EMBRYONIC AND LARVAL HISTORIES 65 



development, but the abdomen is segmented and well 

 formed and the last abdominal segment has its broad 

 plate-like appendages precociously developed. Now 

 although this larval form occurs with only minor 



Fig. 13. Metazoaea, of Corystes cassivelaunus ( x 13). Ab. 3rd ab- 

 dominal segment; G. gills; M. 1st maxillipede; T 8, last thoracic 

 appendage. (After Gurney.) 



variations in such widely different animals as prawns, 

 hermit crabs and true crabs, and thus is in accord- 

 ance with Von Baer's law, yet it cannot possibly 

 be looked upon as representing the adult ancestral 

 type of these animals. The retarded development of 



S. A. K. 5 



