THE EARI.Y EMBRYOLOGY OF THE MOUSE 



rabbit, guinea pig and their close relatives, proved very puzzling to early 

 embryo legists, for the reason that it is the reverse of the condition found in 



IvV.^o" 



Maternal blood 



Ectoplacental cone 



Distal entoderm 



Proximal entoderm 



Extra -embryonic ectoderm 



Embryonic ectoderm 



Proamniotic cavity 



Yolk cavity 



Trophectoderm 



V ^l£±i 



Giant cell 



Degenerating uterine epithelium 





Fig. 8. — ^Longitudinal section at 5 days 12 hours after mating. Projection drawing 



(X300). 



all other chordates. It has been called the inversion of the germ layers. 

 While at first sight it seems to indicate a drastic alteration in early develop- 



