PLACENTA IN PERAMELES 173 



well's statement (1884) that there is such a union in the case 

 of H a 1 m a t u r u s r u f i c o 1 1 i s , as well as his testimony of 

 a fusion between the bilaminar omphalopleure and the uterine 

 wall, have not yet been confirmed. An omphaloplacenta is 

 well developed in Macropods. 



Phalangeridae. — In Trichosurus vulpecula (Hill, 

 1889) and Petaurus sciureus (Semon, 1894) the allantois 

 is similar to that of Macropods. I am also able to state that 

 this is the case for P s e u d o c h i r u s c o o k i . Here again the 

 embryo depends on the work of the trophoblast both of the 

 vascular omphalopleure and of the bilaminar omphalopleure. 



Phascolarctus . — This genus is particularly interesting in 

 possessing, according to Caldwell (1883) and Semon (1894), 

 a respiratory allantois. There is a well-developed omphalo- 

 placenta and also a union in the metrioplacenta between an 

 annular zone of the bilaminar omphalopleure (just outside the 

 simus terminalis) and the uterine mucosa. 



Didelphys. — The allantois does not meet the chorion. 

 The omphaloplacenta is well developed. Certain portions of 

 the ectoderm of the bilaminar omphalopleure are stated by 

 Selenka to form absorptive proliferations similar to those found 

 in certain Eutheria, for example Manis (Weber), and 

 Equus (Ewart). 



Dasyurus. — The allantois shows interesting stages in 

 degeneration. At a particular stage it becomes applied to the 

 chorion which is itself in intimate association with the uterine 

 mucosa. Later the allantois withdraws from the chorion and 

 degenerates considerably, its vascular system practically 

 disappearing. An omphaloplacenta is present as well as a 

 similar annular fusion of the bilaminar omphalopleure with 

 the uterine wall as occurs in Phascolarctus. 



Perameles . — This is a most primitive form possessing 

 a well-developed allantoic placenta and an omphaloplacenta, 

 and there is considerable evidence of absorption in the bilaminar 

 omphalopleure. 



From the above abstract it will be seen that we can, as yet, 

 hardly be said to have a detailed knowledge of the structure, 



