276 



THE EVOLUTION OF MAN. 



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

 portant germ-forms of the ideal Primitive Vertebrate (Fig. 52-61).'^ 



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



Fig. 63.-5. Thrt e-lajered germ. 



Fig. 61. — C. Four-lajered germ (four secondary germ-layers). 



