378 



CRUSTACEA ENTOMOSTRACA. 



the anterior antennae, which are usually short, the posterior are 

 modified to form biramous swimming appendages beset with 

 numerous long setae. The four to six pairs of legs are not always 

 foliaceous swimming feet, but in some cases have the form of 

 cylindrical ambulatory or prehensile appendages. The abdomen, 

 which is ventrally flexed, develops on its dorsal side several 



FIG. 251. Daphnia. A anus ; Br brood-pouch beneath the dorsal reduplicature of the 

 shell ; C Heart the slit-like opening of one side is visible ; D alimentary canal ; G cerebral 

 ganglion; L paired hepatic diverticulum ; O paired eye; Sd shell gland. (After Claus.) 



prominences, which serve to close the brood pouch. It usually 

 consists of three free segments, together with the terminal anal 

 portion, which is beset with rows of hooks. The anal portion 

 begins with two dorsal tactile setae and ends with two hooks or 

 styles, representing the caudal fork of other Entomostraca 

 (Fig. 251). 



The internal organization is simple in correspondence with the 

 small size of the body. The compound eyes (0) fuse together in 



