x FOWL— THIRD DAY 535 



the front end of the brain is reversed in position, what was its 

 ventral side having come to be dorsal. 



The mesoderm segments have increased in number there being 



of amnion; am, amnion; E t eye; H, heart; m.s, mesoderm segments; ot f otocyst; 

 8, indications of preotic mesoderm segments (?) ; v.a, vitelline artery ; v.c, visceral cleft II ; *, portion 

 of splanchnopleure bulging downwards into the yolk, forming a recess in which, lies the head of the 

 embryo. 



now about 25-30 metotic segments and those towards the anterior 

 end are showing a considerable amount of dorsiventral growth. 

 In some embryos (Fig. 236) the series of definitive mesoderm seg- 

 ments is continued far into the head region by what appear to 



