Facts and Factors of Development 



FIG. 10. SURFACE VIEWS OF ENTIRE EGGS. A, before entrance of sper- 

 matozoon ; B, just after entrance of sperm; C, union of egg and sperm 

 nuclei ; D, 2-cell stage ; E, 4-cell stage ; F, 8-cell stage. 



FIG. ii. SECTIONS IN MEDT.VN PLANE OF EMBRYOS. 6", i6-32-cell stage; 

 H, blastula ; /, e.-irly gastrula ; /. late gastrula ; K f early embryo, L, late 

 embryo. 



