159 



large number of publications have appeared, very mauy, ahnost 

 the bulk, of them due to the two investigators already referred 

 to, which have dealt more or less completely with the develop- 

 meut of the orgaii in question in the Rodentia, Cheiroptera, 

 Insectivora, Primates and Carnivora. 



These works I propose briefly to review iu the following pages ; 

 we shall then perhaps be iu a position to discuss the relation 

 between the modes of placeutatiou in the groups of mammals 

 already mentioued, and further to compare them with the much 

 less intimate connection which exists between the maternal and 

 foetal tissues in the 'Non-Deciduata', as well as with the pla- 

 centa of the Marsupials. 



Before proceediug any further, however, I must criticise soine- 

 what iu detail the only comprehensive account yet published of 

 the placeutation of the mouse, the form which I have myself 

 dealt with; I refer of course to the work of Duval (6). The 

 smaller papers of Burckhard (5), Nussbaum (34) and Klebs (24) 

 I shall notice afterwards. 



As I have already pointed out, I find myself in complete agree- 

 ment with all that Duval has said with regard to the arrao ge- 

 ment of the foetal membranes, and the topographical relations of 

 the placenta to the uterus. Also I have very little to add to the 

 account he has given of the formation and ultimate degeneration 

 of the capsularis and adjacent embryouic tissues, and of the 

 changes that take place during the first of his three periods in 

 the allantoidean trophoblast, and overlying subepithelial tissue. 

 What I have to say in this connection may be briefly stated. 



Firstly I must take exception to his terminology when he 

 speaks of subepithelial tissue as 'chorion muqueux', and when he 

 says that the 'capsularis' corresponds to the 'reflexa' in the human 

 subject, the 'placental' region to the 'serotina'. I think that most 

 embryologists will agree that the word 'chorion' should be restricted 

 to a formation of foetal origin; with regard to the second ob- 

 jection, I must point out that there is only an analogy, and not 

 a homology between the structures which Duval has compared, 



