FCETAL NUTRITION: THE PLACENTA 383 



glandular secretion and a lymph transudate almost devoid of 

 cells. It is absorbed by the trophoblast cells, which here and 

 there enlarge to enormous " Nahrzellen " and so increase the 

 absorbing surface. After eight days the food supply becomes 

 inadequate for the developing embryos, and they are transferred 

 to the pouch and nourished by the mammary secretion. 



bit omph. 



proa I 



vascomph. 

 amn. 



-yspi 



ch 



FIG. 79. Diagram showing the arrangement of the foetal membranes in 

 Dasyurus. (From Hill, "On the Foetal Membranes, Placentation and 

 Parturition of the Native Cat (Dasyurus viverrinus)," Anat. Anzeig., 

 vol. xviii., 1900. 



amn., trunk amnion ; all, allantois ; bil.omph, bilaminar omphalopleur ; 

 ch, chorion (diplo-trophoblast) ; coe, extra-embryonic splanchnocele ; 

 proa, proamnion ; proa.l, posterior limit of proamnion ; s.t, sinus ter- 

 minalis ; vasc.omph. vascular omphalopleur ; y.c, cavity of yolk-sac ; y.s, 

 yolk-stalk; yspl, invaginated yolk-sac splanchnopleur : the ectoderm is 

 represented by a thin line, the entoderm by a dotted line, and the 

 mesoderm by a thick line. 



In Dasyurus the allantois is vascular over a small area and 

 comes in contact with the diplo-trophoblast (Fig. 79). But the 

 allantoic vessels degenerate rapidly and completely, and the 

 allantois again lies free in the coelom. In the region of the area 

 vasculosa the wall of the yolk-sac adheres to the uterine 

 epithelium, and, as in the opossum, forms a simple yolk-sac 



