On The Parts Of Animals   

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.
On the Parts of Animals
By Aristotle
Written 350 B.C.E Part 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 three 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