FCETAL NUTRITION: THE PLACENTA 409 



chorion, and fit into vascular crypts in the uterine mucosa 

 from which they are easily retracted at birth. The epithelium 



. 



Q 3 







-M 



CM 



o 



II 

 II 



of the crypts persists as in the cow, and the " osmotic inter- 

 change takes place through two cell-layers of different origin, 

 and of different physiological significance (phylogenetically). 



