Sixty-seven adult and 42 subadult female gray squirrels (Sciurus carolinensis) were collected over a period of one year between December, 1966 and November, 1967 in the vicinity of Blacksburg, Virginia. Each squirrel was classified as being in one of four reproductive states (vaginal orifice closed, vaginal orifice open, pregnant, or lactating). Differences in ovarian and uterine characteristics due to month, age, and reproductive state were analysed by analysis of variance and a multiple range test.

Pregnant adults had significantly (P<0.05) greater paired ovarian weights than lactating adults or those adults with a closed vaginal orifice. Uterine weights in the four reproductive states were all significantly (P<0.05) different, with pregnant adults highest, adults with open vaginal orifices next highest, lactating adults next highest and adults with closed vaginal orifices lowest. Pregnant adults had significantly (P(O.05) more tertiary follicles and significantly (P<0.05) higher sums of follicular diameters than all other reproductive states. Squirrels with open vaginal orifices had significantly (P<0.05) higher average diameters of the four largest follicles than all other reproductive states.

Ovarian and uterine weights of subadults were less than adults during most months. Ovarian and uterine weights increased in late winter, decreased in early spring, increased during the summer and decreased in the fall. Follicular development was more variable, but showed general increases in the summer months. The seasonal trends reflected the frequency of occurrence of the various reproductive states in the monthly samples.

Two experiments were conducted on captive female gray squirrels. In the first experiment it was determined that FSH-P can cause the formation of luteal glands in the absence of HCG injection. LH contamination of FSH-P probably caused the luteinization. There were no significant differences in ovarian response between squirrels receiving HCG subcutaneously and those receiving it intravenously after pretreatment with FSH-P. In the second experiment, 2.0 mg FSH-P/d~ on days 1, 2, 3, 4, 5, 6, and 7 with subcutaneous injection of 200 IU HCG on day 13 produced significantly (p<0.05) more luteal glands than 200~ FSH-P on days l~ 2, 3, 4, 5, 6, and 7 with subcutaneous injection of 200 IU HCG on day 5. However, there were no significant differences in development of tertiary follicles. Squirrels treated with NIH-FSH-S-6 and HCG had development of large tertiary follicles with no luteinization.