332 EDGAR ALLEN 
gray mice coincide, and they are both derived from the same 
original pair of animals. These facts point to a genetic factor 
as partly responsible for variation in the oestrous cycle and 
direct attention to the ovum itself as the ultimate cause. 
The present findings of a much shorter oestrous cycle in the 
mouse than had previously been suspected explains the apparent 
exceptions reported by Kirkham and Smith to an oestrous cycle 
of twenty or seventeen and one-half days’ duration. 
Kirkham (716) reports a case in which ‘‘a set of normal eggs 
in the 2-cell stage was found six days post partem.’” Smith 
(17) reports ovulation in a mouse six and one-half days after 
parturition. These may be explained by a failure to ovulate 
or of the ova to be fertilized at the oestrus following parturition, 
and the recurrence of another oestrous period five days later. 
1. Oestrous changes in the genital tract 
a. The vagina and cervix utert. 1. There is in the mouse 
little discharge from the uterus into the vagina such as occurs 
in menstruating animals. Uterine epithelial cells are not often 
found in the smears. Also, although the uterine cornua during 
the P and O stages are greatly distended with fluid, the vaginal 
mucosa, especially during oestrus, is usually dry. Apparently 
the musculature of the cervix functions as an efficient sphincter. 
2. In the mouse the massing of the cornified cells of the vaginal 
epithelium in clumps (when a standardized smear technique is 
used) indicates that ovulation has already occurred when that is 
to be spontaneous. It is therefore of importance in diagnosing 
ovarian conditions. 
As to the fate of the leucocytes so abundant in the M, stage, 
many degenerate in the lumen. It was stated in the descriptive 
section that during the D interval the vaginal contents were 
viscous and stringy. These stringy masses when spread on 
slides show a fine web structure with polymorphs at the inter- 
stices entangling varying numbers of epithelial cells. The fine 
web processes seem to be made of the greatly attenuated proto- 
plasm of the leucocytes. 
