90 



THE BIOLOGY OF THE FROG 



CHAP. 



Fig. i6. — Segmentation of egg. (After Schultze.) A, two-cell stnge, 

 with the beginning of the second furrow ; B, eight-cell stage, showing 

 the cross furrow at the animal pole ; £, eight-cell stage ; C, D, F, C, 

 sixteen-cell stages, showing variations in the plan of cleavage ; H, thirty- 

 two-cell stage. (From Morgan's "Development of the Frog's Egg.") 



