THE OVARY OF THE SPERMOPHILE 161 
6. Removal of the uterus at any time does not produce 
noticeable effects on the ovaries even after a year’s time. ; 
7. Double ovariectomy performed at any time during the 
period of pregnancy interrupts gestation. If the operation is 
performed after a little more than the first half of pregnancy, 
the placentas with the fetuses simply degenerate. The invo- 
lution of the uterus in these cases is very abnormal. If both 
ovaries are removed late in pregnancy, the animal aborts and 
the uterus undergoes a much more normal involution. The 
removal of only one ovary does not interrupt the pregnancy. 
8. Double ovariectomy at any time prevents the recurrence 
of the cyclic changes in the uterus and produces an atrophy of 
the organ scarcely noticeable within a year. 
9. The corpora lutea apparently do not influence the develop- 
ment of the mammary gland. When the uterus was removed 
very soon after conception, before any signs of pregnancy could 
be noted grossly in the uterus, and before any development of 
the mammary glands could be noted grossly, the developing 
corpora lutea in the ovaries produced no development in the 
mammary glands. This would seem to substantiate the work 
of Lane-Claypon and Starling who attribute to the fertilized egg 
the stimulus for the development of the mammary glands. 
10. The corpus luteum of the spermophile derives its elements 
from the follicle just as Sobotta states occurs in the mouse. The 
luteal cells are the transformed granulosa cells of the follicle. 
The connective tissue and vascular network are derived from 
the cells of the internal theca which spends itself entirely in 
their formation. The capsule of connective tissue surrounding 
the luteal structure is the same external theca which surrounded 
the follicle. ‘The microscopic pictures of the corpora lutea in 
the succeeding stages of their development correspond also to 
Sobotta’s descriptions. It may be well to emphasize the com- 
plexity of the vascular network throughout the luteal structure 
which, when it is completed, brings every luteal cell in intimate 
contact with the blood stream. 
11. The life cycle of the corpus luteum is made up of three 
distinct phases. First, the phase characterized by the presence 
