THOEACOSTEACA. 



4G7 



lobed and used as jaws ; the four anterior maxillipeds are biramous 

 and act as biramous swimming feet ; and behind them, in the macru- 

 rous Decapods, the maxilliped of the third pair also appears as a 

 biramous swimming foot. Gills are as yet wanting, being repre- 



FIG. 307. Larva of Penaftig (after Fr. Miiller) . a, Nanplius form seen from the dorsal sur- 

 face. 6, Hetanauplius stage seen from the left side; MX', anterior maxilhv; Mx 1 ', pos- 

 terior maxilhe ; Ol, sixth and seventh pairs of appendages or first and second 

 maxillipeds. c, Zoa;a stage ; 0, eyes. 



sented by the thin surfaces of the sides of the cephalo-thoracic 

 shield, beneath which a continual current of water flowing from 

 behind forwards is kept up. A short heart with one or two pairs 



