Organisms from Eggs 



133 



of these cells and the egg begins to swim; we say it has 

 reached the first larval, the so-called blastula stage. 

 This happens according 

 to Driesch after the 

 tenth series of cell divi- 

 sions, when the number 

 of cells is theoretically 

 1024, in reality not quite 

 so many (between 800 

 and 900). The next step 

 consists in the cells de- 

 rived from the material 

 A (mesenchyme and mi- 

 cromeres) gliding into 



the hollow sphere, where they form a ring, the physico- 

 A chemical process respon- 



sible for this gliding being 

 yet unknown. At the 

 _g opening of this ring an ac- 

 tive growing of the cells 



of the entoderm into the 



-C 



hollow sphere takes place 



and the hollow cylinder 

 formed by this growth 

 is the intestine (Fig. 14). 

 Why the cells grow into 



Fig. 13 



Fig. 14 



the hollow sphere and not into the opposite direction 

 is unknown. The next step is the formation of a 



