THE PLACENTATION OF PERAMELES. 385 



The Placentation of Perameles. 



(Contributions to the Embryology of tbe Marsupialia — I.) 



By 



Jas. P. Hill, 



Demonstrator of Biology in tlie University of Sydney, N.S.W. 



With Plates 29—33. 



Introduction. 



In a preliminary note (1) communicated to the Linnean 

 Society of New South Wales I recorded the occurrence 

 of an allantoic placenta in Perameles obesula, and 

 gave a short account of its structure based on an exami- 

 nation of a single stage, at that time the only one in my 

 possession. Since then, the acquisition of certain important 

 earlier and later stages has enabled me to study the placenta- 

 tion of Perameles in some detail, and the results of this 

 investigation are presented in the following pages. I am now 

 able not only to amplify the short statement of the preliminary 

 note, but to give a fairly connected account of what I believe 

 are the most important phenomena in the evolution of the 

 Perameles placenta. I am also now able to state that an 

 allantoic placenta in all respects similar to that of P. obesula 

 occurs in the closely related P. nasuta. The stages described 

 consecutively in the following pages have been derived from 

 these two species indifferently, just as pregnant individuals 

 chanced to come to hand ; but so far as I have been able to 

 make out, there are no recognisable differences in the details 



