9 2 



THE BIOLOGY OF THE FROG 



CHAP. 



B 



\ ■ • y 



H 



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

 eight-cell stage seen from one side; />', beginning of sixteen-cell stage; 

 C, thirtv-two-cell stage; D, forty-eight-cell stage; E, F, and G, succes- 

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

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

 egg. (After Morgan.) 



