276 



THE EVOLUTION OF MAN. 



"nif 



Fig. 62-69. — Diagrammatic transverse sections through the most im- 

 portant gei-m-forms of the ideal Primitive Vertebrate (Fig. 52-61).^^ 



Fig, 62, — A. Transverse section through the Gastrula ; two-layered germ. 



Fig. 63. — B. Three-layered germ. 



Fig. 64. — C. Four-layered germ (four secondary germ-layers). 



