DEVELOPMENT OF THE ALBINO RAT 301 
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 
‘Hibuckel,’ or oval fold. Burekhard’s schematic figures (text 
figures 2 to 4) may be consulted to make the phenomenon 
intelligible. 
