl. 1. Mammalia. Ord. Primates, Bruta, Ferae, Glires, Pecora, Belluse,
Cete.

Cl. 2. Aves. Ord. Accipitres, Picse, Anseres, Grallae, Galliuae, Passeres.

Cl. 3. Amphibia. Ord. Reptiles, Serpentes, Nantes.

Cl. 4. Pisces. Ord. Apodes, Jugulares, Thoracici, Abdominales.

Cl. 5. Insecta. Ord. Coleoptera, Hemiptera, Lepidoptera, Neuroptera,
Diptera, Aptera.

Cl. 6. Vermes. Ord. Intestiua, Mollusca, Testacea, Lithophyta, Zoo-
phyta.

This arrangement of classes, is obviously based on ap-
parent gradations of rank ; and the placing of the orders
similarly betrays an endeavour to make successions, begin-
ning with the most superior forms and ending with the
most inferior forms. While the general and vague idea
of perfection, determines the leading character of the
classification, its detailed groupings are determined by
the most conspicuous external attributes. Not only Lin-
naeus, but his opponents, who proposed other systems, were
" under the impression that animals were to be arranged
together into classes, orders, genera, and species, according to
their more or less close external resemblance." This con-
ception survived till the time of Cuvier. "Naturalists."

* This classification, and the three which iuiiow it, 1 quote (aunagmg mjuip
of thiuii) from Prof. Agassiz's "Essay on Classification."

CLASSIFICATION. 299

says Agassiz, "were bent upon establishing one continual
uniform series to embrace all animals, between the links of
which it was supposed there were no unequal intervals.
The watchword of their school was : Natura non facit
talfum. They called tl.eir system la chaine dcs etres."

The classification of Cuvier, based on internal organization
instead of external appearance, was a great advance. Ho
asserted that there are four principal forms, or four general
plans, on which animals are constructed ; and in pursuance
of this assertion, he drew out the following scheme.

First Branch. Animalia Vertebrata
Cl. 1. Mammalia.
Cl. 2. Birds.
Cl. 3. Reptilia.
Cl. 4. Fishes.

Second Branch. Animalia Mollusca.
Cl. 1. Cephalapoda.
Cl. 2. Pteropoda.
Cl. 3. Gasteropoda.
Cl. 4. Acephala.
Cl. 5. Brachiopoda.
Cl. 6. Cirrhopoda.

Third Branch. Animalia Articulate .
Cl. 1. Annelides.
Cl. 2. Crustacea.
Cl. 3. Arachnides.
Cl. 4. Insects.

Fourth Branch. Animalia Radiata.

Cl. 1. ECHINODERMS.

Cl. 2. Intestinal "Worms.

Cl. 3. AcAi,EPiLra.

Ol. 4. Polypi.

Cl. o. Infusoria,

300

THE INDUCTIONS OF BIOLOGY.

But though Cuvier emancipated himself from the concep-
tion of a serial progression throughout the Animal- King-
dom ; sundry of his contemporaries and successors remained
fettered by the old error. Less regardful of the differently-
co-ordinated sets of attributes displayed by the different sub-
kingdoms ; and swayed by the belief in a progressive develop-
ment, which was erroneously supposed to imply the possibility
of arranging animals in a linear series ; they persisted in
thrusting organic forms into a quite unnatural order. The
following classification of Lamarck illustrates this.

INVERTEBRATA.

I. Apathetic Animals.

II.

Cl.

1.

Infusoria.

Cl.

2.

Polypi.

Cl.

3.

Radiaria.

Cl.

4.

TUNICATA.

Cl.

5.

Yermes.

Sensitive Animals.

Cl.

6.

Insects.

Cl.

7.

Arachnids.

Cl.

8.

Crustacea.

Cl.

9.

Annelids.

Cl.

10.

Cirripeds.

Cl.

11.

Conchifera.

Cl.

12.

MOLLUSKS.

III. Intelligent Animals

Cl.

13.

Fishes.

Cl

14.

Reptiles.

Cl.

15.

Birds.

Cl.

16.

Mammaija

Do not feel, and move only by
their excited irritability. No brain,
not elongated medullary mass; no
senses ; forms varied ; rarely articu-
lations.

Feel, but obtain from their sensa-
tions only perceptions of objects, a
sort of simple ideas, which they are
unable to combine to obtain complex
)■ ones. No vertebral column ; a brain
and mostly an elongated medullary
mass; some distinct senses; muscles
attached under the skin ; form sym-
metrical, the parts being in pairs.

VERTEBRATA.

Feel; acquire preservable ideas;
perform with them operations by
which they obtain others ; are intel-
ligent in different degrees. A ver-
• tebral column ; a brain and a spinal
marrow ; distinct senses ; the mus-
cles attached to the internal skele-
ton ; form symmetrical, the parts
being in pairs.

CLASSIFICATION, 301

Passing over sundry classifications in which the serial
arrangement dictated b}r the notion of ascending complexity,
is variously modified by the recognition of conspicuous
anatomical facts, we come to the classifications which recognize
another order of facts — those of development. The embryo-
logical inquiries of Von Baer, led him to arrange animals as
follows : —

I. Peripheric Type. (Rapiata.) Evolutio radiata. The
development proceeds from a centre, producing
identical parts in a radiating order.
II. Massive Type. (Mollusca.) Evolutio contorta. The
development produces identical parts curved around
a conical or other space.

III. Longitudinal Type. (Artictjlata.) Evolutio gemina.

The development produces identical parts arising on
both sides of an axis, and closing up along a line
opposite the axis.

IV. Doubly Symmetrical type. (Vertebrata.) Evolutio

bigemina. The development produces identical
parts arising on both sides of an axis, growing up-
wards and downwards, and shutting up along two
lines, so that the inner layer of the germ is inclosed
below, and the upper layer above. The embryos of
these animals have a dorsal cord, dorsal plates, and
ventral plates, a nervous tube and branchial fissures.

Recognizing these fundamental differences in the modes of
evolution, as answering to fundamental divisions in the
animal kingdom, Von Baer shows (among the Vertebrata at
least) how the minor differences that arise at successively
later stages of evolution, correspond with the minor divisions.

Like the modern classification of plants, the classification
of animals that has now been arrived at, is one in which the
linear older is completely broken up. In his lectures at the
Royal Iustitution, in 1857, Prof. Huxley expressed the rela-

302 THE INDUCTIONS OF BIOLOGY.

tions existing among the several great groups of the animal
kingdom, by placing these groups at the ends of four or five
radii, diverging from a centre. The diagram I cannot
obtain ; but in the published reports of his lectures at the
School of Mines the groups were arranged thus : —

Vertebrata

{Abranchiala)

Mammalia

Aves

Beptilia

[Branehiata)

Amphibia

Pisces

MOLLUSCA

Annulosa

Cephalopoda Heteropoda

)

Articulata

Gasteropoda-

• > Insecta

Arachnids

dioecia

) Myriapoda Crustacea

( Pulmonata Gasteropoda-

\ Pteropoda moncecia

Annuloida

Laniellibranchiata

Annellata Scoleidse

Echinodermata Trematoda

Rotifera

Toeniadae
Turbellaria

•

Nematoidea

C(ELENTERATA

Hydrozoa

Actinozoa.

Protozoa

Infusoria

Spongiadae

Gregarinidae

Noctilucida

Foraminifera

ThaUassicollidce

What remnant there may seem to be of linear succession
in some of these sub-groups, is merely an accident of typo-
graphical convenience. Each of them is to be regarded
simpby as a cluster. Were Prof. Huxley now to revise this
scheme, he would probably separate more completely some of
the great sub-groups, in conformity with the views expressed
in his Hunterian Lectures delivered at the College of Sur-
geons in 1863. And if he were further to develop the
arrangement, by dispersing the sub-groups and sub-sub-
groups on the same principle, there would result an arrange-

CLASSIFICATION. 303

ment perhaps not very much unlike that shown in the an-
nexed diagram.

• •

• WM'amma/c'n . »,

• . • ''.Atm

' .'. I Br/itilln.

V E RTEB'RATA

A-mfikibia \ Pisces

\ •

• • •
\ .* .'* Crustacea

\

I .Alj/ria/ica'a

I

ANNl/LOSA

^ jAnnclida^

\ frcleci!da '

\ ij • •

\ A/Tiuuloida.

Ptcrcficda .'OfiAaAJMt \ Ec\dncdcrfaata\\'

\

\
\

. ,GastfTof>cda
' • dicecia \ I

Gastercficda. • ^Putmonata

mcnacia % •

/ /

MOLLUSCA \ /

Lamelli6ra.nc/iiafa~~—-~. \ / /

""■^-^ ' '

\BracAU/icd& • m»Gregari-nid*

Mollus c oTda-- ji/Ute/tcdq -\^

AscidMda * • * .* " 'Pclya o a. /PROTOZOA

• / . - .

• . / Shcnqida Infuscvttt

xr j •/• m * • •••

JHydrfiBca /. •. •

j

CCELEN TERATA

jLctincsca'

In this diagram, the dots represent orders, the names ot
which it is impracticable to insert. If it be supposed that
when magnified, each of these dots resolves itself into a
cluster of clusters, representing genera and species, an ap-
proximate idea will be formed of the relations among the
successively-subordinate groups constituting the animal king-

304 THE INDUCTIONS OF BIOLOGY.

dom. Besides the subordination of groups and their general
distribution, some other facts are indicated. By the distances
of the great divisions from the general centre, are rudely
symbolized their respective degrees of divergence from the
form of simple, undifferentiated organic matter; which we
mav regard as their common source. Within each group,
the remoteness from the local centre represents, in a rough
way, the degree of departure from the general plan of the
group. And the distribution of the sub-groups within each
group, is in most cases such, that those which come nearest
to neighbouring groups, are those which show the nearest
resemblances to them — in their analogies though not in their
homologies. No diagram, however, can give a correct con-
ception. Even supposing the above diagram expressed the
relations of animals to one another as truly as they can be
expressed on a plane surface, (which of course it does not,) it
would still be inadequate. Such relations cannot be repre-
sented in space of two dimensions ; but only in space of three
dimensions

§ 101. While the classifications of botanists and zoologists
have become more and more natural in their arrangements,
there has grown up a certain artificiality in their abstract
nomenclature. When aggregating the smallest groups into
larger groups, and these into groups still larger, natur-
alists adopted certain general terms expressive of the suc-
cessively more comprehensive divisions ; and the habitual
use of these terms, needful for purposes of convenience, has
led to the tacit assumption that they answer to actualities in
Nature. It has been taken for granted that species, genera,
orders, and classes, are assemblages of definite values — that
every genus is the equivalent of every other genus, in respect
of its degree of distinctness ; and that orders are separated
by lines of demarcation that are as broad in one place as
another. Though this conviction is not a formulated one,
yet the disputes continually arising among naturalists on tho

CLASSIFICATION. 305

questions, whether such and such organisms are specifically
or generically distinct, and whether this or that peculiarity
is or is not of ordinal importance, imply that the conviction
is entertained even where it is not avowed. Yet that dif-
ferences of opinion like these continually arise, and remain
unsettled, except when they end in the establishment of sub-
species, sub-genera, sub-orders, and sub-classes, sufficiently
shows that no such conviction is justifiable. And this ia
equally shown by the impossibility of obtaining an}r definition
of the degree of difference, which warrants each further eleva-
tion in the hierarchy of classes.

It is, indeed, a wholly gratuitous assumption that organ-
isms admit of being placed in groups of equivalent values ;
and that these may be united into larger groups that are
also of equivalent values ; and so on. There is no a priori
reason for expecting this ; and there is no a posteriori evi-
dence implying it, save that which begs the question — that
which asserts one distinction to be generic and another to be
ordinal, because it is assumed that such distinctions must be
either generic or ordinal. The endeavour to thrust plants
and animals into these definite partitions, is of the same
nature as the endeavour to thrust them into a linear series.
Not that it does violence to the facts in anything like the
same degree ; but still, it does violence to the facts. Doubt-
less the making of divisions and sub-divisions, is extremely
useful ; or rather, it is absolutely necessary. Doubtless, too,
in reducing the facts to something like order, they must be
partially distorted. So long a3 the distorted form is not
mistaken for the actual form; no harm results. But it is
needful for us to remember, that while our successively
subordinate groups have a certain general correspondence
with the realities, they inevitably give to the realities a
regularity which does not exist.

§ 102. A general truth of much significance is exhibited
in these classifications. On observing the natures of the

306 THE INDUCTIONS OF BIOLOGY.

attributes which are common to the members of any group
of the first, second, third, or fourth rank, we see that groups
of the widest generality are based on characteristics of the
greatest importance, physiologically considered ; and that the
characteristics of the successively- subordinate groups, are
characteristics of successively -subordinate importance. The
structural peculiarity in which all members of one sub-
kingdom differ from all members of another sub-kingdom, is
a peculiarity that affects the vital actions more profoundly,
than does the structural peculiarity which distinguishes all
members of one class from all members of another class.
Let us look at a few cases.

We saw (§ 56), that the broadest division among the
functions is the division into " the accumulation of force
(latent in food) ; the expenditure of force (latent in the
tissues and certain matters absorbed by them) ; and the
transfer of force (latent in the prepared nutriment or blood)
from the parts which accumulate to the parts which expend."
Now the lowest animals, united under the general name
Protozoa, are those in which there is either no separation of
the parts performing these functions or very indistinct separ-
ation : in the Rhizopoda, all parts are alike accumulators of
force, expenders of force, and transferrers of force; and
though in the most differentiated members of the group, the
Infusoria, there are something like specializations corre-
sponding to these functions, yet there are no distinct tissues
appropriated to them. The animals known as Cceknterata
are characterized in common by the possession of a part
which accumulates force more or less marked off from the
part which does not accumulate force, but only expends it ;
and the Hydrozoa and Actinozoa, which are sub-divisions of
the Ccelenterata, are contrasted in this, that in the one these
parts are very indefinitely distinguished, but in the other
definitely separated, as well as more complicated. Besides a
completer differentiation of the organs respectively devoted
to the accumulation of force and the expenditiire of force,

CLASSIFICATION. 307

the animals classed as Molluscoida, possess rude appliances
for the transfer of force : the peri- visceral sac, or closed
cavity between the intestine and the walls of the body,
serves as a reservoir of absorbed nutriment, from which the
surrounding tissues take up the materials they need. The
more highly-organized animals, belonging to whichever sub-
kingdom, all of them possess definitely-constructed channels
for the transfer of force ; and in all of them, the function of
expenditure is divided between a directive apparatus and
an executive apparatus — a nervous system and a muscular
system. But these higher sub-kingdoms are clearly separated
from each other by differences in the relative positions of
their component sets of organs. Prof. Huxley defines the
type of the Vertebrata, as one in which the ganglionic nervous
system lies on the dorsal side of the alimentary canal, while
the central vascular system lies on its ventral side ; and one
which is yet further characterized by the possession of a
second, and more conspicuous, nervous system, placed on the
dorsal side of the vertebral axis — an extra endowment which
is perhaps the most essentially distinctive. The types of the
Annulosa and Mollusca, are together marked off from the
vertebrate type, by the singleness of the nervous system, and
by its occupation of the ventral side of the body : the
habitual attitudes of annulose and molluscous creatures, is
such that the neural centres are below the alimentary canal
and the haemal centres above. And while by these traits the
annulose and molluscous types are separated from the verte-
brate, they are separated from each other by this, that in
the one the body is " composed of successive segments, '
usually provided with limbs," but the other, the body is not
segmented, " and no true articulated limbs are ever de-
veloped."

The sub-kingdoms being thus distinguished from one an-
other, by the presence or absence of parts devoted to funda-
mental functions, or else by differences in the distributions of
such parts ; we find, on descending to the classes, that these

308 THE INDUCTIONS OF BIOLOGY.

are distinguished from each other, either by modifications in
the structures of fundamental parts, or by the presence or
absence of subsidiary parts, or by both. Fishes and. Am-
phibia are unlike higher vertebrates- in possessing branchiae;
either throughout life or early in life. And every higher
vertebrate, besides having lungs, is characterized by having,
during development, an amnion and an allantois. Mammals,
again, are marked off from Birds and Reptiles by the
presence of mammae, as well as by the form of the occipital
condyles. Among Mammals, the next division is based on
the presence or absence of a placenta. And divisions of the
Placentalia are mainly determined by the characters of the
organs of external action.

Thus, without multiplying illustrations and without de-
scending to genera and species, we see that, speaking gener-
ally, the successively smaller groups, are distinguished from
one another by traits of successively less importance, physio-
logically considered. The attributes possessed in common
by the largest assemblages of organisms, are few in number
but all-essential in kind — affect fundamentally the most vital
actions. Each secondary assemblage, included in one of the
primary assemblages, is characterized by further common
attributes that influence the functions less profoundly. And
bo on with each lower grade of assemblage.

5 103. "WTiat interpretation is to be put on these truths of
classification ? We find that organic forms admit of an
arrangement everywhere expressive of the fact, that along
with certain attributes, certain other attributes, which are
not directly connected with them, always exist. How are
we to account for this fact ? And how are we to account for
the fact that the attributes possessed in common by the
largest assemblages of forms, are the most vitally-important
attributes ?

No one can believe that combinations of this kind may
have arisen fortuitously. Or if any one believes this, it ie

CLASSIFICATION. 309

easy to prove to him that the law of probabilities negatives
the assumption. Even supposing fortuitous combinations of
attributes might result in organisms that would work, we
should still be without a clue to this special mode of com-
bination. The chances would be infinity to one against
organisms which possessed in common certain fundamental
attributes, having also in common numerous non-essential
attributes.

No one, again, can allege that such combinations are
necessary, in the sense that all other combinations are im-
practicable. There is not, in the nature of things, any
reason why creatures covered with feathers should always
have beaks : jaws holding teeth would, in many cases,
have served them equally well or better. The most general
characteristic of an entire sub-kingdom, equal in extent
to the Vertebrata, might have been the possession of nicti-
tating membranes ; while the internal organizations through-
out this sub-kingdom, might have been on many different
plans.

If, on the other hand, this peculiar subordination of attri-
butes which organic forms display, be ascribed to design, other
difficulties suggest themselves. To suppose that a certain
plan of organization was fixed on by a Creator, for each vast
and varied group, the members of which were to lead many
different modes of life ; and that he bound himself to adhere
rigidly to this plan, even in the most aberrant forms of the
group, where some other plan would have been more appro-
priate ; is to ascribe a very strange motive. When we dis-
cover that the possession of seven cervical vertebrae is a
general characteristic of mammals, whether the neck be im-
mensely long, as in the giraffe, or quite rudimentary, as in
the whale ; shall we say that though, for the whale's neck,
one vertebra would have been equally good, and though, for
the giraffe's neck, a dozen would probably have been better
than seven, yet seven was the number adhered to in both
cases, because seven was fixed upon for the mammalian type ?

310 THE INDUCTIONS OF BIOLOGY.

And then, when it turns out that this possession of seven
cervical vertebrae is not an absolutely-universal characteristic
of mammals, shall we conclude that while, in a host of cases,
there is a needless adherence to a plan for the sake of
consistency, there is yet, in some cases, an inconsistent
abandonment of the plan ? I think we may properly refuse
to draw any such conclusion.

What, then, is the meaning of these peculiar relations of
organic forms ? The answer to this question must be post-
poned. Having here contemplated the problem as presented
in these wide inductions which naturalists have reached ; and
having seen what proposed solutions of it are inadmissible ;
we shall see, in the next division of this work, what is the
only possible solution.

CHAPTER XII.

DISTRIBUTION.

§ 104. There is a distribution of organisms in Space, and
there is a distribution of organisms in Time. Looking first
at their distribution in Space, we observe in it two different
classes of facts. On the one hand, the plants and animals of
each species, manifestly have their habitats limited by ex
ternal conditions : they are necessarily restricted to spacea
in which their vital actions can be performed. On the other
hand, the existence of certain conditions does not determine
the presence of organisms that are the fittest for them : there
are many spaces perfectly adapted for life of a high order,
in which only life of a much lower order is found. While,
in this inevitable restriction of organisms to environments
with which their natures correspond, we find a negative
cause of distribution ; there remains to be found that positive
cause of distribution, whence results the presence of organ-
isms in some of the places appropriate to them, and their
absence from other places that are equally appropriate and
more appropriate. Let us consider the phenomena under
these categories.

§ 105. Facts which illustrate the limiting influence of sur-
rounding conditions, are abundant, and familiar to all read-
ers. It will be needful, however, here to cite a few typical
ones of each order.

312 THE .NDUCT10NS OF BIOLOGY.

The confinement of different kinds of plants and different
kinds of animals, to the media for which they are severally
adapted, is the broadest fact of distribution. We have ex-
tensive groups of plants that are respectively sub-aerial and
sub -aqueous ; and of the sub-aqueous, some are exclusively
marine, while others exist only in rivers and lakes. Among
animals, we similarly find some classes confined to the air
and others to the water ; and of the water-breathers, some
are restricted to salt water and others to fresh water. Less
familiar is the fact, that within each of these strongly con-
trasted media, there are further wide-spread limitations. In
the sea, certain organisms exist only between certain depths,
while other organisms exist only between other depths — the
limpet within the littoral zone, and the Globigerina at the
bottom of the Atlantic ; and on the land, there are Floras
and Faunas peculiar to low regions, and others peculiar to
high regions. Next we have the well-known geographical
limitations, made by climate. There are temperatures that
restrict each kind of organism between certain isothermal
lines ; and hygrometric states that prevent the spread of
each kind of organism beyond areas having a certain hu-
midity or a certain dryness. Besides such general limita-
tions, we find much more special limitations. Some minute
vegetal forms occur only in snow. Hot springs have their
peculiar Infusoria. The habitats of certain Fungi are mines
or other dark places. And there are creatures unknown be-
yond the water contained in particular caves. After
these limits to distribution imposed by physical conditions,
come limits of a different class, imposed by the presence
or absence of other organisms. Obviously, graminivorous
animals are confined within tracts which produce plants fit
for them to feed on. Large carnivores cannot exist out of
regions where there are creatures numerous enough and
large enough to serve for prey. The requirements of the
sloth, limit it to certain forest- covered spaces ; and there can
be no insectivorous bats, where there are no niffht- flying

DISTRIBUTION. 313

insects. To these dependences of the relatively-stiperioT
organisms on the relatively-inferior organisms which they
consume, must be added certain reciprocal dependences of
the inferior on the superior. Mr Darwin's inquiries have
shown how generally the fertilization of plants is due to the
agency of insects ; and how certain plants, being fertilizable
only by insects of a certain structure, are limited to regions
inhabited by insects of this structure. Conversely, the spread
of organisms is often bounded by the presence of particular
organisms beyond the bounds — either competing organisms
or organisms directly inimical. A plant that is fit for some
territory adjacent to its own, fails to overrun it, because the
territory is pre- occupied by some plant that is its superior,
either in fertility or power of resisting destructive agencies ;
or else because there lives in the territory some mammal
which browses on its foliage, or bird which devours nearly all
its seeds. Similarly, an area in which animals of a particu-
lar species might thrive, is not colonized by them, because
they are not fleet enough to escape some beast of prey inhab-
iting this area ; or because the area is infested by some in-
sect which destroys them, as the tsetse destroys the cattle in
parts of Africa. Yet another more special series of

limitations, accompanies parasitism. There are parasitic
plants that flourish only on trees of some few kinds ; and
others that have certain animals for their habitats — as the
fungus which is fatal to the silk-worm, or that which so
strangely grows out -of a New Zealand caterpillar. Of
animal-parasitism we have various kinds : severally involv-
ing their specialities of distribution. We have that kind in
which one creature uses another for pxirposes of locomotion ;
as the Chelonobia uses the turtle, and as a certain Ac-
tinia uses the shell inhabited by a hermit-crab. We havo
that kind in which, one creature habitually accompanies
another to share its prey ; like the annelid which takes up
its abode in the shell occupied by a hermit-crab, and snatches
from the hermit-crab, the morsels of food it is eating. "Wo
21

314 THE INDUCTIONS OF BIOLOGY.

have again the commoner parasitism of the Epizoa — animals
which attach themselves to the surfaces of other animals, and
feed on their juices or on their secretions. And once more, we
have the equally common parasitism of the E?ilo~oa — creatures
which live within other creatures. Besides being restricted
ill its distribution to the bodies of the organisms it infests,
each species of parasite has usually still narrower limitations :
in some cases the infested organisms furnish fit habitats for
the parasites only in certain regions ; and in other cases, only
when in certain constitutional states. There are

various more indirect modes in which the distributions of
organisms affect each other. Plants of particular kind3 are
eaten by animals, only in the absence of kinds that are
preferred to them ; and the prosperity of such plants, hence
partly depends on the presence of the preferred plants. Mr
Bates has pointed out that some South American butterflies,
thrive in regions where insectivorous birds would else destroy
them, because they closely resemble butterflies of another
genus which are disliked by those birds. And Mr Darwin
gives cases of dependence still more remote and involved.

Such are the chief negative causes of distribution — the
inorganic and organic agencies, that set bounds to the spaces
which organisms of each species inhabit. Fully to under-
stand their actions, we must contemplate them as working
not separately, but in concert. We have to regard the
physical influences, varying from year to year, as now
producing an extension or restriction of the habitat in this
direction, and now in that ; and as producing secondary
extensions and restrictions, by their effects on other kinds of
organisms. "We have to regard the distribution of each
organism, not only as affected by causes which favour multi-
plication of prey or of enemies within its own area ; but also
by causes which produce such results in neighbouring areas.
We have to conceive the forces by which the limit is
maintained, as including all meteorologic influences, united

DISTRIBUTION. 315

with the influences, direct or more or less re mot of nearly
all co-existing organisms.

One general truth, indicated by sundry of the above illus-
trations, calls for special notice — the truth that organisms
are ever intruding on each other's spheres of existence. Of
the various modes in which this is shown, the commonest is
the invasion of territory. That tendency which we see in
the human races, to overrun and occupy each other's lands,
as well as the lands inhabited by inferior creatures, is a
tendency exhibited by all classes of organisms in all va-
rieties of ways. Among them, as among mankind, there are
permanent conquests, temporary occupations, and occasional
raids. Annual migrations are instances of this process in
its most familiar form. Every spring an inroad is made into
the area which our own fly-catchers occupy, by the swallows
of the South ; and every winter the fieldfares of the North,
come to share the hips and haws of our hedges with native
birds — a partial possession of their territory, which entails
on our native birds, some mortality. Besides these regularly-
recurring raids, there are irregular ones : as of locusts into
countries not usually visited by them ; or of strange birds
which in small flocks from time to time visit areas adjacent
to their own. Every now and then, an incursion ends in
permanent settlement — perhaps in conquest over indigenous
species. Within these few years, an American water-weed
has taken possession of our ponds and rivers, and to some
extent supplanted native water- weeds. Of animals, may be
named a small kind of red ant, having habits allied to those
of tropical ants, which has of late overrun many houses in
London. The case of the rat, which must have taken to
infesting ships within these few centuries, is a good illustra-
tion of the readiness of animals to occupy new places that
are available. And the way in which vessels visiting India,
are cleared of the European cockroach by the kindred Blatta
orientaJis, shows us how these successful invasions last only
until there come more powerful invaders. Organ

316 THE INDUCTIONS OF BIOLOGY.

isms encroach on one another's spheres of existence, in fur-
ther ways than by trespassing on one another's areas : they
adopt one another's modes of life. There are cases in which
this usurpation of habits is slight and temporary ; and there
are cases where it is marked and permanent. Grey crows
frequently join gulls and curlews in picking up food between
tide-marks ; and gulls and curlews may be occasionally seen
many miles inland, feeding in ploughed fields and on moors.
Mr Darwin has watched a fly-catcher catching fish. lie
says that the greater titmouse sometimes adopts the practices
of the shrike, and sometimes of the nuthatch ; and that some
South American woodpeckers are frugivorous, while others
chase insects on the wing. Of habitual intrusions on the
occupations of other creatures, one case is furnished by the
sea-eagle ; which, besides hunting the surface of the land for
prey, like the rest of the hawk-tribe, often swoops down upon
fish. And Mr Darwin names a species of petrel that has
taken to diving, and has a considerable, modified organiza-
tion. These last cases introduce us to a still more
remarkable class of facts of kindred meaning. This intrusion
of organisms on one another's modes of life, goes to the ex-
tent of intruding on one another's media. The great mass
of flowering plants are terrestrial ; and are required to be so
by their process of fructification. But there are some which
live in the water, and protrude only their flowers above the
surface. Nay, there is a still more striking instance : on the
sea-shore may be found an alga a hundred yards inland,
and a phsenogam rooted in salt-water. Among animals,
these interchanges of media are numerous. Nearly all
coleopterous "insects are terrestrial; but the water-beetle,
which like the rest of its order is an air-breather, has
aquatic habits. Water appears to be an especially uufit
medium for a fly ; and yet Mr Lubbock has lately dis-
covered more than one species of fly living beneath the sur-
face of the water, and coming up only occasionally for aii.
Birds, as a class, are especially fitted for an aerial existence j

DISTRIBUTION. 317

buc certain tribes of them have taken to an aquatic existence
— swimming on the surface of the water and making continual
incursions beneath its surface ; and there are some genera
that have wholly lost the power of flight. Among mam-
mals, too, which have limbs and lungs implying an organiza-
tion for terrestrial life, may be named kinds that live more
or less in the water, and are more or less adapted to it. We
have water-rats and otters, which unite the two kinds of life,
and show but little modification ; hippopotami passing the
greater part of their time in the water, and somewhat more
fitted to it; seals living almost exclusively in the sea, and
having the mammalian form greatly obscured ; whales
wholly confined to the sea, and having so little the aspect of
mammals as to be mistaken for fish. Conversely, sundry
inhabitants of the water make more or less prolonged ex-
cursions on the land. Eels migrate at night from one pool
to another. There are fish with specially-modified gills, and
fin-rays serving as stilts, which, when the rivers they in-
habit are partially dried-up, travel in search of better quarters
And while some kinds of crabs do not make land-excursions
beyond high-water mark, other kinds pursue lives almost
wholly terrestrial.

Joining together these two classes of facts, we must regard
the bounds to each species' sphere of existence, as determined
by the balancing of two antagonist sets of forces. The tend-
ency which every species has to intrude on other areas,
other modes of life, and other media, is restrained by the
direct and indirect resistance of conditions, organic and inor-
ganic. And these expansive and repressive energies, vary-
ing continually in their respective intensities, "rhythmically
equilibrate each other — maintain a limit that perpetually
oscillates from side to side of a certain mean.

§ 106. As implied at the outset, the character of a region,
when unfavourable to any species, sufficiently accounts for the
absence of this species ; and thus its absence is not incon-

#18 THE INDUCTI0N3 OF BIOLOGY.

gruous with the hypothesis, that each species was originally
placed in the regions most favourable to it. But the absence
of a species from regions that are favourable to it, cannot be
thus accounted for. Were plants and animals localized wholly
with reference to the fitness of their constitutions to surround-
ing conditions, we might expect Floras to be similar and
Faunas to be similar, where the conditions are similar ; and
we might expect dissimilarities among Floras and among
Faunas, proportionate to the dissimilarities of their conditions.
But we do not find such anticipations verified.

Mr Darwin says that " in the Southern hemisphere, if we
compare large tracts of land in Australia, South Africa, and
western South America, between latitudes 25° and 35°, we shal-
find parts extremely similar in all their conditions, yet it
would not be possible to point out three faunas and floras
more utterly dissimilar. Or again we may compare the pro-
ductions of South America south of lat. 35° with those north
of 25°, which consequently inhabit a considerably different cli-
mate, and they will be found incomparably more closely related
to each other, than they are to the productions of Australia
or Africa under nearly the same climate." Still more striking
are the contrasts which Mr Darwin points out, between closely-
adjacent areas that are totally cut-off from each other. " No
two marine faunas are more distinct, with hardly a fish, shell,
or crab in common, than those of the eastern and western
shores of South and Central America ; yet these great faunas
are separated only by the narrow, but impassable, isthmus of
Panama." On opposite sides of high mountain-chains, also,
there are marked differences in the organic forms — differ-
ences not so marked as where the barriers are absolutely im-
passable ; but much more marked than are necessitated b}'
unlikenesses of physical conditions.

Not less suggestive is the converse fact, that wide geogra-
phical areas which offer decided geologic and meteorologic
contrasts, are peopled by nearly-allied groups of organisms, if
there are no barriers to migration. " The naturalist in tra-

DISTRIBUTION. 319

veiling, for instance, from north to south never fails to be
Btruck by the manner in which successive groups of beings,
specifically distinct, yet clearly related, replace each other.
He hears from closely allied, )Tet distinct kinds of birds,
notes nearly similar, and sees their nests similarly constructed,
but not quite alike, with eggs coloured in nearly the same
manner. The plains near the Straits of Magellan are inhabit-
ed by one species of Rhea (American Ostrich), and north-ward
the plains of La Plata by another species of the same genus ;
and not by a true ostrich or emeu, like those found in Africa
and Australia under the same latitude. On these same plains
of La Plata, we see the agouti and bizcacha, animals having
nearly the same habits as our hares and rabbits and belonging
to the same order of Rodents, but they plainly display an
American type of structure. "We ascend the lofty peaks of
the Cordillera and we find an alpine species of bizcacha ; wre
took to the waters, and we do not find the beaver or musk-
rat, but the coypu and capybara, rodents of the American
type. Innumerable other instances could be given. If we
look to the islands off the American shore, however much
they may differ in geological structure, the inhabitants, though
they may be all peculiar species, are essentially American."

TVhatisthe generalization that expresses these two groups
of facts ? On the one hand, wTe have similarly-conditioned,
and sometimes nearly- adjacent, areas, occupied by quite dif-
ferent Faunas. On the other hand, we have areas remote from
each other in latitude, and contrasted in soil as well as climate,
which are occupied by closely-allied Faunas. Clearly then, as
like organisms are not universally, or even generally, found
in like habitats ; nor very unlike organisms, in very unlike
habitats ; there is no manifest pre-determined adaptation of
the organisms to the habitats. The organisms do not occur
in such and such places, solely because they are either spe-
cially fit for these places, or more fit for them than all other
organisms.

The induction under which these facts come, and whiel;

o20 THE INDUCTIONS OF BIOLOGY.

unites tliera with various other facts, is a totally-different one.
When we see that the similar areas peopled by dissimilar
forms, are those between which there are impassable barriers ;
while the dissimilar areas peopled by similar forms, are those
between which there are no such barriers ; we are at once re-
minded of the general truth exemplified in the last section : —
the truth that each species of organism, tends ever to expand
its sphere of existence — to intrude on other areas, other
modes of life, other media ; and through these perpetually-
recurring attempts to thrust itself into every accessible habitat,
spreads until it reaches limits that are for the time insur-
mountable.

§ 107. We pass now to the distribution of organic forms
in Time. Geological inquiry has established the truth, that
during a Past of immeasurable duration, plants and animals
have existed on the Earth. In all countries their buried
remains are found in greater or less abundance. From com-
paratively small areas, multitudinous different forms have been
exhumed. Every exploration of new areas, and every closer
inspection of areas already explored, brings more such forms
to light. And beyond question, an exhaustive examination of
all exposed strata, and of all strata now covered by the sea,
would disclose forms immensely out-numbering all those at
present known. Further, it is now becoming manifest to
geologists, that even had Ave before us every kind of fossil
which exists, we should still have nothing like a complete
index to the past inhabitants of our globe. It has been long
known that many sedimentary deposits have been so altered
by the heat of adjacent molten matter, as greatly to obscure
the organic remains contained in them. The extensive form-
ations once called " transition," and now re-named " meta-
m orphic," are acknowledged to be formations of sedimentary
origin, from which all traces of such fossil as they probably
included, have been obliterated by igneous action. And the
conclusion forcing itself into acceptance, is, that igneous rock

DISTRIBUTION. 321

haa everywhere resulted from tlie complete melting-up oi
beds of detritus, originally deposited by water. How long the
reactions of the Earth's molten nucleus on its cooled crust,
have been thus destroying the records of Life which this cooled
crust entombed, it is impossible to say ; but there are strong
reasons for believing that the records which remain, bear but,
n small ratio to the records which have been destroyed. Thus
we have but extremely-imperfect data for any conclusions
respecting the distribution of organic forms in Time. Sonio
few generalizations, however, may be regarded as established.

One is, that the plants and animals now existing, mostly
differ from the plants and animals which have existed.
Though there are species common to our present Fauna and
to past Faunas ; yet the fades of our present Fauna differs,
more or less, from the fades of each past Fauna. On carry-
ing out the comparison, we find that past Faunas differ from
each other ; and that the differences between them are pro-
portionate to their degrees of remoteness from each other in
Time, as measured by their relative positions in the sediment-
ary series. So that if we take the assemblage of organic
forms living now, and compare it with the successive assem-
blages of organic forms that have lived in successive geologic
epochs, we find that the farther we go back into the past, the
greater does the unlikeness become : the number of species
and genera common to the compared assemblages, becomes
smaller and smaller ; and the assemblages differ more and
more in their general characters. Though a species of
brachiopod now extant, is almost identical with a species
found in Silurian strata, and though between the Silurian
Fauna and our own, there are sundry common genera of mol-
luscs ; it is still undeniable that there is a proportion between
lapse of time and divergence of organic forms.

This divergence is comparatively slow and continuous
where there is continuity in the geological formations ; but is
sudden and comparatively wide, wherever there occurs a
groat break in the succession of strata. The contrasts which

'622 THE INDUCTIONS OF BIOLOGY.

thus arise gradually or all at once, in formations that are
continuous or discontinuous, are of two kinds. Faunas of
different eras, are distinguished partly by the absence from
one of types that are present in the other ; and partly by the
unlikenesses between the types that are common to both.
Such distinctions between Faunas as are due to the appear-
ance or disappearance of types, are of secondary significance :
they possibly, or probably, do not imply anything more than
migrations or extinctions. The most significant distinctions
are those between successive groups of organisms of the same
type. And among such, as above said, the differences that
arise are, speaking generally, small and continuous where a
series of conformable strata gives proof of continued existence
of the type in the locality : while they are comparatively
large and abrupt, where there is evidence that between the
deposit of the adjacent formations, a long period elapsed.

Another general fact, referred to by Mr Darwin as one
which palaeontology has made tolerably certain, is that forms
and groups of forms which have once disappeared from the
Earth, do not reappear. Some few species and a good many
genera, have continued throughout the whole period geologi-
cally recorded. But omitting these as exceptional, it may be
said that each species after arising, spreading for an era, and
continuing abundant for an era, eventually declines and be-
comes extinct ; and that similarly, each genus during a longer
period increases in the number of its species, and during a
longer period dwindles and at last dies out. Having made
its exit, neither species nor genus ever re-enters. And the
like is true, even of those larger groups called orders. Four
tvpes of reptiles that were once abundant, have not been
found in modern formations, and do not at present exist.
Though nothing: less than an exhaustive examination of all
strata, can prove conclusively that a special or general form of
organization when once lost is never reproduced ; yet so
many facts point to this inference, that its truth can scarcely
be doubted.

DISTRIBUTION. ?>23

To form a conception of the total amount and general
direction of the change that has arisen in organic forms during
the geologic time measured by our sedimentary series, is at
present impossible — the data are insufficient. The immense
contrast between the few and low forms of the earliest-known
Fauna, and the many and high forms of our existing Fauna,
has been commonly supposed to prove, not only great
change but great progress. Nevertheless, this appearance
of progress may be, and prob.ibly is, mainly illusive.
Wider knowledge and increased power of interpretation, have
made it manifest that remains of comparative^ well-organized
creatures, really existed in strata long supposed to be devoid
of them ; and that where they are actually absent, the nature
of the strata often supplies a sufficient explanation of their
absence, without assuming that they did not exist when these
strata were formed. It has now become a tenable hypothesis,
that the successively-higher types fossilized in our successive-
ly-later deposits, indicate nothing more than successive migra-
tions from pre-existing continents, to continents that were
step by step emerging from the ocean — migrations which
necessarily began with the inferior orders of organisms, and
included the successively-superior orders as the new lands
became more accessible to them, and better fitted for them.*

While the evidence usually supposed to prove progres-
sion, is thus untrustworthy, there is trustworthy evidence
that there has been, in many cases, little or no progression.
Though the types which have existed from pakeozoic and me-
sozoic times clown to the present day, are almost universally
changed ; yet a comparison of ancient and modern members
of these types, shows that the total amount of change is not
relatively great, and that it is not manifestly towards a higher
organization. Though nearly all the living forms which have
prototypes in early formations, differ from these prototypes
specifically, and in most cases generically ; yet ordinal pecu-
liarities are, in very numerous cases, maintained from the earli-

* For explanations, sec "Illogical Geology." Essays: Second Series.

824 TUE INDUCTIONS OF BIOLOGY.

est times geologically recorded, down to our own time ; and we
have no visible evidence of superiority in the existing genera
of these orders. In his lecture " On the Persistent Types of
Animal Life," Prof. Huxley enumerates many cases. On
the authority of Dr. Hooker, he stated " that there are Carbon-
iferous plants which appear to be generically ideutical with
some now living ; that the cone of the Oolitic Araucaria is
hardily distinguishable from that of an existing species ; that a
true Pinu8 appears in the Purbecks and a Juglans in the
chalk." Among animals he named palaeozoic and mesozoic
corals which are very like certain extant corals ; genera of Silu-
rian molluscs that answer to existing genera ; insects and arach-
nids in the coal formations, that are not more than generically
different from some of our own insects and arachnids. He
instanced " the Devonian and Carboniferous Pleur acanthus,
which differs no more from existing sharks than these do
from one another ; " early mesozoic reptiles " identical in the
essential characters of their organization with those now liv-
ing ; " and Triassic mammals which did not differ " nearly so
much from some of those which now live, as these differ from
one another." Continuing the argument in his " Anniversary
x\ddresa to the Geological Society " in 1862, Prof. Huxley
gave many cases in which the changes that have taken place,
are not changes towards a more specialized or higher organ-
ization— asking " in what sense are the Liassic Chelonia infe-
rior to those which now exist % How are the Cretaceous
Ichthyosauria, Plesiosauria, or Pterosauria less embryonic
or more differentiated species than those of the Lias ? "
While, however, contending that in most instances " positive
evidence fails to demonstrate any sort of progressive modifi-
cation towards a less embryonic or less generalized type in a
great many groups of animals of long-continued geological
existence ; " Prof. Huxley added, that there are other groups
" co-existing with them, under the same conditions, in which
more or less distinct indications of such a process seem to be
traceable." And in illustration of this, he named that better

distribi t:on. 325

development of the vertebne which characterizes some of
the more modern fishes and reptiles, when compared with an-
cient fishes and reptiles of the same orders ; and the " regu-
larity and evenness of the dentition of the Ajiojplothertum
as contrasting with that of existing Artiodactyles."

The facts thus summed up, do not show that higher forms
have not arisen on the Earth in the course of geologic time,
any more than the facts commenly cited prove that higher
forms have arisen ; nor are they regarded by Prof. Huxley
as showing this. "Were the types which have survived from
palaeozoic and mesozoic periods down to our own day, the
only types ; and did the modifications, rarely of more than
generic value, which these types have undergone, give no
better evidences of increase1 complexity than are actually
given by them ; then it would bt inferable that there has
been no appreciable advance among organic forms. But
there now exist, and have existed during the more recent
geologic epochs, various types which are not known to have
existed in earlier epochs — some of them widely unlike
these persistent types, and some of them nearly allied to
these persistent types. As yet, we know nothing respecting
the origins of these new types. But it is quite possible that
causes like those which have produced generic differences in
the persistent types, may, in some or many cases, have pro-
duced modifications great enough to constitute ordinal differ-
ences— may have resulted in the formation of types that are
now classed as separate. If structural contrasts not exceed-
ing certain moderate limits, are held to mark only generic
distinctions ; and if organisms displaying larger structural
contrasts are considered ordinally or typically distinct ; it is
dear that the persistence of a given type through a long
geologic period without apparently undergoing deviations of
more than generic value, by no means disproves the occurrence
of far greater deviations ; since the forms resulting from such
far greater deviations, being regarded as typically distinct
forms, will not be taken as evidence of great change in the

326 THE INDUCTIONS OF BIOLOGY.

original type. That which. Prof. Huxley's argument proves,
and that only which he considers it to prove, is that organisms
have no innate tendencies to assume higher forms, and that
" any admissible hypothesis of progressive modification, must
be compatible with persistence without progression through
indefinite periods."

One very significant fact must be added, concerning the
relation between distribution in Time and distribution in
Space. I quote it from Mr Darwin : — " Mr Clift many years
ago showed that the fossil mammals from the Australian
caves were closely allied to the living marsupals of that con-
tinent. In South America, a similar relationship is manifest
even to an uneducated eye, in the gigantic pieces of armour
like those of the armadillo, found in several parts of La Plata ;
and Professor Owen has shown in the most striking manner
that most of tie fossil mammals, buried there in such num-
bers, are related to the South American types. This relation-
ship is even more clearly seen in the wonderful collection of
fossil bones made by MM. Lund and Clausen in the caves of
Brazil. I was so much impressed with these facts that I
strongly insisted, in 1839 and 1845, on this ' law of the suc-
cession of types/ — on ' this wonderful relationship in the
same continent between the dead and the living.' Professor
Owen has subsequently extended the same generalization to the
mammals of the Old World. We see the same law in this
author's restorations of the extinct and gigantic birds of New
Zealand. We see it also in the birds of the caves of Brazil.
Mr Woodward has shown that the same law holds good, with
sea-shells, but from the wide distribution of most genera of
molluscs, it is not well displayed by them. Other cases could
be added, as the relation between the extinct and living land-
fihells of Madeira ; and between the extinct and living brack-
ish-water shells of the Aralo-Caspian Sea.'"

The general results then, are these. Our knowledge of
distribution in Time, being derived wholly from the evidence
afforded by fossils, is limited to that geologic time of which

DISTRIBUTION. 327

some records remain : cannot extend to those pre-geologic
times the records of which have been obliterated. From
these remaining records, which probably form but a small
fraction of the whole, the general facts deducible are : — That
such organic types as have lived through successive epochs,
have almost universally undergone modifications of specific
and generic values — modifications which have commonly been
great in proportion as the period has been long. That besides
the types that have persisted from ancient eras down to our
own era, other types have from time to time made their ap-
pearance in the ascending series of our strata — types of which
some are lower and some higher than the types previously
recorded ; but whence these new types came, and whether
anj of them arose by divergence from the previously-recorded
types, the evidence does not yet enable us to say. That in
the course of long geologic epochs, nearly all species, most
gerera, and a few orders, become extinct ; and that a species,
genus, or order, which has once disappeared from the Earth,
never reappears. And, lastly, that the Fauna now occupying
each separate area of the Earth's surface, is very nearly allied
to the Fauna which existed on that area during recent geolo
gic times.

§ 108. Omitting sundry minor generalizations, the exposi-
tion of which would involve too much detail, what is to be
said of these major generalizations ?

The distribution in Space cannot be said to imply that or-
ganisms have been designed for their particular habitats, and
placed in them ; since, besides the habitat in which an organ-
ism is found there are commonly other habitats, as well or
better for it, from which it is absent — habitats to which it
is so much better fitted than organisms now occupying them,
that it extrudes these organisms when allowed the oppor-
tunity. Neither can we suppose that one end has been to
establish varieties of Floras and Faunas ; since, if so, why are
the Floras and Faunas but little divergent in widely-sundered

328 THE INDUCTIONS OF BIOLOGY.

areas between which migration is possible, while they are
markedly divergent in adjacent areas between which migra-
tion is impossible ?

Passing to distributions in Time, there arise the questions
— why during nearly the whole of that vast period geological-
ly recorded, have there existed none of those highest organic
forms which have now overrun the Earth ? — how is it that we
find no traces of a creature endowed with large capacities for
knowledge and happiness ? The answer that the Earth was
not, in remote times, a fit habitation for such a creature, be-
sides being unwarranted by the evidence, suggests the equally
awkward question — why during untold millions of j^earsdid the
Earth remain fit only for inferior creatures ? What, again, is
the meaning of this extinction of types ? To conclude that
the saurian type was replaced by other types at the beginning
of the tertiary period, because this type was not adapted to
the conditions which then arose, is to conclude that this type
could not be modified into fitness for the conditions ; and this
conclusion is quite at variance with the hypothesis that creative
skill is shown in the multiform adaptations of one type to
many ends.

What interpretations may rationally be put on these and
other general facts of distribution in Space and Time, we
shall see in the next division of this work ; to which le* lie
now pass

PART III.

THE EVOLUTION OF LIFE,

22

CHAPTER I.

PRELIMINARY.

§ 109. In the foregoing Part, we have contemplated the
most important of the generalizations to which biologists
have been led by observation of organisms. These Induc-
tions of Biology have also been severally glanced at on their
deductive sides ; for the purpose of noting the harmony that
exists between them, and those primordial truths set forth in
First Principles. Having thus studied the leading pheno-
mena of life separately, we are prepared for studying them in
their ensemble, with the view of arriving at the most general
interpretation of them.

There is an ensemble of vital phenomena presented by each
organism in the course of its growth, development, and decay ;
and there is an ensemble of vital phenomena presented by
the organic world as a whole. Neither of these can be
properly dealt with apart from the other. But the last of
them may be separately treated more conveniently than the
first. What interpretation we put on the facts of structure
and function in each living body, depends entirely on our
conception of the mode in which living bodies in general
have originated. To form some conclusion respecting this
mode — a provisional if not a permanent conclusion — must
therefore be our first slop.

A\re have to choose between two hypotheses — the hypo-
thesis of Special Creation and the hypothesis of Evolution.

332 THE EVOLUTION OF LIFE.

Either the multitudinous kinds of organisms that now exist,
and the still more multitudinous kinds that have existed
during past geologic eras, have been from time to time separ-
ately made ; or they have arisen by insensible steps, through
actions such as we see habitually going on. Both hypo-
theses imply a Cause. The last, certainly as much as the
first, recognizes this Cause as inscrutable. The point at,
issue is, how this inscrutable Cause has worked in the pro
Auction of living forms. This point, if it is to be decided at
all, is to be! decided only by examination of evidence. Lot
us inquire which of these antagonist hypotheses is most con-
gruous with established facts.

CHAPTER II.
GENERAL ASPECTS OF THE SPECTAL-CHEATIOX-IIYPOTHESIS*

§ 110. Early ideas are not usually true ideas. Unde-
veloped intellect, be it that of an individual or that of the
race, forms conclusions which require to be revised and re-
revised, before they reach a tolerable correspondence with
realities. Were it otherwise, there would be no discovery,
no increase of intelligence. What we call the progress of
knowledge, is the bringing of Thoughts into harmony with
Things ; and it implies that the first Thoughts are either
wholly out of harmony with Things, or in very incomplete
harmony with them.

If illustrations be needed, the history of every science
furnishes them. The primitive notions of mankind as to the
structure of the heavens, were wrong ; and the notions
which replaced them were successively less wrong. The
original belief respecting the form of the Earth was wrong ;
and this wrong belief survived through the first civilizations.
The earliest ideas that have come down to us concerning the
natures of the elements were wrong; and only in quite
recent times has the composition of matter in its various
forms been bettei understood. The interpretations of me-
chanical facts, of meteorological facts, of physiological facts,

* Several of the ar^umeuts used in this chapter and in that which follows it,
formed parts of an essay on "the Development Hypothesis," originally published
in 1852

334 THE EVOLUTION OF LIFE.

wore at first wrong. In all these cases men set out with
beliefs which, if not absolutely false, contained but small
amounts of truth disguised by immense amounts of error.

Hence the hypothesis that living beings resulted from
special creations, being a primitive hypothesis, is probably
an untrue hypothesis. If the interpretations of Nature given
b}r aboriginal men, were erroneous in other directions, they
were most likely erroneous in this direction. It would be
strange if, while these aboriginal men failed to reach the truth
in so many cases where it is comparatively conspicuous,
they yet reached the truth in a case where it is compara-
tively hidden.

§ 111. Besides the improbability given to the belief in
special creations, by its association with mistaken early
beliefs in general ; a further improbability is given to it by
its association with a special class of mistaken beliefs. It
belongs to a family of beliefs which have one after another
been destroyed by advancing knowledge ; and is, indeed,
almost the only member of the family that survives among
educated people.

We all know that the savage thinks of each striking phe-
nomenon, or group of phenomena, as caused by some separate
personal agent ; that out of this fetishistic conception there
grows up a polytheistic conception, in which these minor per-
sonalities are variously generalized into deities presiding over
different divisions of nature ; and that these are eventually
furiher generalized. This progressive consolidation of causal
agencies, may be traced in the creeds of all races ; and is
far from complete in the creeds of the most advanced races.
The unlettered rustics who till our fields, do not let the con-
sciousness of a supreme power wholly absorb the aboriginal
conceptions of good and evil spirits, and charms or secret
potencies dwelling in particular objects. The earliest mode
of thinking changes, only as fast as the constant relations
among phenomena are established. Scarcely less

THE SPECIAL-CREATION-HYPOTHESIS. 335

familiar is tlie truth, that while accumulating knowledge
makes these conceptions of personal causal agents gradually
more vague, as it merges them into general causes, it also
destroys the habit of thinking of them as working after the
methods of personal agents. "We do not now, like Kepler,
assume guiding spirits to keep the planets in their orbits.
It is no longer the universal belief that the sea was once for
all mechanically parted from the dry land; or that the
mountains were placed where we see them by a sudden cre-
ative act. All but a narrow class have ceased to suppose
sunshine and storm to be sent in some arbitrary succession.
The majority of educated people have given up thinking of
epidemics as punishments inflicted by an angry deity. Nor
do even the common people regard a madman as one pos-
sessed by a demon. That is to say, we everywhere see
fading away the anthropomorphic conception of the Un-
known Cause. In one case after another, is abandoned that
interpretation which ascribes phenomena to a will analogous
to the human will, working by methods analogous to human
methods.

If, then, of this once-numerous family of beliefs, the im-
mense majority have become extinct, we may not unrea-
sonably expect that the few remaining members of the family
will become extinct. One of these is the belief we are here
considering — the belief that each species of organism was
specially created. Many who in all else have abandoned
the aboriginal theory of things, still hold this remnant of the
aboriginal theory. Ask any tolerably-informed man whether
he accepts the cosmogony of the Indians, or the Greeks, or
the Hebrews, and he will regard the question as next to an
insult. Yet one element common to these cosmogonies he
very likely retains : not bearing in mind its origin. For
whence did he get the doctrine of special creations ? Catechise
him, and he is forced to confess that it was put into his mind
in childhood, as one portion of a story which, as a whole, ho
has long since rejected. Why this fragment is likely to bo

4

33tt

THE EVOLL'TJON OF LIFE.

right while all the rest is wrong, he is unable to say. May
we not then expect, that the relinquishment of all other
parts of this story, will bye and bye be followed by the
relinquishment of this remaining part of it ?

§ 112. The belief which we find thus questionable, both
a.s being a primitive belief and as being a belief belonging to
nn almost-extinct family, is a belief that is not countenanced
by a single fact. No one ever saw a special creation ; no
one ever found proof of an indirect kind, that a special
creation had taken place. It is significant, as Dr Hooker
remarks, that naturalists who suppose new species to be
miraculously originated, habitually suppose the origination
to occur in seme region remote from human observation.
'Wherever the order of organic nature is exposed to the view of
zoologists and botanists, it expels this conception ; and the
conception sur rives only in connexion with imagined places,
where the order of organic phenomena is unknown.

Besides being absolutely without evidence to give it exter-
nal support, this hypothesis of special creations cannot sup-
port itself internally — cannot be framed into a coherent
thought. It is one of those illegitimate symbolic concep-
tions, so continually mistaken for legitimate symbolic concep-
tions (First Principles, § 9), because they remain untested.
Immediately an attempt is made to elaborate the idea into
anything like a definite shape, it proves to be a pseud-idea,
admitting of no definite shape. Is it supposed that a new
organism, when specially created, is created out of nothing ?
If so, there is a supposed creation of matter ; and the crea-
tion of matter is inconceivable — implies the establishment of
a relation in thought between nothing and something — a
relation of which one term is absent — an impossible rela-
tion. Is it supposed that the matter of which the new or-
ganism consists, is not created for the occasion, but is taken
out of its pre-existing forms and arranged into a new form? If
so, we are met by the question — how is the re-arrangement

THE SPECIAL -CREATION- HYPOTHESIS. 837

effected ? Of the myriad atoms going to the composition of
the new organism, all of them previously dispersed through
the neighbouring air and earth, does each, suddenly dis-
engaging itself from its combinations, rush to meet the rest,
unite with them into the appropriate chemical compounds,
and then fall with certain others into its appointed place in
the aggregate of complex tissues and organs ? Surely thus
to assume a myriad supernatural impulses, differing in their
directions and amounts, given to as many different atoms, is a
multiplication of mysteries rather than the solution of a
mystery. For every one of these impulses, not being the
result of a force locally existing in some other form, implies
the creation of force ; and the creation of force is just as
inconceivable as the creation of matter. And thus is it with
all attempted ways of representing the process. The old
Hebrew idea that God takes clay and moulds a new creature,
as a potter might mould a vessel, is probably too grossly an-
thropomorphic to be accepted by any modern defender of the
special-creation doctrine. But having abandoned this crude
belief, what belief is he prepared to substitute ? If a new
organism is not thus produced, then in what way is a new
organism produced ? or rather — in what way can a new
organism be conceived to be produced ? We will not ask for
the ascertained mode, but will be content with a mode
that can be consistently imagined. No such mode, however,
is assignable. Those who entertain the proposition that each
kind of organism results from a divine interposition, do so
because they refrain from translating words into thoughts.
The case is one of those where men do not really believe, but
rather believe they believe. For belief, properly so called,
implies a mental representation of the thing believed; and
no such mental representation is here possible.

§ 113. If we imagine mankind to be contemplated by
some creature as short-lived as an ephemeron, but possessing
intelligence like our own — if we imagine such a being study-

&38 THE EVOLUTION OF LIF£.

Lag men and women, 'during his few hours of life, ana
speculating as to the mode in which they came into existence ;
it is manifest that, reasoning in the usual way, he would
euppose each man and woman to have been separately
created. ISTo appreciable changes of structure occurring in
any of them during the few hours over which hi& observa-
tions extended, this being would probably infer that no
changes of structure were taking place, or had taken place j
and that from the outset, each man and woman had pos-
sessed all the characters then visible — had been orginally
formed with them. This would naturally be the first im-
pression. The application is obvious. A human life
is ephemeral compared with the life of a species ; and even
the period over which the records of human experience
extend, is ephemeral compared with the life of a species.
There is thus a parallel contrast between the immensely-long
series of changes that have occurred during the life of a
species, and that small portion of the series open to our view.
And there is no reason to suppose that the first conclusion
drawn by mankind from this small part of the series visible
to them, is any nearer the truth, than would be the conclu-
sion of the supposed ephemeral being respecting men and
women.

This analogy, suggesting as it does how the hypothesis of
special creations is merely a formula for our ignorance, raises
the question — what reason have we to assume special crea-
tions of species but not of individuals; unless it be that in
the case of individuals we directly know the process to be
otherwise, but in the case of species do not directly know it
to be otherwise ? Have we any ground for concluding that
species were specially created, except the ground that we
have no immediate knowledge of their origin ? And does our
ignorance of the manner in which they arose, warrant us in
asserting that they arose by special creation ?

Another question is suggested by this analogy. Those
who, in the absence of immediate evidence of the way in

THE SPECIAL-CREATIGN-HYTOTHESIS. 339

which species arose, assert that tliey arose not in any way
analogous to that in which individuals arise, but in a totally
distinct way, think that by this supposition they honour the
Unknown Cause of things ; and they oppose any antagonist
doctrine as amounting to an exclusion of divine power from
the world. But if divine power is demonstrated by the
separate creation of each species, would it not have been still
better demonstrated by the separate creation of each indivi-
dual ? "Why should there exist this process of natural gene-
sis ? THiy should not omnipotence have been proved by the
supernatural production of plants and animals everywhere
throughout the world from hour to hour ? Is it replied that
the Creator was able to make individuals arise from one
another in a natural succession, but not to make species thus
arise ? This is to assign a limit to power instead of magni-
fying it. Is it replied that the occasional miraculous origina-
tion of a species was practicable, but that the perpetual miracu-
lous origination of countless individuals was impracticable ?
This also is a derogation. Either it was possible or not pos-
sible to create species and individuals after the same general
method. To say that it was not possible is suicidal in those
who use this argument ; and if it was possible, it is required
to say what end is served by the special creation of species
that would not have been better served by the special creation
of individuals. Again, what is to be thought of the

fact that the great majority of these supposed special creations
took place before mankind existed ? Those who think that di-
vine power is demonstrated by special creations, have to answer
the question — to whom demonstrated? Tacitly or avowedly,
they regard the demonstrations as being for the benefit of
mankind. But if so, to what purpose were the millions
of these demonstrations which took place on the Earth when
there were no intelligent beings to contemplate them ? Did
the Unknowable thus demonstrate his power to himself?
Few will have the hardihood to say that any such demon-
stration was needful. There is no choice but to regard them,

340 THE EVOLUTION OF LIFE.

either as superfluous exercises of power, which is a derogatory
supposition, or as exercises of power that were necessary
because species could not be otherwise produced, which is
also a derogatory supposition.

§ 114. Those who espouse the hypothesis of special cre-
ations, entangle themselves in other theological difficulties.
This assumption that each kind of organism was specially
designed, carries with it the implication that the designer
intended everything that results from the design. There is
no escape from the admission, that if organisms were severally
constructed with a view to their respective ends ; then
the character of the constructor is indicated both by the
ends themselves, and the perfection or imperfection with
which the organisms are fitted to them. Observe the con-
sequences.

Without dwelling on the question put in a recent chap-
ter, why during untold millions of years there existed on
the Earth no beings endowed with capacities for wide
thought and high feeling, we may content ourselves with
asking why, at present, the Earth is largely peopled by
creatures which inflict on each other, and on themselves, so
much suffering? Omitting the human race, whose defects
and miseries the current theology professes to account for,
and limiting ourselves to the lower creation, what must we
think of the countless different pain-inflicting appliances
and instincts with which animals are endowed ? Not only
now, and not only ever since men have lived, has the Earth
been a scene of warfare among all sentient creatures ; but
palceontology shows us that, from the earliest eras geologi-
cally recorded, there has been going on this universal carn-
age. Fossil structures, in common with the structures of
existing animals, show us elaborate weapons for destroying
other animals. We have unmistakable proof that through-
out all past time, there has been a perpetual preying of the
superior on the inferior — a ceaseless devouring of the weak

THE SPEOIAL-CREATION-HYPOTHESIS. 341

by the strong. ITow is this to be explained ? How happens
it that animals were so designed as to render this bloodshed
necessary ? How happens it that in almost every species, the
number of individuals annually born is such that the ma-
jority die of starvation or by violence before arriving at ma-
turity? Whoever contends that each kind of animal was
specially designed, must assert either that there was a deli-
berate intention on the part of the Creator to produce those
results, or that there was an inability to prevent them.
Which alternative does he prefer ? To cast an imputation on
the divine character, or assert a limitation of the divine
power ? It is useless for him to plead that the destruction of
the less powerful by the more powerful, is a means of pre-
venting the miseries of decrepitude and incapacity, and
therefore works beneficently. For even were the chief mor-
tality among the aged instead of among the young, there
would still arise the unanswerable question — why were not
animals constructed in such ways as to avoid these evils ?
why were not their rates of multiplication, their degrees of
intelligence, and their propensities, so adjusted that these
sufferings might be escaped ? And if decline of vigour was
a necessary accompaniment of age, why was it not provided
that the organic actions should end in sudden death, when-
ever they fell below the level required for pleasurable exist-
ence ? Will any one who contends that organisms were
specially designed, assert that they could not have been
designed so as to prevent suffering ? And if he admits that
they could have been made so as to prevent suffering, will
he assert that the Creator preferred so making them as to
inflict suffering ?

Even as thus presented, the difficulty is sufficiently great ;
but it appears immensely greater when we examine the facta
more closely. So long as we contemplate only the preying
of the superior on the inferior, some good appears to be
extracted from the evil — a certain amount of life of a higher
order, is supported by sacrificing a great deal of life of a

342 THE EVOLUTION OF LIFE.

lower order. So long, too, as we leave out all mortality but
that which, by carrying off the least perfect members of each
species, leaves the most perfect members to continue the
species ; we see some compensating benefit reached through
the suffering inflicted. But what shall we say on finding
innumerable cases in which the suffering inflicted brings no
compensating benefit ? What shall we say when we see the
inferior destroying the superior ? "What shall we say on
discovering elaborate appliances for securing the prosperity
of organisms incapable of feeling, at the expense of misery
to organisms capable of happiness ?

Of the animal kingdom as a whole, more than half the
species are parasites. " The number of these parasites,"
says Prof. Owen, " may be conceived when it is stated that
almost every known animal has its peculiar species, and
generally more than one, sometimes as many as, or even
more kinds than, infest the human body." Passing over the
evils thus inflicted on animals of inferior dignity, let us limit
ourselves to the case of man. The Bothriocephalus latin
and the Taenia solium, are two kinds of tape-worm, which
flourish in the human intestines ; producing great constitu-
tional disturbances, sometimes ending in insanity ; and from
the germs of the Taenia, when carried into other parts of the
body, arise certain partially-developed forms known as Cysti-
cerci, Echinococci, and Ccenuri, which cause disorganization
more or less extensive in the brain, the lungs, the liver,
the heart, the eye, &c, often ending fatally after long-
continued suffering. Five other parasites, belonging to
a different class, are found in the viscera of man — the
Trichocephahts, the Oxyuris, the Strongylus (two species),
the Ancylostomum, and the Ascaris ; which, beyond that
defect of nutrition which they necessarily cause, sometimes
induce certain irritations that lead to complete demoraliza-
tion. Of another class of entozoa, belonging to the sub-
division Trematoda, there are five kinds found in different
organs of the human body — the liver and gall ducts, the

THE SPECIAL-CREATION-HYPOTHESIS. 343

portal vein, the intestine, the bladder, the eye. Then we
have the Trichina spiralis, which passes through one phase of
its existence imbedded in the muscles and through another-
phase of its existence in the intestine ; and which, by the
induced disease Trichiniasis, has lately committed such ra-
vages in Germany, as to cause a panic. And to these we
must add the Guinea-worm, which in some part of Africa
and India, makes men miserable by burrowing in their legs.
From this list of entozoa, which is by no means complete,
let us pass to the epizoa. There are two kinds of Acari,
one of them inhabiting the follicles of the skin, and the
other producing the itch. There are other creatures that
bury themselves beneath the skin, and lay their eggs there ;
and there are three species of lice which infest the surface of
the body. Nor is this all : besides animal parasites, there
are sundry vegetal parasites, which grow and multiply at
our cost. The Sarcina ventriculi inhabits the stomach, and
produces gastric disturbance. The Leptothrix buccalis is
extremely general in the mouth, and may have something
to do with the decay of teeth. And besides these, there are
microscopic fungi which produce ringworm, porrigo, pityri-
asis, thrush, &c. Thus the human body is the
habitat of parasites, internal and external, animal and ve-
getal, numbering, if all were set down, some two or three
dozen species ; sundry of which are peculiar to man, and
many of which produce in man great suffering and not un-
frequently death. What interpretation is to be put on these
facts by those who espouse the hypothesis of special crea-
tions ? According to this hypothesis, all these parasites
were designed with a view to their respective modes of life.
They were endowed with constitutions fitting them to live
by absorbing the j iices of the human body ; they were fur-
nished with appliances, often of a formidable kind, enabling
them to root themselves in and upon the human body ; and
they were made prolific in an almost incredible degree, that
their germs might have a sufficient number of chances of

344 THE EVOLUTION OF LIFE.

finding their way into the human body. In short, elaborate
contrivances were combined to insure the continuance of
their respective races ; and to make it impossible for the suc-
cessive generations of men to avoid being preyed upon by
them. "What shall we say to this arrangement ? Shall we
say that man, " the head and crown of things," was provided
as a habitat for these parasites ? Or shall we say that these
degraded creatures, incapable of thought or enjoyment, were
created that they might cause unhappiness to man? One
or other of these alternatives must be chosen by those who
contend that every kind of organism was separately devised
by the Creator. "Which do they prefer ? With the concep-
tion of two antagonistic powers, which severally work good
and evil in the world, the facts are congruous enough. But
with the conception of a supreme beneficence, this gratuitous
infliction of misery on man, in common with all other terres
trial creatures capable of feeling, is absolutely incompatible.

5 115. See then the results of our examination. The
belief in special creations of organisms, is a belief that arose
among men during the era of profoundest darkness ; and it
belongs to a family of beliefs which have nearly all died out
as enlightenment has increased. It is without a solitary
established fact on which to stand ; and when the attempt is
made to put it into definite shape in the mind, it turns out to
be only a pseud-idea. This mere verbal hypothesis, which
men idly accept as a real or thinkable hypothesis, is of the
same nature as would be one, based on a day's observation of
human life, that each man and woman was specially created
— an hypothesis not suggested by evidence, but by lack of
.evidence — an hypothesis which formulates absolute ignorance
into a semblance of positive knowledge. Further, we see that
this hypothesis, wholly without support, essentially inconceiv-
able, and thus failing to satisfy men's intellectual need of an
interpretation, fails also to satisfy their moral sentiment.
It is quite inconsistent with those conceptions of the divina

THE SPECIAL-CREATION-HYPOTHESIS. 345

nature which, they profess to entertain. If infinite power
was to be demonstrated, then, either by the special creation
of every individual, or by the production of species after a
method akin to that in which individuals are produced, it
would be better demonstrated than by the use of the two
methods which the hypothesis assumes to be necessary. And
if infinite goodness was to be demonstrated, then, not only
do the provisions of organic structure, if they are especially
devised, fail to demonstrate it ; but there is an enormous
mass of them which imply malevolence rather than bene-
volence.

Thus, however regarded, the hypothesis of special creations
turns out to be worthless — worthless by its derivation ;
worthless in its intrinsic incoherence ; worthless as absolutely
without evidence ; worthless as not supplying an intellectual
need ; worthless as not satisfying a moral want. We must
therefore consider it as counting for nothing, in opposition
to any other hypothesis respecting the origin of organic
being?.

23

CHAPTER III.

GENERAL ASPECTS OF THE EVOLUTIOX-HYPOTnESIS.

§ 116. Just as the supposition that races of organisms
have been specially created, is discredited by its origin ; so,
conversely, the supposition that races of organisms have
been evolved, is credited by its origin. Instead of being
a conception suggested and accepted when mankind were
profoundly ignorant, it is a conception born in times of com-
parative enlightenment. Moreover, the belief that all organic
forms have arisen in conformity with uniform laws, instead
of through breaches of uniform laws, is a belief that has
come into existence in the most-instructed class, living in
these better-instructed times. Not among those who have
paid no attention to the order of Nature, has this idea made
its appearance ; but among those whose pursuits have famil-
iarized them with the order of Nature. Thus the derivation
of this modern hypothesis is as favourable as that of the
aucient hypothesis is unfavourable

§ 117. A kindred antithesis exists between the two fami-
lies of beliefs, to which the beh'efs we are comparing severally
belong. While the one family has been dying out, the
other family has been multiplying. Just as fast as men
have ceased to regard different classes of phenomena as
caused by special personal agents, acting irregularly ; so fast
have they come to regard these different classes of phe-
nomena as caused by a general agency acting uniformly — the

THE EVOLUTION-HYPOTHESIS. 347

two changes being correlative. And as, on the one hand,
the hypothesis that each species resulted from a supernatural
act, having lost nearly all its kindred hypotheses, may be
t xpected soon to become extinct ; so, on the other hand, the
1 ypothesis that each species resulted from the action of na-
t ural causes, being one of an ever-increasing family of hypo-
theses, may be expected to survive and become established.

Still greater will the probability of its survival and estab-
lishment appear, when we observe that it is one of a particu-
lar genus of hypotheses that has been rapidly extending.
The interpretation of phenomena as resulting from Evolution,
has been independently showing itself in various fields of
inquiry, quite remote from one another. The supposition
that the Solar System has been gradually evolved out of dif-
fused matter, is a supposition wholly astronomical in its
origin and application. Geologists, without being led thereto
by astronomical considerations, have been step by step ad-
vancing towards the conviction, that the Earth has reached
its present varied structure through a process of Evolution.
The inquiries of biologists have proved the falsity of the once
general belief, that the germ of each organism is a minute
repetition of the mature organism, differing from it only in
bulk ; and they have shown, contrariwise, that every organ-
ism, arising out of apparently-uniform matter, advances to its
ultimate multiformity through insensible changes. Among
philosophical politicians, there has been spreading the per-
ception that the progress of society is an evolution : the
truth that " constitutions are not made but grow," is a part
of the more general truth that societies are not made but
»row. It is now universally admitted by philologists, that
languages, instead of being artificially or supernaturally
formed, have been developed. And the histories of religion,
of philosophy, of science, of the fine arts, and of the indus-
trial arts, show that these have passed through stages as un-
obtrusive as those through which the mind of a child passes
on its way to maturity. If then, the recognition of evolu-

348 THE EVOLUTION OF LIFE.

tion as the law of many diverse orders of phenomena, Laa
been spreading ; may we not say that there thence arises the
probability that evolution will presently be recognized as the
law of the phenomena we are considering ? Each further ad-
vance of knowledge, confirms the belief in the unity of
Nature ; and the discovery that evolution has gone on, or is
going on, in so many departments of Nature, becomes a rea-
son for believing that there is no department of Nature in
which ii does not go on.

§ 118. The Irypotheses of Special Creation and Evolution,
are no less contrasted in respect of their legitimacy as hy-
potheses. While, as we have seen, the one belongs to that
order of symbolic conceptions which are proved to be illusive
by the impossibility of realizing them in thought ; the other
is one of those symbolic conceptions which are more or less
completely realizable in thought. The production of all
organic forms by the slow accumulation of modifications upon
modifications, and by the slow divergences resulting from
the continual addition of differences to differences, is mentally
representable in outline, if not in detail. Various orders of
our experiences enable us to conceive the process. Let us
look at one of the simplest.

There is no apparent similarity between a straight line
and a circle. The one is a curve ; the other is defined as
without curvature. The one encloses a space ; the other
will not enclose a space though produced for ever. The one
is finite ; the other may be infinite. Yet, opposite as the
two are in all their properties, they may be connected together
by a series of lines no one of which differs from the adjacent
ones in any appreciable degree. Thus, if a cone be cut by
a plane at right angles to its axis, we get a circle. If, instead
of being perfectly at right angles, the plane subtends with
the axis an angle of 89° 59', we have an ellipse which no
human eye, even when aided by an accurate pair of compasses,
can distinguish from a circle. Decreasing the angle minute

THE EVOLUTION-HYPOTHESIS. 349

by mimite, the ellipse becomes first perceptibly eccentric, then
manifestly so, and by and by acquires so immensely elongated
a form, as to bear no recognizable resemblance to a circle.
By continuing this process, the ellipse changes insensibly into
a parabola. On still further diminishing the angle, the para-
bola becomes an hyperbola. And finally, if the cone be
made gradually more obtuse, the hyperbola passes into a
straight line, as the angle, of the cone approaches 180°. Now
here we have five different species of line — circle, ellipse,
parabola, hyperbola, and straight line — each having its pecu-
liar properties and its separate equation, and the first and
last of which are quite opposite in nature, connected together
as members of one series, all producible by a single process
of insensible modification.

But the experiences which most clearly illustrate to us
the process of general evolution, are our experiences of
special evolution, repeated in every plant and animal. Each
organism exhibits, within a short space of time, a series
of changes which, when supposed to occupy a period inde-
finitely great, and to go on in various ways instead of one
way, give us a tolerably clear conception of organic evo-
lution in general. In an individual development, we have
compressed into a comparatively infinitesimal sj)ace, a series
of metamorphoses equally vast with those which the hypo-
thesis of evolution assumes to have taken place during those
immeasurable epochs that the Earth's crust tells us of. A
tree differs from a seed immeasurably in every respect —
in bulk, in structure, in colour, in form, in specific gravity,
in chemical composition : differs so greatly that no visible
resemblance of any kind can be pointed out between them
Yet is the one changed in the course of a few years into tho
other : changed so gradually, that at no moment can it be
eaid — Now the seed ceases to be, and the tree exists. What
can be more widely contrasted than a newly-born child and
the small, semi-transparent, gelatinous spherule constituting
the human ovum ? The infant is so complex in structure

350 THE EVOLUTION OF LIFE.

that a cyclopedia is needed to describe its constituent parts*
The germinal vesicle is so simple that it may be defined m
a line. Nevertheless, a few months suffice to develope the
one out of the other ; and that, too, by a series of modifica-
tions so small, that were the embryo examined at successive
minutes, even a microscope would with difficulty disclose
any sensible changes. Aided by such facts, the conception
of general evolution may be rendered as definite a concep-
tion as any of our complex conceptions can be rendered. If
instead of the successive minutes of a child's foetal life, we
take successive generations of creatures — if we regard the suc-
cessive generations as differing from each other no more than
the foetus did in successive minutes ; our imaginations must
indeed be feeble if we fail to realize in thought, the evolu-
tion of the most complex organism out of the simplest. If a
single cell, under appropriate conditions, becomes a man in
the space of a few years ; there can surely be no difficulty in
understanding how, under appropriate conditions, a cell may,
in the course of untold millions of years, give origin to the
human race.

It is true that many minds are so unfurnished with those
experiences of Nature out of which this conception is built,
that they find difficulty in forming it. Habitually looking
at things rather in their statical than in their dynamical
aspects, they never realize the fact that, by small increments
of modification, any amount of modification may in time be
generated. That surprise which they feel on finding one
whom they last saw as a boy, grown into a man, becomes
incredulity when the degree of change is greater. To such,
the hypothesis that by any series of changes a protozoon
stould ever give origin to a mammal, seems grotesque — as
grotesque as did Galileo's assertion of the Earth's movement
eeem to the Aristotleans ; or as grotesque as the assertion of
the Earth's sphericity seems now to the New Zealanders.
But those who accept a literally-unthinkable proposition as

THE EVOLUTiON-lliTOTHESlS. 351

quite satisfactory, may not unnaturally be expected to make a
converse mistake.

§ 119. The hypothesis of evolution is contrasted with
the hypothesis of special creations, in a further respect- It is
not simply legitimate instead of illegitimate, because repre-
suitable in thought instead of unrepresentable ; but it has
the support of some evidence, instead of being absolutely
unsupported by evidence. Though the facts at present as-
signable in direct proof that by progressive modifications,
races of organisms that are apparently distinct may result
from antecedent races, are not sufficient ; yet there are nu-
merous facts of the order required. It has been shown
beyond all question that unlikenesses of structure gradually
arise among descendants from the same stock. We find that
there is going on a modifying process of the kind alleged as
the source of specific differences : a process which, though
slow in its action, does, in time, if the circumstances demand
it, produce conspicuous changes — a process- which, to all
appearance, would produce in the millions of years, and under
the great varieties of conditions which geological records
imply, any amount of change.

In the chapters on "Heredity" and "Variation," con-
tained in the preceding Part, many such facts were given ;
and plenty more might be added. Although comparatively
little attention has been paid to the matter until recent times,
the evidence already collected shows that there take place in
successive generations, alterations of structure quite as
marked as those which, in successive short intervals, arise ir
a devekming embryo — nay, often much more marked ; since,
besides differences due to changes in the relative sizes ol
parts, there sometimes arise differences due to additions and
suppressions of parts. The structural modification proved
to have taken place since organisms have been observed, is
not less than the hypothesis demands — bears as great a ratio

352 THE EVOLUTION OF LIFE.

to this brief period, as the total amount of structural change
seen in the evolution of a complex organism out of a simple
germ, bears to that vast period during which living forms
have existed on the Earth.

We have, indeed, much the same kind and quantity of
direct evidence that all organic beings have gradually amen
through the actions of natural causes, which we have that all
the structural complexities of the Earth's crust have arisen
through the actions of natural causes. It may, I think, be
fairly said, that between the known modifications undergone by
organisms, and the totality of modifications displayed in their
structures, there is no greater disproportion than between the
geological changes which have been witnessed, and the to-
tality of geological changes supposed to be similarly caused.
Here and there are pointed out sedimentary deposits now
slowly taking place. At this place, it is proved that a shore
has been encroached on by the sea to a considerable extent
wi'iiin recorded times ; and at another place, an estuary is
known to" have become shallower within the space of some
generations. In one region a general upheaval is going on
at the rate of a few feet in a century ; wbi1^ *h asather
region occasional earthquakes are shown to cause slight
variations of level. Appreciable amounts of denudation by
water are visible in some localities ; and in other localities
glaciers are detected in the act of grinding down the rocky sur-
faces over which they glide. But the changes thus instanced,
are infinitesimal compared with the aggregate of changes tc
which the Earth's crust testifies, even in its still extant sys-
tems of strata. If, then, from the small changes now being
wrought on the Earth's crust by natural agencies, we may
legitimately conclude that by such natural agencies acting
through vast epochs, all the structural complexities of the
Earth's crust have been produced; may we not from the
small known modifications produced in races of organisms
by natural agencies, similarly infer that from natural ageu-

THE EVOLUTION-HYPOTHESIS. 353

ciee have slowly arisen all those structural complexities which
we see in them. ?

The hypothesis of Evolution then, has direct support from
facts which, though small in amount, are of the kind required;
and the proportion which these facts bear to the conclusion
drawn, seems as great as is the proportion between facts and
conclusion which, in another case, produces acceptance of the
conclusion.

§ 120. Let us put ourselves for a moment in the position of
those who, from their experiences of human modes of action,
draw inferences respecting the mode of action of that ultimate
power manifested to us through phenomena. We shall find
the supposition that each kind of organism was separately
designed and put, together, to be much less consistent with
their professed conception of this ultimate power, than is the
supposition that all kinds of organisms have resulted from
one unbroken process. Irregularity of method is a mark of
weakness. Uniformity of method is a mark of strength. Con-
tinual interposition to alter a pre-arranged set of actions,
implies defective arrangement in those actions. The main-
tenance of those actions, and the working out by them of the
highest residts, implies completeness of arrangement. If
human workmen, whose machines as at first constructed
require perpetual adjustment, show their increasing skill by
making their machines self-adjusting ; then, those who figure
to themselves tlia production of the world and its inhabitants
by a " Great Artificer," must admit that the achievement of
this end by a persistent process, adapted to all contingenci *,
implies greater skill than its achievement by the process of
meeting the contingencies as they severally arise.

So, too, it is with the contrast under its moral aspect. "We
saw that to the hypothesis of special creations, a difficulty
is presented by the absence of high forms of life during those
immeasurable epochs of the Earth's existence which geology

354 THE EVOLUTION OF LIFE.

records. But to the hypothesis of evolution, this absence ie
no such obstacle. Suppose evolution, and this question is
necessarily excluded. Suppose special creations, and this
question, unavoidably raised, can have no satisfactory an-
swer. Still more marked is this contrast between the
two hypotheses, in presence of that vast amount of suf-
fering entailed on all orders of sentient beings, by their
imperfect adaptations to their conditions of life ; and the
further vast amount of suffering entailed on them by enemies
and by parasites. We saw that if organisms were severally
designed for their respective places in Nature, the inevitable
conclusion is, that these thousands of kinds of inferior organ-
isms which prey upon superior organisms, were intended to
inflict all the pain and mortality which results. But the hy-
pothesis of evolution involves us in no such dilemma. Slowly,
bat surely, evolution brings about an increasing amount
of happiness : all evils being but incidental. By its essen-
tial nature, the process must everywhere produce greater
fitness to the conditions of existence ; be they what they may.
Applying alike to the lowest and the highest forms of organ-
ization, there is in all cases a progressive adaptation ; and a
survival of the most adapted. If, in the uniform working
out of the process, there are evolved organisms of low types,
which prey on those of higher types, the evils inflicted form
but a deduction from the average benefits. The universal
and necessary tendency towards supremacy and multiplica-
tion of the best, applying to the organic creation as a whole
as well as to each species, is ever diminishing the damage
done — tends ever to maintain those most superior organisms
wh ich, in one way or other, escape the invasions of the infe-
rior, and so tends to produce a type less liable to the inva-
sions of the inferior. Thus the evils accompanying evolu-
tion are ever being self-eliminated. Though there may arise
the question — Why could they not have been avoided?
there does not arise the question — Why were they deliber-

THE EVOLUTION- HYPOTHESIS. 355

ately inflicted? Whatever may "be thought of them, it is
clear that they do not imply gratuitous malevolence.

§ 121. In all respects, then, the hypothesis of evolution
contrasts favourably with the hypothesis of special creation.
It has arisen in comparatively-instructed times, and in the
most cultivated class. It is one of those beliefs in the uni-
form concurrence of phenomena, which are gradually sup-
planting beliefs in their irregular and arbitrary concurrence ;
and it belongs to a genus of these beliefs which has of late
been rapidly spreading. It is a definitely- conceivable hypo-
thesis : being simply an extension to the organic world at
large, of a conception built from our experiences of individual
organisms ; just as the hypothesis of universal gravitation,
was an extension of the conception which our experiences
of terrestrial gravitation had produced. This definitely-con-
ceivable hypothesis, besides the support of numerous ana-
logies, has the support of direct evidence : we have positive
proof that there is going on a process of the kind alleged ;
and though the results of this process, as actually witnessed,
are minute in comparison with the totality of results ascribed
to it, yet they bear to such totality, a ratio as great as that by
which an analogous hj'-pothesis is justified. Lastly, that senti-
ment which the doctrine of special creations is thought neces-
sary to satisfy, is much better satisfied by the doctrine of evolu-
tion ; since this doctrine raises no contradictory implications
respecting the Unknown Cause, such as are raised by the
antagonist doctrine.

And now, having observed how, imder its most general
aspects, the hypothesis of evolution commends itself to us,
by its derivation, by its coherence, by its analogies, by its
direct evidence, by its implications ; let us go on to consider
the several orders of facts which yield indirect support to it.
We will begin by noting the harmonies that exist between
it,, and sundry of the inductions set forth in Part II,

CHAPTER IV.

THE ARGUMENTS FROM CLASSIFICATION.

§ 122. In § 103, we saw that the relations which exist
among the species, genera, orders, and classes of organisms,
are not interpretable as results of any such causes as have
been usually assigned. We will here consider whether they
are interpretable as the results of evolution. Let us first
contemplate some familiar facts.

The Norwegians, Swedes, Danes, Germans, Dutch, and
Anglo-Saxons, form together a group of Scandinavian races,
that are but slightly divergent in their characters. Welsh,
Irish, and Highlanders, though they have differences, have
not differences such as to hide a decided community of na-
ture : they are classed together as Celts. Between the
Scandinavian race as a whole and the Celtic race as a
whole, there is a recognized distinction greater than that
between the sub-divisions which make up one or the other.
And the several peoples inhabiting Southern Europe are more
nearly allied to one another, than the aggregate they form is
allied to the aggregates of Northern peoples. If, again, we
compare these European varieties of man taken as a group,
with that group of Eastern varieties which had a common
origin with it, we see a stronger contrast than between the
European varieties themselves. And once more, ethnolo-
gists find differences of still higher importance, between the
Aryan stock as a whole and the Mongolian stock as a whole,

THE ARGUMENTS FROM CLASSIFICATION. 857

or the Negro stock as a whole. Though these contrasts
are partially obscured by intermixtures ; yet they are not so
obscured as to hide the truths that the inost-nearly-allied
varieties of man, are those which diverged from one ano-
ther at a comparatively-recent period ; that each group
of nearly-allied varieties, is more strongly contrasted with
other such groups that had a common origin with it at a
remoter period ; and so on, imtil we come to the largest
groups, which are the most strongly contrasted, and of whose
divergence no trace is extant.

The relations existing among the classes and sub-classes
of languages, have been briefly referred to by Mr Darwin, in
illustration of his argument. We know that languages have
arisen by evolution. Let us then see what grouping of them
evolution has produced. On comparing the dialects of adja-
cent counties in England, we find that their differences are so
small as scarcely to distinguish them. Between the dialects
of the Northern counties taken together, and those of the
Southern counties taken together, the contrast is stronger.
These clusters of dialects, together with those of Scotland and
Ireland, are nevertheless so similar, that we regard them as
one language. The several languages of Scandinavian Eu-
rope, including English, are much more unlike one ano-
ther, than are the several dialects which each of them in-
cludes ; in correspondence with the fact that they diverged
from one another at earlier periods than did their respective
dialects. The Scandinavian languages have nevertheless a
certain community of character, which distinguishes them as a
group from the languages of Southern Europe ; between
which there are general and special affinities that similarly
unite them into a group formed of sub-groups containing sub-
sub-groups. And this wider divergence between the order
of languages spoken in Northern Europe, and the order of
languages spoken in Southern Europe, answers to the longer
time that has elapsed since their differentiation commenced
Further, these two orders of modern European languages, as

Ji58 THE EVOLUTION OF L1FK.

well as Latin and Greek and certain extinct and spoken
languages of the East, are shown to have traits iu
common, which, notwithstanding the wide gaps between
them, unite them together as one great class of Aryan lan-
guages; radically distinguished from the classes of lan-
guages spoken by the other great divisions of the human
race.

§ 123. Now this kind of subordination of groups, which
we see arises in the course of continuous descent, multiplica-
tion, and divergence, is just the kind of subordination of
groups which plants and animals exhibit : it is just this
kind of subordination which has thrust itself on the attention
of naturalists, in spite of pre-conceptions.

The original idea was that of arrangement in linear order.
We saw that even after a considerable acquaintance with the
structures of organisms had been acquired, naturalists con-
tinued their efforts to reconcile the facts with the notion of a
uni-serial succession. The accumulation of evidence necessi-
tated the breaking up of the imagined chain into groups
and sub-groups. Gradually there arose the conviction that
these groups do not admit of being placed in a line. And the
conception finally arrived at, is, that of certain great sub-
kingdoms, very widely divergent, each made up of classes
much less widely divergent, severally containing orders still
less divergent; and so on with genera and species. The
diagram on page 303, shows the general relations of these
d i visions in their degrees of subordination.

Hence this " grand fact in natural history of the subordina-
tion of group under group, which from its familiarity does
not always sufficiently strike us," is perfectly in harmony
with the hypothesis of evolution. The extreme significance
of this kind of relation among organic forms, is dwelt on by
Mr Dai win ; who shows how an ordinary genealogical tree
represents, on a small scale, a system of grouping analogous to
that which exists among organisms in general, and which is

THE ARGUMENTS FROM CLASSIFICATION. 359

explained on the supposition of a genealogical tree by which
all organisms are affiliated. If, wherever we can trace
direct descent, multiplication, and divergence, this formatic n
of groups within groups takes place ; there results a stron g
presumption that the groups within groups which constitule
the animal and vegetal kingdoms, have arisen by direct
descent, multiplication, and divergence — that is, by evolu-
tion.

§ 124. Strong confirmation of this inference is furnished
by the fact, that the more marked differences which divide
groups, are, in both cases, distinguished from the less
marked differences which divide sub-groups, by this, that
they are not simply greater in degree, but they are more
radical in hind. Objects, as the stars, may present them-
selves in small clusters, which are again more or less aggre-
gated into clusters of clusters, in such manner that the in-
dividuals of each simple cluster, are much closer together
than are the simple clusters composing a compound cluster :
in which case, the kinship that unites groups of groups
differs from the kinship that unites groups, not in nature,
but only in amount. But this is not the case either with
the groups and sub-groups which we know have resulted
from evolution, or with those which we here infer have re-
sulted from evolution. Among these, we find the highest
or most general classes, are separated from one another by
fundamental differences that have no common measure with
the differences that separate small classes. Observe the pa-
rallelism.

We saw that each sub-kingdom of animals is marked o3
from the other sub-kingdoms, by a total unlikencss in its
plan of organization : that is, the members of any sub-kingdom
are bound together, not by some superficial attribute which
they all have, but by some attribute determining the general
nature of their organizations. While, contrariwise, the
members of the smallest groups are united together, and se-
parated from the members of other small groups, bv modi-

860 THE EVOLUTION OF LIFE.

fications which do not affect the essential relations of parts.
That this is just the kind of arrangement which results frora
evolution, the case of languages will show.

If we compare the dialects spoken in different parts of
England, we find scarcely any differences but those of pro-
nunciation : the structures of the sentences are almost
uuiform. Between English and the allied modern languages,
th 3re are decided divergences of structure : there are some
unlikenesses of idiom ; some unlikenesses in the ways of
modifying the meanings of verbs ; and considerable unlike-
nesses in the uses of genders. But these unlikenesses are not
sufficient to hide a general community of organization. A
greater contrast of structure exists between these modern lan-
guages of Western Europe, and the classic languages. That
differentiation into abstract and concrete elements, which is
shown by the substitution of auxiliary words for inflections,
has produced a higher specialization distinguishing these
languages as a group from the older languages. Neverthe-
less, both the ancient and modern languages of Europe, to-
gether with some Eastern languages derived from the same
original, have, under all their differences of organization, a
fundamental community of organization ; inasmuch as all of
them exhibit the formation of words by such a coalescence
and integration of roots as destroys the independent meanings
of the roots. These Aryan languages, and others which
have the amalgamate character, are united by it into a class
distinguished from the aptotic and agglutinate languages ; in
which the roots are eitLei not united at all, or so incompletely
united that one of them still retains its independent meaning.
And philologists find that these fundamental differences which
severally determine the grammatical forms, or modes of com-
bining ideas, are really characteristic of the primary divisions
among languages.

That is to say, among languages, where we know that
evolution has been going on, the greatest groups are marked
off frora one another by the strongest structural contrasts ;
and as the like holds among groups of organisms, there re-

THE ARGUMENTS FROM CLASSIFICATION. 361

Bulls a further reason for inferring that these have been
evolved.

§ 125. There is yet another parallelism of like meaning.
We saw (§ 101) that the successively-subordinate classes,
orders, genera, and species, into which zoologists and botan-
ists segregate animals and plants, have not, in reality,
those definite values conventionally given to them. There aro
well-marked species, and species so imperfectly defined that
certain systcmatists regard them as varieties. Between
genera, strong contrasts exist in many cases ; and in other
cases, contrasts so much less decided as to leave it doubtful
whether they constitute generic distinctions. So, too, is it
with orders and classes : in some of which there have been
introduced intermediate sub-divisions, having no equivalents
in others. Even of the sub- kingdoms the same truth holds.
The contrast between the Molluscoida and the Mollusca, is far
less than that between the Mollusca and the Annulosa ; and
there are naturalists who think that the Fertebrata are so
much more widely separated from the other sub-kingdoms,
than these are from one another, that the Vertehrata should
have a classificatory value equal to that of all the other sub-
kingdoms taken together.

Now just this same indefinitcness of value, or incomplete-
ness of equivalence, is observable in those simple and com-
pound and re-compound groups, which we see arising by
evolution. In every case, the endeavour to arrange the
divergent products of evolution, is met by a difficidty like
that which would meet the endeavour to classify the
branches of a tree, into branches of the first, second, third,
fourth, &c, orders — the difficulty, namely, that branches of
intermediate degrees of composition exist. The illustration
furnished by languages will serve us once more. Some dia-
lects of English are but little contrasted ; others are strongly
contrasted. The alliances of the several Scandinavian tongues
with one another are different in degree. Dutch is much
24

362 THE EVOLUTION OF LIFE

less distinct from German than Swedish is ; while between
the Danish and Swedish there is so close a kinship, that they
might almost be regarded as widely- divergent dialects.
Similarly on comparing the larger divisions, we see that
the various languages of the Aryan stock, have deviated
from the original to very unlike distances. The geneial
conclusion is manifest. While the kinds of human speech
fall into groups, and sub-groups, and sub-sub-groups ; yet
the groups are not equal to one another in value, nor have
the sub-groups equal values, nor the sub-sub-groups.

If, then, the classification of organisms results in several
orders of assemblages, such that assemblages of the same
order are but indefinitely equivalent ; and if, where
evolution is known to have taken place, there have arisen
assemblages between which the equivalence is similarly in-
definite ; there is additional reason for inferring that
organisms are products of evolution.

§ 126. A fact of much significance remains. If groups
of organic forms have arisen by divergence and re-diver-
gence ; and if, while the groups have been developing
from simple groups into compound groups, each group and
sub-group has been giving origin to more complex forms
of its own type ; then it is inferable that there once ex-
isted greater structural likenesses between the members of
allied groups, than exist now. Hence, if we take the
simplest members of any group to be those which have
undergone the least change ; we may expect to find a greater
likeness between them and the simplest members of an allied
group, than we find between the more complex members
of the two groups. This, speaking generally, proves to
be so.

Between the sub-kingdoms, the gaps are extremely wide ;
but such distant kinships as may be discerned, bear out an-
ticipation. Speaking of that extremely-degraded vertebrate
animal the Arrvphioxus, which has several molluscous traits

THE ARGUMENTS FROM CLASSIFICATION. 363

in its organization, Dr Carpenter remarks, that it " furnishes
an apt illustration of another important fact, that it is by
the lowest rather than by the highest forms of two natural
groups, that they are brought into closest relation." What
are the faint traces of community between the Annulosa and
ihe Mollusca ? They are the thread-cells which some of
their inferior groups have in common with the Coelenterata.
More decided approximations exist between the lower
members of classes. In tracing down the Crustacea and
the Arachnida from their more complex to their simpler
forms, zoologists meet with difficulties : respecting some of
these simpler forms, it becomes a question which class they
belong to. The Lepidosiren, about which there have been
disputes whether it is a fish or an amphibian, is inferior in the
organization of its skeleton, to the great majority of both
fishes and amphibia. Widely as they differ from them, the
lower mammals have some characters in common with birds,
which the higher mammals do not possess.

Now since this kind of relationship of groups is not ac-
counted for by any other hypothesis, while the hypothesis of
evolution gives us a clue to it ; we must include it among the
evidences of this hypothesis, which the facts of classification
furnish.

§ 127. What shall we say of these several leading truths
when taken together ? That naturalists have been gradually
sompellcd to arrange organisms in groups within groups ;
and that this is the arrangement which we see arises by
descent, alike in individual families and among races of men,
is a striking circumstance. That while the smallest groups
are the most nearly related, there exist beween the great
sub-kingdoms, structural contrasts of the profoundest kind ;
cannot but impress us as remarkable, when we see that where
it is known to take place, evolution actually produces these
feebly-distinguished small groups, and these strongly-dis-
tinguished great groups. The impression made by these two

364 THE EVOLUTION OF LIFE.

parallelisms, which, add meaning to each other, is deepened
by the third parallelism, which enforces the meaning of both
— the parallelism, namely, that as, between the species,
genera, orders, classes, &c, which naturalists have formed,
there are transitional gradations ; so between the groups,
sub-groups, and sub-sub-groups, which we know to have
been evolved, groups of intermediate values exist. And
these three correspondences between the known results of
evolution, and the results here ascribed to evolution, have
further weight given to them by the circumstance, that the
kinship of groups through their lowest members, is just the
kinship which the hypothesis of evolution implies.

Even in the absence of these specific agreements, the broad
fact of unity amid multiformity, which organisms so strik-
ingly display, is strongly suggestive of evolution. Freeing
ourselves from pre-conceptions, we shall see good reason to
think with Mr Darwin, " that propinquity of descent — the
only known cause of the similarity of organic beings — is the
bond, hidden as it is by various degrees of modification, which
is partly revealed to us by our classifications." "When we
consider that this only known cause of similarity, joined with
the only known cause of divergence, which we have in the
influence of conditions, gives us a key to these likenesses
obscured by unKken esses, to which no consistent interpreta-
tion can otherwise be given, even if purely hypothetical
causes be admitted; we shall see that were there none of
those very remarkable harmonies above pointed out, the
truths of classification would still yield strong support to oui
conclusion.

CHAPTEE V.

THE ARGUMENTS FROM EMBRYOLOGY.

§ 123. There was briefly set forth in § 52, a remarkable
induction established by Von Baer ; who " found that in its
earliest stage, every organism has the greatest number of
characters in common with all other organisms in their
earliest stages ; that at a stage somewhat later, its structure
is like the structures displayed at corresponding phases by a
less extensive multitude of organisms ; that at each subse-
quent stage, traits are acquired which successively distin-
guish the developing embryo from groups of embryos that it
previously resembled — thus step by step diminishing the
class of embryos which it still resembles ; and that thus the
class of similar forms is finally narrowed to the species of
which it is a member." Though this generalization is to be
taken with qualifications, yet, as an average truth, it may
be regarded as beyond question ; and as an average truth, it
has a profound significance.

For if we follow out in thought the implications
of this truth — if we conceive the germs of all kinds
of organisms simultaneously developing ; if after taking
their first step together, we imagine at the second step, one
half of the vast multitude diverging from the other half; if,
at the next step, we mentally watch each of these great
assemblages beginning to take two or more routes of
development ; if we represent to ourselves this bifurcation
simultaneously going on, stage after stage, in all the

366 THE EVOLUTION OV LIFE

branches ; we shall see that there must result an aggregate
analogous, in its arrangement of parts, to a tree. If this vast
genealogical tree be contemplated as a whole, made up of
trunk, great branches, secondary branches, and so on, as far
as the terminal twigs ; it will be perceived that all the
various kinds of organisms represented by these terminal
twigs, forming the periphery of the tree, will stand related to
each other in small groups, which are united into groups of
groups, and so on. The embryological tree, expressing the
developmental relations of organisms, will be similar to tho
tree which symbolizes their classificatory relations. That
subordination of classes, orders, genera, and species, to which
naturalists have been gradually led, is just that subordination
which results from the divergence and re-divergence of
embryos, as they all unfold. On the hypothesis of evolution,
this parallelism has a meaning — indicates that primordial
kinship of all organisms, and that progressive differentiation
of them, which the hypothesis alleges. But on any other
hypothesis the parallelism is meaningless : or rather, it
raises a difficulty ; since it implies either an effect without a
cause, or a design without a purpose.

§ 129. It was said above, that this great embryological
law is to be taken with certain qualifications. The resem-
blances which hold together great groups of embryos in their
early stages, and which hold together smaller and smaller
groups in their later and later stages, are not special or
exact, but general or approximate ; and in some cases, the
conformity to this general law is very imperfect. These
irregularities, however, instead of being at variance with the
hypothesis of evolution, afford further support to it.

Observe, first, that the only two other possible suppositions
respecting developmental changes, are negatived, the one by
this general law and the other by the minor nonconformities
to it. If it be said that the conditions of the case necessi-
tated the derivation of all organisms from simple gei-ms, and

THE ARGUMENTS FROM EMBRYOLOGY. 367

therefore necessitated a morphological unity in their primitive
states ; there arises the obvious answer, that the morphologi-
cal unity thus implied, is not the only morphological unity
to be accounted for. Were this the only unity, the various
kinds of organisms, setting out from a common primordial
form, should all begin from the first to diverge individually,
as so many radii from a centre ; which they do not. If, other-
wise, it be said that organisms were framed upon certain
types, and that those of the same type continue developing
together in the same direction, until it is time for them to
begin putting on their specialities of structure ; then, the
answer is, that when they do finally diverge, they ought
severally to develop in direct lines towards their final forms.
No reason can be assigned why, having once parted company,
some should progress towards their final forms by irregular
or circuitous routes. On the hypothesis of design, such de-
viations are inexplicable.

The hypothesis of evolution, however, while it pre-supposes
those general relations among embryos which are found tc
exist, also affords explanations of these minor nonconformities.
If, as any rational theory of evolution pre-supposes, the pro-
gressive differentiations of organic forms from one another
during past times, have resulted, as they are resulting still,
from the direct and indirect effects of external conditions —
if organisms have become different, either by immediate
adaptations to unlike habits of life, or by the mediate adapta-
tions resulting from preservation of the individuals most
fitted for such habits of life, or by both ; and if the embryonic
changes are related to the changes that were undergone by
ancestral races ; then these irregularities must be expected.
For the successive changes in modes of life pursued by
successive ancestral races, can have had no regularity of
sequence. In some cases they must have been more numerous
than in others ; in some cases they must have been greater
in degree than in others ; in some cases they must have been
to lower modes, in some cases to higher modes, and in some

36S THE EVOLUTION OF LIFE.

cases to modes neither higher nor lower. Of two connate racea
which diverged in the remote past, the one may have had
descendants that have remained tolerably constant in theii
habits, while the other niay have had descendants that have
passed through widely-aberrant modes of life ; and yet some
of these last may have eventually taken to modes of life like
those of the divergent races derived from the same stock.
And if the metamorphoses of embryos, indicate, in a general
way, the changes of structure undergone by ancestors ; then,
the later embryologic changes of such two allied races, will
be somewhat different, though they may end in very similar
forms. An illustration will make this clear. Mr Darwin
says : — " Petrels are the most aerial and oceanic of birds, but
in the quiet sounds of Tierra del Fuego, the Pujjinuria
berardl, in its general habits, in its astonishing power of
diving, its manner of swimming, and of flying when un-
willingly it takes flight, would be mistaken by any one for
an auk or grebe ; nevertheless, it is essentially a petrel, but
with many parts of its organization profoundly modified."
Now if we suppose these grebe-like habits to be continued
through a long epoch, the petrel-form to be still more ob-
scured, and the approximation to the grebe- form still closer ;
it is manifest that while the chicks of the grebe and the
Pujjinuria will, during their early stages of development,
display that likeness involved by their common derivation
from some early type of bird, the chick of the Pujjinuria
will eventually begin to show deviations, representative of
the ancestral petrel-structure, and will afterwards begin to
Lose these distinctions, and assume the grebe- structure.

Hence, remembering the perpetual intrusions of organisms
on one another's modes of life, often widely different ; and
remembering that these intrusions have been going on from
the beginning ; we shall be prepared to find that the general
Law of embryologic parallelism, is qualified by irregularities
that are mostly small, in many cases considerable, and

THE ARGUMENTS FROM EMBRYOLOGY. 36'.)

occasionally great. The hypothesis of evolution accounts for
these : it does more — it implies the necessity of them.

§ 130. The substitutions of organs and the suppressions
of organs, are among those secondary embryological phe-
nomena which harmonize with the belief in evolution
but cannot be reconciled with any other belief. There are
cases where, during its earlier stages of development, an
embryo possesses organs that afterwards dwindle away, as
there arise other organs to discharge the same functions.
And there are cases where organs make their appearance,
grow to certain points, have no functions to discharge, and
disappear by absorption.

AVe have a remarkable instance of this substitution in the
successive temporary appliances for aerating the blood,
which the mammalian embryo exhibits. During the first
phase of its development, the mammalian embryo circulates
its blood through a system of vessels distributed over what
is called the area vasculosa — a system of vessels homologous
with one which, among fishes, serves for aerating the blood
until the permanent respiratory organs come into play.
After a time, there buds out from the mammalian embryo, a
vascular membrane called the allantois, homologous with
one which, in birds and reptiles, replaces the first as a
breathing apparatus. But while in the higher ovipai'ous
vertebrates, the allantois serves the purpose of a lung during
the rest of embryonic life, it does not do so in the mamma-
lian embryo. In implacental mammals, it aborts, having no
function to discharge ; and in the higher mammals, it
becomes " placcntiferous, and serves as the means of inter-
communication between the parent and the offspring " — be-
comes an organ of nutrition more than of respiration. Now
since the first system of external blood-vessels, not being in
contact with a directly-oxygenated medium, cannot be very
serviceable to the mammalian embryo as a lung ; and since

<J70 THE EVOLUTION OF LIFE.

the second system of external blood-vessels is, to tho im-
placental embryo, of no greater avail than the first ; and
since the communication between the embryo and the
placenta among placental mammals, might as well or better
have been made directly, instead of by metamorphosis oi
the allantois ; these substitutions appear unaccountable as
results of design. But they are quite congruous with tho
supposition, that the mammalian type arose out of lower
vertebrate types. For in such case, the mammalian embryo,
passing through states representing, more or less distinctly,
those which its remote ancestors had in common with the
lower Vertebrata, develops these subsidiary organs in like
ways with the lower Vertebrata.

Even more striking than the substitutions of organs are
the suppressions of organs. Mr Darwin names some cases
as " extremely curious ; for instance, the presence of teeth
in foetal whales, which when grown up have not a tooth in
their heads ; * * * It has even been stated on good
authority that rudiments of teeth can be detected in the
beaks of certain embryonic birds." Not even temporary
functions can be assigned for these organs that are first
built up and then pulled down again. -They are absolutely
useless — their formation is absolutely superfluous. Irrecon-
cilable with any teleological theory, they do not even har-
monize with the theory of fixed types which are maintained
by the development of all the typical parts, even where not
wanted ; seeing that the disappearance of these incipient
organs during foetal life, spoils the typical resemblance.
But while to all other hypotheses these facts are stumbling-
blocks, they yield strong support to the hypothesis of evolu-
tion.

^-*" Allied to these cases, are the cases of what has been called
retrograde development. Many parasitic creatures and
creatures which, after leading active lives for a time, eventu-
ally become fixed, lose, in their adult states, the limbs and
senses which they had when young. It moy be alleged-

THE ARGUMENTS FROM EMBRYOLOGY. t57l

however, that these creatures could not secure the habitats
needful for them, without possessing during their larva]
stages, eyes and swimming appendages which eventually
become useless ; that though, by losing these, their organiza*
tion retrogresses in one direction, it progresses in another
direction ; and that, therefore, they do not exhibit the need-
less development of a higher type on the way to a lower
type. Nevertheless there are instances of a descent in
organization, following an apparently-superfluous ascent.
Mr Darwin says that in some genera of cirripedes, " the
Larvae become developed either into hermaphrodites having
the ordinary structure, or into what I have called comple-
mented males, and in the latter, the development has
assuredly been retrograde ; for the male is a mere sack, which
lives for a short time, and is destitute of mouth, stomach,
or other organ of importance, excepting for reproduc-
tion."

§ 131. Comparative embryology shows us that besides
substitutions of organs, there are what may be called substi
tuted modes of development. The same kind of structure
is not always produced in the same way ; and some allied
groups of organisms have modes of evolution which appear
to be radically contrasted. The two modes are broadly dis-
tinguishable as the direct and the indirect. They may
severally characterize the general course of evolution as u
whole, and the course of evolution in particular organs.

Thus in the immense majority of articulate animals,
metamorphoses, more or less marked and more or less
numerous, are passed through on the way to maturity. The
familiar transformations of insects show us how circuitous is
the route by which the embryo-form arrives at the adult form,
among some divisions of the Articulata. But there are
other divisions, as the lower Aracfaiida, in which the unfold-
ing of the egg into the adult takes place in tho simplest
manner : the substance grows towards its appointed shapt

372 THE EVOLUTION OF LIFE.

by tlie shortest route. The Mollusca furnish contrasts which^
though less marked, are essentially of the same nature. Among
some Gasteropods, according to Vogt, the germ-mass, after
undergoing its earliest changes in the same way as germ-
masses in general, begins to transform itself bodily into the
finished structure : in one part, the component cells coalesce
lo form the heart, in another part to form the liver, and so
on. But in other classes of molluscs, as the Cephalopods,
the e?ubryo is moulded out of the blastoderm, or superficial
layer of the germ-mass ; and the various organs, mostly aris-
ing out of this blastoderm by a process of budding, reach
their ultimate shapes through successive modifications, while
they grow at the expense of the nutriment absorbed from
the rest of the germ-mass. And this indirect development
is universal among the Vertebrata.

Now on contemplating in their ensemble, the facts thus
briefly indicated, we may trace among these irregularities
something like a general rule. The indirect development
characterizes the most-highly-organized forms. In the
sub-kingdom Vertebrata, which, considered as a whole, stands
far above the rest in complexity, the development is uniformly
indirect. It is indirect in the great mass of the Articulata.
It is indirect in the highest Mollusca. Conversely, it is direct
in a large proportion of the lower types. The eggs of
Protozoa, of Coelenterata, of inferior Annuloida, originate the
respective structures proper to them, by transformations that
are almost immediate ; each of the cycle of forms passed
through, is assumed, when the proper time comes, in the
simplest way; and where they multiply by budding, the
substance of the bud passes by as short a process as may be,
into the finished form. Where among the simpler types of
animals, the evolution is indirect, its indirectness generally
appears to be related to some transitional mode of life, which
the larva passes through on its way to maturity ; and where
we find direct evolution among the more complex types, it is

THE ARGUMENTS FROM EMBRYOLOGY. o~'<i

in their most degraded members : instance the Aren't among
the Articulata*

We have before found that the facts of social organization
furnish us with hints towards interpreting the phenomena
exhibited in individual organisms. Let us see whether
analogies hence derived, do not help us here. A factory, or
other producing establishment, or a town made up of such
establishments, is an agency for elaborating some commodity
consumed by society at large ; and may be regarded as
analogous to a gland or viscus in an individual organism. If,
now, we inquire what is the primitive mode in which one of
these producing establishments grows up, we find it to be
this. A single worker, who himself sells the produce of his
labour, is the germ. His business increasing, he employs
helpers — his sons or others ; and having done this, he be-
comes a vendor not only of his own handiwork, but of that
of others. A further increase of his business compels him to
multiply his assistants, and his sale grows so rapid that he is
obliged to confine himself to the process of selling ; that is,
he ceases to be a producer, and becomes simply a channel
through which the produce of others is conveyed to the
public. Should his prosperity rise yet higher, he finds that
he is unable to manage even the sale of his commodities, and
has to employ others, probably of his own family, to aid him
in selling ; that is, to him as a main channel are now added
subordinate channels ; and so on continuously. Moreover,
* It may be urged that the mode of development is obviously related to the
tize of the mass which is to be transformed into the embryo. Doubtless it is
true that direct transformation is characteristic of small ova, and indirect trans-
formation of large ova ; and some such connexion may be necessary. Very pos-
sibly that polarity of the physiological units, which determines the specific structure
will not act throughout a large mass in such way as to transform it bodily into
the specific structure ; though it will thus act throughout a small mass. But that
the bulk of the ovum is not the sole cause of this difference of method, is proved
by the fact that in some cases where the development is comparatively direct, as
in Acteon, the ovum is very much larger than in cases where it is comparatively
indirect, as in minute iueccte.

374 TITE EVOLUTION OF LIFE.

when there grow up in one place, as a Manchester or a
Birmingham, many establishments of like kind, this process
is carried still further. There arise factors and agents, who
are the channels through which are transmitted the pro-
duce of many mills ; and we believe that primarily, these
factors were manufacturers who undertook to dispose of the
produce of smaller houses as well as their own, and ultimately
became salesmen only. Now this, which is the original
mode in which social agencies of all kinds are evolved,
does not continue to be the mode. There is a tendency
everywhere manifested to substitute a direct process for this
indirect process. Manufacturing establishments are no
longer commonly developed through the series of modifica-
tions above described ; but mostly arise by the immediate
transformation of a number of persons into master, clerks,
foremen, workers, &c. Instead of business-partnerships
being formed, as they originally were, by some slow unob-
trusive union between traders and their sons or assistants ;
we now have joint-stock-companies resulting by sudden
metamorphoses of groups of citizens. The like is true with
larger and more complex social agencies. A new town in
the United States arises not at all after the old method of
gradual accumulations round a nucleus, and successive small
modifications of structure accompanying increase of size ;
but it grows up over a large area, according to a pre-deter-
mined plan ; and there are developed at the outset, those
various civil, ecclesiastical, and industrial centres, which the
incipient city will require. Even in the formation of
colonies we may similarly see, that the whole type of social
organization proper to the race from which the colony comes,
begins at once to show itself. There is not a gradual passing
through all those developmental phases passed through by
the mother- society ; but there is a comparatively direct
transformation of the assemblage of colonists, into a social
organism allied in structure to the social organism of which
it was au offset.

THE ARGUMENT'S FROM EMBRYOLOGY. 375

Let us now return to the development of individual
organisms ; carrying back this idea with us. On the
hypothesis of evolution, all organs must have been originally
formed after the indirect method, by the accumulation of
modifications upon modifications ; and if the development of
(he embryo repeats the development of ancestral races,
organs must be thus formed in the embryo. To a consider-
able extent they are thus formed. There is a striking
parallelism between the mode in which, as above described,
manufacturing agencies are originally evolved, and the
mode in which secreting organs are evolved. Out of the
group of bile-cells forming the germ of the liver, some
centrally-placed ones, lying next to the intestine, are trans-
formed into ducts through which the secretion of the peri-
pheral bile-cells is poured into the intestine ; and as the peri-
pheral bile-cells multiply, there similarly arise secondary
ducts emptying themselves into the main ones ; tertiary ones
into these ; and so on. But while in this and in other
organs, the development remains in a great degree indhect ;
there are organs, as the heart, in which it is comparatively
direct. The heart of the vertebrate enibiyo does not arise
from a bud ; but it is first traceable as an aggregated mass
of cells, becoming distinct from the cells amid which it is
imbedded : its transformation into a contractile chamber, is
effected by the consolidation of its outer cells while its inner
cells liquify. And the comparatively direct development
thus displayed in some organs of the higher embryos, is, as
we have seen, characteristic of the entire development in
many lower embryos.

On the hypothesis of evolution, the direct mode of de-
velopment in animals, must have been substituted for the
indirect mode ; as we see that it is substituted in societies.
How comes it to have been substituted ? By studying the
cause of the substitution in the social organism, we may
perhaps get some insight into its cause in the individual or-
ganism. The direct mode of forming social agencies

376 THE EVOLUTION OF LIFE.

replaces the indirect mode, when these social agencies have
either been so long established, or have become so prevalent, or
both, as to modify the people's habits and ideas. Groups
of citizens unite into corporate bodies which quickly organ-
ize, because the habit of forming such combinations has so
far modified the thoughts and feelings of citizens, that it
becomes natural to them thus to arrange themselves. So
too, is it with the men who form a colony. The rapid as-
sumption by them of a social structure, as similar as circum-
stances permit to the structure of the mother- society, is
manifestly due to the fact, that the organization of the
mother-society has moulded the emotions and beliefs of its
members into conformity with itself; so that when some of
its members are transferred to a colony, they arrange
themselves directly into a structure of like type with that
of the mother-society : they do not repeat all the stages
through which the mother- society passed, because their
natures have been too far modified to allow of their doing
this. That action and reaction between a social

organism and its units, which we here see accounts for
changes in modes of social development, must be paralleled
by the action and reaction between an individual organism
and its units. Various classes of phenomena compelled
us to conclude, that each kind of organism is composed cf
physiological units, having certain peculiarites which force
them to arrange themselves into the form of the species to
which they are peculiar. And in the chapters on Genesis,
Heredity, and Variation, we saw reason to believe, that
while the polarities of the physiological units determine the
structure of the organism as a whole; the organism as a
whole, if its structure is changed by incident forces, reacts
on the physiological units, and modifies them towards con-
formity with its new structure. Now this action and reac-
tion between an organic aggregate and its units, tending
ever to bring the two into absolute harmony, must be con-
tinually making the developmental processes more direct ;

THE ARGUMENTS FROM EMBRYOLOGY. 377

and will show its effects in all kinds of ways and degree3,
according to the ancestral history of each species. Suppos-
ing it were possible for a race of organisms to have con-
iraued propagating itself through an indefinitely-long
period without any change of conditions, necessitating
change of structure ; there woidd be reached so complete a
iongruity between the organic aggregate and its physiologi-
cal units, that the units would arrange themselves directly
•nto a structure like that of the adult organism : the germ
tvould put on the proper characters of the species, with little
or no transposition of substance. But in the absence of
any such constancy of conditions and structure, what may we
expect ? "We may expect that where the conditions and
structure have been most constant, the mode of develop-
ment will be the most direct ; and that it will be the most
indirect, where there have been the greatest and most
numerous changes in the habits and structures of ancestral
races of organisms. And we may also expect that develop-
mental changes corresponding to early ancestral forms, will
undergo an obliteration that is great in proportion to the
fixity of organization that has been since maintained. The
facts appear in harmony with this conclusion. We see a
comparatively-direct development in those inferior tvpes of
animals, which show us, by their inferiority, that they have
not, since the commencement of organic life, passed through
many sets of changes. And where we find direct de-
velopment among higher types of animals, it characterizes
the simpler rather than the more complex members of the
types.

Between different parts in the same embryo, there are un-
likenesses in the method of formation, which seem to have
kindred meanings. The heart, of which the development is
in great measure direct, is an organ that appears compara-
tively early among the ascending grades of organic forms ;
and having appeared, retains throughout the character of a
hollow muscle. Conversely, the organs which develop with
25

378 THE EVOLUTION OF LIFE.

great indirectness, are the organs of external relation ,
which, in the progress of organic forms, undergo varioua
metamorphoses. Some light, too, is thus thrown on

certain irregularities in the order of development of organs.
If we contemplate those continuous actions and reactions
which tend ever to establish a balance between an organic
aggregate and its units ; we shall see that the effect which
the units composing any organ, produce on the organism as a
whole, will depend, partly on the permanence of such organ,
and partly on its proportional mass. The influence of any
force, is a product of its amount multiplied into the time during
which it has acted. Hence, a larger part of the aggregate
acting for a shorter time, will impress itself on the phy-
siological units, as much as a smaller part acting for a
longer time ; and may thus begin to show its influence in
the developmental changes, as soon as, or even earlier than, a
part that has existed for a greater period. Thus it becomes
comprehensible why, in certain Eatozoa which have im-
mensely-developed generative systems, the rudiments of the
generative systems are the first to become visible. And
thus are also explicable, anomalies such as those pointed
out by Prof. Agassiz — the appearance, in some cases, of
traits characterizing the species, at an earlier period of
development than traits characterizing the genus.

§ 132. So that while the embryologic law enunciated by
Von Baer, is in harmony with the hypothesis of evolution,
and is, indeed, a law which this hypothesis implies ; the
minor nonconformities to the law, are also interpretable by
this hypothesis. Parallelism between the courses of develop-
ment in species that had a common ancestry, is liable to be
variously modified in correspondence with the later ancestral
forms passed through after divergence of such species. The
substitution of a direct for an indirect process of formation,
which we have reason to believe will show itself, both in the
unfolding of the entire organism and in the unfolding of par*

THE ARGUMENTS FROM EMBRYOLOGY. '67V

ticular organs, niust obscure the enibryologic history. And
the parts influencing the whole in degrees varying with their
masses, there results a further influence which, from the out-
set, must begin to modify the metamorphoses of each kind of
embryo ; and cause it to show incipient divergences from
embryos which had ancestral histories the same as its own.
Thus we find three different causes conspiring in endless
ways and degrees, to produce deviations from the general law
— causes which are manifestly capable of producing, under
special conditions, changes in apparent contradiction to this
law.

CHAPTER VI.

THE ARGUMENTS FROM MORPHOLOGY.

§ 133. Leaving out of consideration the parallelism oi
development which characterizes organisms belonging to each
group, that community of plan which exists among them
when they are mature, is extremely remarkable and extremely
suggestive. As before shown (§ 103), neither the supposition
that these combinations of attributes which unite classes are
fortuitous, nor the supposition that no other combinations
were practicable, nor the supposition of adherence to pre-
determined typical plans, suffices to explain the facts. An
instance will best prepare the reader for seeing the true
meaning of these fundamental likenesses.

Under the immensely-varied forms of insects, greatly elon-
gated like the dragon-fly, or contracted in shape like the
lady-bird, winged like the butterfly, or wingless like the
flea, we find this character in common — there are primarily
twenty segments. These segments may be distinctly marked,
or they may be so fused as to make it difficult to find the
divisions between them. This is not all. It has been
shown that the same number of segments is possessed by all
the Crustacea. The highly- consolidated crab, and the squilla
with its long, loosely -jointed divisions, are composed of the
same number of somites. Though, in the higher crustaceans,
some of these successive indurated rings, forming the exo-
skeleton, are never more than partially marked off from each

TilE ARGUMENTS FROM MORPHOLOGY. 381

other ; yet they are indentifiable as homologous with
segments, which, in other crustaceans, are definitely
divided. What, now, can be the meaning of this

community of structure among these hundreds of thousands of
species filling the air, burrowing in the earth, swimming in
the water, creeping about among the sea- weed, and having
such enormous differences of size, outline, and substance, as
that no community would be suspected between them ? Why
under the down-covered body of the moth and under the
hard wing-cases of the beetle, should there be discovered the
same number of divisions as in the calcareous framework of
the lobster ? It cannot be by chance that there exist just
twenty segments in all these hundreds of thousands of species.
There is no reason to think it was necessary, in the sense
that no other number would have made a possible organism.
And to say that it is the result of design — to say that the Cre-
ator followed this pattern throughout, merely for the purpose
of maintaining vhe pattern — is to assign a motive which, if
avowed by a human being, we should call whimsical. No
rational interpretation of this and hosts of like morphological
truths, can be given except by the hypothesis of evolution ;
and from the hypothesis of evolution they are corollaries.
If organic forms have arisen from common stocks by per-
petual divergences and redivergcnces — if they have continued
to inherit, more or less clearly, the characters of ancestral
races; then there will naturally result these communities of
fundamental structure among extensive assemblages of crea-
tures, that have severally become modified in countless ways
and degrees, in adaptation to their respective modes of
life. To this let it be added, that while the belief

in an intentional adhesion to a pre-determincd pattern
throughout a whole group, is totally negatived by the occur-
rence of occasional deviations from the pattern ; such devi-
ations are reconcilable with the belief in evolution. As
pointed out in the last chapter, there is reason to think that
remote ancestral traits, will be obscured more or less according

582 THE EVOLUTION OF LIFE.

as the superposed modifications of structure, have or have
not been great or long maintained. Hence, though the occur-
rence of articulate animals, such as spiders and mites, having
fewer than twenty segments, is fatal to the supposition that
twenty segments was decided on for the three groups of
superior Articulata; it is not incongruous with the supposition,
that some primitive race of articulate animals, bequeathed to
these three groups this common typical character — a character
which has nevertheless, in many cases, become greatly ob-
scured, and in some of the most aberrant orders of these
classes, quite lost.

§ 134. Besides these wide-embracing and often deeply-
hidden homologies, which hold together different animals,
there are the scarcery-less significant homologies between
different organs of the same animal. These homologies,
like the others, are obstacles to the supernatural interpreta-
tions, and supports of the natural interpretation.

One of the most familiar and instructive instances is
furnished by the vertebral column. Snakes, which move
sinuously through and over plants and stones, obviously
need a segmentation of the bony axis from end to end ; and
inasmuch as flexibility is required throughout the whole
length of the body, there is advantage in the comparative
uniformity of this segmentation : the creature's movements
would be impeded if, instead of a chain of vertebrae varying
but little in their lengths, there existed in the middle of the
series some long bony mass that would not bend. But in most
of the higher Fertebrata, the mechanical actions and reac-
tions demand that while some parts of the vertebral axis shall
be flexible, other parts shall be inflexible. Inflexibility is
especially requisite in that part of the vertebral column
called the sacrum ; which, in mammals and birds, forms a
fulcrum exposed to the greatest strains which the skeleton
has to bear. Now in both mammals and birds, this rigid
portion of the vertebral column is not made of one long

THE ARGUMENTS FROM MORPHOLOGY. 383

segment or vertebra, but of several segments fused to-
gether. In man there are five of these confluent sacral
vertebrae ; and in the ostrich tribe they number from seven-
teen to twenty. Why is this ? Why, if the skeleton of
each species was separately contrived, was this bony mass
made by soldering together a number of vertebrae like those
forming the rest of the column, instead of being made out of
one simple piece ? And why, if typical uniformity was to be
maintained, does the number of sacral vertebras vary within
the same order of birds ? Why, too, should the develop-
ment of the sacrum be by the round-about process of first
forming its separate constituent vertebrae, and then de-
stroying their separateness ? In the embryo of a mammal
or bird, the substance of the vertebral column is, at the out-
set, continuous. The segments that are to become vertebrae,
arise gradually in the midst of this originally-homogeneous
axis. Equally in those parts of the spine which are to
remain flexible, and in those parts which are to grow
rigid, these segments are formed ; and that part of the spine
which is to compose the sacrum, having passed out of its ori-
ginal unity into disunity, by separating itself into segments,
passes again into unity by the coalescence of these segments.
To what end is this construction and re-construction ? If,
originally, the spine in vertebrate animals consisted from
head to tail of separate moveable segments, as it docs still in
fishes and some reptiles — if, in the evolution of the higher
Vertcbrata, certain of these moveable segments were ren-
dered less moveable with respect to each other, by the
mechanical conditions to which they are exposed, and at
length became relatively immoveable ; it is comprehensible
why the sacrum formed out of them, should continue ever
after to show more or less clearly its originally-segmented
structure. But on any other hypothesis, this segmented
structure is inexplicable. "We see the same law in

comparing the wonderfully complex jaws and legs in crusta-
ceaus," says Mr Darwin • referring to the well-known fact

384: THE EVOLUTION OF LIFE.

that those numerous lateral appendages which, in the lowei
crustaceans most of them serve as legs, and have like shapes^
are, in the higher crustaceans, some of them represented by
enormously-developed claws, and others by variously-modi-
fied foot-jaws. "It is familiar to abnost every one," ho
continues, " that in a flower the relative position of tho
sepals, petals, stamens, and pistils, as well as their intimate
structure, are intelligible on the view that they consist of
metamorphosed leaves arranged in a spire. In monstrous
plants we often get direct evidence jof the possibility of one
organ being transformed into another ; and we can actually
see in embryonic crustaceans and in many other animals, and
in flowers, that organs, which when mature become extremely
different, are at an early stage of growth exactly alike."
* * * " Why should one crustacean, which has an. ex-
tremely complex mouth formed of many parts, consequently
always have fewer legs ; or conversely, those with many legs
have simpler mouths ? Why should the sepals, petals,
stamens, and pistils in any individual flower, though fitted
for such widely-different purposes, be all constructed on the
same pattern ? "

To these and countless similar questions, the theory of
evolution furnishes the only rational answer. In the course
of that change from homogeneity to heterogeneity of struc-
ture, displayed in evolution under every form, it will neces-
sarily happen that from organisms made up of numerous
like parts, there will arise organisms made up of parts more
and more unlike : which unlike parts will nevertheless con-
tinue to bear traces of their primitive likeness.

§ 135. One more striking morphological fact, near akin
to some of the facts dwelt on in the last chapter, must be
here set down — the frequent occurrence, in adult animals
and plants, of rudimentary and useless organs, which are
homologous with organs that are developed and useful in
allied animals and plants. In the last chapter we saw that

THE ARGUMENTS FHOM MORPHOLOGY. b85

during the development of embryos, there often arise organs
which disappear on being replaced by other organs dis-
charging the same functions in different ways ; and that in
some cases, organs develop to certain points, and are then
re-absorbed without performing any functions. But very
generally, the partially-developed organs are retained
throughout life.

The osteology of the higher Fertcbrata, supplies abundant
examples. Vertebral processes which, in one tribe, are fully
formed and ossified from independent centres, are, in other
tribes, mere tubercles not having independent centres of
ossification. While in the tail of this animal, the vertebrae
are severally composed of centrum and appendages, in the
tail of that animal, they are simple osseous masses without
any appendages ; and in another animal, they have lost their
individualities by coalescence with neighbouring vertebrae
into a rudimentary tail. From the structures of the limbs,
analogous facts are cited by comparative anatomists. The
undeveloped state of certain metacarpal bones, characterizes
whole groups of mammals. In one case we find the normal
number of digits ; and, in another case, a smaller number
with an atrophied digit to make out the complement. Here is
a digit with its full number of phalanges ; and there a digit of
winch one phalange has been arrested in its growth. Still
more remarkable are the instances of entire limbs being rudi-
mentary ; as in certain snakes, which have hind legs hidden
beneath the integument. So, too, is it with the dermal ap-
pendages. Some of the smooth-skinned amphibia have scales
buried in the skin. The seal, which is a mammal considerably
modified in adaptation to an aquatic life, and which uses its
feet mainly as paddles, has toes that still bear external nails ;
but the manatee, which is a much more transformed main-
raal, has nailless paddles, which, when the skin is re-
moved, are said, by Humboldt, to display rudimentary nails
at the ends of the imbedded digits. Nearly all birds are
covered with developed feathers, severally composed of a shaft

J386 THK EVOLUTION OF LIFE.

bearing fibres, each of which again bears a fringe of down.
But in some birds, as in the ostrich, various stages of arrested
development of the feathers may be traced ; beginning with
the unusually-elaborated feathers of the tail, and ending with
those about the beak, which are reduced to simple hairs. Nor
is this the extreme case. In the Apteryx we see the whole
of the feathers ^educed t< a hair-like form. Again, the hair
which commonly covers the body in mammals, is compara-
tively rudimentary over the greater part of the human body,
and is in some parts reduced to mere down — down which
nevertheless proves itself to be homologous with the hair of
mammals in general, by occasionally developing into the
original form. Numerous cases of aborted organs are given
by Mr Darwin, of which a few may be here added. " No-
thing can be plainer," he remarks, "than that wings are formed
for flight, yet in how many insects do we see wings so reduced
in size as to be utterly incapable of flight, and not rarely
lying under wing-cases, firmly soldered together?" * * *
" In plants with separated sexes, the male flowers often have
a rudiment of a pistil ; and Kblreuter found that by crossing
such male plants with an hermaphrodite species, the rudi-
ment of the pistil in the hybrid offspring was much increased
in size ; and this shows that the rudiment and the perfect pistil
are essentially alike in nature." And then, to complete the
proof that these undeveloped parts are marks of descent from
races in which they were developed, there are not a few direct
experiences of this relation. " We have plenty of cases of
rudimentary organs in our domestic productions — as the
stump of a tail in tailless breeds — the vestige of an ear in
earless breeds — the re-appearance of minute dangling horns
in hornless breeds of cattle."

Here, as before, the teleological doctrine fails utterly;
for these rudimentary organs are useless, and occasionally
even detrimental. The doctrine of typical plans is equally
out of court ; for while, in some members of a group, rudi-
mentary organs completing the general type are traceable,

THE ARGUMENTS FROM MORPHOLOGY. 387

in other members of the same group, such organs are unre-
presents d. There remains only the doctrine of evolution ;
aud to this, these rudimentary organs offer no difficulties.
On the contrary, they are among its most striking evi-
dences.

S 136. The general truths of morphology thus coincide in
tneir implications. Unity of type, maintained under extreme
dissimilarities of form and mode of life, is explicable as re-
sulting from descent with modification ; but is otherwise
inexplicable. The likenesses disguised by unlikenesses, which
the comparative anatomist discovers between various organs
in the same organism, are worse than meaningless if it be
supposed that organisms were severally framed as we now
see them ; but they fit in quite harmoniously with the belief,
that each kind of organism is a product of accumidated
modifications upon modifications. And the presence in all
kinds of animals and plants, of functionally-useless parts
corresponding to parts that are functionally-useful in allied
animals and plants, while it is totally incongruous with the
belief in a construction of each organism by miraculous in-
terposition, is just what we are led to expect by the belief
that organisms have arisen by progression.

CHAPTER VII.

THE ARGUMENTS FROM DISTRIBUTION.

§ 137. In §§ 105 and 106, we contemplated the phenomena
of distribution in Space. The general conclusions reached,
in great part based on the evidence brought together by Mr
Darwin, were that, " on the one hand, we have similarly-con
ditioned, and sometimes nearly-adjacent, areas, occupied by
quite different Faunas. On the other hand, we have areas
remote from each other in latitude, and contrasted in soil as
well as climate, which are occupied by closely-allied Faunas."
Whence it was inferred that " as like organisms are not uni-
versally, or even generally, found in like habitats ; nor very
unlike organisms, in very unlike habitats ; there is no manifest
pre-determined adaptation of the organisms to the habitats."
In other words, the facts of distribution in Space, do not
conform to the hypothesis of design. At the same

time we saw that " the similar areas peopled by dissimilar
forms, are those between which there are impassable barriers ;
while the dissimilar areas peopled by similar forms, are those
between which there are no such barriers ;" and these
generalizations appeared to be in harmony with the abund-
antly-illustrated truth, " that each species of organism tends
ever to expand its sphere of existence — to intrude on other
areas, other modes of life, other media."

By way of showing still more clearly the effects of this
competition among races of organisms, let me here add some
recently-published instances of the usurpations of areas, and

THE ARGUMENTS FltOM DISTRIBUTION. 389

changes of distribution hence resulting. In the Natural His-
tory Review for January, 1864, Dr Hooker quotes as follows
from, some New Zealand naturalists : — "You would be surprised
at the rapid spread of European and other foreign plants in
this country. All along the sides of the main lines of road
through the plains, a Polygonum (auiculare), called ' Cow
Grass/ grows most luxuriantly, the roots sometimes two feet
in depth, and the plants spreading over an area from four to
five feet in diameter. The dock (Rumex obtustfolius or it!,
crisjjus) is to be found in every river bed, extending into the
valleys of the mountain rivers, until these become mere tor-
rents. The sow-thistle is spread all over the country, growing
luxuriantly nearly up to G000 feet. The water-cress increases
in our still rivers to such an extent, as to threaten to choke
them altogether : * * * I have measured stems twelve feet
long and three-quarters of an inch in diameter. In some of
the mountain districts, where the soil is loose, the white clover
is completely displacing the native grasses, forming a close
sward. * * * In fact, the young native vegetation appears
to shrink from competition with these more vigorous in-
truders." " The native (Maori) saying is, ' as the white
man's rat has driven away the native rat, so the European
fly drives away our own, and the clover kills our fern, so
will the Maoris disappear before the white man himself.' "

Given this universal tendency of the superior to over-
run the habitats of the inferior ; let us consider what, on the
hypothesis of evolution, will be the effects on the geo-
graphical relationships of species.

§ 138. A race of organisms cannot expand its sphere of
existence, without subjecting itself to new external conditions.
Those of its members which spread over adjaceut areas,
inevitably come in contact with circumstances partially
different from their previous circumstances ; and such of
them as adopt the habits of other organisms, necessarily
experience rc-actions more or less contrasted with the re

390 THE EVOLUTION OF LIFE.

actions before experienced. Now if changes of organic
structure are caused, directly or indirectly, by changes in
the incidence of forces ; there must result unlikenesses of
structure between the divisions of a race which colonizes
new habitats. Hence, in the absence of obstacles to migra-
tion, we may anticipate manifest kinships between the
animals and plants of one area, and those of areas adjoining it.
This inference corresponds with an induction before set
down (§ 106). In addition to the illustrations of it already
quoted from Mr Darwin, his pages furnish others. One is
that species which inhabit islands are habitually allied to
species which inhabit neighbouring main lands ; and an-
other is that the faunas of clustered islands show marked
similarities. " Thus the several islands of the Galapagos
Archipelago are tenanted," says Mr Darwin, "in a quite
marvellous manner, by very closely related species ; so that
the inhabitants of each separate island, though mostly dis-
tinct, are related in an incomparably closer degree to each
other than to the inhabitants of any other part of the world."
Mr Wallace has traced " variation as specially influenced by
locality " among the Papilionidce inhabiting the East Indian
Archipelago : showing how " the species and varieties of
Celebes possess a striking character in the form of the
anterior wings, different from that of the allied species and
varieties of all the surrounding islands ; " and how " tailed
species in India and the western islands lose their tails as
they spread eastward through the archipelago." During
his travels on the Upper Amazons, Mr Bates found that
" the greater part of the species of Ithomice changed from
one locality to another, not further removed than 100 to 200
miles ; " that " many of these local species have the appear-
ance of being geographical varieties ; " and that in some
species " most of the local varieties are connected with their
parent form by individuals exhibiting all the shades of
variation."

Further general relationships are to be inferred. If

THE ARGUMENTS FROM DISTRIBUTION. 391

luces of organisms, ever being thrust by pressure of popula-
tion into new habitats, undergo modifications of structure as
they diverge more and more widely in space, it follows that,
speaking generally, the widest divergences in Space will
indicate the longest periods during which the descendants
from a common stock have been subject to modifying con-
ditions ; and hence that, among organisms of the same
group, the smaller constrasts of structure will be limited
to the smaller areas. This we find : " varieties being,''
as Dr Hooker says in his Flora of Tasmania, "more re-
stricted in locality than species, and these again than
genera." Again, if races of organisms spread, and

as they spread are altered by changing incident forces ; it
follows that where the incident forces vary greatly within
given areas, the alterations will be more numerous than in
equal areas which are less- variously conditioned. This, too,
proves to be the fact. Dr Hooker points out that the most
uniform regions have the fewest species ; while in the most,
multiform regions the species are the most numerous.

§ 139. Let us consider next, how the hypothesis of
evolution corresponds with the facts of distribution, not over
different areas, but through different media. If all forms of
organisms have descended from some primordial simplest
form, it follows that, since this primordial simplest form
must have inhabited some one medium out of the several
media which organisms now inhabit, the peopling of other
media by its descendants, implies migration from one
medium to others — implies adaptations to media quite unlike
the original medium. To speak specifically — water being
the medium in which the lowest living forms exist, it is
implied that the earth and the air have been colonized from
the water. Great difficulties appear to stand in the way of
this assumption. Ridiculing those who contend for the uni-
serial development of organic forms, who have, indeed, laid
themselves open to ridicule by their many untenable pro-

392 THE EVOLUTION OF LIFE.

positions, Von Baer writes — "A fish, swimming towards
the shore, desires to take a walk, but finds his fins useless.
They diminish in breadth for want of use, and at the same
time elongate. This goes on with children and grandchil-
dren for a few millions of years, and at last who can be as-
tonished that the fins become feet ? It is still more natural
",hat the fish in the meadow, finding no water, should gape
after air, thereby, in a like period of time developing
lungs ; the only difficulty being that in the meanwhile,
a few generations must manage without breathing at
all." Though, as thus presented, the belief in a

transition looks laughable ; and though such derivation of
terrestrial vertebrates by direct modification of the piscine
type, is untenable ; yet we must not therefore conclude that
no migrations of the kind alleged can have taken place.
The adage that " truth is stranger than fiction," applies quite
as much to Nature in general as to human life. Besides the
fact that there are certain fish which actually do " take a
walk " without any very obvious reason ; and besides the
fact that sundry fish ramble about on land when impelled
to do so by the drying- up of the waters inhabited by them ;
there is the still more astounding fact, that one kind of fish
climbs trees. Few things seem more obviously impossible,
than that a water-breathing creature without efficient linibs>
should ascend eight or ten feet up the trunk of a palm ; and
yet the Andbas scandens does as much. To previous testi-
monies on this point, Capt. Mitchell has recently added
others. Such remarkable cases of temporary changes of
media, will prepare us for conceiving how, under special con-
ditions, permanent changes of media may have taken place ;
and for considering how the doctrine of evolution is eluci
dated by them.

Both marine organisms and fresh-water organisms, are
many of them left from time to time partially or completely
without water ; and the creatures which show the power to
change their media temporarily or permanently, are in very

THE ARGUMENTS i ROM DISTRIBUTION. 393

many cases, of the kinds mo3t liable to be thus deserted by
their medium. Let us consider what the sea-shore shows
us. Twice a-day the rise and the fall of the tide.,

covers and uncovers countless plants and animals, fixed and
moving ; and through the alternation of spring and neap
tides, it residts that the exposure of the organisms living low
down on the beach, varies both in frequency and duration :
while some of them are left dry only once a fortnight for a
very short time, others a little higher up, are left dry during
two or three hours at several ebb tides every fortnight.
Then by small gradations we come to such as, living at the
top of the beach, are bathed by salt-water only at long in-
tervals ; and still higher to some which are but occasionally
splashed in stormy weather. "What, now, do we find among
the organisms thus subject to various regular and irregular
alternations of media ? Besides many plants and many fixed
animals, we find numerous moving animals ; some of which
are confined to the lower zones of this littoral region, but others
of which wander over the whole of it. Omitting the humbler
animal forms, it will suffice to observe that each of the two
great sub-kingdoms, Mollusca and Articulata, supplies ex-
amples of creatures having a wide excursiveness within this
region. "We have gasteropods which, when the tide is down,
habitually creep snail-like over sand and sea- weed, even up as
far as high- water mark. We have several kinds of crustaceans,
of which the crab is the most conspicuous, running about on
the wet beach, and sometimes rambling beyond the reach of
the water. And then note the striking fact, that each of these
forms thus habituated to changes of media, is allied to forms
that are mainly or wholly terrestrial. On the West Coast of
Ireland, marine gasteropods are found on the rocks three hun-
dred feet above the sea, where they are only at long intervals
wetted by the spray ; and though between gasteropods of this
class and land- gasteropods the differences are considerable, yet
the land-gasteropods are more closely allied to them than to
any other Mollusca. Similarly, the two highest orders of
2G

394 the evolution or life.

crustaceans have their species which live occasionally, or
almost entirely, out of the water : there is a kind of lobster
in the Mauritius which climbs trees ; and there is the land-
crab of the West Indies, which deserts the sea when it reaches
maturity, and re- visits it only to spawn. Seeing, thus, how
there are many kinds of marine creatures whose habitat
habitually exposes them to changes of media ; how some of
the higher kinds so circumstanced, show a considerable adapt-
ation to both media ; and how these amphibious kinds are
allied to kinds that are mainly or wholly terrestrial ; we
shall see that the migrations from one medium to another,
which evolution pre- supposes, are by no means impracticable.
With such evidence before us, the assumption that the dis-
tribution of the Vertehrata through media so different as air
and water, may have been gradually effected in some analogous
manner, would not be altogether unwarranted, even had we
no clue to the process. We shall find, however, a tolerably
distinct clue. Though rivers, and lakes, and pools,

have no sensible tidal variations, they have their rises and
falls, regular and irregular, moderate and extreme. Especially
in tropical climates, we see them annually full for a certain
number of months, and then dwindling away and drying up.
This drying up may reach various degrees, and last for various
periods : it may go to the extent only of producing a liquid
mud, or it may reduce the mud to a hardened, fissured solid ;
it may last for a day or two or for months. That is to say,
aquatic forms which are in one place annually subject to a
slight want of water for a short time, are elsewhere subject
to greater wants for longer times : we have gradations of
transition, analogous to those which the tides furnish. Now
it is well known that creatures inhabiting such waters, have,
in various degrees, powers of meeting these contingences.
The contained fish either bury themselves in the mud
when the dry season comes, or ramble in search of other
waters. This is proved by evidence from India, Guiana, Siam,
Ceylon ; and some of these fish, as the Anabas scandens, are

THE ARGUMENTS FROM DISTRIBUTION. SQft

known to survive for days out of the water. But the facts of
greatest significance are furnished by an allied class of
Fertebrata, almost peculiar to habitats of this kind. The
Amphibia are not, like fish, habitually found in waters that
are never partially or wholly dried up ; but they nearly all
inhabit waters which, at certain seasons, evaporate, in great
measure or completely — waters in which most kinds of fish
cannot exist. And what are the leading structural traits of
these Amphibia? They have two respiratory systems —
pulmonic and branchial — variously developed in difierent
orders ; and they have two or four limbs, also variously de-
veloped. Further the class Amphibia consists of two groups,
in one of which this duality of the respiratory system is
permanent, and the development of the limbs always incom-
plete ; and in the other of which the branchiae disappear as
the lungs and limbs become fully developed. The lowest
group, the Perennibranchiata, have organs homologous with
the air-bladders of fishes, transformed in various degrees
into lungs, until " in the Siren, the pulmonic respiration is
more extensive and important than the branchial ; " and to
these creatures, having a habitat partially aerial and partially
aquatic, there are at the same time supplied, in the shallow
water covering soft mud, the mechanical conditions which
render swimming difficult, and rudimentary limbs useful.
In the higher group, the Caducibranchiata,, we find still more
suggestive transformations. Having at first a structure re-
sembling that which is permanent in the perennibranchiate
amphibian, the larva of the caducibranchiate amphibian,
pursues for a time a similar life; but eventually, the
changes are carried further in the same direction : the respir-
ation of air, originally supplementary to the respiration of
water, predominates over it more and more, till it replaces it
entirely ; and an additional pair of legs is produced. This
having been done, the creature either becomes, like the Triton,
one which quits the water only occasionally ; or, like the
Frog, one which pursues a life mainly terrestrial, and returns

396 THE EVOLUi'ION OF LIFE.

to the water now and then. Finally, if we ask under what
conditions this metamorphosis of a water-breather into an
air-breather completes itself, the answer is — it completes it-
self at the time when the shallow pools inhabited by the
larvae, are being dried up by the summer's sun.*

See, then, how significant are the facts when thus brought
together. There are particular habitats in which animals are
subject to changes of media. In such habitats exist animals
having, in various degrees, the power to live in both media,
consequent on various phases of transitional organization.
Near akin to these animals, there are some that, after passing
their early lives in the water, acquire more completely the
structures fitting them to live on land, to which they then
migrate. Lastly, we have closely-allied creatures like the
Surinam toad and the terrestrial salamander, which, though
they belong by their structures to the class Amphibia, are
not amphibious in their habits — creatures the larvae of which
do not pass their early lives in the water, and yet go through
these same metamorphoses ! Must we then think that the
distribution of kindred organisms through different media,
presents an insurmountable difficulty ? On the contrary,
with facts like these before us, the evolution-hypothesis
supplies possible interpretations of many phenomena that are
else unaccountable. Realizing the way in which such changes
of media are in some cases gradually imposed by physical
conditions, and in other cases voluntarily commenced and
slowly increased in the search after food ; we shall begin to
understand how, in the course of evolution, there have arisen

* While these pages are passing through the press, Dr Hooker has obliged
me by pointing out, that " plants afford many excellent examples " of analogous
transitions. He says that among true " water plants," there are found, in the
same species, varieties which have some leaves submerged and some floating ;
other varieties in which they are all floating ; and other varieties in which they
are all submerged. Further, that many plants characterized by floating leaves,
and which have all their leaves floating when they grow in deeper water, are
found with partly aerial leaves when they grow in shallower water ; and thai
slsewhere they occur in almost dry soil with all their leaves aerial.

THE ARGUMENTS FROM DISTRIBUTION. 397

those strange obscurations of one type by the externals oJ
another type. When we see land-birds occasionally feeding
by the water-side, and then learn that one of them, the water-
ouzel, an " anomalous member of the strictly terrestrial
thrush family, wholly subsists by diving — grasping the stones
with its feet and using its wings under water " — we are en-
abled to comprehend how, under pressure of population,
aqxiatic habits may be acquired by creatures organized for
aerial life ; and how there may eventually arise an ornithic
type, in which the traits of the bird are very much disguised.
Finding among mammals, some that in search of prey or
shelter, have taken to the water in various degrees, we shall
cease to be perplexed on discovering the mammalian structure
hidden under a fish-Like form, as it is in the Cetacea. Grant
that there has ever been going on that re-distribution of
organisms, which we see still resulting from their intrusions
on one another's areas, media, and modes of life ; and we
have an explanation of those multitudinous cases in which
homologies of structure are complicated with analogies. And
while it accounts for the occurrence in one medium of or-
ganic types fundamentally organized for another medium,
the doctrine of evolution accounts also for the accompany-
ing unfitnesses. Either the seal has descended from some
mammal which little by little became aquatic in its habits,
in which case the structure of its hind limbs has a mean-
ing ; or else it was specially framed for its present habi-
tat, in which case the structure of its hind limbs is incom-
prehensible.

§ 140. The facts respecting distribution in Time, which
have more than any others been cited both in proof and in
disproof of evolution, are too fragmentary to be conclusive
either way. Were the geological record complete, or did it,
as both TTniformitarians and Progressionists have habitually
assumed, give us traces of the earliest organic forms ; the
evidence hence derived, for or against, would have had more

398 THE EVOLLXION of life.

weight than any other evidence. As it is, all we can do is to
see whether such fragmentary evidence as remains, is con-
gruous with the hypothesis.

Palaeontology has shown that there is a " general relation
between lapse of time and divergence of organic forms "
(§ 107) ; and that " this divergence is comparatively slow and
continuous, where there is continuity in the geological forma-
tions, but is sudden and comparatively wide, wherever there
occurs a great break in the succession of strata." Now this
is obviously what we should expect. The hypothesis implies
structural changes that are not sudden but gradual. Hence,
where conformable strata indicate a continuous record, we
may expect to find successions of forms only slightly different
from one another ; while we may rationally look for consider-
able contrasts between the groups of forms fossilized in adjacent
strata, where there is evidence of a great blank in the record .

The permanent disappearances of species, of genera, and of
orders, which we saw to be a fact tolerably- well established, is
also a fact for which the belief in evolution prepares us.
If later organic forms have in all cases descended from
earlier organic forms, and have diverged during their descent,
both from their prototypes and from one another ; then it
obviously follows, that such of them as become extinct at any
epoch, will never re-appear at a subsequent epoch ; since
there can never again arise a concurrence and succession of
conditions, such as those under which each particular type
was evolved.

Though comparisons of ancient and modern organic forms,
prove that many types have persisted through enormous
periods of time, without undergoing great changes ; it wa«
shown that such comparisons do not disprove the occur-
rence in organic forms, of changes great enough to produce
what are called different types. The result of inductive in-
quiry we saw to be, that while a few modern higher types
yield signs of having been developed from ancient lower
types ; and while there are many modern types which may

THE ARGUMENTS FROM DISTRIBUTION. 399

have been thus developed, though we are without evidence that
they have been so ; yet that " any admissible hypothesis of
progressive modification must be compatible with persistence
without progression through indefinite periods." Now these
results are quite congruous with the hypothesis of evolution.
As rationally interpreted, evolution must in all cases be
understood to result, directly or indirectly, from the incidence
of forces. If there are no changes of conditions, entailing
organic changes, organic changes are not to be expected.
Only in organisms which fall under conditions, in conformity
to which there arise additional modifications answering to
additional needs, will there be that increased heterogeneity
which characterizes higher forms. Hence, though the facts
of palaeontology cannot be held to prove evolution, yet they
are in harmony with it ; and some few of them yield it
support.

§ 141. One general truth respecting distribution in Time,
is, however, profoundly significant. If, instead of contem-
plating the relations among past forms of life taken by them-
selves, we contemplate the relations between them and the
forms now existing ; we find a connexion which is in perfect
harmony with the belief in evolution, but quite irreconcil-
able with any other belief.

Note, first, how full of meaning is the close kinship that
exists between the aggregate of organisms now living,
and the aggregate of organisms which lived in the most
recent geologic times. In the last-formed strata, nearly all
the imbedded remains are those of species which still flourish.
Strata a little older, contain a few fossils of species now ex-
tinct ; though, usually, species greatly resembling extant ones-
Of the remains found in strata of still earlier date, the ex-
tinct species form a larger per centage ; and the differences be-
tween them and the allied species now living, are more marked.
That is to say, the gradual change of organic types in Time,
which we before saw is indicated by the geological record, ia

400 THE EVOLU'liON OF LIFE.

equally indicated by the relation between existing organic
types and organic types of the epoch preceding our own.
The evidence completely accords with the belief in a descent
of present life from past life. Doubtless such a

kinship is not incongruous with the doctrine of special crea_
tions. It may be argued that the introduction, from time to
time, of new species better fitted to the somewhat changed
conditions of the Earth's surface, would result in an apparent
alliance between our living Flora and Fauna, and the Floras
and Faunas that lately lived. No one can deny it. But on
passing from the most general aspect of the alliance, to its
more special aspects, we shall find this interpretation com-
pletely negatived.

For besides a close kinship between the aggregate of sur-
viving forms and the aggregate of forms that have died out
in recent geologic times ; there is a peculiar connexion of
like nature between present and past forms in each great
geographical region. The instructive fact before cited from
Mr Darwin, is the " wonderful relationship in the same con-
tinent between the dead and the living." This relationship
is not explained by the supposition that new species have
been at intervals supernaturally placed in each habitat, as the
habitat became modified ; since, as we saw, species are by no
means uniformly found in the habitats to which they are best
adapted. It cannot be said that the marsupials imbedded in
recent Australian strata, having become extinct because of
unfitness to some new external condition, the existing mar-
supials were then specially created to fit the modified en
vironment ; since sundry animals found elsewhere, aro
so much more completely in harmony with these new
Australian conditions, that, when taken to Australia, they
rapidly extrude the marsupials. While, therefore, the simi-
larity between the existing Australian Fauna and the Fauna
which immediately preceded it over the same area, is just
that which the belief in evolution leads us to expect ; it
is a similarity which cannot be otherwise accounted for.

THE ARGUMENTS FROM DISTRIBUTION. 40!

And so is it with parallel relations in New Zealand, in South
America, and in Europe.

§ 142. Given, then, that pressure which species exercise
on one another, in consequence of the universal overfilling of
their respective habitats — given the resulting tendency to
thrust themselves into one another's areas, and media, and
modes of life, along such lines of least resistance as from
time to time are found — given besides the changes in modes
of life, hence arising, those other changes which physical
alterations of habitats necessitate — given the structural
modifications directly or indirectly produced in organisms
by modified conditions ; and the facts of distribution in
Space and Time are accounted for. That divergence and re-
divergence of organic forms, which we saw to be shadowed
forth by the truths of classification and the truths of embry-
ology, we see to be also shadowed forth by the truths of
distribution. If that aptitude to multiply, to spread, to
separate, and to differentiate, which the human races have in
all times shown, be a tendency common to races in general,
as we have ample reason to assume ; then there will result
that kind of relation among the species, and genera, and
orders, peopling the Earth's surface, which we find exists.
Those remarkable identities of type discovered between or-
ganisms inhabiting one medium, and strangely-modified or-
ganisms inhabiting another medium, are at the same time
rendered comprehensible. And the appearances and disap-
pearances of species which the geological record shows us, as
well as the connexions between successive groups of species
from early eras down to our own, cease to be inexplicable.

CHAPTEE VIII.

nOW IS ORGANIC EVOLUTION CAUSED?

§ 143. Already it has been necessary to speak of tho
causes of organic evolution in general terms ; and now we
are prepared for considering them specifically. The task
before us is to deduce the leading facts of organic evolution,
from those same first principles which evolution . at large
conforms to.

Before attempting this, however, it will be instructive to
glance at the causes of organic evolution that have been
from time to time alleged.

§ 144. The theory that plants and animals of all kinds
were gradually evolved, seems to have been at first accom-
panied only by the vaguest conception of cause — or rather,
by no conception of cause properly so called, but only by the
blank form of a conception. One of the earliest who in
modern times (1735) contended that organisms are indefi-
nitely modifiable, and that through their modifications they
have become adapted to various modes of existence, was
De Maillet. But though De Maillet supposed all living
beings to have arisen by a natural, continuous process, ho
does not appear to have had any definite idea of that which
determines this process. In 1794, in his Zoonomia,

Dr Darwin gave reasons (sundry of them valid ones) for
believing that organized beings of every kiud, have de-

HOW IS ORGANIC EVOLUTION CAUSED? 403

ecended from one, or a few, primordial germs ; and along
with some observable causes of modification, which he points
out as aiding the developmental process, he apparently
ascribes it, in part, to a tendency given to such germ or
germs when created. He suggests the possibility " that all
warm-blooded animals have arisen from one living filament,
which The Great First Cause endued with animality, with
the power of acquiring new parts, attended with new pro-
pensities, directed by irritations, sensations, volitions, and
associations ; and thus possessing the faculty of continuing
to improve by its own inherent activity. " In this passage
we see the idea to be, that evolution is pre-determined
by some intrinsic proclivity. "It is curious," savs

Mr Charles Darwin, " how largely my grandfather, Dr
Erasmus Darwin, anticipated the erroneous grounds of
opinion, and the views of Lamarck." One of the anticipa-
tions was this ascription of development to some inherent
tendency. To the " plan general de la nature, et sa marche
uniforme dans ses operations," Lamarck attributes " la
progression evidente qui existe dans la composition de
l'organisation des animaux ; " and " la gradation reguliere
qu'ils devroient offrir dans la composition de leur organ-
isation," he thinks is rendered irregular by secondary
causes. Essentially the same in kind, though some-

what different in form, was the conception put forth in the
Vestiges of Creation ; the author of which contends " that
the several series of animated beings, from the simplest and
oldest up to the highest and most recent, are, under the pro-
vidence of God, the results, first, of an impulse which has
been imparted to the forms of life, advancing them, in defi-
nite times, by generation, through grades of organization
terminating in the highest dicotyledons and vertebrata ; ''
and that the progression resulting from these impulses, is
modified by certain other causes. The broad general con-
trasts between lower and higher forms of life, are regarded
by him as due to an innate aptitude to give birth to forms

104 THE EVOLUTION OF LIFE.

0/ more perfect structures. The last to re-emin*

ciate this doctrine has been Prof. Owen ; who asserts " the
axiom of the continuous operation of creative power, or of
the ordained becoming of living things." Though these
highly-general expressions do not suggest any very definite
idea, yet they imply the belief that organic progress is a
result of some in-dwelling tendency to develop, supernatur-
ally impressed on living matter at the outset — some ever-
acting constructive force, which, independently of other
forces, moulds organisms into higher and higher forms.

In whatever way it is formulated, or by whatever language
it is obscured, this ascription of organic evolution to some
aptitude naturally possessed by organisms, or miraculously
imposed on them, is unphilosophical. It is one of those ex-
planations which explains nothing — a shaping of ignorance
into the semblance of knowledge. The cause assigned is not
a true cause — not a cause assimilable to known causes — not
a cause that can be anywhere shown to produce analogous
effects. It is a cause unrepresentable in thought : one of
those illegitimate symbolic conceptions which cannot by any
mental process be elaborated into a real conception. In
brief, this assumption of a persistent formative power, in-
herent in organisms, and making them unfold into higher
forms, is an assumption no more tenable than the assump-
tion of special creations : of which, indeed, it is but a modi-
fication ; differing only by the fusion of separate unknown
processes into a continuous unknown process.

§ 145. Along with this intrinsic tendency to progress,
supposed to be primordially impressed on them, Dr Darwin
held that animals have a capacity for being modified by pro-
cesses which their own desires initiate. He speaks of
powers as "excited into action by the necessities of the
creatures which possess them, and on which their existence
depends ; " and more specifically he says that " from their
first rudiment or primordium, to the termination of th^ir

HOW IS ORGANIC EVOLUTION CAUSED? 405

lives, all animals undergo perpetual transformations ; which
are in part produced by their own exertions, in consequence
of their desires and aversions, of their pleasures and their
pains, or of irritations, or of associations ; and many of these
acquired forms or properties are transmitted to their pos-
terity " While it embodies a belief for which a great deal
is to be said, this passage involves the assumption that,
desires and aversions, existing before experiences of the ac-
tions to which they are related, were the originators of the
actions, and therefore of the structural modifications caused
by them. In his JPhilosophie Zoologique, Lamarck

much more specifically asserts " le sentiment inte'rieur,"
to be in all creatures that have developed nervous svs-
tems, an independent cause of those changes of form which
are due to the exercise of organs : distinguishing it from
that simple irritability possessed by inferior animals, which
cannot produce what we call a desire or emotion ; and
holding that these last, along with all "qui manquent
de systeme nerveux, ne vivent qu'a l'aide des excitations
ijii'ils recoiveut de l'exterieur." Afterwards he says — "je
reconnus que la nature, obligee d'abord d'emprunter des
milieux environnans la puissance excitahice des mouvemens
vitaux et des actions des animaux imparfaits, sut, en com-
posant de plus en plus 1'organisation animate, transporter cetto
puissance dans l'interieur meme de ces etres, et qu'd la fin,
elle parvint a mettre cette meme puissance a la disposition
de l'individu." And still more definitely he contends that
if one considers " la progression qui se montre dans la com-
position de 1'organisation, " * * * "alors on eut pu aperce-
voir comment les besnins, d'abord reduits a, nullite, et dont
le nombre ensuite s'est accru graduellement, ont amene* le
penchant aux actions propres a y satisfaire; comment los
actions devenucs habituelles et energiques, ont occasionne* le
developpement des organes qui les executent."

Now though this conception of Lamarck is more precisely
etated, and worked out with much greater elaboration and

406 THE EVOLUTION OF LIFE.

wider knowledge of the facts, it is essentially the same as
that of Dr Darwin ; and along with the truth it contains,
contains also the same error more distinctly pronounced.
Merely noting that desires or wants, acting directly only
on the nervo-muscular system, can have no immediate in-
fluence on very many organs, as the viscera, or such external
appendages as hair and feathers ; and observing, further,
that even some parts which belong to the apparatus of
external action, such as the bones of the skull, cannot be
made to grow by increase of function called forth by desire ; it
will suffice to point out that the difficulty is not solved, but
simply slurred-over, when needs or wants are introduced as
independent causes of evolution. True though it is, as Dr
Darwin and Lamarck contend, that desires, by leading to
increased actions of motor organs, may induce further de-
velopments of such organs ; and true as it probably is, that
the modifications hence arising, are transmissible to offspring ;
yet there remains the unanswered question — Whence do these
desires originate ? The transferrence of the exciting power
from the exterior to the interior, as described by Lamarck,
begs the question. How comes there a wish to perform an
action not before performed ? Until some beneficial result has
been felt from going through certain movements, what can
suggest the execution of such movements? Every desire
consists primarily of a mental representation of that which
is desired, and secondarily excites a mental representation of
the actions by which it is attained ; and any such mental
representations of the end and the means, imply antecedent
experience of the end and antecedent use of the means. To
assume that in the course of evolution there from time to
time arose new kinds of actions dictated by new desires, is
simply to remove the difficulty a step back.

§ 146. Changes of external conditions are named by Dr
Darwin, as causes of modifications in organisms. Assigning,
us evidence of original kinship, that marked similarity of

HOW IS ORGANIC EVOLUTION CAUSED? 407

type which exists among animals, he regards then devia-
tions from one another, as caused by differences in their
modes of life : such deviations being directly adaptive.
Enumerating various appliances for procuring food, he says
they all " seem to have been gradually produced during many
generations by the perpetual endeavour of the creatures to
supply the want of food, and to have been delivered to their
posterity with constant improvement of them for the pur-
poses required." And the creatures possessing these va-
rious appliances, are considered as having been rendered
unlike, by seeking for food in unlike ways. As illustrating
the alterations wrought by changed circumstances, he names
the acquired characters of domestic animals. La-

marck has elaborated the same view in detail : using for the
purpose, with great ingenuity, his extensive knowledge of
the animal kingdom. From a passage in the Avertissement,
it would at first sight seem, that he looks upon direct adapt-
ation to new conditions, as the chief cause of evolution. He
says — "Je regardai comme certain que le mouvement des
fluides dans l'interieur des animaux, mouvement qui c'est
progressivement accelere avec la composition plus grande de
l'organisation ; et que V influence des circonstances nouvelles,
a mesure que les animaux s'y exposerent en se repandant
dans tous les lieux habitables, furent les deux causes g£n^-
rales qui ont amene les differens animaux a l'etat ou nous les
voyons actuellement." But elsewhere, the view he expresses
appears decidedly different from this. He asserts that "dans
sa marche, la nature a commence, et recommence encore tous
les jours, par former les corps organises les plus simples ; "
and that " les premieres ebauches de l'animal et du vegetal
£tant formees dans les lieux et les circonstances convenables,
les facultes d'une vie commencante et d'un mouvement or-
ganique etabli, ont necessairement developpe peu a peu les
organes, et qu'avec le temps elles les ont diversifies ainsi que
' les parties." And then, further on, he puts in italics this
proposition : — " La progression dans la composition de Vor*

4-08 THE EVOLUTION OF LIFE.

ganisation suhit, ca et la, dans la serie generale lies animaux,
des anomalies operees par V influence des cir con stances d* habi-
tation, et par celle des habitudes contractees." These, and
sundry other passages, joined with his general scheme of
classification, make it clear that Lamarck conceived adaptivo
modification to be, not the cause of progression, but the
cause of irregularities in progression. The inherent tend-
ency which organisms have, to develop into more perfect
forms, would, according to him, result in a uniform series of
forms ; but varieties in their conditions work divergences of
structure, which break up the series into groups : groups
which he nevertheless places in uni-serial order, and regards
as still substantially composing an ascending succession.

§ 147. These speculations, crude as they may be considered,
show much sagacity in their respective authors, and have
done good service. Without embodying the truth in a de-
finite shape, they contain adumbrations of it. Not directly,
but by successive approximations, do mankind reach correct
conclusions ; and those who first think in the right direction,
loose as may be their reasonings, and wide of the mark as
their inferences may be, yield indispensable aid by framing
provisional conceptions, and giving a bent to inquiry.

Contrasted with the dogmas of his age, the idea of De
Maillet was a great advance. Before it can be ascertained
how organized beings have been gradually evolved, there
must be reached the conviction that they have been gradu-
ally evolved; and this conviction he reached. His wild
notions as to the way in which natural agencies acted in the
production of plants and animals, must not make us forget
the merit of his intuition that animals and plants were pro-
duced by natural causes. In Dr Darwin's brief ex-
position, the belief in a progressive genesis of organisms, is
joined with an interpretation having considerable definite-
ness and coherence. In the space of ten pages he not only
indicates several of the leading classes of facts which suppor'

FTOW IS ORGANIC EVOLUTION CAUSED 4^0

the hypothesis of evolution, but he does something towards
elucidating the process of evolution. His reasonings show
us an unconscious mingling of the belief in a supernaturally-
impressed tendency to develop, with the belief in a develop-
ment arising from the changing incidence of conditions.
Probably had he pursued the inquiry further, this last belief
would have grown at the expense of the first. La-

marck, in elaborating this general conception, has given
greater precision to both its truth and its error. Asserting
the same imaginary factors and the same real factors, he has
traced out their supposed actions in detail ; and has, in con-
sequence, committed himself to a greater number of un-
tenable positions. But while, in trying to reconcile the
facts with a theory which is only an adumbration of the
truth, he laid himself open to the criticisms of his con-
temporaries ; he proved himself profounder than his con-
temporaries, by seeing that evolution, however caused, has
been going on. If they were wise in not indorsing a theory
which fails to account for a great part of the facts ; they
were unwise in ignoring that degree of congruity with the
tacts, which shows the theory to contain some fundamental
verity.

Leaving out, however, the imaginary factors of evolution
which these speculations allege, and looking only at the one
actual factor which Dr Darwin and Lamarck assign as
accounting for some of the phenomena ; it is manifest from
our present stand-point, that this, so far as it is a cause of
evolution, is a proximate cause and not an ultimate cause.
To say that functional adaptation to conditions, produces
either evolution in general, or the irregularities of evolution,
is to raise the further question — why is there a functional
adaptation to conditions ? — why do use and disuse generate
appropriate changes of structure ? Neither this nor any other
interpretation of biologic evolution which rests simply on (he
basis of biologic induction, is an ultimate interpretation. The
biologic induction must itself be interpreted. Only when
27

410 THE EVOLUTION OF LIFE.

the process of evolution of organisms, is affiliated on the
process of evolution in general, can it be truly said to be
explained. The thing required is to show that its various
results are corollaries from first principles. We have to
reconcile the facts with the universal laws of the redistribu-
tion of matter and motion.

CHAPTER IX.

EXTERNAL FACTOKS.

^ 148. TVken illustrating the rhythm of motion (First
Principles, § 94) it was pointed out that besides the daily
and annual alternations in the quantities of light and heat
which any portion of the Earth's surface receives from the
Sun, there are alternations which require immensely- greater
periods to complete. Reference was made to the fact, that
" every planet, during a certain long period, presents more of
its northern than of its southern hemisphere to the Sun at the
time of its nearest approach to him ; and then again, during
a like period, presents more of its southern hemisphere than
of its northern — a recurring co-incidence which, though
causing in some planets no sensible alterations of climate, in-
volves in the case of the Earth an epoch of 2.1,000 years,
during which each hemisphere goes through a cycle of tem-
perate seasons, and seasons that are extreme in their heat
and cold." Further, it was pomted out that there is a varia-
tion of this variation. The slow rhythm of temperate and in-
temperate climates, which takes 21,000 years to complete,
h self undergoes exaggeration and mitigation, during epochs
(hat are far longer. The Earth's orbit slowly alters in
form : now approximating to a circle ; and now becoming
more eccentric. During the period at which the Earth's
orbit has least eccentricity, the temperate and intemperate
climates which repeat their cycle in 21.000 years, arc

412 VHE EVOLUTION OF LIFE.

severally less temperate and less intemperate, than when,
some one or two millions of years later, the Earth's orbit has
reached its extreme of eccentricity.

Thus, besides those daily variations in the quantities of light
and heat received by organisms, and responded to by varia-
tions in their functions ; and besides the annual variations in
the quantities of light and heat which organisms receive,
and similarly respond to by variations in their functions;
there are variations that severally complete themselves in
21,000 years and in some millions of years — variations to
which there must also be a response in the changed functions
of organisms. The whole vegetal and animal kingdoms,
are subject to a quadruply -compounded rhythm in the in-
cidence of the forces on which life primarily depends — a
rhythm so involved in its slow working round, that at
no time during one of these vast epochs, can the in-
cidence of these forces be exactly the same as at any other
time. To the direct effects so produced on organ-

isms, have to be added much more important indirect effects.
Changes of distribution must result. Certain redistributions
are occasioned even by the annual variations in the quantities
of the solar rays received by each part of the Earth's surface.
The migrations of birds thus caused, are familiar. So too
are the migrations of certain fishes : in some cases from one
part of the sea to another ; and in some cases from salt water
to fresh water. Now just as the yearly changes in the amounts
of light and heat falling on each locality, yearly extend
and restrict the habitats of many organisms that are able to
move about with some rapidity ; so must these alternations
of temperate and intemperate climates produce extensions
and restrictions of habitats. These extensions and restric-
tions, though slow, will be universal — will affect the habitats
of stationary organisms as well as those of locomotive ones.
For if during an astronomic era, there is going on at any
limit to a plant's habitat, a diminution of the winter's cold
or summer's heat, which had before stopped its spread at

EXTERNAL FACTORS. 413

that limit; then, though the individual plants arc fixed,
yet the species will move : the seeds of plants living at the
limit, will produce individuals that survive beyond the limit.
The gradual spread so effected, having gone on for some ten
thousand years, the opposite change of climate will begin to
cause retreat : the tide of each species will during the one
half of a long epoch, slowly flow into new regions, and
then will slowly ebb away from them. Further, this rise
and fall in the tide of each species, will, during far longer
intervals, undergo increasing rises and falls and then de-
creasing rises and falls. There will be an alternation of
spring tides and neap tides, answering in its period to the
changing eccentricity of the Earth's orbit.

These astronomical rhythms, therefore, entail on organisms
unceasing changes in the incidence of forces in two ways.
They directly subject them to variations of solar influences,
in such a manner that each generation is somewhat differently
affected in it3 functions ; and they indirectly bring afbout
complicated alterations in the environing agencies, by carry-
ing each species into the presence of new physical conditions.

§ 149. The power of geological actions to modify every-
where the circumstances in which plants and animals are
placed, is conspicuous. In each locality, denudation slowly
uncovers different deposits ; and slowly changes the exposed
areas of deposits already uncovered. Simultaneously, the
alluvial beds that are being formed, are qualitatively affected
by these progressive changes in the natures and proportions of
the strata denuded. The inclinations of surfaces and their
directions with respect to the Sun, are at the same time
altered ; and the organisms existing on them are thus having
their thermal conditions continually altered, as well as their
drainage. Igneous action, too, complicates these gradual
modifications. A flat region cannot be step by step thrust
up into a protuberance, without unlike climatic changes
being produced in its several parts by their exposures to dif-

414:

THE EVOLUTION OF LIFE.

ferent aspects. Extrusions of trap, wherever they take
place, revolutionize the localities ; both over the areas covered,
and over the areas on which their detritus is left. And
where volcanoes are formed, the ashes they occasionally send
out, modify the character of the soil throughout large sur-
rounding tracts.

In like manner alterations in the Earth's crust, cause the
ocean to be ever subjecting the organisms it contains to new
combinations of conditions. Here the water is being deep-
ened by subsidence, and there shallowed by upheaval. "While
the falling upon it of sediment brought down by neighbour-
ing large rivers, is raising the sea-bottom in one place; in
another, the habitual rush of the tide is carrying away the
sediment previously deposited. The mineral character of
the submerged surface on which sea- weeds grow and molluscs
crawl, is everywhere occasionally changed : now by the
bringing away from an adjacent shore some previously un-
touched strata ; and now by the accumulation of organic
remains, such as the shells of pteropods or of foraminifera.
A further series of alterations in the circumstances of marine
organisms, is entailed by changes in the movements of the
water. Each modification in the outlines of neighbouring
shores, makes the tidal streams vary their directions or
velocities, or both. And the local temperature is from time
to time raised or lowered, because some far-distant re-ar-
rangement of the Earth's crust, has wrought a divergence in
those circulating currents of warm and cold water which
pervade the ocean.

These geologically-caused changes in the physical charac-
ters of each environment, occur in ever-new combinations, and
with ever-increasing complexity. As already shown (First
Principles, § 118), it follows from the law of the multiplication
of effects, that during long periods, each tract of the Earth's
surface increases in heterogeneity of both form and substance
Hence plants and animals of all kinds, are, in the course of
generations, subject by these alterations in the crust of the

EXTERNAL FACTORS.

415

Earth, to sets of incident forces which differ from previous
6ets, both by changes in the proportions of the factors, and,
occasionally, by the addition of new factors.

§ 150. Variations in the astronomical conditions joined
with variations in the geological conditions, bring about
variations in the meteorological conditions. Those extremely
slow alternations of elevation and subsidence, which there is
reason to believe take place over immense areas, here pro-
ducing a continent where once there was a fathomless ocean,
and there causing wide seas to spread where in a long past
epoch there stood snow-capped mountains, gradually work
great atmospheric changes. While yet the highest parts of
an emerging surface of the Earth's crust, exist as a cluster of
islands, the plants and animals which in course of time migrate
to them, have climates that are peculiar to small tracts of
land surrounded by large tracts of water. As, by successive
upheavals, greater areas are exposed, there begin to arise
sensible contrasts between the states of their peripheral parts
and their central parts : the sea and land breezes, which
daily moderate the extremes of temperature near the shores,
cease to affect the interiors ; and the interiors, less qualified
too in their heat and cold by such ocean-currents as bathe
the shores, acquire more decidedly the characters due to
their latitudes. Along with the further elevations which
unite the members of the archipelago into a continent, there
come new meteorologie changes, as well as exacerbations of
the old. The winds, which were comparatively uniform in
their directions and periods when only islands existed, grow
involved in their distribution, and widely- different in dif-
ferent parts of the continent. The quantities of rain which
they discharge and of moisture which they absorb, vary
everywhere according to the proximity to the sea and to
surfaces of land having special characters.

Other complications result from variations of height above
the sea : elevation producing a decrease of heat and conse-

416 THE EVOLUTION OF LIFE.

quentty an increase in the precipitation of water — a precipit-
ation that takes the shape of snow where the elevation is
very great, and of rain where it is not so great. The gather-
ing of clouds and descent of showers around mountain tops,
are familiar to every tourist. Inquiries in the neighbouring
valleys, prove that within distances of a mile or two the
recurring storms differ in their frequency and violence.
Xay, even a few yards off, the meteorologic conditions vary in
such regions : as witness the way in which the condensing
vapour keeps eddying roimd on one side of some high crag,
while the oiher side is clear ; or the way in which the snow-
line runs irregularly to many different heights, in ail the minor
valleys and ravines and hollows of each mountain side.

Climatic variations that are thus geologically produced,
being compounded with those which result from the slow
astronomical changes ; and no correspondence existing be-
tween the geologic and the astronomic rhythms ; it results
that the same plexus of actions never recurs. Hence the
incident forces to which the organisms of every locality are
exposed by atmospheric agencies, are ever passing into un-
paralleled combinations ; and these are on the average ever
becoming more complex.

§ 151. Besides changes in the incidence of inorganic
forces, there are equally continuous, and still more involved,
changes in the incidence of forces which organisms exercise
on one another. As before pointed out (§ 105), the plants
and animals inhabiting each locality, are held together in so
entangled a web of relations, that any considerable modifica-
tion which one species undergoes, acts indirectly on many
other species ; and eventually changes, in some degree, the
circumstances of nearly all the rest. If an increase of heat,
or modification of soil, or decrease of humidity, causes a par-
ticular kind of plant either to thrive or to dwindle ; an
unfavourable or favourable effect is wrought on all such
competing kinds of plants, as are not immediately influenced

EXTERNAL FACTORS. 417

in the same way. The animals which eat the seeds or browse
on the leaves either of the plant primarily affected or those of
its competitors, are severally altered in their states of nutri-
tion and in their numbers ; and this change presently tells
on various predatory animals and parasites. And since each
of these secondary and tertiary changes, becomes itself a-
centre of others ; the increase or decrease of each species,
produces "waves of influence which spread and reverberate
and re-reverberate, throughout the whole Flora and Fauna
of the locality.

More marked and multiplied still, arc the ultimate effects
of those causes •which make possible the colonization of neigh-
bouring areas. Each intruding plant or animal, besides the
new inorganic conditions to which it is subject, is subject to
organic conditions considerably different from those to which
it has been habituated. It has to compete with some organ-
isms unlike those of its preceding habitat. It must preserve
itself from enemies not before encountered. Or it may meet
with a species over which it has some advantage greater
than any that it had over the species it was previously in
contact with. Even where migration does not bring it face
to face with new competitors or new enemies or new prey,
it inevitably experiences new proportions among these.
Further, an expanding species is almost certain to invade
more than one adjacent region. Spreading north or south, it
will come among the plants and animals, here of a level
district and there of a hilly one — here of an inland tract,
and there of a tract bordered by the sea. And while differ-
ent groups of its members 'will thus expose themselves to
the actions and re-actions of different Floras and Faunas,
these different Floras and Faunas will simultaneously have
their organic conditions changed by the intruders.

This process becomes gradually more active and more-
complicated. Though in particular cases, a plant or animal
may fall into simpler relations with the living things around,
than those it was before placed in ; yet it is manifest thut,

418 THE EVOLUTION OF LIFE.

on the average, the organic environments of organisms have
been increasing in heterogeneity. As the number of speciee
with which each species is directly or indirectly implicated,
multiplies, each species is oftener subject to changes in the
organic actions which influence it. These more frequent
changes severally grow more involved. And the corre-
sponding reactions affect larger Floras and Faunas, in ways
increasingly complex and varied.

§ 152. When the astronomic, geologic, meteorologic, and
organic agencies that are at work on each species of organ-
ism, are contemplated as becoming severally more compli-
cated in themselves, and at the same time as co-operating in
ways that are always more or less new ; it will be seen that
throughout all time, there has been an exposure of organisms
to endless successions of modifying causes which gradually
acquire an intricacy that is scarcely conceivable. Every
kind of plant and animal may be regarded as for ever pass-
ing into a new environment — as perpetually having its
relations to external circumstances altered, either by their
changes with respect to it when it remains stationary, or by
its changes with respect to them when it migrates, or by
both.

Yet a further cause of progressive alteration and compli-
cation in the incident forces, exists. All other things con-
tinuing the same, every additional faculty by which an
organi&m is brought into relation with external objects, as
well as every improvement in such faculty, becomes a means
of subjecting the organism to a greater number and variety
of external stimuli, and to new combinations of external
stimuli. So that each advance in complexity of organization,
itself becomes an added source of complexity in the incidence
of external forces.

Once more, every increase in the locomotive powers of
animals, increases both the multiplicity and the multiformity
of tbe actions of things upon them, and of their reactions

EXTERNAL FACTORS. 419

upon tilings. Doubling a creature's activity, quadruples the
area that comes within the range of its excursions : thus
augmenting in number and heterogeneity, the external
agencies which act on it during any given interval.

By compounding the actions of these several orders of
factors, there is produced a geometric progression of changes,
increasing with immense rapidity. And there goes on an
equally rapid increase in the frequency with which the com-
binations of the actions are altered, and the intricacies of
their co-operations enhanced.

CHAPTER X.

INTERNAL FACTORS.

§ 153. We saw at the outset (§§ 10—16), that organic
matter is built up of molecules so extremely unstable, that
the slightest variation in their conditions destroys their
equilibrium ; and causes them either to assume altered
structures or to decompose. But a substance which is beyond
all others changeable by the actions and reactions of the
forces liberated from instant to instant within its own
mass, must be a substance that is beyond all others change-
able by the forces acting on it from without. If their
composition fits organic aggregates for undergoing with
special facility and rapidity those re-distributions of matter
and motion whence result individual organization and life :
then their composition must make them similarly apt to
imdergo those permanent re-distributions of matter and mo-
tion which are expressed by changes of structure, in corre-
spondence with permanent re-distributions of matter and
motion in their environments.

Already in First Principles, when considering the phe-
nomena of Evolution in general, the leading characters and
causes of those changes which constitute organic evolution,
were briefly traced. Under each of the derivative laws of
force to which the passage from an incoherent, indefinite
homogeneity to a coherent, definite heterogeneity, conforms,
were given illustrations drawn from the metamorphoses ot

INTERNAL FACTORS. 421

living bodies. Here it will be needful to contemplate tho
several resulting processes as going on at once, in both
individuals and species.

§ 154. Our postulate being tbat organic evolution in ge-
neral commenced with homogeneous organic matter, just as
the evolution of individual organisms commences, we have
first to remember that the state of homogeneity is an un-
stable state (First Principle?, § 109). In any aggregate
"the relations of outside and inside, and of comparative
nearness to neighbouring sources of influence, imply the re-
ception of influences that are unlike in quantity or quality,
or both ; and it follows that \mlike changes will be produced
in the parts thus dissimilarly acted upon." Further, " if
any given whole, instead of being absolutely uniform through-
out, consists of parts distinguishable from each other — if
each of these parts, while somewhat unlike other parts, is
uniform within itself; then, each of them being in unstable
equilibrium, it follows that while the changes set up within
it must render it multiform, they must at the same time
render the whole more multiform than before ; " and hence,
" whether that state with which we commence be or be not
une of perfect homogeneity, the process must equally be
towards a relative heterogeneity." This loss of

homogeneity which the special instability of organic aggre-
gates fits them to display more promptly and variously than
any other aggregates, must be shown in more numerous
ways in proportion as the incident forces are more numerous.
Every differentiation of structure being a result of some
difference in the relations of the parts to the agencies acting
on them, it follows that the more multiplied and more unlike
the agencies, the more varied must be the differentiations
wrought. Hence the gravitation from a state of homogeneity
to a state of heterogeneity, will be conspicuously shown in
proportion as the environment is complex. This

'ransition from a uniform to a multiform state, must con-

422 THE EVOLUTION OF LIFE.

tinue through successive individuals. Given a series of or-
ganisms, each of which is developed from a portion of a
preceding organism, and the question is, whether, after
exposure of the series for a million years to changed incident
forces, one of its members will be the same as though the
incident forces had only just changed. To say that it will,
is implicitly to deny the persistence of force. In relation to
any cause of divergence, the whole series of such organisms
may be considered as fused together into a continuously-
existing organism ; and when so considered, it becomes
manifest that a continuously-acting cause will go on working
a continuously-increasing effect, until some counteracting
cause prevents any further effect.

But now if any primordial organic aggregate, must, in itself
and through its descendants, gravitate from uniformity to
multiformity, in obedience to the more or less multiform
forces acting on it ; what must happen if these multiform
forces are themselves ever undergoing slow variations and
complications ? Clearly the process, ever- advancing towards
a temporary limit but ever having its limit removed, must
go on unceasingly. On those structural changes wrought
in the once homogeneous aggregate by an original set of in-
cident forces, will be superposed further changes wrought
by a modified set of incident forces ; and so on throughout
all time. Omitting for the present those circumstances
which check and qualify its consequences, the instability of
the homogeneous must be recognized an ever-acting cause of
organic evolution, as of all other evolution.

"While it follows that every organism, considered as an in-
dividual and as one of a series, tends thus to pass into a more
heterogeneous state ; it also follows that every species, con-
sidered as an aggregate of individuals, tends to do the like.
Throughout the area it inhabits, the conditions can never
be absolutely uniform : its members must, in different parts
of its area, be exposed to different sets of incident forces.
Still more decided must this difference of exposure be when

INTERNAL FACTORS. 423

its members spread into other habitats. Those expansive
and repressive energies which set to each species a limit that
perpetually oscillates from side to side of a certain mean, are,
as we lately saw, frequently changed by new combinations
of the external factors — astronomic, geologic, meteorologic,
and organic. Hence there from time to time arise lines of di-
minished resistance, along which the species flows into new
localities. Such portions of the species as thus migrate, are
subject to circumstances markedly contrasted with its average
circumstances. And from multiformity of the circumstances,
must come multiformity of the species.

Thus the law of the instability of the homogeneous, has here
a three-fold corollary. As interpreted in connexion with the
ever-progressing, ever-complicating changes in external fac-
tors, it brings us to the conclusion that there must be a pre-
vailing tendency towards greater heterogeneity in all kinds
of organisms, considered both individually and in successive
generations ; as well as in each assemblage of organisms con-
stituting a species ; and, by consequence, in each genus,
order, and class

§ 155. When considering the causes of evolution in
general, we further saw (First Principles, § 116), that the
multiplication of effects aids continually to increase that
heterogeneity into which homogeneity inevitably lapses. It
was pointed out that since " the several parts of an aggre-
gate are differently modified by any incident force ; " and
that since " by the reactions of the differently modified parts
the incident force itself must be divided into differently
modified parts ; " it follows that " each differentiated di-
vision of the aggregate thus becomes a centre from which
a differentiated division of the original force is again
diffused. And since unlike forces must produce unlike
results, each of these differentiated forces must produce,
throughout the aggregate, a further series of differentia-
tions."" And to this it was added, that in proportion ii£

424

THE EVOLUTION OF LIFE.

the heterogeneity increases, the complications arising from
this multiplication of effects grow more marked ; since
the more strongly contrasted the parts of an aggregate
become, the more different must be their reactions upon
incident forces, and the more unlike must be the secondary
sets of effects which these modified incident forces initiate ;
and since every increase in the number of unlike parts
increases the number of such differentiated incident forces,
and such secondary sets of effects.

How this multiplication of effects conspires with the in-
stability of the homogeneous, to work an increasing multi-
formity of structure in an organism, was shown at the time ;
and the foregoing pages contain further incidental illustra-
tions. Under the head of Adaptation (§ 69), it was shown
that a change in one function must act and re-act through
ever-complicating perturbations on the rest; and that, eventu-
ally, all parts of the organism must be modified in their
states. Suppose that the head of a mammal becomes very
much more weighty — what must be the indirect results?
The muscles of the neck are put to greater exertions ; and
its vertebras have to bear additional tensions and pressures,
caused both by the increased weight of the head, and the
stronger contractions of the muscles that support and move the
head. These muscles also affect their own attachments : several
of the dorsal spines have augmented strains put on them ;
and the vertebrae to which they are fixed, are more severely
taxed. Further, this heavier head and the more massive
neck it necessitates, require a stronger fulcrum : the whole
thoracic arch, and the fore limbs which support it, are sub-
ject to greater continuous stress and more violent occasional
shocks. And the required strengthening of the fore- quarters
cannot take place, without the centre of gravity being
changed, and the hind limbs being differently reacted upon
during locomotion. Any one who compares the outline
of the bison with that of its congener, the ox, will clearly
see how profoundly a heavier head affects the entire osseous

INTERNAL FACTORS. 425

and muscular systems. Besides this multiplica-

tion of mechanical effects, there is a multiplication of
physiological effects. The vascular apparatus is modified
throughout its whole structure, by each considerable modifi-
cation in the proportions of the body. Increase in the size
of any organ, implies a quantitative, and uften a qualitative,
reaction on the blood ; and so alters the nutrition of all other
organs. Such physiological correlations are exemplified in the
many differences that accompany difference of sex. That the
minor sexual peculiarities are brought about by the physio-
logical actions and reactions, is shown both by the fact that
they are commonly but faintly marked until the fundamentally
distinctive organs are developed ; and that when the de-
velopment of these is prevented, the minor sexual peculiarities
do not arise. No further proof is, I think, needed,

that in any individual organism or its descendants, a new
external action must, besides the primary internal change
which it works, work sundry secondary changes, as well as
tertiary changes still more multiplied. That tendency to-
wards greater heterogeneity which is given to an organ-
ism by disturbing its environment, is helped by the tendency
which every modification lias to produce other modifications
— modifications which must become more numerous in pro-
portion as the organism becomes more complex. And
then, lastly, among the indirect and involved manifestations
of this tendency, we must not omit the innumerable small
irregularities of structure that result from the crossing of
dissimilarly-modified individuals. It was shown (§§ 89, 90)
'hat what are called "spontaneous variations," are inter-
pretable as results of miscellaneously compounding the
changes wrought in different lines of ancestors by different
conditions of life. These still more complex and multi-
tudinous effects so produced, are thus further illustrations of
the multiplication of effects.

Equally in the aggregate of individuals constituting a
species, does multiplication of effects become the continual
28

426 THE EVOLUTION OF LIFE.

cause of increasing multiformity. The lapse of a species into
divergent varieties, initiates frc«h combinations of forces
tending to work further divergences. The new varieties
compete with the parent species in new ways ; and so add new
elements to its circumstances. They modify somewhat the
conditions of other species existing in their habitat, or intc
whose habitat they have spread; and the modifications
wrought in such other species, become additional sources of
influence. The Flora and Fauna of every region are united
by their entangled relations into a whole, of which no part
can be affected without affecting the rest. Hence, each dif-
ferentiation in a local assemblage of species, becomes the
cause of further differentiations in such assemblage.

§ 15G. One of the universal principles to which we saw
that the re- distribution of matter and motion conforms, is
that in any aggregate made up of mixed units, incident
forces produce segregation — separate unlike units and unite
Like units ; and it was shown that the increasing integration
and definiteness which characterizes each part of an evolving
organic aggregate, as of every other aggregate, results from
this (First Principles, § 126). It remains here to be
pointed out, that while the actions and reactions going on
between organisms and their ever-changing environments,
add to the heterogeneity of organic structures, they also
give to the heterogeneity this growing distinctness. At
first sight the reverse might be inferred. It might be argued
that any new set of effects wrought in an organism by some
new set of external forces, must tend more or less to obliter-
ate the effects previously wrought — must produce confusion
or indefiniteness. A little consideration, however, will dissi-
pate this impression.

Doubtless the condition under which alone increasing de-
finiteness of structure can be acquired by any part of an or-
ganism, either in an individual or in successive generations, is
that such part shall be exposed to some set of tolerably-con-

INTERKAL FACTORS. 427

elant forces; and doubtless, continual change of circumstances
interferes with this. But the interference can never be con-
siderable. For the pre-existing structure of an organism pre-
vents it from living under any new conditions except such as
are congruous with the fundamental characters of its organiza-
tion— such as subject its essential organs to actions substan-
tially the same as before. Great changes must kill it. Hence,
it can continuously expose itself and its descendants, only to
those moderate changes which do not destroy the general har-
mony between the aggregate of incident, forces and the ag-
gregate of its functions. That is, it must remain under
influences calculated to make greater the definiteness of
the chief differentiations already produced. If, for ex-
ample, we set out with an animal in which a rudimentary
vertebral column with its attached muscular system has
been established ; it is clear that the mechanical arrange-
ments have become thereby so far determined, that sub-
sequent modifications are extremely likely, if not certain, to
be consistent with the production of movement by the action
of muscles on a flexible central axis. Hence, there will con-
tinue a general similarity in the play of forces to which tho
flexible central axis is subject ; and so, notwithstanding the
metamorphoses which the vertebrate type undergoes, there
will be a maintenance of conditions favourable to increasing
definiteness and integration of the vertebral column. More-
over, this maintenance of such conditions becomes secure in
proportion as organization advances. Each further com-
plexity of structure, implying some further complexity in
the relations between an organism and its environment, must
tend to specialize the actions and reactions between it and its
environment — must tend to increase the stringency with
which it is restrained within such environments as admit of
those special actions and reactions for which its structure fits
it ; that is, must further guarantee the continuance of those
actions and reactions to which its essential organs respond,
and therefore the continuance of the segregating process.

428 THE EVOLUTION OF LIFE.

How in each species, considered as an aggregate of indi-
viduals, there must arise stronger and stronger contrasts
between those divergent varieties which result from the
instability of the homogeneous and the multiplication of
effects, needs only oe briefly indicated. It has already
been shown (First Principles, § 126), that in conformity to
the universal law that mixed units are segregated by like
incident forces, there are produced increasingly-definite
distinctions among varieties, wherever there occur definitely-
distinguished sets of conditions to which the varieties are re-
spectively subject.

§ 157. Probably in the minds of some, the reading of this
chapter has been accompanied by a running commentary, to
the effect that the argument proves too much. The apparent
implication is, that the passage from an indefinite, incohe-
rent homogeneity to a definite, coherent heterogeneity in
organic aggregates, must have been going on universally ;
whereas we find that in many cases there has been persist-
ence without progression. This apparent implication, how-
aver, is not a real one.

For though every environment on the Earth's surface
undergoes changes ; and though usually the organisms
which each environment contains, cannot escape certain
resulting new influences ; yet occasionally such new in-
fluences are escaped, by the survival of species in the un-
changed parts of their habitats, or by their spread -into
neighbouring habitats which the change has rendered like
their original habitats, or by both. Any alteration in the
temperature of a climate or its degree of humidity, is Jn-
likely to affect simultaneously the whole area occupied by a
species; and further, it can scarcely fail to happen that the
addition or subtraction of heat or moisture, will give to a
part of some adjacent area, a climate like to that to which
the species lias been habituated. If, again, the circumstances
of a species are modified by the intrusion of some foreign

INTERNAL FACTORS. 429

kind of plant or animal, it follows that since the intruders
will probably not spread throughout its whole habitat, the
species will, in one or more localities, remain unaffected by
them. Especially among marine creatures, must there fre-
quently occur cases in which modifying causes are con-
tinually eluded. Much more uniform as are the physical
conditions to which the sea exposes its inhabitants, it becomes
possible for such of them as live on widely-diffused food, to
be widely distributed; and wide distribution generally pre-
vents the members of a species from being all subject to the
same cause. Our commonest cirrhiped, for instance, subsisting
on minute creatures that are everywhere dispersed through
the sea ; needing only to have some firm surface on which
to build up its shell ; and in scarcely any danger from sur-
rounding animals; is able to exist on shores so widely remote
from one another, that nearly every change in the actions of
incident forces, must fall within narrower areas than that
which the species occupies. In nearly every case, therefore,
a portion of the species will survive unmodified. Its easily-
transported germs will take possession of such new habitats
as have been rendered fitter by the change that has unfitted
some parts of its original habitat. Hence, on successive
occasions, while some parts of the species are slightly trans-
formed, another part may continually escape transformation
by migrating hither and thither, where the simple condi-
tions needed for its existence recur in nearly the same com-
binations as before. And it will so become possible for it
to survive, with comparatively trifling structural changes,
throughout long geologic periods.

§ 158. The results to which we find ourselves led, aro
thes3.

In subordination to the different amounts and kinds of
forces to which its different parts are exposed, every in-
dividual organic aggregate, like all other aggregates, tends
to pass from its original indistinct simplicity towards a more

430 THE EVOLUTION OF LTPE.

distinct complexity. Unless we deny the persistence of
force, we must admit that the gravitation of an organisn.-'s
structure from an indefinitely homogeneous to a definitely
heterogeneous state, must be cumulative in successive genera-
tions, if the forces causing it continue to act. And for the
like reasons, the increasing assemblage of individuals arising
from a common stock, is also liable to lose its original
uniformity ; and, in successive generations, to grow more
pronounced in its multiformity.

These changes, which would go on to but a comparatively
small extent were organisms exposed to constant external
conditions, are kept up by the continual changes in external
conditions, produced by astronomic, geologic, meteorologic,
and organic agencies : the average result being, that on
previous complications of structure wrought by previous
incident forces, new complications are continually superposed
by new incident forces. And hence simultaneously arises
increasing heterogeneity in the structures of individuals, in
the structures of species, and in the structures of the Earth's
Flora and Fauna.

But while, in very many or in most cases, the ever-
changing incidence of forces is ever adding to the complexity
of organisms, and to the complexity of the organic world as a
whole ; it does this only where its action cannot be eluded.
And since, hy migration, it is possible for species to keep
themselves under conditions that are tolerably constant ;
there must be a proportion of cases in which greater hetero-
geneity of structure is not produced.

Uniting these three propositions, we are brought to a eon
elusion which, so far as it goes, appears to be in harnior.y
with the facts. We find progression to result, not from a
special, inherent tendency of living bodies, but from a general
average effect of. their relations to surrounding agencies.
While we are not called on to suppose that there exists in
organisms any primordial impulse which makes them con-
tinually unfold into more heterogeneous forms; -we see

INTERNAL FACTORS. 431

that a liability to be unfolded arises from the actions and
reactions between organisms and their fluctuating environ-
ments. And we see that the existence of such a cause of
development, presupposes the non-occurrence of development
where this fluctuation of actions and reactions does not
come into play.

To show, however, that there must arise a certain general
tendency to the production of more heterogeneous aggregates,
is not sufficient. It is quite conceivable that aggregates
should be rendered more heterogeneous by changing incident
forces, without having given to them that peculiar form of
heterogeneity required for carrying on the functions of life.
Hence it remains now to inquire, how the production and
maintenance of this peculiar form of heterogeneity is insured.

CHAPTER XL

DIRECT EQUILIBRATION.

§ 159. Every change is of necessity towards a balance of
loi ces ; ana of necessity can never cease until a Dalance ot lorces
is reached. When treating of equilibration under its general
aspects (First Principles, Part II., Chap, xvi.), we saw that
in every aggregate having compound movements, there
tends continually to be established a moving equilibrium ;
since any unequilibrated force to which such an aggregate
is subject, if not of a kind to overthrow the aggregate al-
together, must continue modifying its state until an equi-
librium is brought about. And we saw that the structure
simultaneously reached must be " one presenting an arrange-
ment of forces that counterbalance all the forces to which the
aggregate is subject ; " since, " so long as there remains a
residual force in any direction — be it excess of a force
exercised by the aggregate on its environment, or of a force
exercised by its environment on the aggregate, equilibrium
does not exist ; and therefore the re-distribution of matter
must continue."

It is essential that this truth should here be fully under-
stood ; and to the end of insuring a clear comprehension of
it, some re-illustration is desirable. The case of the Solar
System will best serve our purpose. An assemblage of bodies,
each of which has its simple and compound motions, that
severally alternate between two extremes, and the whole of

DIEECT EQUILIBRATION. 433

which has its involved perturbations, that now increase and
now decrease, is heie presented to us. Suppose a new
force were brought to bear on this moving equilibrium — say
by the arrival of some wandering mass, or by an additional
momentum given to one of the existing masses — what would
be the result ? If the strange body or the extra force were
very large, it might so derange the entire system as to cause
its collapse : by overthrow of its rhythmical movements, the
moving equilibrium might rapidly be changed into a com-
plete equilibrium. But what if the incident force, falling on
the system from without, proved insufficient to overthrow it?
There would then arise a set of perturbations which would,
in the course of an enormous period, slowly work round into
a modified moving equilibrium. The effects primarily ini-
pyessed on the adjacent masses, and in a smaller degree on
the remoter masses, would soon become complicated with the
secondary effects impressed by the disturbed masses on one
another ; and these again with tertiary effects. Waves of
perturbation would continue to be propagated throughout
the entire system ; until, around a new centre of gravity,
there had been established a set of planetary motions more
or less different from the preceding ones. All this would
necessarily follow from the truth, that any new force brought
to bear on a moving equilibrium, must gradually be used up
in overcoming the forces that resist the divergence it gener-
ates : which antagonizing forces, being then no longer op-
posed, set up i counter-action, ending in a compensating
divergence in the opposite direction, that is followed by a
re-compensating divergence ; and so on, until there is either
established some additional rhythmical movement, or some
equivalent modification of the pre-existing rhythmical move-
ments. Now though instead of being, like the Solar
System, in a state of independent moving equilibrium, an
organism is in a state of dependent moving equilibrium
(First Principles, § 130) ; yet this does not prevent the
manifestation of the same law. Every animal daily obtains

434 THE EVOLUTION OF LIFE.

from without, a supply of force to replace the force
which it expends ; but this continual giving to its parts a
new momentum, to make up for the momentum continually
lost, does not interfere with the carrying on of actions and
reactions like those just described. Here, as before, we have
a definitely-arranged aggregate of parts, which we call
organs, having their definitely-established actions and re-
actions, which we call functions. These rhythmical actions
or functions, and the various compound rhythms resulting
from their combinations, are in such adjustment as to balance
the actions to which the organism is subject : there is a con-
stant or periodic genesis of forces, which, in their kinds,
amounts, and directions, suffice to antagonize the forces
which the organism has constantly or periodically to bear.
If then there exists this state of moving equilibrium among
a definite set of internal actions, exposed to a definite set of ex-
ternal actions ; what must result if any of the external actions
are changed ? Of course there is no longer an equilibrium.
Some force which the organism habitually generates, is too
great or too small to balance some incident force ; and there
arises a residuary force exerted by the environment on the
organism, or by the organism on the environment. This
residuary force — this unbalanced force, of necessity expends
itself in producing some change of state in the organism.
Acting directly on some organ and modifying its function,
it indirectly modifies dependent functions, and remotely
influences all the functions. As we have already seen
(§§ 68, 69), if this new force is permanent, its effects must
be gradually diffused throughout the entire system ; until it
has come to be equilibrated in working those structural re-
arrangements which produce an exactly counterbalancing
force.

The bearing of this general truth on the question we are
now dealing with, is obvious. Those modifications upon
modifications, which the unceasing mutations of their en-
vironments have been all along generating in organisms,

DIRECT EQUILIBRATION. 435

have been in each case modifications involved by the
establishment of a new balance with the new combination of
conditions. In every species throughout all geologic time,
there has been perpetually going on a rectification of the
equilibrium, that has been perpetually disturbed by the
alteration of surrounding circumstances ; and every further
heterogeneity has been the addition of a structural change
entailed by a new equilibration, to the structural changes
entailed by previous equilibrations. There can be no other
ultimate interpretation of the matter, since change can have
no other goal. Any fresh force brought to bear on an
aggregate in a state of moving equilibrium, must do one of
two things : it must either overthrow the moving equi-
librium altogether, or it must alter without overthrowing it ;
and the alteration must end in the establishment of a new
moving equilibrium. Hence in organisms, death or restora-
tion of the physiological balance, are the only alternatives.

This equilibration between the functions of an organism
find the actions in its environment, may be either direct or
indirect. The new incident force may either immediately
call forth some counteracting force, and its concomitant
structural change ; or it may be eventually balanced by some
otherwise-produced change of function and structure.
These two processes of equilibration are quite distinct, and
must be separately dealt with. We will devote this chapter
to the first of them.

§ 160. Direct equilibration is that process currently
known as adaptation. We have already seen (Part II.,
Chap, v.), that individual organisms become modified when
placed in new conditions of life — so modified as to re-adjust
the powers to the requirements ; and though there is great
difficulty in disentangling the evidence, we found reason for
thinking (§ 82) that structural changes thus caused by
functional changes are inherited. In the last chapter, it
v/as argued that if, instead of the succession of individuals

436 THE EVOLUTION 01' LIFE.

constituting a species, there were a continuously-existing
individual, any such functional and structural divergence as
we see produced by a new incident force, would necessarily
go on increasing until the new incident force was counter-
poised ; and that the replacing of a continuously- existing
individual by a succession of individuals, each formed out, of
the mod ified substance of its predecessor, will not prevent the
like effect from being produced — the persistence of force
negativing any other inference. Here we further find, that
this limit towards which any such organic change advances,
in the species as in the individual, is a new moving equi-
librium adjusted to the new arrangement of external forces.

But now, what are the conditions under which alone, direct
equilibration can occur ? Are all the modifications that serve
to re-fit organisms to their environments, directly adaptive
modifications? And if otherwise, which are the directly
adaptive and which are not ? How are we to distinguish
between them ?

Manifestly, for any moving equilibrium to be gradually
altered, it is needful, first, that some force shall operate upon .
it ; and, second, that the force shall not be such as to over-
throw it. If in the environment there exists some agency
that would act advantageously on an organism were the or-
ganism a little modified, but which does not act on it in the
absence of the required modification ; it is clear that this
agency cannot itself tend to produce the modification. On
the other hand, if the external agency be of such kind, that
individuals of the species whenever affected by it, are either
killed or so injured that the production of vigorous offspring
is much interfered with, there cannot be directly wrought in
tho species, any such alteration as will fit it to cope with
this external agency. The only new incident forces which
can work the changes of function and structure required to
bring any animal or plant into equilibrium with them, are
such incident forces as operate on this animal or plant,
either continuously or frequently. They must be capable

•DIRECT EQUILIBRATION. 437

of appreciably changing that set o** complex rhythmical
actions and reactions constituting the life of the organism ;
and yet must not usually produce perturbations that are
fatal. Let us see what are the limits to direct equilibra-
tion hence arising.

§ 161. In plants, organs engaged in nutrition, and exposed
to variations in the amounts and proportions of matters and
forces utilized in nutrition, may be expected to undergo cor-
responding variations. We find evidence that they do this.
The "changes of habit " which are common in plants, when
taken to places unlike in climate or soil to those before in-
habited by them, are changes of parts in which the modified
external actions directly produce modified internal actions.
The characters of the stem and shoots as woody or succulent,
erect or procumbent ; of the leaves in respect of their sizes,
thicknesses, and textures ; of the roots in their degrees of
development and modes of growth ; are obviously in imme-
diate relation to the characters of the environment. A per-
manent difference in the quantity of light or heat, affects, day
after day, the processes going on in the leaves. Habitual
rain or drought, alters all the assimilative actions, and
appreciably influences the organs that carry them on. Some
particidar substance, by its presence in the soil, gives new
qualities to some of the tissues ; causing greater rigidity or
flexibility, and so affecting the general aspect. Here, then,
we have, in plants, changes tending to bring about in them,
modified arrangements of functions and structures, in equi-
librium with modified sets of external forces.

But now let us turn to other classes of organs possessed by
plants — organs which are not at once attected in their actions
by the variations of incident forces. Take first the organs
of defence. Many plants are shielded against animals that
would else devour them, by formidable thorns ; and others,
like the nettle, by stinging hairs. These must be counted
among the appliances by which equilibrium is maintained

438 THE EVOLUTION OF LIFE.

between the actions in the organism and the actions in ita
environment ; seeing that all other things remaining the
same, if these defences were absent, the destruction by herb-
ivorous animals would be so increased, that the number of
young plants annually produced would not suffice, as it now
does, to balance the mortality, and the species would there-
fore disappear. But these defensive appliances, though they
aid in maintaining the balance between inner and outer
actions, cannot have been directly called forth by the outer
actions which they serve to neutralize; for these outer
actions do not continuously affect the functions of the plant
even in a general way, still less in the special Way required.
Suppose a species of nettle bare of poison-hairs, to be habit-
ually eaten by some mammal intruding on its habitat ; the
agency of this mammal would have no direct tendency to
develop poison-hairs in the plant ; since the individuals
devoured could not bequeath changes of structure, even were
the actions of a kind to produce them ; and since the in-
dividuals that perpetuated themselves, would be those on
which the new incident force had not fallen. An-

other class of organs similarly circumstanced, are those of
reproduction. Like the organs of defence, these are not,
during the life of the individual plant, variably exercised by
variable external actions ; and therefore do not fulfil those
conditions under which structural changes may be directly
caused by changes in the environment. The generative
apparatus contained in every flower, acts only once during
its existence ; and even then, the parts subserve their ends
in a passive rather than an active way. Functionally-pro-
duced modifications are therefore out of the question. If a
plant's anthers are so placed, that the insect which most
commonly frequents its flowers, is sure to come in contact
with the pollen, and to fertilize with it other flowers of the
same species ; and if this insect, dwindling away or dis-
appearing from the locality, leaves behind no insects that
have such shapes aud habits as cause them to do the same

DIRECT EQUILIBRATION. 439

thing efficiently, but only some which do it inefficiently ; it
is clear that the change of its conditions, has no ininiediate
tendency to work in the plant any such structural change
as shall bring about a new balance with its conditions. For
the anthers, which, even when they discharge their functions,
do it simply by standing in the way of the insect, are, under
the supposed circumstances, left untouched by the insect ;
and this remaining untouched, cannot have the effect of so
modifying the stamens as to bring the anthers into a position
to be touched by some other insect. Only those individuals
whose parts of fructification so far differed from the average
form of the species, that some other insect could serve them
as pollen-carrier, would be sufficiently prolific to have good
chances of perpetuating themselves. And on their progeny,
inheriting the deviation, there would act no external force
directly calculated to make the deviation greater, and the
adaptation more complete ; since the new circumstances to
which re-adaptation is required, are such as do not in the
least alter the equilibrium of functions constituting the life
of the individual plant.*

§ 162. Among animals, adaptation by direct equilibration
is similarly traceable, wherever, during the life of the indi-
vidual, an external change generates some constant or re-
peated change of function. This is conspicuously the case
with such parts of an animal as are immediately exposed to
diffused influences, like those of climate, and with such parts
of an animal as are occupied in its mechanical actions on the
environment. Of the one class of cases, the darkening or
lightening of the skin, that follows exposure to greater or
less heat, may be taken as an instance ; and with the otber
class of cases, we are made familiar by the increase and de-
crease which use and disuse cause in the organs of motion
and manipulation. It is needless here to exemplify these :
they were treated of in the Second Part of this work.

But in animals, as in plants, there are many indispensable

44:0 THE EVOLUTION OF LIFE.

offices fulfilled, by parts, between which and the external con ■
ditions they respond to, there is no such action and reaction
as can directly produce an equilibrium. This is especially
manifest with dermal appendages. Some ground, perhaps,
exists for the conclusion that the greater or less development
of hairs, is in part immediately due to increase or decrease of
demand on their passive function, as non-conductors of heat ;
but be this as it may, it is impossible that there can exist
any such cause for those immense developments of hairs which
we see in the quills of the porcupine, or those complex de-
velopments of them known as feathers. Such an enamelled
armour as is worn by the Lepidosteus, is inexplicable as a direct
result of any functionally- worked change. For purposes of
defence, such an armour is as needful, or more needful, for
hosts of other fishes ; and did it result from any direct re-
action of the organism against any offensive actions it was
subject to, there seems no reason why other fishes should not
have developed similar protective coverings. Of

sundry reproductive appliances, the like may be said. The
secretion of an egg-shell round the substance of an egg, in
the oviduct of a bird, is quite inexplicable as a consequence
of some functionally- wrought modification of structure, im-
mediately caused by some modification of external con-
ditions. The end fulfilled by the egg-shell, is that of
protecting the contained mass against certain slight pressures
and collisions, to which it is liable during incubation. How,
by any process of direct equilibration, could it come to have
the required thickness? or, indeed, how could it come to
exist at all? Suppose this protective envelope to be too
weak, so that some of the eggs a bird lays are broken or
cracked. In the first place, the breakages or crackings are
actions of a kind which cannot react on the maternal organ-
ism, in such way as to cause the secretion of thicker shells
for the future : to suppose that they can, is to suppose that
the bird understands the cause of the evil, and that the
secretion of thicker or thinner shells can be controlled by its

DIRECT EQUILIBRATION. 441

will. In the second place, such developing chicks as are
contained in the shells which crack or break, are almost
certain to die; and cannot, therefore, acquire any appro-
priately-modified constitutions : even supposing any con-
ceivable relation could be shown, between the impression
received and the change required. Meanwhile, such eggs as
escape breakage, are not influenced at all by the require-
ment ; and hence, on the birds developed from them, there
cannot have acted any force tending to work the needful
adjustment of functions. In no way, therefore, can a direct
equilibration between constitution and conditions be here
produced. Even in organs that can be modified

by certain incident forces into correspondence with such
incident forces, there are some re-adjustments which cannot
be effected by the direct balancing of inner and outer actions.
It is thus with the bones. The majority of the bones have
to resist muscular strains ; and it is a familiar fact that
variations in the muscular strains, call forth, by reaction,
variations in the strengths of the bones. Here there is
direct equilibration. But though the greater massiveness
acquired by bones subject to greater strains, may be ascribed
to a counter-acting force evoked by a force brought into
action; it is impossible that the acquirement of greater
lengths by bones can be thus accounted for. It has been
supposed that the elongation of the metatarsals in wading
birds, has resulted from direct adaptation to conditions of
life. To justify this supposition, however, it must be shown
that the mechanical actions and reactions in the legs of a
wading bird, differ from those in the legs of other birds ;
and that the differential actions are equilibrated by the extra
lengths. There is not the slightest evidence of thLs. The
metatarsals of a bird, have to bear no appreciable strains
but those due to the superincumbent weight. Standing in
the water does not appreciably alter these strains ; and even
if it did, an increase in the lengths of these bones would not
fit them any better to meet the altered strains.
29

442 THE EVOLUTION OF LITE.

§ 163. The conclusion at which we arrive is, then, that
there go on in all organisms, certain changes of function and
structure that are directly consequent on changes in the
incident forces — inner changes by which the outer changes
are balanced, and the equilibrium restored. Such re-equi-
librations, which are often conspicuously exhibited in in-
dividuals, we have reason to believe continue in successive
generations ; until they are completed by the arrival at
structures fitted to the modified conditions. But, at the
same time, we see that the modified conditions to which or-
ganisms may be adapted by direct equilibration, are con-
ditions of certain classes only. That a new external action
may be met by a new internal action, it is needful that i*;
shall either continuously or frequently be borne by the in-
dividuals of the species, without killing or seriously injuring
them; and shall act in such way as to affect their functions.
And we find on examination, that many of the environing
changes to which organisms have to be adjusted, are not of
these kinds : being changes which either do not immediately
affect the functions at all, or else affect them in ways that
prove fatal.

Hence there must be at work some other process, which
equilibrates the actions of organisms with the actions they
are exposed to. Plants and animals that continue to exist,
are necessarily plants and animals whose powers balance the
powers that act on them ; and as their environments
change, the changes which plants and animals undergo, must
necessarily be changes towards a re- establishment of the
balance. Besides direct equilibration, there must therefore
be an indirect equilibration. How this goes on we have now
to inquire.

CHAPTER XIL

INDIRECT EQUILIBRATION.

§ 164. Besides those perturbations produced in the movui£
equilibrium of any organism by special disturbing forces,
there are ever going on many other perturbations — some
which are the still-reverberating effects of disturbing forces
previoush* experienced by the individual, and others which
are the still-reverberating effects of disturbing forces expe-
rienced by ancestral individuals ; and the multiplied devia-
tions of function so caused, imply multiplied deviations of
structure. In § 155 there was re-illustrated the truth, set
forth at length when treating of Adaptation (§ 69), that an
organism in a state of moving equilibrium, cannot have
extra function thrown on any organ, and extra growth pro-
duced in such organ, without there being entailed correlative
changes throughout all other functions, and eventuallv
throughout all other organs. And when treating of Varia-
tion (§ 90), we saw that individuals which have been made,
by their different circumstances, to deviate functionally and
structurally from the average type in different directions,
will bequeath to their joint offspring, compound perturbations
of function and compound deviations of structure, endlessly
varied in their kinds and amounts. That is to say, besides
the primary perturbations and deviations directly caused in
organisms by altered actions in their environments, there
are ever being indirectly caused, secondary and tertiary per-

444 THE EVOLUTION OF LIFE.

turbations and deviations, which, when compounded with one
another from generation to generation, work innumerable
slight modifications in the moving equilibria and correlative
structures throughout the species.

Now if the individuals of a species are thus necessarily
made unlike, in countless ways and degrees — if the compli-
cated sets of rhythms which we call their functions, though
similar in their general characters, are dissimilar in their
details — if in one individual the amount of action in a par-
ticular direction is greater than in any other individual, or if
here a peculiar combination gives a resulting force which is
not found elsewhere ; then, among all the individuals, some
will be less liable than others to have their equilibria over-
thrown by a particular incident force, previously unexperi-
enced. Unless the change in the environment is of so vio-
lent a kind as to be universally fatal to the species, it must
affect more or less differently the slightly different moving
equilibria which the members of the species present. It
cannot but happen that some will be more stable than others,
when exposed to this new or altered factor. That is to say,
it cannot but happen that those individuals whose functions^
are most out of equilibrium with the modified aggregate of
external forces, will be those to die ; and that those will sur-
vive whose functions happen to be most nearly in equilibrium
with the modified aggregate of external forces.

But this survival of the fittest, implies multiplication of
the fittest. Out of the fittest thus multiplied, there will, as
before, be an overthrowing of the moving equilibrium wher-
ever it presents the least opposing force to the new incident
force. And by the continual destruction of the individuals
that are the least capable of maintaining their equilibria in
presence of this new incident force, there must eventually be
arrived at an altered type completely in equilibrium with the
altered conditions.

§ 165. Tins survival of the fittest, which I have hare

INDIRECT EQUILIBRATION. 445

sought to express in mechanical terms, is that which Mr Dar-
win has called " natural selection, or the preservation of
favoured races in the struggle for life." That there is going
on a process of this kind throughout the organic world,
Mr Darwin's great work on the Origin of Species has shown
to the satisfaction of nearly all naturalists. Indeed, when
once enunciated, the truth of his hypothesis is so obvious as
scarcely to need proof. Though evidence may be required
to show that natural selection accoimts for everything ascribed
to it, yet no evidence is required to show that natural selec-
tion has always been going on, is going on now, and must,
ever continue to go on. Recognizing this as an a priori cer-
tainty, let us contemplate it under its two distinct aspects.

That organisms which live, thereby prove themselves fit to
live, in so far as they have been tried ; while organisms which
die, thereby prove themselves in some respects unfitted for
living ; are facts no less manifest, than is the fact that this
self-acting purification of a species, must tend ever to insure
adaptation between it and its environment. This adaptation
may be either so maintained or so produced. Doubt-

less many who have looked at Nature with philosophic eyes,
have observed that death of the worst and multiplication of
the best, must result in the maintenance of a constitution
in harmony with surrounding circumstances. That the aver-
age vigour of any race would be diminished, did the diseased
and feeble habitually survive and propagate ; and that the
destruction of such, through failure to fulfil some of the con-
ditions to life, leaves behind those which are able to fulfil the
conditions to life, and thus keeps up the average fitness to
the conditions of life ; are almost self-evident truths. But
to recognize " natural selection " as a means of preserving
an already-established balance between the powers of a spe-
cies and the forces to which it is subject, is to recognize it
only in its simplest and most general mode of action. It ia
the more special mode of action with which we are here con-
cerned. This more special mode of action, Mr Dar-

446 THE EVOLUTION OF LIFE.

win has been the first to perceive. To him we owe the dis-
covery that natural selection is capable of producing fitness
between organisms and their circumstances ; and he, too, has
the merit of appreciating the immensely-important conse-
quences that follow from this. He has worked up an enormous
Diass of evidence into an elaborate demonstration, that this
" preservation of favoured races in the struggle for life," is
an ever-acting cause of divergence among organic forms.
He has traced out the involved results of the process with
marvellous subtlety. He has shown how hosts of otherwise
inexplicable facts, are fully accounted for by it. In brief, he
has proved that the cause he alleges is a true cause ; that it
is a cause which we see habitually in action ; and that the
results to be inferred from it, are in harmony with the phe-
nomena which the Organic Creation presents, both as a whole
and in its details. Let us glance at a few of the more im-
portant interpretations which the hypothesis furnishes.

A soil possessing some ingredient in unusual quantity,
may supply to a plant an excess of the matter required for a
certain class of its tissues ; and may cause all the parts formed
of such tissues to be abnormally developed. Suppose that
among these are the hairs clothing its surfaces, including
those which grow on its seeds. Thus furnished with some-
what longer fibres, its seeds, when shed, are carried a little
further by the wind before they fall to the ground. The
young plants growing up from them, being rather more
widely dispersed than those produced by other individuals of
the same species, will be less liable to smother one another ;
and a greater number may therefore reach maturity and
fructify. Supposing the next generation subject to the same
peculiarity of nutrition, some of the seeds borne by its mem-
bers will not simply inherit this increased development of
hairs, but will carry it further ; and these, still more advan-
taged in the same way as before, will, on the average, have
still more numerous chances of continuing the race. Thus,
by the survival, generation after generation, of those possess-

INDIRECT EQUILIBRATION. 447

ing these longer hairs, and the inheritance of successive incre-
ments of growth in the hairs, there may result a seed deviat-
ing greatly from the original. Other individuals of the
same species, subject to the different physical conditions of
other localities, may develop somewhat thicker or harder
coatings to their seeds : so rendering their seeds less digest-
ible by the birds that devour them. Such thicker-coated
seeds, by escaping undigested more frequently than thinner-
coated ones, will have additional chances of growing up and
leaving offspring ; and this process, acting in a cumulative
manner through successive years, will produce a seed diverg-
ing in another direction from the ancestral type. Again,
elsewhere, some modification in the physiologic actions of
the plant, may lead to an unusual secretion of an essential
oil in the seeds ; which rendering them unpalatable to crea-
tures that would otherwise feed on them, may diminish the
destruction of the seeds, so giving an advantage to the variety
in its rate of multiplication ; and this incidental peculiarity
proving a preservative, will, as before, be gradually increased
by natural selection, until it constitutes another divergence.
Now in these and countless analogous cases, we see that plants
may become better adapted, or re-adapted, to the aggregate of
surrounding agencies, not through any direct action of such
agencies upon them, but through their indirect action —
through the destruction by them of the individuals which are
least congruous with them, and the survival of those which
are most congruous with them. All these slight variations
of function and structure, arising among the members of a
species, serve as so many experiments ; the great majority of
which fail, but a few of which succeed. Just as we see that
each plant bears a multitude of seeds, out of which some two or
three happen to fulfil all the conditions required for reaching
maturity, and continuing the race; so Ave see that each species
is perpetually producing numerous slightly-modified forms,
deviating in all directions from the average, out of which
most fit the surrounding conditions no better than their pa-

448 THE EVOLUTION OF LIFE.

rents, or not so well, but some few of which fit the conditio na
better; and doing so, are enabled the better to preserve them-
selves, and to produce offspring similarly capable of preserv-
ing themselves. Among animals the like process re-
sults in the like development of various structures which
cannot have been affected by the performance of functions —
their functions being purely passive. The thick shell of u
mollusk, is inexplicable as a result of direct reactions of the
organism against the external actions to which it is exposed ;
but it is quite explicable as a result of the survival, genera-
tion after generation, of individuals whose thicker coverings
protected them against enemies. Similarly with such a
dermal structure as that of the tortoise. Though we have evi-
dence that the skin where it is continually exposed to pres-
sure and friction may thicken, and so re-establish the equi-
librium, by opposing a greater inner force to a greater outer
force ; yet we have no evidence that a coat of armour like
that of the tortoise can be so produced. Nor, indeed, are the
conditions under which only its production in such a man-
ner could be accounted for, fulfilled ; since the surface of the
tortoise is not exposed to greater pressure and friction than
the surfaces of other creatures. This massive carapace, and
the strangely-adapted osseous frame-work which supports it,
are unaccountable as results of evolution, unless through the
process of natural selection. Thus, too, is it with the pro-
duction of colours in birds and in insects ; the formation ol
odoriferous glands in mammals ; the growth of such excres-
cences as those of the camel. Thus, in short, is it with all
those organs of animals, which do not play active parts in the
compound rhythms of their functions.

Besides giving us explanations of structural characters
that are otherwise unaccountable, Mr Darwin shows how
natural selection explains peculiar relations between indi-
viduals in certain species. Such facts as the dimorphism of
the primrose and other flowers, he proves to be quite in har-
mony with his hypothesis, though stumbling-blocks to all

INDIRECT EQUIL/BRAT10N. 449

other hypotheses. "While the production of neuters among
bees and ants, is inexplicable as a result of direct adaptation,
natural selection affords a feasible solution of it. The various
differences that accompany difference of sex, sometimes
slight, sometimes very great, are similarly accounted for.
As before suggested (§ 79), natural selection appears capa-
ble of producing and maintaining the right proportion of
the sexes in each species ; and it requires but to contemplate
the bearings of the argument, to see that the formation of
different sexes may itself have been determined in the same
way.

To convey here an adequate idea of Mr Darwin's doctrine,
in the immense range of its applications, is of course impos-
sible. The few illustrations just given, serving but dimly to
indicate the many classes of phenomena interpreted by it,
are set down simply to remind the reader what Mr Darwin's
hypothesis is, and what are the else insoluble problems which
it solves for us.

§ 1G6. But now, though it seems to me that we are thus
supplied with a key to phenomena which are multitudinous
and varied beyond all conception ; it also seems to me that
there is a moiety of the phenomena which this key will not
unlock. Mr Darwin himself recognizes use and disuse of
parts, as causes of modifications in organisms ; and does this,
indeed, to a greater extent than do some who accept his
general conclusion. But I conceive that he does not re-
cognize them to a sufficient extent. "While he conclusively
shows that tbe inheritance of changes of structure, caused by
changes of function, is utterly insufficient to explain a great
mass — probably the greater mass — of morphological pheno-
mena : I think he leaves unconsidered a mass of morphological
phenomena that are explicable as results of functionally-
acquired modifications, transmitted and increased, and which
are not explicable as results of natural selection.

By induction, as well as by inference from the hypothesis

450 THE EVOLUTION OF LLFE.

of natural selection, we know that there exists a balance
among the powers of organs which habitually act together —
such proportions among them, that no one has any consider-
able excess of efficiency. We see, for example, that through-
out the vascular system, there is maintained an equilibrium
between the powers, that is, the developments, of the com-
ponent parts : in some cases, under excessive exertion, the
heart gives way, and we have enlargement ; in other cases
the large arteries give way, and we have aneurisms ; in other
cases the minute blood-vessels give wray — now bursting, now
becoming chronically congested. That is to say, in the
average constitution, no superfluous strength is possessed
by any of the appliances for circulating the blood. Take,
again, a set of motor organs. Great strain here causes the
fibres of a muscle to tear. There the muscle does not yield
but the tendon snaps. Elsewhere neither muscle nor tendon
is damaged, but the bone breaks. Joining with these instances
the general fact, that under the same adverse conditions,
different individuals show their slight differences of consti-
tution by going wrong some in one way and some in an-
other ; and that even in the same individual, similar adverse
conditions will now affect one viscus and now another ; it
becomes manifest that though there cannot be maintained
an accurate or absolute balance among the powers of the
organs composing an organism, yet the excesses and de-
ficiencies of power are extremely slight. That they must be
extremely slight, is, as before said, a deduction from the
hypothesis of natural selection. Mr Darwin himself argues
" that natural selection is continually trying to economize hi
every part of the organization. If under changed conditions
of life a structure before useful becomes less useful, any
diminution, however slight, in its development, will be seized
on by natural selection, for it will profit the individual not
to have its nutriment wasted in building up an useless struc-
ture." In other words, if any muscle has more fibres than
can be utilized, or if a bone be stronger than needful, no axl-

INDIRECT EQUILIBRATION. 461

vantage results, but rather a disadvantage — a disadvantage
which will decrease the chances of survival. Hence

it becomes a corollary, that among any organs which habit-
ually act in concert, an increase of one can be of no service
unless there is a concomitant increase of the rest. The co
operative parts must vary together ; otherwise variation will
be detrimental. A stronger muscle must have a stronger bone
to resist its contractions; must have stronger correlated mus-
cles and ligaments to secure the neighbouring articulations ;
must have larger blood-vessels to bring it supplies ; must
have a more massive nerve to bring it stimulus, and some
extra development of a nervous centre to supply this extra
stimulus. The question arises, then, — does spontaneous
variation occur simultaneously in all these co-operative
parts ? Have we any reason to think that they spontaneously
increase or decrease together ? The assumption that they
do, seems to me untenable ; and its untenability will, I think,
become conspicuous if we take a case, and observe how ex-
tremely numerous and involved are the variations which
must be supposed to occur together. In illustration

of another point, we have already considered the modifica-
tion required to accompany increased weight of the head.
Instead of the bison, however, the moose deer, or the extinct
Irish elk, will here best serve our purpose. In this species
the male has enormously-developed horns, which are used for
purposes of offence and defence. These horns, weighing up-
wards of a hundred- weight, are carried at great mechanical
disadvantage — supported as they are along with the massive
skull which bears them, at the extremity of the outstretched
neck. Further, that these heavy horns may be of use in
fighting, the supporting bones and muscles must be strong
enough, not simply to carry them, but to put them in
motion with the rapidity required for giving blows. Let us,
then, ask how, by natural selection, this complex apparatus
of bones and muscles can have been developed, pari passu
with the horns ? If we suppose the horns to have originally

452 THE EVOLUTION OF LIFE.

been of like size with those borne by other kinds of deer ;
and if we suppose that in certain individuals, they became
larger by spontaneous variation ; what would be the con-
comitant changes required to render their greater size useful ?
Other things equal, the blow given by a larger horn woidd
be a blow given by a heavier mass moving at a smaller
velocity : the momentum would be the same as before ; and
the area of contact with the body struck being somewhat
increased, while the velocity was decreased, the injury done
would be less. That the horns may become better weapons,
the whole apparatus which moves them must be so strength-
ened as to impress more force on them, and to bear the more
violent reactions of the blows given. The bones of the skull
on which the horns are seated must be thickened ; otherwise
they will break. To render the thickening of these bones
advantageous, the vertebrae of the neck must be further de-
veloped ; and without the ligaments that hold together these
vertebra?, and the muscles which move them, are also enlarged^
nothing will be gained. Such modifications of the neck will
be useless, or rather will be detrimental, if its fulcrum be noi
made capable of resisting intenser strains : the upper dorsal
vertebrae and their spines must be strengthened, that they
may withstand the more violent contractions of the neck-
muscles ; and like changes must be made on the scapular
arch. Still more must there be required a simultaneous de-
velopment of the bones and muscles of the fore-legs; since
each of these extra growths in the horns, in the skull, in the
neck, in the shoulders, adds to the burden which the fore-
legs have to bear ; unless this deer with its heavier horns,
head, neck, and shoulders, had stronger fore-legs, it would
not only suffer from loss of speed but wovdd even fail in fight.
Hence, to make larger horns of use, additional sizes must be
acquired by numerous bones, muscles, and ligaments, as well
as by the blood-vessels and nerves on which their actions
depend. On calling to mind how the spraining of a single
small muscle in the foot, incapacitates for walking, or how a

INDIRECT EQUILIBRATION. 4G3

permanent weakness in one of its ligaments will greatly
diminish the power of a limb, it will be seen that unless all
these many changes are simultaneously made, they may as
well be none of them made — or rather, they had better be
none of them made ; since, the enlargements of some parts,
by putting greater strains on connected parts, would render
them relatively weaker if they remained unenlarged. Thus,
then, to account by the hypothesis of natural selection, for such
a structure as that of the moose deer, or the extinct Irish elk,
we must suppose a spontaneous increase in the size of the
horns, to be accompanied by a spontaneous increase in each
of these numerous bones and muscles and ligaments directly
and indirectly implicated in the use of the horns. Can we
with any propriety do this ? I think not. It would be a
strong supposition that the vertebras and muscles of the neck,
spontaneously enlarged at the same time as the horns. It
would be a still stronger supposition that the upper dorsal
vertebrae not only at the same time spontaneously became
more massive, but also spontaneously altered their pro-
portions in appropriate ways, by the development of their
immense neural spines. And it would be an assumption
still more straining our powers of belief, that along with
heavier horns there should spontaneously take place the re-
quired strengthenings of the scapular arch and the fore-legs.
Besides the multiplication of directly-cooperative organs,
the multiplication of organs that do not cooperate, save in
the degree implied by their combination in the same organ-
ism, seems to me a further hindrance to the development of
special structures by natural selection alone. Where the lifo
is comparatively simple, or where surrounding circumstances
render some one function supremely important, the survival
of the fittest may readily bring about the appropriate struc-
tural change, without any aid from the transmission of func-
tionally-acquired modifications. But in proportion as the
life grows complex — in proportion as a healthy existence
cannot be secured by a large endowment of .come one power,

454 T1IE EVOLUTION OF LIFE.

but demands many powers ; in the same -proportion do there
arise obstacles to the increase of any particular power, by
"the preservation of favoured races in the struggle for
life." As fast as the faculties are multiplied, so fast does it
become possible for the several members of a species to have
various kinds of superiorities over one another. While one.
saves its life by higher speed, another does the like by clearer
vision, another by keener scent, another by quicker hearing,
another by greater strength, another by unusual power of
enduring cold or hunger, another by special sagacity, another
by special timidity, another by special courage ; and others by
other bodily and mental attributes. Now it is unquestionably
true that, other things equal, each of these attributes, giving
its possessor an extra chance of life, is likely to be transmitted
to posterity. But there seems no reason to suppose that it will
be increased in subsequent generations by natural selection.
That it may be thus increased, the individuals not possess-
ing more than average endowments of it, must be more fre-
quently killed off than individuals highly endowed with it ;
and this can happen onty when the attribute is one of greater
importance, for the time being, than most of the other attri-
butes. If those members of the species which have but
ordinary shares of it, nevertheless survive by virtue of other
superiorities which they severally possess ; then it is not easy
to see how this particular attribute can be developed by
natural selection in subsequent generations. The probability
seems rather to be, that by gamogenesis, this extra endow-
ment will, on the average, be diminished in posterity — just
serving in the long run to compensate the deficient endow-
ments of other individuals, whose special powers lie in other
directions ; and so to keep up the normal structure of the
species. The working out of the process is here somewhat
difficult to follow ; but it appears to me that as fast as the
number of bodily and mental faculties increases, and as fast as
the maintenance of life comes to depend less on the amount
of any one, and more on the combined action of all ; so

INDIRECT EQUILIBRATION. |.V,

fast does the production of specialities of character by
natural selection alone, become difficult. Particularly does
this seem to be so with a species so multitudinous in its
powers as mankind ; and above all does it seem to be
so with such of the human powers as have but minor shares
in aiding the struggle for life — the aesthetic faculties, for
example.

It by no means follows, however, that in cases of this kind,
and cases of the preceding kind, natural selection plays no
part. Wherever it is not the chief agent in working organic
changes, it is still, very generally, a secondary agent. The
survival of the fittest must nearly always further the produc-
tion of modifications which produce fitness ; whether they be
modifications that have arisen incidentally, or modifications
that have been caused by direct adaptation. Evidently, those
individuals whose constitutions or circumstances have facili-
tated the production in them of any structural change con-
sequent on any functional change demanded by some new
external condition, will be the individuals most likely to live
and to leave descendants. There must be a natural selection
of functionally-acquired peculiarities, as well as of incidental
peculiarities ; and hence such structural changes in a species
as result from changes of habit necessitated by changed cir-
cumstances, natural selection will render more rapid than
they would otherwise be.

There are, however, some modifications in the sizes and
forms of parts, which cannot have been aided by natural
selection ; but which must have resulted wholly from the
inheritance of functionally-produced alterations. The dwind-
ling away of organs of which the undue sizes entail no
appreciable evils, furnishes the best evidence of this. Take,
for an example, that diminution of the jaws and teeth which
characterizes the civilized races, as contrasted with i\a
savage races.* How can the civilized races have be?n bene-

* I am indebted to Mr Flower for the opportunity of examining the collection
of 6kullfl in the Museum of the College of Surgeons for verification of this. V'i

456 THE EVOLUTION OF LIFE.

6 ted in the struggle for life, by the slight decrease ia
these comparatively-small bones ? No functional superiority
possessed by a small jaw over a large jaw, in civilized life,
can be named as having caused the more frequent survival
of small-jawed individuals. The only advantage which
smallness of jaw might be supposed to give, is the advantage
of economized nutrition ; and this could not be great enough
to further the preservation of men possessing it. The de-
crease of weight in the jaw and co-operative parts, that has
arisen in the course of many thousands of years, does not
amount to more than a few oimces. This decrease has to be
divided among the many generations that have lived and
died in the interval. Let us admit that the weight of these
parts diminished to the extent of an ounce in a single gener-
ation (which is a large admission) ; it still cannot be con-
tended that the having to carry an ounce less in weight, or
the having to keep in repair an ounce less of tissue, could
sensibly affect any man's fate. And if it never did this —
nay, if it did not cause a, frequent survival of small-jawed in-
dividuals where large-jaAved individuals died ; natural selec-
tion could neither cause nor aid diminution of the jaw and

fortunately the absence, in most cases, of some or many teeth, prevented me
from arriving at that specific result which would have been given by weighing a
number of the under jaws in each race. Simple inspection, however, disclosed
a sufficiently-conspicuous difference. The under jaws of Australians and Negroes,
when placed side by side with those of Englishmen, were visibly larger, not only
relatively but absolutely. One Australian jaw only, did I observe, that was about
of the same actual size as an average English jaw ; and this (probably the jaw of
a woman) belonging as it did to a much smaller skull, bore a much greater ratio
to the whole body of which it formed part, than did an English jaw of the same
actual size. In all the other cases, the under jaws of these inferior races (con-
taining larger teeth than our own) were absolutely more massive than our own-
often exceeding them in all dimensions ; and relatively to the smaller skeletons
of these inferior races, they were very much more massive. Let me add that the
Aus'-ialian and Jvegro jaws are thus strongly contrasted, not with all British jaws,
but only with the jaws of the civilized British. An ancient British skull in the
collection, possesses a jaw almost or quite as massive as those of the Australian
skulls. And this is in harmony with the alleged relation between greater size of
jaws and greater action of jaws, involved by the habits of savages.

INDIRECT EQLTLLU RATION. 4-07

il& appendages. Here, therefore, the decreased action of
these parts which has accompanied the growth of civilized
habits (the use of tools and the disuse of coarse food), must
have been the sole cause at work. During civilization this
decrease of function has affected, more or less, all individuals.
Through direct equilibration, diminished external stress on
these parts, has resulted in diminution of the internal forces
by which this stress is met. From generation to generation,
this lessening of the parts consequent on functional decline
has been inherited. And since the survival of individuals
must always have been determined by more important struc-
tural traits, this trait can have neither been facilitated nor
retarded by natural selection.

5 167. Returning: from these extensive classes of facts for
which Mr Darwin's hypothesis does not account, to the still
more extensive classes of facts for which it does account, and
which are unaccountable on any other hypothesis ; let us
consider in what way this hypothesis is expressible in terms
of the general doctrine of evolution. Already it has been
pointed out that the evolving of modified types by " natural
selection or the preservation of favoured races in the struggle
for life," must be a process of equilibration, since it residts
in the production of organisms that are in equilibrium with
their environments ; and at the outset of this chapter, some-
thing was done towards showing how this continual survival
of the fittest, may be understood as the progressive estab-
lishment of a balance between inner and outer forces. Here,
however, we must consider the matter more closely. It re-
mains to be shown that this process conforms to the same
o-cneral mechanical principles as do all other equilibrations.

On previous occasions we have contemplated the assem-
blage of individuals composing a species, as an aggregate in
a state of moving equilibrium. We have seen that its
powers of multiplication give it an expansive force which ia
antagonized by other forces ; and that through the rhyth-
SO

458 TIl£ EVOLUTION OF LIFE.

mical variations in these two sets of forces, there is main-
tained an oscillating limit to its habitat, and an oscillating
limit to its numbers. On another occasion (§ 96) it was
shown that the aggregate of individuals constituting a
species, has a kind of general life, which, " like the life of an
individual, is maintained by the unequal and ever- varying
actions of incident forces on its different parts." We saw
that "just as, in each organism, incident forces constantly
produce divergences from the mean state in various direc-
tions, which are constantly balanced by opposite divergences
indirectly produced by other incident forces ; and just as the
combination of rhythmical functions thus maintained, con-
stitutes the life of the organism ; so, in a species, there is
through gamogenesis a perpetual neutralization of those con-
trary deviations from the mean state, which are caused in its
different parts by different sets of incident forces ; and it is
similarly by the rhythmical production and compensation of
these contrary deviations, that the species continues to live."
Hence, to understand the way in which a species is affected by
causes which destroy some of its units and favour the multi-
plication of others, we must consider it as a whole whose units
are held together by complex forces that are ever balancing
themselves and ever being disturbed — a whole whose moving
equilibrium is continually being modified, and through
which waves of perturbation are continually being pro-
pagated. Thus much premised, let us next call to
mind in what way moving equilibria in general are changed.
In the first place, the necessary effect wrought by a new in-
cident force falling on any part of an aggregate with balanced
motions, is to produce a new motion in the direction of least
resistance. In the second place, the new incident force is
gradually used up in overcoming the opposing forces, and
when it is all expended the opposing forces produce a recoil
— a reverse deviation that counter-balances the original de-
viation. Consequently, to consider whether the moving equi-
librium of a species is modified in the same wav as moving

INDIRECT EQUILIBRATION. 459

equilibria in general, is to consider whether, when exposed tt
a new force, a species yields in the direction of least resist-
ance ; and whether, by its thus yielding, there is generated
in the species a compensating change in the opposite direc-
tion. "We shall find that it does both these things.

For what, expressed in mechanical terms, is the effect
wrought on a species by some previously-unknown enemy,
that kills such of its members as fail in defending them-
selves ? The disappearance of those individuals which meet
the destroying forces by the smallest defensive forces, is tan-
tamount to the yielding of the species as a whole at the
places where the resistances are the least. Or if by some
general influence, such as alteration of climate, the members
of a species are subject to any increase of certain external
actions that are ever tending to overthrow their equilibria,
and which they are ever counter-balancing by the absorp-
tion of nutriment, which are the first to die ? Those that
are least able to generate the internal actions which antagon-
ize these external actions. If the change be an increase of
the winter's cold, then such members of the species as have
unusual powers of getting food or of digesting food, or such
as are by their constitutional aptitude for making fat, fur-
nished with reserve stores of force, available in times of
scarcity, or such as have the thickest coats and so lose least
heat by radiation, survive ; and their survival implies that
in each of them the moving equilibrium of functions presents
such an adjustment of internal forces, as prevents its over-
throw by the modified aggregate of external forces. Con-
versely, the members that die, are, other things equal, those
deficient in the power of meeting the new action by an equi-
valent counter-action. Thus, in all cases, a species con-
eidei'ed as an aggregate in a state of moving equilibrium,
has its state changed by the yielding of its fluctuating
mass wherever this mass is weakest in the relation to the
special forces acting on it. The conclusion is, indeed, a
truism. But now, what must follow from the de-

460 TIIE EVOLUTION OF LITE.

struction of the least-resisting individuals and survival ci
the most-resisting individuals ? On the moving equilibrium
of the species as a whole, existing from generation to gener-
ation, the effect of this deviation from the mean state is to
produce a compensating deviation. For if all such as are de-
ficient of power in a certain direction are destroyed, what
must be (he influence on posterity ? Had those which are
destroyed lived and left offspring, the next generation would
have had the same average balance of powers as preceding
generations : there would have been a like proportion of in-
dividuals less endowed with this power, and individuals more
endowed with this power. But the more-endowed individuals
being alone left to continue the race, there must result a new
generation characterized by a larger average endowment of
this power. That is to say, on the moving equilibrium con-
stituted by a species, an action producing change in a given
direction, is followed, in the next generation, by a reaction
producing an opposite change. Observe, too, that these
effects correspond in their degrees of violence. If the altera-
tion of some external factor is so great that it leaves alive
only a few individuals, characterized by extreme endowments
of the power required to antagonize it ; then, in succeeding
generations, there is a rapid multiplication of individuals
similarly characterized by extreme endowments of this power
— the force impressed calls out an equivalent conflicting
force. Moreover, the change is temporary where the cause
is temporary, and permanent where the cause is permanent.
All that are deficient in the needful attribute having been
killed off; and the survivors having the needful attribute in
a comparatively high degree ; there will descend from thera,
not only some possessing equal amounts of this attribute with
themselves, but also some possessing less amounts of it. If
the agency which proves fatal to them has not continued in
action, such less-endowed individuals will multiply ; and the
species, after sundry oscillations, will return to its previous
mean state. But if this agency be a persistent one, such less

INDIRECT EQUILIBRATION. 461

endowed individuals will be continually killed off; and
eventually none but the highly-endowed individuals will be
produced — a new moving equilibrium, adapted to the new
environing conditions, will result.

It may be objected that this mode of expressing the facts
does not include the numerous cases in which a species be-
comes modified in relation to surrounding agencies that
do not actively influence it — cases like that of the plant
which acquires hooked seed-vessels, by which it lays hold of
the skins of passing animals, and makes them the distributors
of its seeds — cases in which the outer agency has no direct
tendency at first to affect the species, but in which the species
so alters itself as to take advantage of the outer agency
To cases of this kind, however, the same mode of inter
pretation applies on simply changing the terms. While, in
the aggregate of influences amid which a species exists, there
are some which tend to overthrow the moving equilibria oi
its members, there are others which facilitate the maintenance
of their moving equilibria, and some which are capable of
giving their moving equilibria increased stability : instance
the spread into their habitat of some new kind of prey, which
is abundant at seasons when other prey is scarce. ISow what
is the process by which the moving equilibrium in any
species, becomes adapted to some additional external factor
which furthers its maintenance ? Instead of an increased
resistance to be met and counter-balanced, there is here a
diminished resistance ; and the diminished resistance is
equilibrated in the same way as the increased resistance. As,
in the one case, there is a more frequent survival of those in-
dividuals whose peculiarities of constitution enable them best
to resist the new adverse factor ; so, in the other case, there
is a more frequent survival of individuals whose peculiarities
of constitution enable them to take advantage of the new
favourable factor. In each member of the species, the balance
of functions and correlated arrangement of structures, differ
slightly from those existing in other members. To say that

462 THE EVOLUTION OF LIFE.

among all its members, one is better adapted than the rest to
take advantage of some before-nnused agency in the environ-
ment, is to say that its moving equilibrium is, in so far, more
stably adjusted with respect to the aggregate of surrounding
influences. And if, as a consequence, this individual main-
tains its moving equilibrium when others fail to do so, and
produces offspring which do the like — that is, if individuals
thus characterized multiply and supplant the rest ; there is
evidently, as before, a process by which an equilibration be-
tween the organism and its environment is effected, not im-
mediately but mediately, through the continuous intercourse
between the species as a whole and the environment.

§ 168. Thus we see that indirect equilibration does what-
ever direct equilibration cannot do. It is scarcely possible
too much to emphasize the conclusion, that all these processes
by which organisms are re-fitted to their ever-changing
environments, must be equilibrations of one kind or other.
As authority for this conclusion, we have not simply the
universal truth that change of every order is towards equi-
librium ; but we have also the truth which holds throughout
the organic world, that life itself is the maintenance of a moving
equilibrium between inner and outer actions — the continuous
adjustment of internal relations to external relations; or the
maintenance of a correspondence between the forces to which
an organism is subject and the forces which it evolves. For
if the preservation of life is the preservation of such a moving
equilibrium, it becomes a corollary that those changes which
enable a species to live under altered conditions, are changes
towards equilibrium with the altered conditions.

Hence, all such changes being equilibrations, their differ-
ences can be nothing but differences in the ways through
which they result. If they are not effected immediately,
they must be effected mediately. A priori, therefore, we
may be certain that all processes of modification which do

INDIRECT EQUILIBRATION. 463

not come within the class of direct equilibrations, must come
within the class of indirect equilibrations.

Examination of the facts confirms this conclusion. Tho
external factors to which a species is exposed, are of two
kinds. They are such as act continuously or frequently on the
individuals ; or they are such as do not act continuously or
frequently on the individuals. To a factor which continuously
or frequently acts on the individuals, the functions of the in-
dividuals re-adjust themselves — there is direct equilibration.
While a factor which does not act continuously or- fre-
quently on the individuals, acts continuously on the species as
a whole — either destroying such of the members as are least
capable of resisting it, or fostering such of the members as
are most capable of taking advantage of it. And by the
absti'action, generation after generation, of those least in
equilibrium with the new factor ; or by the extra multipli-
cation, generation after generation, of those most in equi-
librium with the new factor ; the species as a whole is event-
ually brought into complete equilibrium with the new factor
— there is indirect equilibration.

CHAPTER XIII.

THE CO-OPERATION OF THE FACTORS.

S 1C9. Thus the phenomena of organic evolution, maj be
Interpreted in the same way as the phenomena of all other
evolution. Those universal laws of the re- distribution of
matter and motion, to which things in general conform, are
conformed to by all living things ; whether considered in
their individual histories, in their histories as species, or in
their aggregate history. However otherwise they may ordin-
arily be expressed, the truths of development as exhibited in
the animal and vegetal kingdoms, prove to be expressible as
manifestations of those abstract truths set forth in First
Principles. Fully to see this, it will be needful for us to con-
template in their ensemble, the several processes separately
described in the four preceding chapters.

If the forces acting on any aggregate remain the same, the
changes produced by them in the aggregate will presently
reach a limit, at which the constant outer forces are balanced
by the constant inner forces ; and thereafter no further me-
tamorphosis will take place. Hence, that there may be
continuous changes of structure in organisms, there must be
continuous changes in the incident forces. This condition to
the evolution of animal and vegetal forms, we find to be
fully satisfied. The astronomic, geologic, and meteorologic
changes that have been slowly but incessantly going on, and
have been increasing iu the complexity of their combinationn.

THE CO-OPERATION OF THE FACTORS. 465

have been perpetually altering the circumstances of organ-
isms ; and organisms, as they have become more numerous in
their kinds' and higher in their kinds, have been perpetually
altering one another's circumstances. Thus, for those pro-
gressive modifications upon modifications which organic evo-
lution implies, we find a sufficient cause in the modifications
after modifications, which every environment over the Earth's
surface has been undergoing, throughout all geologic and pre-
gcologic times. The progressive inner changes for

which we thus find a cause in the continuous outer changes,
conform, eo far as we can trace them, to that universal law of
the instability of the homogeneous, which is manifested
throughout evolution in general. We see that in organisms,
as in all other things, the exposure of different parts to
different kinds and amounts of incident forces, has necessi-
tated their differentiation ; and that for the like reason,
aggregates of individuals have been lapsing into varieties,
and species, and genera, and classes. We also see that in
each type of organism, as in the aggregate of types, the mul-
tiplication of effects has continually aided this transition from
a more homogeneous to a more heterogeneous state. And
yet again, we see that that increasing segregation, and con-
comitant increasing definiteness, which characterizes the
growing heterogeneity of organisms, has been insured by the
necessary maintenance of them under combinations of forces
not greatly unlike preceding combinations — by the continual
destruction of those which expose themselves to aggregates
of external actions markedly incongruous with the aggregates
of their internal actions, and the survival of those subject
only to comparatively small incongruities. Finally,

we have found that each change of structure, superposed on
preceding changes, has been a re-equilibration necessitated by
the disturbance of a preceding equilibrium. The maintenance
of life being the maintenance of a balanced combination of
functions, it follows that individuals and species that have
continued to live, are individuals and species in which the

406 THE EVOLT TICN OF LIFE.

balance of functions Las not been overthrown. Inevitably,
therefore, survival through successive changes of conditions,
implies successive adjustments of the balance to the new con-
ditions. This deduction we find to be inductively verified
What is ordinarily called adaptation, is, when translated into
mechanical terms, direct equilibration. And that process
which, under the name of natural selection, Mr Darwin has
shown to be an ever-acting means of fitting the structures of
organisms to their circumstances, we find, on analysis, to be
expressible in mechanical terms as indirect equilibration.

The actions that are here specified in succession, are in
reality simultaneous ; and they must be so conceived before
organic evolution can be rightly understood. Some aid
towards so conceiving them, will be given by the annexed
table, representing the co-operation of the factors.

§ 170. Respecting this co-operation of these factors, it re-
mains only to point out their respective shares in producing
the total result ; and the way in which the proportions of
their respective shares vary as evolution progresses.

At first, changes in the amounts and combinations of ex-
ternal inorganic forces, astronomic, geologic, and meteoro-
logic, were the only causes of the successive modifications
undergone by organisms ; and these changes have continued,
and must still continue, to be causes of such modifications.
As, however, through the diffusion of organisms, and the
consequent differential actions of inorganic forces on them,
there arose unlikenesses among organisms, producing varieties,
species, genera, orders, classes, &c. ; the actions of organisms
on one another became new sources of organic modifications.
And as fast as types have multiplied, and become more com-
plex ; so fast have the mutual actions of organisms come to
be more influential factors in their respective evolutions.
Until, eventually, as we see exemplified in the human race,
they have come to be the chief factors.

Passing from the external causes of change to the internal

THE CO- OP?1, RATION OF THE FACTORS.

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468 THE EVOLUTION OF LIFE.

processes of change entailed by them, we see that these, too,
have varied in their proportions — that which was originally
the most important and almost the sole process, becoming
gradually less important, if not at last the least important.
Always there must have been, and always there must con-
tinue to bo, a survival of the fittest : natural selection must
have been in operation at the outset, and can never cease to
operate. While yet organisms had comparatively feeble
powers of co-ordinating their actions, and adjusting them to
environing actions, natural selection worked almost alone in
moulding and re-moulding organisms into fitness for their
changing environments ; and natural selection has re-
mained almost the sole agency by which plants and in-
ferior orders of animals have been modified and developed
The equilibration of organisms that are comparatively passive,
is necessarily effected indirectly, by the action of incident
forces on the species as a whole. But along with the gradual
evolution of organisms having some activity, there grows up
a kind of equilibration that is relatively direct. In propor-
tion as the activity increases, direct equilibration plays a
more important part. Until, when the nervo-muscular
apparatus becomes greatly developed, and the power of vary-
ing the actions to fit the varying requirements becomes con-
siderable, the share taken by direct equilibration rises into
co-ordinate importance. "We have seen reason to think that
as fast as essential faculties multiply, and as fast as the num-
ber of organs that co-operate in any given function increases,
indirect equilibration through natural selection, becomes less
and less capable of producing specific adaptations ; and re-
mains fully capable only of maintaining the general fitness
of constitution to conditions. Simultaneously, the production
of adaptations by direct equili oration, takes the first place —
indirect equilibration serving to facilitate it. Until at length,
among the civilized human races, the equilibration becomes
mainly direct : the action of natural selection being restricted
to the destruction of those who are constitutionally too feeble

THE COOPERATION OF THE FACTORS. 469

to live, even with external aid. As the preservation of in-
capables is habitually secured by our social arrangements ;
and as very few except criminals are prevented by their in-
feriorities from leaving the average number of offspring (in-
deed the balance of fertility is probably in favour of the in-
ferior) ; it results that survival of the fittest, can scarcely at
all act in such way as to produce specialities of nature, either
bodily or mental. Here the specialities of nature, chiefly
mental, which we see produced, and which are so rapidly
produced that a few centuries show a considerable change,
must be ascribed almost wholly to direct equilibration.*

* As having an instructive bearing on the question of the varieties of Man,
let me here refer to a paper on " The Origin of the Human Races " read before
the Anthropological Society, March 1st, 1864, by Mr Alfred Wallace— a gentle-
man well known among naturalists, as having independently thought out the
hypothesis of natural selection, though at a later date, and less elaborately, than
Mr Darwin. In this paper, Mr Wallace shows, very clearly I think, that along
with the attainment of that degree of intelligence implied by the use of imple-
ments, clothing, &c, there arises a tendency for modifications of brain to take the
place of modifications of body — still, however, regarding the natural selection of
spontaneous variations, as the cause of the modifications. But if the foregoing
arguments be valid, natural selection here plays but the secondary part of fur-
thering the adaptations otherwise caused. It is true that, as Mr Wallace argues,
and as I have myself briefly indicated (see Westminster Review, for April, 1S"j_',
pp. 4a6 — 501), the natural selection of races, leads to the survival of the more
cerebrally-devcloped, while the less cerebrally-developcd disappear. But
though natural selection acts freely in the struggle of one society with another ;
yet, among the units of each society, its action is so interfered with, that there
remains no adequate cause for the requirement of mental superiority by one
race over another, except the inheritance of functionally-produced modifica-
tions. This view, however, agrees equally well with Mr. Wallace's conclu-
sion, that at a certain stage of evolution, the brain begins to change much
more than the body.

CHAPTER XIV.

THE CONVERGENCE OF THE EVIDENCES.

§ 171. Of the three classes of evidences that have "neon
assigned, the a priori, which we took first, were partly nega-
tive, partly positive.

On considering the " General Aspects of the Special-crea-
tion-hypothesis," we discovered it to be worthless. Discredited
by its origin, and wholly without any basis of observed fact,
we found that it was not even a thinkable hypothesis ; and
while thus intellectually illusive, it turned out on examina-
tion to have moral implications quite at variance with the
professed beliefs of those who hold it.

Contrariwise, the " General Aspects of the Evolution-hy-
pothesis," begot the stronger faith in it the more nearly they
were considered. By its lineage and its kindred, it was
found to be as closely allied with the proved truths of modern
science, as is the antagonist hypothesis with the proved
errors of ancient ignorance. Instead of being a mere pseud-
idea, we saw that it admitted of elaboration into a definite
conception — so showing its legitimacy as an hypothesis. In-
stead of positing a purely fictitious process, the process which
it alleges, we saw to be one that is actually going on around
us. To which add, that morally considered, this hypothesis
presents no irreconcilable incongruities.

Thuy, even were we without further means of judging,

THE CONVERGENCE OF 1HE EVIDENCES. 471

there could be no rational hesitation which of the two views
6hould be entertained.

§ 172. Further means of judging, however, we found to
be afforded by bringing the two hj'potheses face to face with
the general truths established by naturalists. These induct-
ive evidences were dealt with in four chapters.

" The Arguments from Classification " were these. Organ-
isms fall into groups within groups ; and this is the arrange-
ment which we see results from evolution, where it is known
to take place. Of these groups within groups, the great or
primary ones are the most unlike, the sub-groups are less
unlike, the sub-sub-groups still less iinlike, and so on ; and
this, too, is a characteristic of groups demonstrably produced
by evolution. Moreover, indefiniteness of equivalence among
the groups, is common to those which we know have been
evolved, and those here supposed to have been evolved. And
then there is the further significant fact, that divergent
groups are allied through their lowest rather than their
highest members — a truth which the hypothesis of evolution
implies.

Of "the Arguments from Embryology," the first and most
striking is, that when the developments of embrj'os are traced
from their common starting point, and their divergences and
re-divergences symbolized by a genealogical tree, there is
manifest a general parallelism between the arrangement of.
its primary, secondary, and tertiary branches, and the
arrangement of the divisions and sub-divisions of our classi-
fioations — a general parallelism to be anticipated as a result
of evolution. Kor do those minor deviations from this
general parallelism, which at first sight look like difficulties,
fail, on closer observation, to become additional supports ;
since those traits of a common ancestry which embryology
reveals, arc, if modifications have resulted from changed con-
ditions, liable to be distorted or disguised in quite different
ways and degrees in different lines of descendants

472 THE EVOLUTION OF LIFE.

We next considered "the Arguments from Morphology."
Leaving out those kinships among organisms disclosed by
their developmental metamorphoses, the kinships which their
adult forms show are profoundly significant. The remarkable
unities of type which are found under such different exter-
nals, are inexplicable except as results of community of de-
scent with non-community of modification. Again, each
organism analyzed apart, shows us, in the likenesses obscured
by unlikenesses of its component parts, a peculiarity of struc-
ture that can be ascribed only to the formation of a more
heterogeneous organism out of a more homogeneous one.
And once more, the habitual existence of rudimentary organs,
homologous with organs that are developed in allied animals
or plants, while it admits of no other rational interpretation,
has a satisfactory interpretation given to it by the hypo-
thesis of evolution.

Last of the inductive evidences, came " the Arguments from
Distribution." While the phenomena of distribution in
Space, prove to be unaccountable as results of designed adapt-
ation of organisms to their habitats, they prove to be
accountable as results of the competition of species, and the
spread of the superior into the habitats of the inferior, fol-
lowed by the changes which new conditions induce. Though
the phenomena of distribution in Time, are so fragmentary
that no positive conclusion can be drawn from them ; yet all
of them are reconcileable with the hypothesis of evolution, and
some of them yield it strong support — especially the near
relationship that exists between the living and extinct
types of each great geographical area.

In each of these four groups, we thus found several argu-
ments which point to the same conclusion ; and the con-
clusion pointed to by the arguments of any one group, is that
pointed to by the arguments of all the other groups. This
coincidence of coincidences, would give to the induction a
very high degree of probability, even were it not enforced
by deduction.

THE CONVERGENCE OF THE EVIDENCES. 473

§ 173. But the conclusion deductively reached, is in har-
mony with the inductive conclusion. Passing from the evi-
dence that evolution has taken place, to the question — How
has it taken place ? we find in known agencies and known
processes, adequate causes of its phenomena.

In astronomic, geologic, and meteorologic changes, ever in
progress, ever combining in new and more involved ways,
we have a set of inorganic factors to which all organisms are
exposed; and in the varying and complicating actions of
organisms on one another, we have a set of organic factors
that alter with increasing rapidity. Thus, speaking gener-
ally, all members of the Earth's Flora and Fauna are con-
tinually passing into new environments — experience per-
petual re-arrangements of external forces.

Each organic aggregate, whether considered individually
or as a continuously-existing species, is modified afresh by
each fresh distribution of external forces. To its pre-exist-
ing differentiations, new differentiations are added ; and thus
that lapse from a more homogeneous to a more heterogeneous
state, which would have a fixed limit were the circumstances
fixed, has its limit perpetually removed by the perpetual
change of the circumstances. Meanwhile, that growing com-
plexity of structure thus produced, must, in the average of
cases, be accompanied by an increasing definiteness of struc-
ture ; since only those organisms can survive which subject
themselves to aggregates of forces that are not, in their essen-
tials, greatly unlike those with which their structures cor-
respond. And at the same time that progression is thus
necessitated as a general result ; yet, as change of structure
arises only where there is change in the distribution of forces,
it will not take place in organisms which elude changes
in the distribution of forces, by migration or otherwise.

These modifications upon modifications which result in
evolution structurally considered, are the accompaniments
of those functional alterations continually required to re-
equilibrate inner with outer actions. That moving equi-
31

174 THE EVOLUTION OF LIFE.

Librium of inner actions corresponding with outer actions,
which constitutes the life of an organism, must either be
overthrown by a change in the outer actions, or must undergo
perturbations that cannot end until there is a re-adjusted
bain nee of functions and correlative adaptation of structures.
Wherever the external changes are such as to be continuously
or frequently operative on individuals, this direct equilibra-
tion must go on.

But where the external changes are either such as are
fatal when experienced by the individuals, or such as act on
the individuals in ways that do not affect the equilibrium of
their functions ; then the re-adjustment results through the
effects produced on the species as a whole — there is indirect
equilibration. By natural selection or survival cf the fittest
— by the preservation in successive generations of those
whose moving equilibria happen to be least at variance with
the requirements, there is eventually produced a changed
equilibrium completely in harmony with the requirements.

And thus it results that those universal laws of the re-dis-
tribution of matter and motion, which are conformed to by
evolution in general, are conformed to by organic evolution.

§ 174. Even were this the whole of the evidence assign-
able for the belief that organisms of all orders have been
gradually evolved, this belief would have a warrant much
higher than that of very many belief's that are regarded aa
established. When we see that there are strong a priori pro-
babilities in its favour, and wholly adverse to the antagonist
hypothesis — when an examination of the facts which natural-
ists have accumulated, leads us to several groups of inductions
which unite in supporting it — and when the characteristics
which conspire to show that organic evolution has been going
on, prove to be deducible from those universal actions known
to work evolution of all other kinds ; we have a combination
of proofs which might suffice were there no more to be said.

Bat the evidence is far from exhausted. At the outset of

THE CONVERGENCE OF THE EVIDENCES. 475

the argument, it was remarked that the ensemble of vital
phenomena presented by the organic world as a whole, can-
not be properly dealt with apart from tlie ensemble of vital
phenomena presented by each organism, in the course of its
growth, development, and decay. The interpretation of either
implies interpretation of the other ; since the two are in
reality parts of one process. Hence, the validity of any
hypothesis respecting the one class of phenomena, may be
tested by its congruity with phenomena of the other class.
We are now about to pass to the more special phenomena of
development, as displayed in the structures and functions of
individual organisms. If the hypothesis that plants and
animals have been progressively evolved, be true, it must
furnish us with keys to these phenomena. We shall find that
it does this; and by doing it, gives numberless additional
vouchers for its truth.

APPENDIX

[The following letter, originally written for publication in the North
American Review, but declined by the Editor in pursuance of
a general rule, and eventually otherwise published in the United
States, I have thought well to append to this first volume of the
Principles of Biology. / do this because the questions which it
discusses are dealt with in this volume ; and because the further ex-
planations it furnishes seem, needful to prevent misapprehensions.]

ON ALLEGED " SPONTANEOUS GENERATION," AND ON THE
HYPOTHESIS OF PHYSIOLOGICAL UNITS.

The Editor of the North American Review.
Sir,

It is in most cases unwise to notice adverse criticisms.
Either they do not admit of answers or the answers may be left to
the penetration of readers. When, however, a critic's allegations
touch the fundamental propositionsof a book, and especially when they
appear in a periodical having the position of the North American
Review, the case is altered. For these reasons the article on
" Philosophical Biology," published in your last number, demands
from me an attention which ordinary criticisrjs do not.

It is the more needful for mc to notice ii, because its two leading
objections have the one an actual fairness and the other an apparaut
fairness ; and in the absence of explanations from me, they will be
considered as substantiated even by many, or perhaps most, of those
who have read the work itself — much more by those who have not
read it. That to prevent the spread of misapprehensions I ought to
say something, is further shown by the fact that the same two objec-
tions have already been made in England — the one by Dr. Child,
of Oxford, in his Essays on Physiological Subjects, and the other by
a writer in the Westminster Review for July, 18G5.

In the note to which your reviewer refers, I have, as he says, tacitly
repudiated the belief in "spontaneous generation;" and that I have
done this in such a way as to leave open the door for the interpre-
tation given by him is true. Indeed the fact that Dr. Child, whose
criticism is a sympathetic one, puts the same construction on this
note, proves that your reviewer has but drawn what seems to be a
necessary inference. Nevertheless, the inference is one which I did
not intend to be drawn.

In explanation, let me at the outset remark that I am placed at a
disadvantage in having had to omit that part of the System of
Philosophy which deals with Inorganic Evolution. In the orginal
programme wili be found a parenthetic reference to this omitted
part) which should, as there stated, precede the Principles of Biology.

480

Two volumes are missing. The closing chapter of the second, were
it written, would deal with the evolution of organic matter — the
step preceding the evolution of living forms. Habitually carrying
with me in thought the contents of this unwritten chapter, I have,
in some cases, expressed myself as though the reader had it before
him ; and have thus rendered some of my statements liable to
misconstructions. Apart from this, however, the explanation of the
apparent inconsistency is very simple, if not very obvious. In the first
place, I do not believe in the " spontaneous generation" commonly
alleged, and referred to in the note ; and so little have I associated
in thought this alleged "spontaneous generation" which I dis-
believe, with the generation by evolution which I do believe, that the
repudiation of the one never occurred to me as liable to be taken for re-
pudiation of the other. That creatures having quite specific structures are
evolved in the course of a few hours, without antecedents calculated
to determine their specific forms, is to me incredible. Not only the
established truths of Biology, but the established truths of science
in general, negative the supposition that organisms having struc-
tures definite enough to identify them as belonging to known genera
and species, can be produced in the absence of germs derived from
antecedent organisms of the same genera and species. If there can
suddenly be imposed on simple protoplasm the organization which
constitutes it a Paramecium, I see no reason why animals of greater
complexity, or indeed of any complexity, may not be constituted
after the same manner. In brief, I do not accept these alleged facts
as exemplifying Evolution, because they imply something immensely
beyond that which Evolution, as I understand it, can achieve. In
the second place, my disbelief extends not only to the alleged cases
of " spontaneous generation," but to every case akin to them. The
very conception of spontaneity is wholly incongruous with the con-
ception of Evolution, for this reason 1 regard as objectionable Mr.
Darwin's phrase " spontaneous variation " (as indeed he does himself) ;
and I have sought to show that there are always assignable causes of
variation. No form of Evolution, inorganic or organic, can be
spontaneous ; but in every instance the antecedent forces must be
adequate in their quantities, kinds, and distributions, to work the
observed effects. Neither the alleged cases of " spontaneous gene-
ration," nor any imaginable cases in the least allied to them, fulfil
this requirement.

If, accepting these alleged cases of " spontaneous generation," I
had assumed, as your reviewer seems to do, that the evolution of
organic life commenced in an analogous way ; then, indeed, I should
have left myself open to a fatal criticism. This supposed " spon-
taneous generation" habitually occurs in menstrua that contain
either organic matter, or matter originally derived from organisms ;
and such organic matter, proceeding in all known cases from organ-
isms cf a higher kind, implies the pre-existence of such highci

481

organisms. By what kind of logic, then, is it inferrible that
organic life was initiated after a manner like that in which Infusoria
are said to be now spontaneously generated? Where, before life
commenced, were the superior organisms from which these lowest,
organisms obtained their organic matter? Without doubting that
there are those who, as the reviewer says, "can penetrate deeper
than Mr. Spencer has done into the idea of universal evolution,"
and who. as he contends, prove this_ by accepting the doctrine of
" spontaneous generation" ; I nevertheless think that I can penetrate
deep enough to see that a tenable hypothesis respecting the origin
of organic life must be reached by some other clue than that fur-
nished by experiments on decoction of hay and extract of beef.

From what I do not believe, let me now pass to what I do believe.
Granting that the formation of organic matter, and the evolution of
life in its lowest forms, may go on under existing cosmical condi-
tions; but believing it more likely that the formation of such matter
and such forms, took place at a time when the heat of the Earth's
surface was falling through those ranges of temperature at which
the higher organic compounds are unstable; I conceive that the
moulding of such organic matter into the simplest types, must have
commenced with portions of protoplasm more minute, more in-
definite, and more inconstant in their characters, than the lowest
Rhizopods — less distinguishable from a mere fragment of albumen
than even the Protogenes of Professor Haeckel. The evolution" of
specific shapes must, like all other organic evolution, have resulted
from the actions and reactions between such incipient types and
their environments, and the continued survival of those which hap-
pened to have specialities best fitted to the specialities of their en-
vironments. To reach by this process the comparatively well-spe-
cialized forms of ordinary Infusoria, must, I conceive, have taken an
enormous period of time.

To prevent, as far as may be, future misapprehension, let me
elaborate this conception so as to meet the particular objections
raised. The reviewer takes for granted that a " first organism "
must be assumed by me, as it is by himself. But the conception of
a " first organism," in anything like the current sense of the words,
is wholly at variance with conception of evolution; and scarcely
less at variance with the facts revealed by the microscope. The
lowest living things are not properly speaking organisms at all; for
they have no distinctions of parts — no traces of organization. It is
almost a misuse of language to call them " forms" of life: not only
are their outlines, when distinguishable, too nnspecific for description,
but they change from moment to moment and are never twice alike,
either in two individuals or in the same individual. Even the word
"type" is applicable in but a loose way ; for there is little constancy
in their generic characters : according as the surrounding conditions
determine, they undergo transformations now of one kind and now of

482

another. And the vagueness, the inconstancy, the want of appre-
ciable structure, displayed by the simplest of living things as we
now see them, are characters (or absences of characters) which, on
the hypothesis of Evolution, must have been still more decided
when, asat first, no " forms," no " types," no " specific shapes," had
been moulded. That " absolute commencement of organic life on
the globe," which the reviewer says I " cannot evade the admission
of," I distinctly deny. The affirmation of universal evolution is in
itself the negation of an " absolute commencement " of anything.
Construed in terms of evolution, every kind of being is conceived as
a product of modifications wrought by insensible gradations on a
pre-existing kind of being ; and this holds as fully of the supposed
"commencement of organic life" as of all subsequent developments
of organic life. It is no more needful to suppose an " absolute
commencement of organic life " or a " first organism," than it is
needful to suppose an absolute commencement of social life and a
first social organism. The assumption of such a necessity in this
last case, made by early speculators with their theories of " social
contracts " and the like, is disproved by the facts ; and the facts,
so far as they are ascertained, disprove the assumption of such a
necessity in the first case. That organic matter was not produced
all at once, but was reached through steps, we are well warranted
in believing by the experiences of chemists. Organic matters are
produced iu the laboratory by what we may literally call artificial
evolution. Chemists find themselves unable to form these complex
combinations directly from their elements ; but they succeed in form-
ing them indirectly, by successive modifications of simpler combina-
tions. In some binary compound, one element of which is present
in several equivalents, a change is made by substituting for one of
these equivalents an equivalent of some other element ; so producing
a ternary compound. Then another of the equivalents is replaced,
and so on. For instance, beginning with ammonia, N H3, a higher
form is obtained by replacing one of the atoms of hydrogen
by an atom of methyl, so producing methjl-amine, N (C H3 H2) j
and then, under the further action of methyl, ending in a
further substitution, there is reached the still more compound sub-
stance dimethyl-amine, N (C H„) (C H,) H. And in this manner
highly complex substances are eventually built up. Another
characteristic of their method is no less significant. Two com-
plex compounds are employed to generate, by their action upon
one another, a compound of still greater complexity : different
heterogeneous molecules of one stage, become parents of a mole-
cule a stage higher in heterogeneity. Thus, having built up acetic
acid out of its elements, and having by the process of substitution de-
scribed above, changed the acetic acid into propionic acid, and propi-
onic into butyric, of which the formula is < ^ k m Q\ \ '

483

this complex compound, by operating on anotner complex
compound, such as the dimethyl-aniine named above, gene-
rates one of still greater complexity, butyrate of dimethyl-amine

| C O (H 0()C Hj) HjN (C n3> (c na) II. See, then, the
remarkable parallelism. The progress towards higher types of
organic molecules is effected by modifications upon modifications ;
as throughout Evolution in general. Each of these modifications is
a change of the molecule into equilibrium with its environment — an
adaptation, as it were, to new surrounding conditions to which it is
subjected ; as throughout Evolution in general. Larger, or more
integrated, aggregates (for compound molecules are such) arc
successively generated; as throughout Evolution in general. More
complex or heterogeneous aggregates are so made to arise, one out
of another ; as throughout Evolution in general. A geometrically-
increasing multitude of these larger and more complex aggregates
so produced, at the same time results ; as throughout Evolution in
general. And it is by the action of the successively higher forms
on one another, joined with the action of environing conditions, that
the highest forms are reached ; as throughout Evolution in general.
When we thus see the identity of method at the two extremes
— when we see that the general laws of evolution, as they are exem-
plified in known organisms, have been unconsciously conformed to
by chemists in the artificial evolution of organic matter; we can
scarcely doubt that these laws were conformed to in the natural
evolution of organic matter, and afterwards in the evolution of the
simplest organic forms. In the early world, as in the modern
laboratory, inferior types of organic substances, by their mutual
actions under fit conditions, evolved the superior types of organic
substances, ending in organizable protoplasm. And it can hardly
be doubted that the shaping of organizable protoplasm, which is a
substance modifiable in multitudinous ways with extreme facility,
went on after the same manner. As I learn from one of our
first chemists, Prof. Erankland, protein is capable of existing
under probably at least a thousand isomeric forms ; and, as
we shall presently see, it is capable of forming, with itself
and other elements, substances yet more intricate in composi-
tion, that are practically infinite in their varieties of kind.
Exposed to those innumerable modifications of conditions which
the Earth's surface afforded, here in amount of light, there in

amount of heat, and elsewhere in the mineral quality of its aqu< 9

medium, this extremely changeable substance must have undergone
now one, now another, of its countless metamorphoses. And to the
mutual influences of its metamorphic forms under favouring con-
ditions, we may ascribe the production of the still more composite,
still more sensitive, still more variously-changeable portions of
organic matter, which, iu masses more minute and simpler thai.

481

existing Protozoa, displayed actions verging little by little
into those called vital — actions -which protein itself exhibits in a
certain degree, and which the lowest known living things exhibit
only in a greater degree. Thus, setting out with inductions from
the experiences of organic chemists at the one extreme, and
with inductions from the observations of biologists at the other
extreme, we are enabled deductively to bridge the interval — ■
are enabled to conceive how organic compounds were evolved, and
how, by a continuance of the process, the nascent life displayed in
these became gradually more pronounced. And this it is which
has to be explained, and which the alleged cases of " spontaneous
generation ". would not, were they substantiated, help us in the least
to explain.

It is thus manifest, I think, that I have not fallen into the alleged
inconsistency. Nevertheless, I admit that your reviewer was
justified in inferring this inconsistency ; and I take blame to mysolf
for not having seen that the statement, as I have left it, is opci to
misconstruction.

I pass now to the second allegation — that in ascribing to certain
specific molecules, which I have called " physiological uniTs " the
aptitude to build themselves into the structure of the organism to
which they are peculiar, I have abandoned my own principle, f.nd
have assumed something beyond the re-distribution of MaUer and
Motion. As put by the reviewer, his case appears to be well made
out ; and that he is not altogether unwarranted in so putting it,
may be admitted. Nevertheless, there docs not in reality exist the
supposed incongruity.

Before attempting to make clear the adequacy of the conception
which I am said to have tacitly abandoned as insufficient, lot me
remove that excess of improbability the reviewer gives to it, t)y the
extremely-restricted meaning with which he uses the word mtcham-
eal. In discussing a proposition of mine he says : —

" He then cites certain remarks of Mr. Paget on the permanent effects
wrought in the blood by the poison of scarlatina and small-pox, as justify-
ing the belief that such a 'power' exists, and attributes the repair of a
wasted tissue to ' forces analogous to those by which a crystal reproduces
its lost apex.' (Neither of which phenomeua, however, is explicable by
mechanical causes.)"

Were it not for the deliberation with which this last statement is
made, I should take it for a slip of the pen. As it is, however, I
have no course left but to suppose the reviewer unaware of the fact
that molecular actions of all kinds are now not only conceived as
mechanical actions, but that calculations based on this conception of
them, bring out the results that correspond with observation. There
is no kind of re-arrangement among molecules (crystallization
beint; one) which the modern physicist does not think of,

483

Mid correctly reason npon, in terms of forces and motions like
those of sensible masses. Polarity is regarded as a resultant of
such forces and motions ; and when, as happens in many cases,
light changes the molecular structure of a crystal, and alters its
.polarity, it does this by impressing, in conformity with mechanical
laws, new motions on the constituent molecules. That the reviewer
should present the mechanical conception under so extremely limited
a form, is the more surprising to me because, at the outset of the
very work he reviews, 1 have, in various passages, based inferences
on those immense extensions of it which he ignores ; indicating, for
example, the interpretation it yields of the inorganic chemical
changes effected by heat, and the organic chemical changes effected
by light (Principles of Biology, § \o.)

Premising, then, that the ordinary idea of mechanical action must
be greatly expanded, let us enter upon the question at issue — the
sufficiency of the hypothesis that the structure of each organism is
determined by the polarities of the special molecules, or physiologi-
cal units, peculiar to it as a species, which necessitate tendencies
towards special arrangements. My proposition and the reviewer's
criticism upon it, will be most conveniently presented if I quote in
full a passage of his from which 1 have already extracted some ex-
pressions. He says : —

"It will be noticed, however, that Mr. Spsncer attributes the possession
of these 'tendencies,' or 'proclivities,' to natural inheritance from
ancestral organisms ; and it may be argued that he thus saves the
mechanist theory and his own consistency at the same time, inasmuch as
he derives even the 'tendencies' themselves ultimately from the environ-
ment. To this we reply, that Mr. Spencer, who advocates the nebular
hypothesis, cannot evade the admission of an absolute commencement of
organic life on the globe, and that the 'formative tendencies,' without
which he cannot explain the evolution of a single individual, could not
have been inherited by the first organism. Besides, by his virtual denial
of spontaneous generation, he denies that the first organism was evolved
out of the inorganic world, and thus shuts himself off from the argument
(otherwise plausible) that its 'tendencies' were ultimately derived fro i
the environment."

This assertion is already in great measure disposed of by what
lias been said above. Holding that, though not " spontaneously
generated," those minute portions of protoplasm which first dis-
played b the feeblesjj degree that changeability taken to imply life,
were evolved, I am not debarred from the argument that the '"ten-
dencies" of the physiological units are derived from the inherited
effects of environing actions. If 'the conception of a ':rirst organ-
ism " were a necessary one, the reviewer's objection would bo valid.
If there were an " absolute commencement" of life, a definite line
parting organic matter from the simplest living forms, I should be
placed in the predicament he describes. But as the doctrine of
Evolution itself tacitly negatives any such distinct separation ; and
■ts the negation is the moro confirmed by the facts the more w«

436

know of thcra ; I do not feel that I am entangled in the alleged
difficulty. My reply might end here ; but as the hypothesis in ques-
tion is one not easily conceived, and very apt to be misunderstood,
I will attempt a further elucidation of it.

Much evidence now conspires to show that molecules of the sub-
stances we call elementary are in reality compound ; and that, by
the combination of these with one another, and re-combinations of
the products, there are formed systems of systems of molecules, un-
imaginable in their complexity. Step by step as the aggregate
molecules so resulting, grow larger and increase in heterogeneity,
they become more unstable, more readily transformable by small
forces, more capable of assuming various characters. Those com-
posing organic matter transcend all others in size and intricacy of
structure ; and in them these resulting traits reach their extreme.
As implied by its name protein, the essential substance of which
organisms are built, is remarkable alike for the variety of its meta-
morphoses and the facility with which it undergoes them : it changes
from one to another of its thousand isomeric forms on the slightest
change of conditions. Now there are facts warranting the belief
that though these multitudinous isomeric forms of protein will not
unite directly with one another, yet they admit of being linked to-
gether by other elements with which they combine. And it is
very significant that there are habitually present two other elements,
sulphur and phosphorus, which have quite special powers of holding
together many equivalents — the one being pentatomic and the other
hexatomic. So that it is a legitmate supposition (justified by analo-
gies) that an atom of sulphur may be a bond of union among half-
a-dozen different isomeric forms of protein; and similarly with phos-
phorus. A moment's thought will show that, setting out with the
thousand isomeric forms of protein, this makes possible a number of
these combinations almost passing the power of figures to express.
Molecules so produced, perhaps exceeding in size and complexity
those of protein as those of protein exceed those of inorganic matter,
may, I conceive, be the special units belonging to special kinds of
organisms. By their constitution they must have a plasticity, or
sensitiveness to modifying forces, far beyond that of protein ; and
bearing in mind not only that their varieties are practically infinite
in number, but that closely allied forms of them, chemically in-
different to one another as they must be, may coexist in the same
aggregate, we shall see that they are fitted for entering into un-
limited varieties of organic structures.

The existence of such physiological units, peculiar to each species
of organism, is not unaccounted for. They are evolved simul-
taneously with the evolution of the organisms they compose — they
differentiate as fast as these organisms differentiate; and are made
multitudinous in kind by the same actions which make the organism
they compose multitudinous in kind. This conceptiou is clearly

487

representable in terms of the mechanical hypothesis. Every
physicist will endorse the proposition that in each aggregate there
tends to establish itself an equilibrium between the forces exercised
by all the units upon each and by each upon all. Even in masses
of substance so rigid as iron and glass, there goes on a molecular
re-arrangement, slow or rapid according as circumstances facilitate,
which ends only when there is a complete balance between the actions of
the parts on the whole and the actions of the whole on the parts : the
implication being that every change in the form or size of the whole,
necessitates some redistribution of the parts. And though in cases
like these, there occurs only a polar re-arrangement of the molecules,
without changes in the molecules themselves; yet where, as often
happens, there is a passage from the colloid to the crystalloid state,
a change of constitution occurs in the molecules themselves. These
truths are not limited to inorganic matter: they unquestionably
hold of organic matter. As certainly as molecules of alum have a
form of equilibrium, the octahedron, into which they fall when the
temperature of their solvent allows them to aggregate, so certainly
must organic molecules of each kind, no matter how complex, have
a form of equilibrium in which, when they aggregate, their complex
forces are balanced — a form far less rigid and definite, for the
reason that they have far less definite polarities, are far more un-
stable, and have their tendencies more easily modified by environing
conditions. Equally certain is it that the special molecules having
a special organic structure as their form of equilibrium, must be
reacted upon by the total forces of this organic structure ; and that,
if environing actions lead to any change in this organic structure,
these special molecules, or physiological units, subject to a changed
distribution of the total forces acting upon them will undergo
modification — modification which their extreme plasticity will
render easy. By this action and reaction I conceive the physio-
logical units peculiar to each kind of organism, to have been
moulded along with the organism itself. betting out with
the stage in which protein in minute aggregates, took on
those simplest differentiations which fitted it for differently-
conditioned parts of its medium, there must have unceasingly
gone on perpetual re-adjustments of balance between aggregates
and their units — actions and reactions of the two, in which the
units tended ever to establish the typical form produced by actions
and reactions in all antecedent generations, while the aggregate, if
changed in form by change of surrounding conditions, tended ever
to impress on the units a corresponding change of polarity, causing
them in the next generation to reproduce the changed form — their
uew form of equilibrium.

This is the conception which I have sought to convey, thou;, h
it seems unsuccessfully, in the Principles of Biology ; and which I
have there used to interpret the many involved and mysterionf

488

phenomena of Genesis, Heredity, and Variation. In one respect
only am I conscious of having so inadequately explained myself,
as to give occasion for a misinterpretation — the one made by
the Westminster reviewer above referred to. By him, as by your
own critic, it is alleged that in the idea of " inherent tendencies "
I have introduced, under a disguise, the conception of " the
archseus, vital principle, nisus formativus, and so on." This
allegation is in part answered by the foregoing explanation.
That which I have here to add, and did not adequately ex-
plain in the Principles of Biology, is that the proclivity of units
of each order towards the specific arrangement seen in the
organism they form, is not to be understood as resulting
from their own structures and actions only ; but as the product
of these and the environing forces to which they are exposed.
Organic evolution takes place only on condition that the masses of
protoplasm formed of the physiological units, and of the assimilable
materials out of which others like themselves are to be multiplied,
are subject to heat of a given degree — are subject, that is, to the
unceasing impacts of undulations of a certain strength and period ;
and, within limits, the rapidity with which the physiological units
pass from their indefinite arrangement to the detinite arrangement
they presently assume, is proportionate to the strengths of the
etherial undulations falling upon them. In its complete form, then,
the conception is that these specific molecules, having the immense
complexity above described, and having correspondent^ complex
polarities which cannot be mutually balanced by any simple form
of aggregation, have, for the form of aggregation in which
all their forces are equilibrated, the structure of the adult
organism to which they belong ; and that they are compelled
to fall into this structure by the co-operation of the en-
vironing forces acting on them, and the forces they exercise on one
another — the environing forces being the source of the power which
effects the re-arrangement, and the polarities of the molecules deter-
mining the direction in which that power is turned. Into this con-
ception there enters no trace of the hypothesis of an " archseus or
vital principle;" and the principles of molecular physics fully justify it.
It is, however, objected that "the living body in its develop-
ment presents a long succession of differing forms ; a continued
series of changes for the whole length of which, according to Mr.
Spencer's hypothesis, the physiological units must have an 'inherent
tendency.' Could we more truly say of anything, 'it is unrepresent-
able in thought 1 '" I reply that if there is taken into account an
element here overlooked, the process will not be found " unrepre-
sentable in thought." This is the element of size or mass. To
satisfy or balance the polarities of each order of physiological units,
not only a certain structure of organism, but a certain size of
organism is needed; for the complexities of that adult struetnre

489

in which the physiological units are equilibrated, cannot be
represented within the small bulk of the embryo. In many
minute organisms, where the whole mass of physiological units
required for the structure is present, the very thing does take
place which it is above implied ought to take place. The mass
builds itself directly into the complete form. This is so with
Acari, and among the nematoid Entozoa. But among higher
animals such direct transformations cannot happen. The mass
of physiological units required to produce the size as well as
the structure that approximately equilibrates them, is not ail
present, but has to be formed by successive additions — addi-
tions which in viviparous animals are made by absorbing,
and transforming into these special molecules, the organizable
materials directly supplied by the parent, and which in ovi-
parous animals are made by doing the like with the organ-
izable materials in the " food-yelk,"' deposited by the parent in the
same envelope with the germ. Hence it results that, under such
conditions, the physiological units which first aggregate into the
rudiment of the future organism, do not form a structure like that
of the adult organism, which, when of such small dimensions, does
not equilibrate them. They distribute themselves so as partly tu
satisfy the chief among their complex polarities. The vaguely-dif-
ferentiated mass thus produced cannot, however, be in equilibrium.
Each increment of physiological units formed and integrated by it,
changes the distribution of forces ; and this has a double effect. It
tends to modify the differentiations already made, bringing them a
step nearer to the equilibrating structure; and the physiological
units next integrated, being brought under the aggregate of polar
forces exercised by the whole mass, which now approaches a step
nearer to that ultimate distribution of polar forces which exists in
the adult organism, are coerced more directly into the typical struc-
ture. Thus there is necessitated a series of compromises. Each
successive form assumed is unstable and transitional : approach to
the typical structure going on hand in hand with approach to the
typical bulk.

Possibly 1 have not succeeded by this explanation, any more than
by the original explanation, in making this process " representable
in thought." It is manifestly untrue, however, that I have, as
alleged, re-introduced under a disguise the conception of a " vital
principle." That I interpret embryonic development in terms of
Mutter and Motion, cannot, I think, be questioned. Whether the
interpretation is adequate, must be a matter of opinion ; but it is
clearly a matter of fact, that I have not fallen into the inconsistency
asserted by your reviewer. At the same time 1 willingly admit that,
in the absence of certain statements which I have now supplied, he
was not unwarranted in representing my conception in the way thaf,
he has done.

32

490

But while I consider that what your reviewer has said on these
two essential points, falls within the limits of legitimate criticism ; I
do not consider that he is justified in much that he says by im-
plication respecting my general views.

In the first place, he conveys a totally wrong idea of the mode
of interpretation he criticizes. He gives his readers no con-
ception of the immense extensions which modern science has made
of the " mechanical theory," now applied to the solution of all phy-
sical phenomena whatever ; but he has deliberately restricted its ap-
plications in a way that produces an appearance of difficulty where
no difficulty exists. The common uses of the words " mechanical "
and " mechanist," are such as inevitably call up in all minds the
notions of visible masses of matter acting on one another by mea-
surable forces and producing sensible motions. In the absence of
explanations or illustrations serving to enlarge the conception thus
suggested, so as to bring within it the oscillations of the molecules
of matter, and the undulations of the molecules of ether pervading
all space, even the cultivated reader must carry with him an ex-
tremely crude and narrow idea of the " mechanist theory," and can-
not fail to be struck with the seeming absurdity of interpreting vital
phenomena in mechanical terms. But the reviewer says nothing
to prevent misconceptions so arising. He gives no hint that heat,
light, and electricity, are now all recognized as "modes of mo-
tion;" and that most of their phenomena are mechanically inter-
preted, while the rest are regarded as mechanically interpretable.
He does not explain that the "mechanist" theory in its comprehen-
sive form embraces actions such as those by which variations in the
solar spots cause variations in our magnetic needles, and actions such
as those through which Sirius tells us what substances are contained
in his atmosphere. True he makes a passing reference to chemical
changes as being included by me under the conception of mechanical;
but he leaves this as a dead statement quite unintelligible to the
general reader ; and in the typical example he gives of my mode of in-
terpretation (the development of vertebrae by transverse strains) he
deliberately excludes the physio-chemical and chemical actions which
I imply as co-operating, and describes me as attributing the effects
entirely to the pressures and tensions caused by muscular move-
ments ! (See p. 408). Instead of the developed ideas of
Matter and Motion everywhere implied throughout the Principles
of Biology, the reviewer leads everyone to suppose that I bring to
bear on biological problems nothing beyond the vulgar ideas of
Matter and Motion, and leaves me responsible for the ludicrous
incongruity !

That, however, which I regard as most reprehensible in his criti-
cism is the way in which he persists in representing the System of
Philosophy I am working out as a materialistic system. Already he
has once before so represented it, and the injustice of so represent-

491

nig It lias been pointed ont. He knows that I have repeatedly and
emphatically asserted that our conceptions of Matter and Motion
are but symbols of an Unknowable Reality ; that this Reality cannot
be that which we symbolize it to be ; and that as manifested beyond
consciousness under the forms of Matter and Motion, it is the same
as that which, in consciousness, is manifested as Feeling and Thought.
Yet he continues to describe me as reducing everything to dead
mechanism. If his statement on pp. 383-4 has any meaning at all,
it means that there exists some "force operating ab extra" some
" external power " distinguished by him as " mechanical," which is
not included in that immanent force of which the universe is a mani-
festation; though whence it comes he does not tell us. This con-
ception he speaks of as though it were mine ; making it seem that I
ascribe the moulding of organisms to the actiou of this " mechani-
cal " " external power," which is distinct from the Inscrutable Cause
of things. Yet he either knows, or has ample means of knowing, that
I deny every such second cause : indeed he has himself classed me as
an opponent of dualism. I recognize no forces within the organism,
or without the organism, but the variously-conditioned modes of the
universal immanent force ; and the whole process of organic evolu-
tion is everywhere attributed by me to the co-operation of its vari-
ously-conditioned modes, internal and external. That this has been
all along my general view, is clearly shown in the closing paragraph
of First Principles, where I have said —

"A Power of which the nature remains for ever inconceivable, and
to which no limits in Time or Space can be imagined, works in us certain
effects. These effects have certain likenesses of kind, the most general of
which we class together under the names of Matter, Motion, and Force ;
and between these effects there are likenesses of connection, the most
constant of which we class as laws of the highest certainty. Analysis
reduces these several kinds of effect to one kind of effect ; and these
several kinds of uniformity to one kind of uniformity. And the highest
achievement of Science is the interpretation of all orders of phenomena,
as differently-conditioned manifestations of this one kind of elfect, under
differently-conditioned modes of this one kind of uniformity. But when
Science has done this, it has done nothing more than systematize our
experience ; and has in no degree extended the limits of our experience.
We can say no more than before, whether the uniformities are as
absolutely necessary, as they have become to our thought relatively
necessary. The utmost possibility for us, is an interpretation of the
process of things as it presents itself to our limited consciousness; but
now this process is related to the actual process, we are unable to
conceive, much less to know. Similarly, it must be remembered

that while the connection between the phenomenal order and the
ontological order is for ever inscrutable ; so is the connection between the
conditioned forms of being and the unconditioned form of being for
ever inscrutable. The interpretation of all phenomena in terms of Matter,
Motion, and Force, is nothing more than the reduction of our complex
6ymbols of thought, to the simplest symbols; and when the equation has
been brought to its lowest terms the symbols remain symbols still. Hence
the reasonings contained in the foregoing pages, afford no support to
either of the antagonist hypotheses respecting the ultimate nature of

492

things. Their implications are no more matenalistio than they are
spiritualistic ; and no more spiritualistic than they are materialistic.
Any argument which is apparently furnished to either hypothesis, is
neutralized by as good an argument furnished to the other. The
Materialist, seeing it to be a necessary deduction from the law of correla-
tion, that what exists in consciousness under the form of feeling, is
transformable into an equivalent of mechanical motion, and by
consequence into equivalents of all the other forces which matter
exhibits ; may consider it therefore demonstrated that the phenomena of
consciousness are material phenomena. But the Spiritualist, setting out
with the same data, may argue with equal cogency, that if the forces
displayed by matter are cognizable only under the shape of those
equivalent amounts of consciousness which they produce, it is to be
inferred tbat these forces, when existing out of consciousness, are of the
same intrinsic nature as when existing in consciousness ; and that so is
justified the spiritualistic conception of the external world, as consisting of
something essentially identical with what we call mind. Manifestly, the
establishment of correlation and equivalence between the forces of the outer
and the inner worlds, may be used to assimilate either to the other ; ac-
cording as we set out with one or other term. But he who rightly inter-
prets the doctrine contained in this work, will see that neither of these
terms can be taken as ultimate. He will see that though the relation of
subject and object renders necessary to us these antithetical conceptions of
Spirit and Matter ; the one is no less than the other to be regarded as but
a sign of the Unknown Reality which underlies both."

This is the conception which your reviewer continues to speak
of as " mechanical " and " mechanist ;" without giving his reade- s
any suspicion of the qualified sense in which only these words can
be applied. If he thinks that by doing this he has represented the
conception with fairness, or with any approach to fairness, I cannot,
agree with him.

I am, Sir,

Yours, &c,

HERBERT SPENCER.
London, December 5, 1868.

rxonm usiurt
N. C. State College

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