18 .TAS. P. BILL. 



palmar surface directed iiiesially. Hind limb paddle-like, 

 digits not indicated, plantar surface directed mesially. 



Footal Membranes. 



The foetal membranes in M. par ma have the same general 

 arrangement as in ^pyprymnus rufescens, as described 

 by Semon (2, p. 25), i. e. the embryo enclosed in its amnion 

 lies in the extra-embryonic splanchnocoele surrounded by the 

 upper part of the yolk-sac — the yolk-sac splanchnopleure — 

 which is invaginated into the cavity of the latter. The 

 splanchnocoele is closed externally by a discoidal area of 

 chorion, round the margin of which the yolk-sac splanchno- 

 pleure becomes continuous with the vascular omphalopleure. 

 The allantois is a comparatively small short-stalked vesicle, 

 which never reaches and fuses with the chorion, but lies per- 

 manently buried in the splanchnocoele. 



The entire globular embryonic formation of this stage of 

 M. parma has a diameter of 15 mm. 



In Plate 2, fig. 9, the cavity of the yolk-sac has been 

 opened by the removal of the greater part of the bilaminar 

 omphalopleure, exposing the embryo in its amnion, closely 

 surrounded by the invaginated yolk splanchnopleure {y. spL), 

 together with the inner surface of the vascular area {vase. 

 ompJi.). 



The discoidal area of chorion, concealed in the figure by 

 the embryo, is readily distinguishable externally from the 

 vascular omphalopleure by its more transparent and smoother 

 appearance. Compared with the extent of the chorionic area 

 in Perameles and in Phascolarctus, where, according to 

 Caldwell (8), the chorion has a diameter of 12 mm., the area 

 is here a small one, measuring in greatest diameter 4'5 mm. 



The surface of the vascular area (vascular omphalopleure) 

 presents a roughened reticulate appearance in correspondence 

 with the ridged surface of the uterine mucosa. It is distin- 

 guished from the bilaminar omphalopleure by its denser and 

 darker appearance. The latter (Plate 2, fig. 9, Ml. omph.) 



