DEVELOPMENT OF THE ALBINO RAT 57 



ine mucosa shows a distinct reaction to their presence. Localized 

 thickenings of the uterine mucosa, sufficient to cause localized 

 swellings of the uterine tube, indicating the position of the ova, 

 are evident. I have experienced more difficulty in successfully 

 fixing the vesicles during this stage than any of the earlier or 

 later stages studied. Although my material contains 58 vesicles 

 of the stage under consideration, none of them may be regarded 

 as being well fixed, and the majority of them are so folded as a 

 result of contraction during fixation that they are of little value 

 as objects for especial study. That the vesicles are still un- 

 attached to the uterine wall is readily determined by the fact 

 that the shrivelled vesicles are found lying free in the depres- 

 sions of the uterine mucosa, lined by a low cubic epithelium, 

 intact throughout, and retaining its normal relation to the 

 mucosa. The molding in these mucosal depressions no doubt 

 gives the size of the respective vesicles as in vivo. 



It is not my purpose at this time to consider more than super- 

 ficially the changes affecting the uterine mucosa during ovum 

 implantation in the albino rat. It is hoped that this may be 

 the subject of a future communication. It is the purpose in the 

 present communication to confine consideration to the develop- 

 ment of the ovum itself. Many of the observations recorded 

 by Burckhard on the implantation of the ovum of the mouse 

 and the formation of the decidua, I find equally adapted to 

 similar phenomena in the albino rat. Differences are to be 

 observed in certain details which it is not the purpose to enter 

 into here. Grosser gives a number of excellent figures (67 to 

 70, and 112 to 116) showing implantation and decidua formation 

 in the albino rat; to these the interested reader is referred for 

 the present. The thickening of the mucosa affects primarily 

 its antimesometrial portion. During this process of thickening, 

 the mucosal fold in which the ovum primarily finds lodgment, 

 becomes deepened and converted into a funnel shaped crypt 

 communicating with the uterine lumen, and surrounded by the 

 'Eibuckel/ or oval fold. Burckhard's schematic figures (text 

 figures 2 to 4) may be consulted to make the phenomenon 

 intelligible. 



