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. And
similarly no blood-vessel has in itself a separate individuality;
but they all form parts of one whole. For an isolated bone, if such
there were, would in the first place be unable to perform the office
for the sake of which bones exist; for, were it discontinuous and
separated from the rest by a gap, it would be perfectly unable to
produce either flexure or extension; nor only so, but it would
actually be injurious, acting like a thorn or an arrow lodged in the
flesh.
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