500 A. A. W. HUBREOHT. 



minal Layers of Sorex,'^ can hardly be anything else than the 

 predisposed zonary region of attachment. It is, however, 

 worthy of note that when the attachment comes about the 

 trophoblast cells that are applied against the maternal surface 

 are by no means more bulky, but rather excessively flattened. 

 This may be consequent upon a very rapid increase in surface 

 of the blastocyst. 



Figs. 4 and 5 give us the two earliest phases of the attach- 

 ment of the blastocyst. 



The fact that the two uteri, No. 53 and No. 73, contained 

 together no less than fifteen blastocysts, which have all been 

 sectionised, enables us to follow all the phases of this attach- 

 ment in detail. Three of the fifteen are not yet adherent to the 

 maternal surface ; and of the remaining twelve, those that may 

 be said to represent the very earliest stage are as yet only 

 adherent by a small portion of the belt-shaped region ; others 

 are already attached on one side ; the majority, however, are 

 fixed all round, so that the fixation certainly comes about in a 

 very short space of time. In a few of the cases here mentioned 

 there was no visible change either in the maternal proliferated 

 cells or in the flattened embryonic trophoblast cells, against 

 the inner surface of which the still more flattened hypoblast 

 can be easily detected. These cases, no doubt, represent the 

 earliest incipient stages. 



In the next stage there is a change both in certain of the 

 trophoblast and in certain of the maternal cells, in some cases 

 the maternal, in other the embryonic cells taking the lead. 

 The changes in the embryonic cells affect both the aspect of 

 the protoplasm and of the nucleus. 



When examined in the preserved sections the cells are seen 

 to contain fine filaments which testify both to a small increase 

 in bulk of these flattened cells and to a more frothy arrange- 

 ment of their protoplasm. In some cases the nucleus of these 

 modified trophoblast cells is readily distinguishable, in others 

 it has undergone a transformation into smaller, deeply stained 

 granules, that (figs. 51 and 49) sometimes even become ex- 

 tremely minute. 



