382 



OSBORAr. 



[Vol. I. 



EXPLANATION OF PLATE. 



al. Region of the chorion, contain- 

 ing the allantois and stalk of 

 the yolk-sac. 



amb. Amoeboid attaching cells, cov- 

 ering yolk-sac placentae. 



tia. Umbilical arteries. 



be. Blood corpuscles. 



d. d. Ducts of utricular glands. 



e. Embryos. 



ep. Epithelium, forming inner lining 



of uterine wall. 

 fb. Fcetal blood-vessels of yolk-sac 



placenta. 



m. hy. Mesoblast and hypoblast (?) of 



yolk-sac. 

 ov. Ovary. 

 ovd. Oviduct. 

 s. Septa from muscular into mucous 



coat of uterus. 

 5/. Sinus terminalis. 

 sz. Subzonal membrane. 

 ub. Utricular blood-vessels. 

 ut. f. Folds of uterine wall. 

 ut. Muscular wall of uterus. 

 z^g. Vagina. 

 yp. Yolk-sac placenta. 



Fig. I. — Right uterus of Didclphys, with a portion of the wall removed, 

 showing the arrangement of the embryos, the folds of the uterine wall, and 

 the series of yolk-sac placentae. Two embryos, e^ and e^, have been re- 

 moved. The specimen as drawn is now preserved in the Morphological 

 Laboratory. The drawing represents twice the natural size. 



Fig. 2. — Two Didelphys embryos in which the yolk-sac placentre are free, 

 while other portions of the chorion have coalesced with each other and with 

 the amnion of one of the embryos, Ci The second embryo e' has lost its amni- 

 otic investment. 



Fig. 3. — An enlarged section of a portion of the entire uterine walls with 

 one of the folds and the edge of one of the yolk-sac placentae in situ. The 

 drawing is semi-diagrammatic. The thicker portions of the placenta, yp, 

 represent areas where the attaching cells are cut obliquely. 



Fig. 4. — Camera drawing of the edge of one of the yolk-sac placentae 

 ■with a subjacent fold of the uterine wall. Enlarged about 350 diameters. 



