PHYLUM ARTHROPODA — CLASS CRUSTACEA 



285 



of the race. Briefly stated ontogeny recapitulates pliylogeny. There 

 is still some doubt as to the validity of this generalization in direct 

 application. 



A classical example which is frequently cited is that of the devel- 

 opment of the shrimp, Penaeus, which hatches out as a nauplius larva, 



Nftuplius «t*c{<« 



Fig. 160. — Nauplius stage of the barnacle, Balanus. (Courtesy of General Bio- 

 logical Supply House.) 



Fig. 161, 



iSchizopod 



Fig. 162. 



Fig. 161. — Zoea and Megalops stages of developing Crustacea. Crabs include 

 these stages in their development. (Courtesy of General Biological Supply House.) 



Fig. 162. — Schizopod or mysis stage through which the shrimp and lobster pass. 

 (Courtesy of General Biological Supply House.) 



having a single median eye and only three pairs of appendages. 

 Following the molt, this nauplius changes to become the Prozoea 

 stage, possessing six pairs of appendages. The next molt brings on 

 segmentation and some change in form. This stage is called the Zoea 



