CLASS OF CRUSTACEA. 



489 



from the thorax, and this last part of the body is composed 

 of a series of seven rings, each carrying a pair of limbs. 

 Thus, as we have already said, there is not any carapace, the 

 eyes are not pedunculated, there are no branchiae properly so 

 called, but the respiration is performed by means of various 

 appendages borrowed from the locomotory apparatus. Na- 

 turalists arrange under this group, 



1. The amphipoda, which have the abdomen well developed, 

 and carry under the thorax a double series of respiratory 

 vesicles, formed by the internal branchiae of the limbs. The 

 prawns of rivulets and the talitri (Fig. 169) offer us these 

 characters. 



2. The loemodipoda, which resemble the preceding in the 

 disposition of the organs of respiration, but which have only 

 a rudimentary abdomen. 



Fig. 518. Anilocra. 



Fig. 519. Limnadia.* 



3. The isopoda, in whom the abdomen is, on the contrary, 

 well developed, and carries beneath a series of false branchial 

 limbs. The anilocra (Fig. 518), the sphaeroma, and the class 

 woodlouse, cloportus (oniscus) belong to this order. 



576. The branchiopoda, as we have already said, are 

 small crustacea, whose limbs no longer serve for walking, but 

 assume the form of foliaceous plates, constituting at one and 

 the same time organs of natation and respiration. Such are the 

 limnadiae, which have been already mentioned (Fig. 519), the 



* One of the valves of the carapace has been amoved. 



