ON CRUSTACEA. 
263 
which the sexual organs of the male have been observed, have 
them double, and placed under the first leaflets of the tail, 
where they are indicated by threads and hooks. 
The entomostraca are the only animals of this class, among 
which some are found whose sexes are not distinct. Never- 
theless, they are still separate in the limulse, for a considera- 
ble portion of the testa of these animals is filled in some of 
them by ovaries, and in otheis by organs which may be com- 
pared to the vasa deferentia, &c. of crabs and astaci. 
The caligi have at the posterior part of their body two cylin- 
drical threads, more or less long, divided into a multitude of 
small articulations, and which have been considered as exter- 
nal ovaries (but sometimes also as respiratory organs.) The 
branchipes have the sexes separate, and the males are easily 
distinguished from the. females, by the claws in the form of 
forceps, and the prehensile tentacula with which their head is 
furnished. 
All the individuals of the genus apus are conformed in a 
similar manner, and appear to be females, if they are not 
hermaphrodites. They have never been observed to couple. 
All have on each of the feet of the eleventh pair a capsule with 
two valves, enclosing the eggs, which are of a fine red. The 
limnadise appear to exhibit the same mode of generation. 
In the genus daphnis there are both females and males ; but 
the latter are infinitely more rare, and appear to exist like the 
males of the aphides, only at a certain period of the year. A 
single act of sexual intercourse suffices in these entomostraca, 
as in the aphides, to beget and impregnate seven or eight 
generations of females, which are developed in succession. 
The organ of generation in the female consists of two ovaries, 
whose form is that of vessels, and which extend on each side 
of the abdomen, from the first segment to the sixth, where 
they open separately on the back of the animal into an empty 
