104 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



;. B). The characteristic features of the gastrula 

 >hupe is cup-like, (2) that it has a simple internal cavity 



3 T3 



H-s 



irchenteron which romiminirates with the exterior by a single 

 primitive mouth or protostoma, and (3) that its wall consists 



