452 CRUSTACEA. 



and a long multiarticulate flagellum, which, however, may be more or 

 less rudimentary. The anterior antennae, which are always longer 

 in the male, often bear a short accessory flagellum and present 

 numerous modifications in their special form. In the Hyperina they 

 are very short in the female ; while in the male they are of consider- 

 able length and are closely beset with olfactory hairs. The posterior 

 antennae are frequently longer than the anterior : in the male 

 TyphidiK they are folded in a zigzag fashion, and in the Corophiidee 



Ov I* H 



G. 357. Pkronima, gedentaria, a, female; I, male. O, eyes; A, A!', the two pairs of an 

 tennse ; Kf, jaws ; D, intestine ; H, heart and aorta ; E, gills ; OB, ovary ; N, nervous 

 system ; Dr, glands in the chela of the fifth pair of legs ; G, genital opening. 



are modified to form strong pediform appendages. In the female, on 

 the contrary, they may be degenerated and represented only by the 

 basal joint (Pkronima) (fig. 357, a and b). 



The mandibles are powerful biting plates with a sharp, usually 

 toothed edge and a lower masticating process. They usually possess a 

 three-jointed palp, which is occasionally reduced. The anterior bi- 



