EMBRYOLOGY OF ECHINODER3IS. 



123 



like ; and long, perforated spines (x) run from their prox- 

 imal ends inwards and forwards over the dorsal surface 

 of the stomach. A similar process (e) is sent inwards and 

 forwards over the ventral surface of the stomach from the 



Fig. 71. 

 Fig. 71. — Dorsal view of the fully developed pluteus of Arbacia 

 ?imctulata. (Drawn from nature by Mr. B. P. Colton.) 

 For explanation see Fig. 73. 



