CH. IV] 



CLEAVAGE OF THE EGG 



33 



infolding of the outer harder crust of the egg. These wrinkles 

 are best seen in the upper hemisphere ; subsequently they dis- 

 appear. It will be found on cutting in two an egg in the 

 process of cleavage that the furrow is also extending through 



B 



D 



H 



FIG. 12. Segmentation of egg and formation of blastopore (H, I). A. Eight-cell 

 stage. B. Beginning of sixteen-cell stage. C. Thirty-two-cell stage. D. Forty- 

 eight-cell stage (unusually regular) . E, F. Two sides of same egg in later cleavage. 

 G. Still later cleavage. H. Dorsal lip of blastopore. I. Circular blastopore (with 

 lower pole toward observer). 



the protoplasm of the egg, i.e. dividing the contents into two 

 parts. When the superficial furrow has encircled the egg, the 

 substance also has been divided. 



