276 



THE EVOLUTION OF MAN. 



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

 portant germ-forms of the ideal Primitive Vertebrate (Fig. 52-61). 89 



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



Fig. 63. — jB. Three-layered germ. 



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



