346 REPRODUCTION 



Fetal Membranes. 



Umbilical Vesicle. The umbilical vesicle represents that 

 part of the vitellus which has not been constricted off to form 

 the gut tract. (Figs. 101, 102, 103.) It furnishes nutriment to 

 the embryo for a short time and is then largely cut off from 

 the body. It gradually shrivels (Figs. 107, 108), and with that 

 part of the duct external to the abdomen is cast off either before 



FIGS. 1 02 AND 103. 



a, chorion with villi. The yilli are shown to be best developed in the part of the 

 chorion to which the allantois is extending; this portion ultimately becomes the 

 placenta; b, space between the true and false amnion; c, amniotic cavity; d, situation 

 of the intestine, showing its connection with the umbilical vesicle; e, umbilical 

 vesicle;/, situation of heart and vessels; g, allantois. (Kirkes.) 



or at parturition. .Vessels develop in its walls and absorb the 

 nourishment in it to be conveyed to the embryo. But in the 

 human being more satisfactory arrangements for nutrition are 

 soon made and its function ceases. 



Amnion. When the embryo has become depressed, as it 

 were, into the substance of the blastoderm, and while the body 

 cavity is being formed, the layers of the somatopleure grow up 

 over the embryo to meet and blend dorsally. (Figs. 107, 108.) 

 The two layers of which the somatopleure is composed separate , 



