365 



ation period of Didelphys as barely eight days, whicli if the above 

 time be reliable shows an exceedingly close agreement between the 

 two forms. 



Foetal Membranes, 



In their general arrangement and structnral relations the foetal 

 membranes of Dasyurus conform to the ordinary Marsupial type. 

 The outer wall limiting the entire embryonic vesicle, is distinguishable 

 as in other Marsupials into three zones, of which two are constituted 

 by the membrane bounding the yolk-sac cavity, and the third by the 

 chorion i. e. that part of the extra-embryonic somatopleure which re- 

 mains after separation of the amnion. For the former membrane 



'^ l/ii.omüfi. 



-- proA.l. 

 -■va.sc.ompk. 



a.mn. 



Diagram showing the arrangement of the foetal membranes in Dasyurus. 



amn. trunk amnion; all. allantois; Ml. omph. bilaminar omphalopleure; cä. chorion ; 

 ooe. extraembryonic splanchnocoele; proa, proamnion; proa. I. posterior limit of proam- 

 nion; s. t. sinus terminalis; vase. omph. vascular omphalopleure; y. c cavity of yolk 

 sac; y. s. yolk-stalk; y. spl. invaginated yolk-sac splanchnopleure. The ectoderm is 

 represented by a thin line, the entoderm by a dotted line and the mesoderm by a thick line. 



