420 



H. H. Newman and J. T. Patterson. 



19 



p,s. 



P'iG. 18. A section taken through the middle of the head process. In this region 

 the entoderm is very intimately associated with the mesoderm, especially in the 

 central part of the section. X 130. 



P'iG. 19. A section taken through the primitive pit. It shows the primitive 

 streak proliferating mesoderm in the characteristic manner. X 130. 



