BLASTULA, GASTRULA 



331 



larger quantity of yolk at the lower pole of the egg. For the 

 same reason the succeeding divisions take place slightly more 

 rapidly at the upper pole of the egg, and hence the cells 



Fig. 196. — Blastula. 



Fig. 197. — Blastula, later stage. 



Fig. 198.— Gastrulation. 



Fig. 199. — Gastrulation, later stage. 



here are also somewhat smaller. The cells have a decided 

 tendency to round up after division and so give the whole 

 somewhat the apjDearance of a mulberry. Hence, this is called 



