On The Parts Of Animals   

Every systematic science, the humblest and the noblest alike, seems to
admit of two distinct kinds of proficiency; one of which may be
properly called scientific knowledge of the subject, while the other
is a kind of educational acquaintance with it. For an educated man
should be able to form a fair off-hand judgement as to the goodness or
badness of the method used by a professor in his exposition. To be
educated is in fact to be able to do this; and even the man of
universal education we deem to be such in virtue of his having this
ability. It will, however, of course, be understood that we only
ascribe universal education to one who in his own individual person is
thus critical in all or nearly all branches of knowledge, and not to
one who has a like ability merely in some special subject. For it is
possible for a man to have this competence in some one branch of
knowledge without having it in all.
It is plain then that, as in other sciences, so in that which inquires
into nature, there must be certain canons, by reference to which a
hearer shall be able to criticize the method of a professed
exposition, quite independently of the question whether the statements
made be true or false. Ought we, for instance (to give an illustration
of what I mean), to begin by discussing each separate species-man,
lion, ox, and the like-taking each kind in hand inde. pendently of the
rest, or ought we rather to deal first with the attributes which they
have in common in virtue of some common element of their nature, and
proceed from this as a basis for the consideration of them separately?
For genera that are quite distinct yet oftentimes present many
identical phenomena, sleep, for instance, respiration, growth, decay,
death, and other similar affections and conditions, which may be
passed over for the present, as we are not yet prepared to treat of
them with clearness and precision. Now it is plain that if we deal
with each species independently of the rest, we shall frequently be
obliged to repeat the same statements over and over again; for horse
and dog and man present, each and all, every one of the phenomena just
enumerated. A discussion therefore of the attributes of each such
species separately would necessarily involve frequent repetitions as
to characters, themselves identical but recurring in animals
specifically distinct. (Very possibly also there may be other
characters which, though they present specific differences, yet come
under one and the same category. For instance, flying, swimming,
walking, creeping, are plainly specifically distinct, but yet are all
forms of animal progression.) We must, then, have some clear
understanding as to the manner in which our investigation is to be
conducted; whether, I mean, we are first to deal with the common or
generic characters, and afterwards to take into consideration special
peculiarities; or whether we are to start straight off with the
ultimate species. For as yet no definite rule has been laid down in
this matter. So also there is a like uncertainty as to another point
now to be mentioned. Ought the writer who deals with the works of
nature to follow the plan adopted by the mathematicians in their
astronomical demonstrations, and after considering the phenomena
presented by animals, and their several parts, proceed subsequently to
treat of the causes and the reason why; or ought he to follow some
other method? And when these questions are answered, there yet remains
another. The causes concerned in the generation of the works of nature
are, as we see, more than one. There is the final cause and there is
the motor cause. Now we must decide which of these two causes comes
first, which second. Plainly, however, that cause is the first which
we call the final one. For this is the Reason, and the Reason forms
the starting-point, alike in the works of art and in works of nature.
For consider how the physician or how the builder sets about his work.
He starts by forming for himself a definite picture, in the one case
perceptible to mind, in the other to sense, of his end-the physician
of health, the builder of a house-and this he holds forward as the