72 • J. r. HILL. 



own for Dasyurus, and I venture to think the agreement is 

 oven greater than would appear from Assheton's conclusions. 

 In adopting the view that the more active growth of the 

 region of the blastocyst wall immediately surrounding the 

 inner cell-mass is the sole causal agent in effecting the separa- 

 tion and peripheral spreading of the entodermal cells, I cannot 

 but feel, in view of his own description and figures and of my 

 own results, that he has attributed a much too exclusive import- 

 ance to that phenomenon and a much too passive role to the 

 entodermal cells themselves. In Dasyurus the inward migra- 

 tion and the later peripheral spreading of the entodermal 

 cells is effected without any such marked unequal growth of 

 the blastocyst wall as occurs, according to Assheton, in the 

 rabbit, as the direct outcome of their own inherent activity, 

 and I believe the possession of a like activity characterises 

 the entodermal cells of the rabbit. The evidence of Assheton's 

 own fig. 40, which shows in surface view a portion of the 

 vesicle wall with the peripheral entodermal cells in relation 

 thereto, and which should be compared with my figs. 68 and 

 69, conclusively demonstrates, to my mind, the possession by 

 these cells of amceboid properties, and thus support is 

 afforded for the belief that the separation of the entodermal 

 cells from the formative cell group (inner cell-mass) is here 

 also the expression of an actual migration. Whether or not 

 the strands of protoplasm which Assheton ('08, *09) describes 

 as present in the sheep, pig, ferret, and goat, connecting the 

 inner lining of the inner mass to the wall of the blastocyst, 

 and which he intei-prets as tending " to show that the inner 

 lining of the inner mass is of common origin with the wall of 

 the blastocyst,'' are of any significance in the present connec- 

 tion, I cannot certainly determine. 



4. Summary. 



The results and conclusions set forth in the preceding 

 pages of this chapter may be summarised as follows : 



(1) The unilaminar wail of the blastocyst of Dasyurus con- 



