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. 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 the other two; and it was this
length which led nature to assign to them their hard support, so as to
ensure their straightness and inflexibility; just as she has
assigned to sanguineous animals their bones or their fish-spines, as
the case may be. To come now to Insects. In these the arrangement is
quite different from that of the Cephalopods; quite different also
from that which obtains in sanguineous animals, as indeed has been
already stated. For in an insect there is no distinction into soft and
hard parts, but the whole body is hard, the hardness, however, being
of such a character as to be more flesh-like than bone, and more
earthy and bone-like than flesh. The purpose of this is to make the
body of the insect less liable to get broken into pieces.
9
There is a resemblance between the osseous and the vascular systems;
for each has a central part in which it begins, and each forms a
continuous whole. For no bone in the body exists as a separate thing
in itself, but each is either a portion of what may be considered a
continuous whole, or at any rate is linked with the rest by contact
and by attachments; so that nature may use adjoining bones either as
though they were actually continuous and formed a single bone, or, for
purposes of flexure, as though they were two and distinct
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