EMBRYOLOGY OF ECHINODERMS. 



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. Dorsal view of the fully developed pluteus of Arhacia 

 punctulata. (Drawn from nature by Mr. B. P. Colton.) 

 For explanation see Fig. 73. 



