Various Works

  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