128 DELLA DRIPS 
April 15. As a result of strenuous efforts, the females were 
obtained while in rut and every day through the period of 
pregnancy, which was found to be twenty-eight days. Two or 
more were sacrificed each day. 
The ovarian cycle was now completed. Ovaries were at hand 
for every week of the year except during the hibernation period 
when only a sufficient number of animals was sacrificed to make 
sure there were no changes taking place in these organs. For 
the period of pregnancy, a time which is especially related to 
ovarian activity, there were ovaries for even fractions of a day. 
The period of rut evidently follows immediately on the awaken- 
ing of the spermophiles in the spring. Ovulation follows on 
coitus. Most of the females are impregnated in a very short 
time. The period of pregnancy follows. From the time of 
ovulation until about September 1 the ovaries contain corpora 
lutea. These approach their greatest size about July 1. From 
September 1 to 15 the large corpora lutea have disappeared. 
With a disappearance of the corpora lutea, there is a very notice- 
able rapid growth of the follicles together with a noticeable 
decrease in size. The, ovaries which in July consisted almost 
entirely of large corpora lutea with a small amount of ovarian 
stroma containing a few atretic follicles, by September 15 con- 
tained no corpora lutea, but instead, many medium and good-sized 
growing follicles containing very little liquor folliculi, but filled 
with mitotic figures. 
In this paper descriptions will be presented, gross and micro- 
scopic, of the ovaries which, as the year goes around, show the 
characteristic changes of their cycle. 
A typical ovary of the early fall will be presented first; second, 
one of the late fall just before hibernation, with its inactivity, 
and, third, one of the early spring, showing the characteristics 
of the rutting season. For the fourth period, the period of 
pregnancy, several ovaries will be described, marking the suc- 
cessive changes occurring in the corpora lutea principally. 
Finally, will be presented descriptions of a number of ovaries 
of the summer months, which show the final stages in the life 
history of the corpora lutea and the corresponding notable 
differences in the rest of the ovary. 
