52 



DEVELOPMENT OF THE FROG'S EGG [Cn. V 



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

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



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

 still smaller than before. At 2.15 P.M., the opening containing 



