PLACENTA IN PERAMELES 175 



of placentatioii which undoubtedly obtained in the original 

 protoplacental group. 



Into a full treatment of this there is no need for me to enter. 

 It has been ably discussed by Hill and the facts and conclu- 

 sions embodied in the preceding pages can only l)e regarded as 

 confirming and strengthening his expressed opinions. 



(d) The E e 1 a t i o n of the Allantoic Placenta- 

 t i o n of P e r a m e 1 e s to that of the E u t h e r i a . 



This question I will discuss but briefly, reserving its full 

 treatment for some future occasion when adequately fixed 

 and preserved late gestation stages of Perameles may 

 perhaps be available. 



It is with some pleasure that I have been able to bring the 

 method of allantoplacental formation of Perameles into 

 line with that occurring in the simpler Eutherian forms. In 

 fact it may be said in general that the only difference between 

 the two is one of degree. There are the same characteristics 

 of passivity of the uterine epithelium and activity of the 

 trophoblast with a division of the latter into a cytoblastic and 

 plasmodial layers. After preliminary diploplasmatic prepara- 

 tion the allantois becomes fixed and an apposition of the two 

 blood-streams becomes effected. I might here briefly refer 

 to the resemblances between the earlier stages of allanto- 

 placentation in Perameles and the dog and rabbit. In 

 Text-fig. 3 I have indicated the main points of Schoenfeld's 

 fig. 14 (1903) representing an early stage of chorionic invasion 

 in the dog. A somewhat comparable stage in Perameles is 

 represented by Text -fig. 4. The agreement in the method of 

 foetal invasion is evident. In the dog, however, according to 

 Schoenfeld, the uterine epithelium does not form a syncytium. 



In the rabbit, on the other hand, as in many other E u t h e r i a , 

 such a maternal syncytium is. formed, and here the early stages 

 show an even more significant resemblance to those occurring 

 in Perameles. Particularly I may refer to Schoenfeld's 

 (1903) figs. 4, 5, and 6, PI. xxi, and those of Maximow (1900, 

 figs. 1 and 2, PI. xxx). 



