646 The American Naturalist. [July, 
The stages 'studied were from three days after impregnation to 
All sections were cut with the embryo in situ. In tli^ earliest stage 
examined little or no swelling was noticeable on the external surface of 
the uterine cornu. Sections through the cornu showed that the pres- 
ence of the egg had induced very great changes in the mucosa ; the 
most noticeable change being its increased thickness. In the stages 
immediately following the mucosa with its glands is turned inwards at 
both poles of the cavity, forming heavy lips around each pole of the 
latter. A little later the cavity containing the embryo becomes barrel- 
shaped, but remains so only a short time. The uterine glands become 
contorted, and extend peripherally almost to the annular muscular 
coat. The swelling of the cornu seems to be greatest on the side 
opposite the mesometrium. This is probably due to the fact that at 
that point there is least resistance. The spherical foetal membranes 
touch the mucosa in an annulus about the embryonic or blastedermic 
vesicle, as they must necessarily do on account of the form of the 
latter and the tube in which it lies. The poles of the embryonic 
vesicle which do not come in close contact with the mucosa are, 
however, very small during the early stages. 
The rapid growth of the embryonic vesicle seemingly expands the 
cavity of the cornu, and as the cornu does not become enlarged be- 
yond each pole of the vesicle the mucosa must necessarily touch the 
chorion at all points except over a very small area at each pole. 
In the succeeding stages the glands become very glassy in appear- 
ance, and contractile muscular bands were noticed about each gland, 
their function probably being to force out the "uterine milk," or se- 
cretion for the nourishment of the embryo at this stage. 
Later, when the velli of the permanent chorion are developed, the 
glands cease their activity, and are transformed into crypts to receive 
the velli of the chorion. The glands at the poles remain unchanged. 
Their axial ends are turned towards the embryonic vesicle. They re- 
tain their contorted or spiral form and vasi ular appearance. The 
•r and width slightly, but it does not increase in width as 
cavity containing the embryo elongates. It reaches its 
width at a time when the embryonic vesicle is about one 
meter and almost spherical in form. The axial ends of all 
glands, in the cavity containing the embryo, beginning 
arliest stages, are pushed from 
