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of reagents, as well as by the exarnination of the tissues fresh, 

 I raight be able to add something to the description he had al- 

 ready given; and even if this were not the case, I feit that I 

 should at least have learnt the anatomy of the placenta. 



The somewhat extended investigation which I have now com- 

 pleted enables me to corroborate very many of Duval's statements; 

 indeed, as an account of the formation of the greater part of the 

 placenta from tissues which are entirely, (if we except the ma- 

 ternal blood) of embryonic origin, and of the topographical rela- 

 tions between the foetal membranes and the uterus, his description 

 leaves very little to be desired ; and it would be quite super- 

 fluous on my part to do more than refer the reader to his figures 

 and my own diagrams (Figs. 8 — 11) merely remarking that for 

 'ectoplacenta' I have substituted Hubrecht's expression 'trophoblast', 

 to signify the layer of cells which, as I have elsewhere pointed 

 out, is homologous with the false amnion of the Sauropsida, and 

 plays an all-important part in the nutrition of the mammalian 

 embryo. 



On the other hand I am obliged to differ in many respects 

 from what Professor Duval has said of the complicated histolog- 

 ical changes that take place during the development of the pla- 

 centa; I prefer therefore to postpone a critical consideration of 

 his views until I have given a detailed description of my own 

 observations. I shall then, I hope, be in a position to discuss from 

 the comparative standpoint the processes of a similar nature which 

 are known to occur in other mammals. 



First, however, I must refer briefly to the methods I have employed. 



In all stages of placentation the uteri have been preserved in 

 toto in corrosive sublimate, corrosive sublimate and acetic with 

 and without the addition of absolute alcohol, in Perenyi's fluid and 

 in Mann's picro-corrosive-formol. Further, in the youngest stages, 

 the uteri have been injected with various fixing reagents, prin- 

 cipally with Flemming, Hermann, and other osmic mixtures; in 

 later stages the uteri have been cut into segments, the muscularis 

 cut through on the anti-mesometric side, and the pieces placed 



