184 



formations are super-iruposed upon the débris of degenerating 

 glands; and inasmuch as this process of degeneration is always 

 preceded by hypertrophy and syncytial formation in the epithelium 

 of the glands itself, it is easy to understaud that the most careful 

 observation is necessary in order to distinguish between the two 

 syncytia of trophoblastic and of maternal origin. 



With regard to the disappearance of the surface epithelium the 

 balance of opinion seerns to be fairly equal ; with regard to the 

 formation of the syncytium statements are more diverse. 



Personally I have not at my disposal the mateiïal which would 

 enable me to come to a definite conclusion on my own account; 

 and I hardly think it legitimate to argue from other groups to 

 the Carnivora. But from what I have observed in the two late 

 stages of the Cat's placenta which I possess, 1 may perhaps say 

 that I think, judging merely by the accuracy of his figures of 

 these stages, that Duval has a very good claim to be believed. 



Geiieral remarks. 



As is well-known the placenta is an organ which has been largely 

 employed in determining the mutual relationships of the various 

 groups of Mammalia. Not only have the Eutheria been separated 

 from the Marsupials as Placental Mammals, but, further, the 

 characters of the placenta itself have been used first to divide 

 the Eutheria into 'non-decicluate' and 'deciduate' forms, and then 

 to subdivide the latter into the two groups of Zonoplacentalia, 

 including Hyrax, Elephas, and the Carnivora, and Discoplacentalia, 

 consisting of the Rodents, Insectivores, Bats, and Primates. 



As far as the possession of a placenta is concerned every one 

 will admit of course that the distinction between Metatheria and 

 Eutheria no longer exists. Hill (19) has shown that in Perameles 

 there is a very intimate connection between maternal and foetal 

 tissues, the latter being vascularized by the allantois; the con- 

 nection, indeed, is so intimate that at birth the foetal tissues 

 remain behind and are absorbed in situ. At the same time the 

 placenta so formed cannot be directly compared with that in any 



