THE OVARY OF THE SPERMOPHILE 163 
From these results, the following conclusions were drawn as to 
the functions of the corpora lutea in the ovaries of spermophiles: 
The corpora lutea fix the period of estrus by preventing the 
development and the ripening of follicles until the time for the 
next rutting season is at hand. 
The corpus luteum is a gland with two internal secretions, 
both of which have specific effects on the uterus, one bringing 
about the changes incident to pregnancy and the other effecting 
the normal involution of the organ. The first internal secretion 
is represented in the luteal cells during the period of pregnancy 
by granules which are very similar in their location and staining 
reactions to the granules in the A cells of the islands of Langer- 
hans, the glands of internal secretion of the pancreas, described 
by Bensley. The granules of the luteal cells, however, are 
much larger than those of the A cells, being very easily seen 
with high powers of the microscope. No mitochondrial granules 
or filaments could be observed, perhaps because of the abun- 
dance of the granulations in the protoplasm. These luteal cell 
eranules are very much like other secretion granules described 
by various writers as occurring in the secreting serous cells of 
several glands of the body. 
The majority of writers have agreed that there is no fatty 
product demonstrable in the corpus luteum of several species of 
animals and man in the very early stages. They all seem to 
have been of the same opinion that the activity of the ovarian 
gland of internal secretion begins with the appearance of the 
lipoid droplets in the cells. These lipoid droplets were con- 
sidered by them to be the evidence of the secretory activity of 
the corpus luteum. Its period of activity would then begin 
when these droplets begin to appear in the cells, which time 
varies with different species, but in all seems to be about the 
time of the fixation of the blastocyst. This activity lasts, they 
consider, for varying periods in different species. In the rabbit, 
Cohn, Fraenkel, and Niskoubina consider that it lasts for nine 
or ten days, when regression sets in about the fifteenth day. 
Van der Stricht says that in the bat the lipoid droplets are in 
much greater abundance during the second half of the period 
