shows a ventral view of a male and female preserved crayfish.
The male is easily distinguished from the female by the presence of
a pair of modified first swimmerets called gonopods, which are
enlarged and directed forward. These structures are used by
the male to transfer sperm to the female. Note also the small
openings to each vas deferens at the bases of the fifth pairs of
walking legs (the right leg of this specimen has been
removed). The vasa deferentia conduct sperm from the testes to
the outside of the crayfish. On the female crayfish observe
the opening to the seminal receptacle (which receives sperm from the
male) as well as the openings to the oviducts at the bases of the
third pairs of walking legs.