52 



DEVELOPMEXT OF THE FROG'S EGG [Cir. V 



B 



Fig. 18. — Diagrams to show extent of movement of dorsal lip of blastopore and 

 rotation (F) of embryo. (After Ptliiger.) 



yolk -plug. The diameter of the circle around the yolk-plug is 

 still smaller than before. At 2.15 p.m., the opening containing 



