The Carides are distinguished from the Carcinoid species by the
presence of a tail; and from the Caraboids by the absence of claws.
This is explained by their large number of feet, on which has been
expended the material for the growth of claws. Their feet again are
numerous to suit their mode of progression, which is mainly by
swimming.
Of the parts on the ventral surface, those near the head are in some
of these animals formed like gills, for the admission and discharge of
water; while the parts lower down differ in the two sexes. For in
the female Carabi these are more laminar than in the males, and in the
female crabs the flap is furnished with hairier appendages. This gives
ampler space for the disposal of the ova, which the females retain
in these parts instead of letting them go free, as do fishes and all
other oviparous animals. In the Carabi and in the Crabs the right claw
is invariably the larger and the stronger. For it is natural to
every animal in active operations to use the parts on its right side
in preference to those on its left; and nature, in distributing the
organs, invariably assigns each, either exclusively or in a more
perfect condition, to such animals as can use it. So it is with tusks,
and teeth, and horns, and spurs, and all such defensive and
offensive weapons.
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