Facts anil luw tors of Development 



25 



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 ; /:, 4-cell stage ; F, 8-cell stage. 



Fig. 11. Sections in Median Plane of Embryos. G, 16-32-cell stage; 

 H, blastula; /, early gastrula; /, late gastrula; A.', early embryo, /., late- 

 embryo. 



