METABOLIC GILVDIENTS 71 



region, and passing inward to form the mesoderm. 

 Most of the region of the embryo behind the head in 









['(gr 



^i 





16 



A 



(^1 



'^^ 



17 



Figs. 16, 17. — Transverse sections of chick embryo at ditTcrcnt 

 levels, to show developmental gradients. 



Fig. 14 and the extreme posterior region of the embr\'o 

 in Fig. 15 are at about this stage of development. 



