306 



COMPARATIVE ANATOMY 



blastic tissue into which the allantoic villi do not penetrate. 

 The omphaloidean placenta has disintegrated and disappeared 

 altogether, and with it the distal wall of the yolk-sac, so that 

 now the epithelium of the proximal wall of the yolk-sac is 



Fig. 77 



Diagrammatic transverse section of a pregnant uterus, illustrating the later 

 phase of placentation. all, allantois ; am, amnion ; bv, uterine blood- 

 vessels ; em, embryo; gt, uterine glands; /w 2 , secondary lumen of 

 uterus ; ms.m, mesometrium ; mus, muscular wall of uterus ; PI, 

 allantoidean placenta ; p.yk, proximal wall of yolk-sac ; umb, stalk of 

 yolk-sac ; Ut, uterus. 



exposed in the new lumen of the uterus, from which it 

 absorbs nutriment in the form of fat globules secreted by 

 the uterine glands. At an earlier stage certain cells in 

 the uterine wall in the region of the allantoidean placenta^ 

 were full of glycogen granules, and now somewhat similarj 



