THE OSTRACODA 



63 



secondary shifting of position. A similar organ has been found in 

 one species of Cijpridina. 



It is not unlikely that at least one pair of limbs is involved in 

 the composition of the penes of male Ostracods. 



Aliwenfavn System. — The oesophagus is narrow and has nniscular 

 walls. Its upper or posterior end projects into the capacious niid- 



FiG. 37. 



A, f'oMith post-oial a]ipeiidage of CypridUia mediterranea. B, tlio samo of Mocrociipri.i 

 suixijica. C, lifth post-oral appeiifiaj^e of Cypridina inediterranea. D, tlift .same of Macroctiprin 

 succinea. K, one lariuis of the caudal (area, of Cypridina sqv.aniosii, seen from the side. (After 

 G. W. Miiller.) 



gut, and in the Podocopa is armed internally with chitinous ridges 

 and teeth. In the Bairdiidae this apparatus is most fully developed 

 and forms an efficient "gastric mill," moved by extrinsic and 

 intrinsic muscles, for the trituration of the food. 



The mid-gut in the Podocopa is divided into two parts by a con- 

 striction. Hepatic caeca may be absent as in Ci/pridina, numerous 

 and small as in Ilaloci/jiris, or large and reduced to a single pair 

 which may extend into the shell-ca\ity, as in Cyprididae. 



