144 T. THOMSON FLYNN 



preparatory proliferatioji is soon interfered with by the destruc- 

 tive action of the blastocyst on the uterine epithelium. 



Hill (1897, p. 398) institutes a comparison between Pera- 

 meles and Sorex in the matter of the proliferation of the 

 uterine epithelium. As a consequence, however, of his belief 

 in the degeneration of the chorionic ectoderm and the 

 persistence of the uterine e'pithelium in Perameles he 

 could not carry the comparison far enough. 



In Sorex, Hubrecht states that over the future allau- 

 toidean and omphaloidean placental areas the epithelium 

 undergoes a tremendous proliferation and development into 

 a cell aggregate of relatively great thickness. 



The history of this maternal formation in the allantoic 

 placental area of Sorex is, I think, worthy of particular 

 consideration and of comparison with what happens in 

 Perameles. Hubrecht shows (1894, p. 49*2 seq.) that, in 

 the shrew, the imclei of tlie epithelial proliferation become 

 arranged in fan-shaped groups at comparatively regular 

 distances, the centre of each group being ^\^thout nuclei 

 (1894, fig. 69). 



• In the following stage ', says Hubrecht, ' this arrangement 

 becomes converted into a functionally more important one. 

 The centre of the fan-shaped structure becomes an open crypt, 

 ihe protoplasm breaking up and the peripheral nuclei forming 

 the epithelial lining of the crypt. The uterine epithelium 

 breaks away from under the crypt and the inner lining of the 

 crypt solders with tlie surrounding epithelial surface at the 

 lower border ' (p. 498). 



It is quite eas}'' to see the resemblance between the shrew 

 and Perameles in respect of the phenomenon here described. 

 In Ijoth there is intense epithelial proliferation, particularly 

 in the placental area. The resulting nuclei or cells are in both 

 arranged in nest-like groups. \\Tiile in the bandicoot these 

 groups remain practically unaltered, in Sorex they are 

 transformed into epithelial crypts. Nevertheless, as I have 

 shown above, the proliferated nuclei in Perameles 

 take on a more or less definite arrangement as 



