92 



THE BIOLOGY OF THE FROG 



CHAP. 



/ 



B 



H 



Fig. 17. — Segmentation of the egg and formation of the blastopore. A, 

 eight-cell stage seen from one side; i?, beginning of sixteen-cell stage; 

 C thirty-tvvo-cell stage; D, forty-eight-cell stage; E,F,a.x\d G, succes- 

 sive later stages of cleavage ; H, beginning of the blastopore in the torm 

 of a small crescent ; /, circular blastopore on the vegetative side of the 

 egg. (After Morgan.) 



