BY JAS. P. HILL. 581 



processes. The uterine mucosa is very richly supplied with blood, 

 the maternal capillaries forming a network on and near the 

 surface of the mucosa, so that foetal and maternal blood are thus 

 brought into ver}'- close relation, readily allowing of transfusion. 

 The allantois of Perameles is thus functional both as a respiratory 

 organ and as an organ of nutrition — a distinct advance upon the 

 (according to Semon) purely respiratory function of the organ in 

 Fhascolarctus. 



In view of this discovery of a true allantoic placenta of the 

 discoidal type in Perameles, the Marsupialia as a class can no 

 longer be included among the Aplacentalia and the, up to this, 

 universally recognised character of Marsupials " no allantoic 

 placenta " likewise no longer holds good. 



The Macropod embr3^os available for examination consist of 

 intra-uterine embryos of Macropus parma, M. rnficollis, M. rohus- 

 ticfi, and Jf. major. In this note it need only be mentioned that 

 I am able to confirm Semon's belief that in the arrangement of 

 their foetal membranes Macropods would be found to conform to 

 his first type, as exemplified by Aepyprynuius, in which the 

 allantois never comes into any connection with the serous mem- 

 brane. 



I desire to tender my sincere thanks to Prof. J. T. Wilson for 

 many valuable suggestions during the course of my work. 



EXPLANATION OF PLATE. 



Diagram of the foetal membranes of Perameles ohesula. 



The ectoderm is indicated by a thin line, the mesoderm by a thick line, 

 and the entoderm by a dotted line. 



Reference letters. 



all.c, allantoic cavity; all.sf., allantoic stalk; amn., amnion; cce., extra- 

 embryonic coelom; vies., mesenchyme of outer surface of allantois fused 

 with mesenchyme of serous membrane; pro., prokalymma of Semon; s. t., 

 fcinus terminalis; ?(/., uterine wall; y.s., yolk sac; i/.s.iv., invaginated 

 portion of yolk sac wall. 



