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 

 limnadiae 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 



