Dipterous insects
never have a posterior sting. For the very reason of their being
dipterous is that they are small and weak, and therefore require no
more than two feathers to support their light weight; and the same
reason which reduces their feathers to two causes their sting to be in
front; for their strength is not sufficient to allow them to strike
efficiently with the hinder part of the body. Polypterous insects,
on the other hand, are of greater bulk-indeed it is this which
causes them to have so many feathers; and their greater size makes
them stronger in their hinder parts. The sting of such insects is
therefore placed behind. Now it is better, when possible, that one and
the same instrument shall not be made to serve several dissimilar
uses; but that there shall be one organ to serve as a weapon, which
can then be very sharp, and a distinct one to serve as a tongue, which
can then be of spongy texture and fit to absorb nutriment. Whenever,
therefore, nature is able to provide two separate instruments for
two separate uses, without the one hampering the other, she does so,
instead of acting like a coppersmith who for cheapness makes a spit
and lampholder in one. It is only when this is impossible that she
uses one organ for several functions.
The anterior legs are in some cases longer than the others, that
they may serve to wipe away any foreign matter that may lodge on the
insect's eyes and obstruct its sight, which already is not very
distinct owing to the eyes being made of a hard substance.
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