178 EICHARD ASSHETON. 



walls as, say, 10 is to 10, theu whea the hydrostatic pressure 

 (P) is to the rate of growth (R) of the cell walls as say 8 : 10, it 

 follows that the cells will not be so much stretched as when 

 P : R : : 10 : 10. 



The actual pressure within the vesicle no doubt does not 

 diminish, more probably it increases, but the relation of P : R 

 is altered by the fact that additional resistance is now added 

 without by the walls of the uterus. At any rate, it upsets the 

 ratio formerly existing. 



The result, I believe, is that now the rate of growth of the 

 cells of the wall is as compared with the rate of increase 

 in size of the blastodermic vesicle greater than it was before, so 

 that when a cell " grows '^ and " divides " it no longer becomes 

 at once stretched out, but forms a rounded granular cell, or 

 group of cells, as in figs. 5 and 6. The cells which are for 

 the time inactive will remain flattened, for elasticity is not an 

 attribute of protoplasm. 



This is the case at the lower pole of the blastodermic vesicle 

 and at the lower sides. In the region near the embryonic 

 disc (where it has all along been assumed that there is a more 

 active growth) it is found that almost every cell has evinced 

 signs of activity, for here the whole area has become thickened, 

 and the cells far more closely packed than they were, and almost 

 columnar instead of being flattened (fig. 8). 



It is, I believe, usual to describe the first attachment as 

 occurring between the ectoplacenta of the embryo and the 

 placental lobe of the uterus. This I am convinced is not an 

 accurate statement. The first actual attachment is between 

 the lower parts of the blastodermic vesicle and the periplacental 

 and obplacental folds. 



The exact course of the procedure I am doubtful about, but 

 I believe it to be a combination of at least two main causes, 

 but it may involve more ; or possibly it is wholly due to only 

 one of the two I am about to mention. 



The first attachment is efi'ected by means of the "papillae," 

 or thickened spots of epiblast of the lower pole of the embryo 

 already described (figs. 5 and 6, «., b., c). In fig. 7 one of 



