On The Parts Of Animals   

milk may be dealt with in the treatise on Generation, for the former
of these fluids is the very starting-point of the generative process,
and the latter has no other ground of existence than generative
purposes.
Part 8
We have now to consider the remaining homogeneous parts, and will
begin with flesh, and with the substance that, in animals that have no
flesh, takes its place. The reason for so beginning is that flesh
forms the very basis of animals, and is the essential constituent of
their body. Its right to this precedence can also be demonstrated
logically. For an animal is by our definition something that has
sensibility and chief of all the primary sensibility, which is that of
Touch; and it is the flesh, or analogous substance, which is the organ
of this sense. And it is the organ, either in the same way as the
pupil is the organ of sight, that is it constitutes the primary organ
of the sense; or it is the organ and the medium through which the
object acts combined, that is it answers to the pupil with the whole
transparent medium attached to it. Now in the case of the other senses
it was impossible for nature to unite the medium with the sense-organ,
nor would such a junction have served any purpose; but in the case of
touch she was compelled by necessity to do so. For of all the
sense-organs that of touch is the only one that has corporeal
substance, or at any rate it is more corporeal than any other, and its
medium must be corporeal like itself.
It is obvious also to sense that it is for the sake of the flesh that
all the other parts exist. By the other parts I mean the bones, the
skin, the sinews, and the blood-vessels, and, again, the hair and the
various kinds of nails, and anything else there may be of a like
character. Thus the bones are a contrivance to give security to the
soft parts, to which purpose they are adapted by their hardness; and
in animals that have no bones the same office is fulfilled by some
analogous substance, as by fishspine in some fishes, and by cartilage
in others.
Now in some animals this supporting substance is situated within the
body, while in some of the bloodless species it is placed on the
outside. The latter is the case in all the Crustacea, as the Carcini
(Crabs) and the Carabi (Prickly Lobsters); it is the case also in the
Testacea, as for instance in the several species known by the general
name of oysters. For in all these animals the fleshy substance is
within, and the earthy matter, which holds the soft parts together and
keeps them from injury, is on the outside. For the shell not only
enables the soft parts to hold together, but also, as the animal is
bloodless and so has but little natural warmth, surrounds it, as a
chaufferette does the embers, and keeps in the smouldering heat.
Similar to this seems to be the arrangement in another and distinct
tribe of animals, namely the Tortoises, including the Chelone and the
several kinds of Emys. But in Insects and in Cephalopods the plan is
entirely different, there being moreover a contrast between these two
themselves. For in neither of these does there appear to be any bony
or earthy part, worthy of notice, distinctly separated from the rest
of the body. Thus in the Cephalopods the main bulk of the body
consists of a soft flesh-like substance, or rather of a substance
which is intermediate to flesh and sinew, so as not to be so readily
destructible as actual flesh. I call this substance intermediate to
flesh and sinew, because it is soft like the former, while it admits
of stretching like the latter. Its cleavage, however, is such that it
splits not longitudinally, like sinew, but into circular segments,
this being the most advantageous condition, so far as strength is
concerned. These animals have also a part inside them corresponding to
the spinous bones of fishes. For instance, in the Cuttle-fishes there
is what is known as the os sepiae, and in the Calamaries there is the
so-called gladius. In the Poulps, on the other hand, there is no such
internal part, because the body, or, as it is termed in them, the
head, forms but a short sac, whereas it is of considerable length in