ON THE ORIGIN AND 



[CHAP. 



the Medusiform stage becomes less and less im- 

 portant. 



The great majority of the higher Crustacea go 



through well-marked metamorphoses. Figs. 37 and 



FIG. 37, Larva of Prawn, Nauplius stage (after F. Miiller). 38, Larva of Prawn, 

 more advanced, Zoe'a stage. 



38 represent two stages in the development of the 

 prawn. In the first (Fig. 37), representing the young 

 animal as it quits the egg, the body is more or less 

 oval and unsegmented ; there is a median frontal 

 eye, and three pairs of natatory feet, the first pair 

 simple, while the two posterior are two-branched. 

 Very similar larvae occur in various other groups of 

 Crustacea. They were at first regarded as mature 



