114 CRUSTACEA. 



means of their feet, appear to us to establish a positive line of 

 demarcation between the former and the latter. We have 

 consulted several erudite naturalists with respect to these 

 transformations, but none of them have observed a change of 

 skin to occur. The antennse of the Entomostraca, whose form 

 and number greatly vary, serve for natation in several. The 

 eves are rarely placed on a pedicle, and when this is the case, 

 that pedicle is a mere lateral prolongation of the head, and is 

 never articulated at base ; they are frequently closely ap- 

 proximated and even form but one. The organs of genera- 

 tion are situated at the origin of the tail ; it hcjs been thought, 

 but erroneously, that their seat was in the antennse of the 

 male. This tail(l) is never terminated by a fan-like fin, nor 

 does it present those false feet observed in the Malacostraca. 

 The ova are collected under the back, or are external, and 

 covered by a common envelope, and resemble one or two 

 small clusters at the bast of the tail ; it appears that they can 

 be kept in a desiccated state for a long period without losing 

 their properties. 



It is only after a third change of skin that these animals 

 become adult and capable of continuing their species. It has 

 been proved, with resplct to some of them, that a single copu- 

 lation fecundifies several successive generations. 



ORDER I. • 



BRANCHIOPODA. 



A mouth composed of a labrum, two mandibles, a ligula, 

 and one or two pairs of jaws, and branchiae, the first of 



the form of the body or the number of feet. Tfeese organs in some, the Arguli for 

 instance, experience changes which modify their uses. 



(1) If we except the Phyllopa, the last feet are thoracic, or foot-jaws (Cypns). 



