Distal entoderm ■ 



Proximal entoderm 



Extra-embryonic 

 ectoderm 



Embryonic ectoderm 





Maternal blood 



Secondary giant cell 





© 



^3- ^®' 



(5s/5.^ 





8^1 ^=2:^^0^ Ectoplacental cone 



Posterior amniotic fold 



Proamniotic cavity 



-Reichert's membrane 



Fig. io. — Scagittal section of mouse embryo of 6 days 13 hours, showing early 

 stage of mesoderm formation. Projection drawing (X300) except that Reichert's 

 membrane is drawn in part from adjacent section. 



14 



