EMBRYONIC AND LARVAL HISTORIES 71 



of typically three paired coelomic pouches (Fig. 16 

 a.c., m.c. and JP.&), which are derived as paired hollow 

 outgrowths from the gut. It will be noticed that 

 this mode of origin of the coelom is very different from 

 that which occurs in the Trochosphere larva, where 



- - a. c. 



Fig. 16. Diagram of Auricularia larva of an Echinoderm, seen from 

 the right side. m. mouth; an. anus; r. post-oral ciliated band; 

 a.c. anterior left coelom sac which will' be converted into the axial 

 sinus; m.c. middle left coelom sac which will be converted into 

 the hydrocoel ; p.c. posterior left coelom sac which will form 

 gonocoel or the reproductive organs. The corresponding coelom 

 sacs of the right side are not shown. 



the coelomic mesoblast forms two paired solid bands 

 of cells which become subsequently segmented and 

 hollowed out to form the segmented coelom sacs of 

 the adult. The fate of the coelom pouches of the Au- 

 ricularia is also very different from that of the coelom 



