THE OESTROUS CYCLE IN THE MOUSE She 
2 to 3, 9 to 10, 14 to 16, 23 to 24, and 34 days before she was 
killed. A gross examination showed the ovarian and uterine 
vessels to be relatively small and inconspicuous. The uterine 
cornua were small in diameter and quite opaque. The periova- 
rian sacs were slightly distended. 
Cross-sections of the vagina (fig. 11) show a semicollapsed 
lumen crowded with masses of non-nucleated, cornified, deeply 
red-staining, epithelial cells. The epithelium has no basement 
membrane and the deepest layer of the germinativum is in inti- 
mate relation with the connective-tissue cells of the stroma. 
There are eleven or twelve layers of epithelial cells under the 
granular and horny layers, which are everywhere superficial 
and intact except for the delaminated masses in the lumen. 
There are very few or no mitoses present in the germinative 
layers. Leucocytes are also absent. 
The lumina of the uterine cornua are not entirely collapsed, 
but contain in several of the sections a few nucleated epithelial 
cells. The basement membrane of the uterine epithelium is 
entirely lacking and in its place is a broad red-staining band. 
The deeper edges of the epithelial cells and the most superficial 
stroma cells are involved in it, and their structures contained in 
this band become blurred and take the stain poorly. Small 
vacuoles are apparent in and among the epithelial cells. A very 
few leucocytes have already entered the degenerate band or zone 
under the epithelium. 
The oviducts are moderately distended. Vacuoles are present 
in the non-ciliated epithelium of the segments adjacent to the 
uteri and in the ciliated regions extrusion of nuclei is general 
(fig. 19). 
Eight ova are present in the second segments of the tubes. 
Membranes and maturation spindles are intact in every case, 
and polar bodies are still adherent. The animal was killed then 
during the second day after ovulation. 
There are from ten to fourteen medium-sized follicles in which 
the liquor folliculi is beginning to form at the poles. There are 
none sufficiently distended to indicate the approach of an ovu- 
lation. A very few small and medium-sized atretic follicles 
are present. 
