In Insects this organ, which is the seat of sensation, lies, as
was stated in the first treatise, between the head and the cavity
which contains the stomach. In most of them it consists of a single
part; but in others, for instance in such as have long bodies and
resemble the Juli (Millipedes), it is made up of several parts, so
that such insects continue to live after they have been cut in pieces.
For the aim of nature is to give to each animal only one such dominant
part; and when she is unable to carry out this intention she causes
the parts, though potentially many, to work together actually as
one. This is much more clearly marked in some insects than in others.
The parts concerned in nutrition are not alike in all insects, but
show considerable diversity. Thus some have what is called a sting
in the mouth, which is a kind of compound instrument that combines
in itself the character of a tongue and of lips. In others that have
no such instrument in front there is a part inside the mouth that
answers the same sensory purposes. Immediately after the mouth comes
the intestine, which is never wanting in any insect. This runs in a
straight line and without further complication to the vent;
occasionally, however, it has a spiral coil. There are, moreover, some
insects in which a stomach succeeds to the mouth, and is itself
succeeded by a convoluted intestine, so that the larger and more
voracious insects may be enabled to take in a more abundant supply
of food.
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