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. u. SECTIONS IN MEDIAN PLANE OF EMBRYOS. G, i6-32-cell stage; 

 //, blastula ; 7, early gastrula; /, late gastrula; K t early embryo, L, late 

 embryo. 



