easy course of investigation; we have also dealt with division, and
the mode of conducting it so as best to attain the ends of science,
and have shown why dichotomy is either impracticable or
inefficacious for its professed purposes.
Having laid this foundation, let us pass on to our next topic.
5
Of things constituted by nature some are ungenerated,
imperishable, and eternal, while others are subject to generation
and decay. The former are excellent beyond compare and divine, but
less accessible to knowledge. The evidence that might throw light on
them, and on the problems which we long to solve respecting them, is
furnished but scantily by sensation; whereas respecting perishable
plants and animals we have abundant information, living as we do in
their midst, and ample data may be collected concerning all their
various kinds, if only we are willing to take sufficient pains. Both
departments, however, have their special charm. The scanty conceptions
to which we can attain of celestial things give us, from their
excellence, more pleasure than all our knowledge of the world in which
we live; just as a half glimpse of persons that we love is more
delightful than a leisurely view of other things, whatever their
number and dimensions. On the other hand, in certitude and in
completeness our knowledge of terrestrial things has the advantage.
Moreover, their greater nearness and affinity to us balances
somewhat the loftier interest of the heavenly things that are the
objects of the higher philosophy. Having already treated of the
celestial world, as far as our conjectures could reach, we proceed
to treat of animals, without omitting, to the best of our ability, any
member of the kingdom, however ignoble. For if some have no graces
to charm the sense, yet even these, by disclosing to intellectual
perception the artistic spirit that designed them, give immense
pleasure to all who can trace links of causation, and are inclined
to philosophy. Indeed, it would be strange if mimic representations of
them were attractive, because they disclose the mimetic skill of the
painter or sculptor, and the original realities themselves were not
more interesting, to all at any rate who have eyes to discern the
reasons that determined their formation. We therefore must not
recoil with childish aversion from the examination of the humbler
animals. Every realm of nature is marvellous: and as Heraclitus,
when the strangers who came to visit him found him warming himself
at the furnace in the kitchen and hesitated to go in, reported to have
bidden them not to be afraid to enter, as even in that kitchen
divinities were present, so we should venture on the study of every
kind of animal without distaste; for each and all will reveal to us
something natural and something beautiful. Absence of haphazard and
conduciveness of everything to an end are to be found in Nature's
works in the highest degree, and the resultant end of her
generations and combinations is a form of the beautiful.
If any person thinks the examination of the rest of the animal
kingdom an unworthy task, he must hold in like disesteem the study
of man. For no one can look at the primordia of the human frame-blood,
flesh, bones, vessels, and the like-without much repugnance. Moreover,
when any one of the parts or structures, be it which it may, is
under discussion, it must not be supposed that it is its material
composition to which attention is being directed or which is the
object of the discussion, but the relation of such part to the total
form. Similarly, the true object of architecture is not bricks,
mortar, or timber, but the house; and so the principal object of
natural philosophy is not the material elements, but their
composition, and the totality of the form, independently of which they
have no existence.
The course of exposition must be first to state the attributes
common to whole groups of animals, and then to attempt to give their
explanation. Many groups, as already noticed, present common
attributes, that is to say, in some cases absolutely identical
affections, and absolutely identical organs,-feet, feathers, scales,
and the like-while in other groups the affections and organs are
only so far identical as that they are analogous. For instance, some
groups have lungs, others have no lung, but an organ analogous to a
lung in its place; some have blood, others have no blood, but a
fluid analogous to blood, and with the same office. To treat of the
common attributes in connexion with each individual group would
involve, as already suggested, useless iteration. For many groups have
common attributes. So much for this topic.
As every instrument and every bodily member subserves some partial
end, that is to say, some special action, so the whole body must be
destined to minister to some Plenary sphere of action. Thus the saw is
made for sawing, for sawing is a function, and not sawing for the saw.
Similarly, the body too must somehow or other be made for the soul,
and each part of it for some subordinate function, to which it is
adapted.
We have, then, first to describe the common functions, common,
that is, to the whole animal kingdom, or to certain large groups, or
to the members of a species. In other words, we have to describe the
attributes common to all animals, or to assemblages, like the class of
Birds, of closely allied groups differentiated by gradation, or to
groups like Man not differentiated into subordinate groups. In the
first case the common attributes may be called analogous, in the
second generic, in the third specific.
When a function is ancillary to another, a like relation
manifestly obtains between the organs which discharge these functions;
and similarly, if one function is prior to and the end of another,
their respective organs will stand to each other in the same relation.
Thirdly, the existence of these parts involves that of other things as
their necessary consequents.
Instances of what I mean by functions and affections are
Reproduction, Growth, Copulation, Waking, Sleep, Locomotion, and other
similar vital actions. Instances of what I mean by parts are Nose,
Eye, Face, and other so-called members or limbs, and also the more
elementary parts of which these are made. So much for the method to be
pursued. Let us now try to set forth the causes of all vital
phenomena, whether universal or particular, and in so doing let us
follow that order of exposition which conforms, as we have
indicated, to the order of nature.
Book II
1
THE nature and the number of the parts of which animals are
severally composed are matters which have already been set forth in
detail in the book of Researches about Animals. We have now to inquire
what are the causes that in each case have determined this
composition, a subject quite distinct from that dealt with in the
Researches.
Now there are thre
e degrees of composition; and of these the first
in order, as all will allow, is composition out of what some call
the elements, such as earth, air, water, fire. Perhaps, however, it
would be more accurate to say composition out of the elementary
forces; nor indeed out of all of these, but out of a limited number of
them, as defined in previous treatises. For fluid and solid, hot and
cold, form the material of all composite bodies; and all other
differences are secondary to these, such differences, that is, as
heaviness or lightness, density or rarity, roughness or smoothness,
and any other such properties of matter as there may be. second degree
of composition is that by which the homogeneous parts of animals, such
as bone, flesh, and the like, are constituted out of the primary
substances. The third and last stage is the composition which forms
the heterogeneous parts, such as face, hand, and the rest.
Now the order of actual development and the order of logical
existence are always the inverse of each other. For that which is
posterior in the order of development is antecedent in the order of
nature, and that is genetically last which in nature is first.
(That this is so is manifest by induction; for a house does not
exist for the sake of bricks and stones, but these materials for the
sake of the house; and the same is the case with the materials of
other bodies. Nor is induction required to show this. it is included
in our conception of generation. For generation is a process from a
something to a something; that which is generated having a cause in
which it originates and a cause in which it ends. The originating
cause is the primary efficient cause, which is something already
endowed with tangible existence, while the final cause is some
definite form or similar end; for man generates man, and plant
generates plant, in each case out of the underlying material.)
In order of time, then, the material and the generative process must
necessarily be anterior to the being that is generated; but in logical
order the definitive character and form of each being precedes the
material. This is evident if one only tries to define the process of
formation. For the definition of house-building includes and
presupposes that of the house; but the definition of the house does
not include nor presuppose that of house-building; and the same is
true of all other productions. So that it must necessarily be that the
elementary material exists for the sake of the homogeneous parts,
seeing that these are genetically posterior to it, just as the
heterogeneous parts are posterior genetically to them. For these
heterogeneous parts have reached the end and goal, having the third
degree of composition, in which degree generation or development often
attains its final term.
Animals, then, are composed of homogeneous parts, and are also
composed of heterogeneous parts. The former, however, exist for the
sake of the latter. For the active functions and operations of the
body are carried on by these; that is, by the heterogeneous parts,
such as the eye, the nostril, the whole face, the fingers, the hand,
and the whole arm. But inasmuch as there is a great variety in the
functions and motions not only of aggregate animals but also of the
individual organs, it is necessary that the substances out of which
these are composed shall present a diversity of properties. For some
purposes softness is advantageous, for others hardness; some parts
must be capable of extension, others of flexion. Such properties,
then, are distributed separately to the different homogeneous parts,
one being soft another hard, one fluid another solid, one viscous
another brittle; whereas each of the heterogeneous parts presents a
combination of multifarious properties. For the hand, to take an
example, requires one property to enable it to effect pressure, and
another and different property for simple prehension. For this
reason the active or executive parts of the body are compounded out of
bones, sinews, flesh, and the like, but not these latter out of the
former.
So far, then, as has yet been stated, the relations between these
two orders of parts are determined by a final cause. We have, however,
to inquire whether necessity may not also have a share in the
matter; and it must be admitted that these mutual relations could
not from the very beginning have possibly been other than they are.
For heterogeneous parts can be made up out of homogeneous parts,
either from a plurality of them, or from a single one, as is the
case with some of the viscera which, varying in configuration, are
yet, to speak broadly, formed from a single homogeneous substance; but
that homogeneous substances should be formed out of a combination of
heterogeneous parts is clearly an impossibility. For these causes,
then, some parts of animals are simple and homogeneous, while others
are composite and heterogeneous; and dividing the parts into the
active or executive and the sensitive, each one of the former is, as
before said, heterogeneous, and each one of the latter homogeneous.
For it is in homogeneous parts alone that sensation can occur, as
the following considerations show.
Each sense is confined to a single order of sensibles, and its organ
must be such as to admit the action of that kind or order. But it is
only that which is endowed with a property in posse that is acted on
by that which has the like property in esse, so that the two are the
same in kind, and if the latter is single so also is the former.
Thus it is that while no physiologists ever dream of saying of the
hand or face or other such part that one is earth, another water,
another fire, they couple each separate sense-organ with a separate
element, asserting this one to be air and that other to be fire.
Sensation, then, is confined to the simple or homogeneous parts.
But, as might reasonably be expected, the organ of touch, though still
homogeneous, is yet the least simple of all the sense-organs. For
touch more than any other sense appears to be correlated to several
distinct kinds of objects, and to recognize more than one category
of contrasts, heat and cold, for instance, solidity and fluidity,
and other similar oppositions. Accordingly, the organ which deals with
these varied objects is of all the sense-organs the most corporeal,
being either the flesh, or the substance which in some animals takes
the place of flesh.
Now as there cannot possibly be an animal without sensation, it
follows as a necessary consequence that every animal must have some
homogeneous parts; for these alone are capable of sensation, the
heterogeneous parts serving for the active functions. Again, as the
sensory faculty, the motor faculty, and the nutritive faculty are
all lodged in one and the same part of the body, as was stated in a
former treatise, it is necessary that the part which is the primary
seat of these principles shall on the one hand, in its character of
general sensory recipient, be one of the simple parts; and on the
other hand shall, in its motor and active character, be one of the
heterogeneous parts. For this reason it is the heart which in
sanguineous animals constitutes this central part, and in bloodless
animals it is that which takes the place of a heart. For the heart,
like the other viscera, is one of the homogeneous parts; for, if cut
up, its pieces are homogeneous in substance with each other. But it is
at the same time heterogeneous in virtue of its definite
configuration. And the same is true of the other so-called viscera,
which are indeed formed from the same material as the heart. For all
these viscera have a sanguineous character owing to their being
situated upon vascular ducts and branches. For just as a stream of
water deposits mud, so the various viscera, the heart excepted, are,
as it were, deposits from the stream of blood in the vessels. And as
to the heart, the very starting-point of the vessels, and the actual
seat of the force by which the blood is first fabricated, it is but
what one would naturally expect, that out of the selfsame nutriment of
which it is the recipient its own proper substance shall be formed.
Such, then, are the reasons why the viscera are of sanguineous aspect;
and why in one point of view they are homogeneous, in another
heterogeneous.
2
Of the homogeneous parts of animals, some are soft and fluid, others
hard and solid; and of the former some are fluid permanently, others
only so long as they are in the living body. Such are blood, serum,
lard, suet, marrow, semen, bile, milk when present, flesh, and their
various analogues. For the parts enumerated are not to be found in all
animals, some animals only having parts analogous to them. Of the hard
and solid homogeneous parts bone, fish-spine, sinew, blood-vessel, are
examples. The last of these points to a sub-division that may be
made in the class of homogeneous parts. For in some of them the
whole and a portion of the whole in one sense are designated by the