ATTACHMENT OP MAMMALIAN EMBRYO TO UTEEUS. 187 



Summary. 

 Section 1. 



(i) The blastodermic vesicle of the rabbit becomes first 

 attached to the walls of the uterus by its lower pole. 



(ii) This attachment of the lower pole is regarded as the re- 

 sult of a mechanical pressure of certain spots or knobs of 

 thickened epiblast of the blastodermic vesicle upon the epithe- 

 lium of the uterus (the pressure being the hydrostatic pressure 

 within the vesicle), whereby the uterine epithelium is pierced 

 and the knobs of epiblast become embedded in the connective 

 tissue below. 



(iii) These knobs of epiblast, as also the thickening along 

 the trager region, are regarded as being the direct result of a 

 destruction of the equilibrium between the rate of increase of 

 the hydrostatic pressure within the blastodermic vesicle and 

 the rate of growth of the cellular wall of the vesicle, under 

 which conditions the epiblast had hitherto remained practically 

 at a constant measure of thickness. 



The destruction of the equilibrium is brought about by the 

 additional pressure put upon the expanding blastodermic 

 vesicle by the resistance of the uterine walls. This is a con- 

 tinuation of the same series of forces which in my former 

 paper were supposed to account for the peculiar shape of the 

 blastodermic vesicle and apparent growth round of the hypo- 

 blast. 



(iv) In the trager region the attachment is eflPected in a 

 rather different manner. Here the activity of the epiblast is 

 greater than at the lower pole, so that here the thickening is 

 of a more general and more rapid character, which results in a 

 somewhat extensive and irregular area instead of isolated 

 knobs of thickened epiblast. Also the soft tissue imme- 

 diately underlying the epithelium of the uterus is here very 

 extensive. 



Thus the conditions are not such as to cause a perforation of 



