THE BIOLOGY OF THE FROG 



CHAP. 



B 



D 





H 



I 



FlG. 17. Segmentation of the egg and formation of the blastopore. ./, 

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

 C, thirty-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.) 



