482 



Illinois Natural History Survey Bulletin 



Vol 23, Art. 5 



nile males were, of course, much smaller after which development was rapid. The 



than for adults, the difference being great- maximum diameter of the glands in each 



er in the fall than in the spring. species was about 25 millimeters, reached 



Weight of testes, which may be a some- during the latter half of December. The 



what more accurate indication of breeding spring maximum observed was about 23 



Fig. 10. — Testes of adult and juvenile squirrels. A, adult fox squirrel ; B, adult gray 

 squirrel; C, juvenile fox squirrel; D, juvenile gray squirrel. Epididymis removed in right 

 example of each pair. Coles and Piatt counties, late January, 1944. 



stage than testes length, showed greater 

 fluctuation during the breeding seasons 

 than the length measurement. In fox 

 squirrels, peak average weights of 7.38 

 grams and 7.84 grams for the testes were 

 reached in late December and late April, 

 respectively. In gray squirrels, corres- 

 ponding data, less reliable due to fewer 

 samples, averaged 6.16 grams for the testes 

 early in January and 5.73 in May; the 

 average of a small number of samples in 

 early April was 5.80 grams. Adult and 

 juvenile testes are illustrated in fig. 10. 



Gowper's Glands. — The location, 

 large size and relationship to breeding 

 activity of the Cowper's glands make them 

 a good criterion by which to judge the 

 sexual condition of males. These glands, 

 fig. 11, are paired, discoid bodies, the 

 function of which is production of sperm- 

 carrying fluid. The glands, coiled like a 

 Polygyra snail shell, are situated one on 

 each side of the rectum. Connection with 

 the penis is by duct. When turgid, these 

 glands extend posteriorly, distending the 

 anal orifice and increasing the average 

 body length by about 10 millimeters. 



Enlargement in the Cowper's glands in 

 both species was first observed in October, 



millimeters, attained about the end of May 

 in fox squirrels and the last 2 weeks of 

 June in gray squirrels. The number of 

 gray squirrels examined was so small that 

 the data for them may not be representa- 1 

 tive; comparable data for the fox squirrel 

 indicate that the peak diameter of 

 Cowper's glands in the gray squirrel 

 was reached earlier in June than is shown 

 in table 14. Following cessation of 

 breeding in the summer, these glands be- 

 came dormant and decreased so greatly m\ 

 size that, in August, September and Oc- 

 tober, they were diflfiicult to find, even by 

 dissection of the animals. 



Scrotum. — Field observations showed 

 that, as the breeding season progressed, 

 the scrotum became comparatively smooth, 

 and both skin and hair assumed an oily, 

 brown-stained appearance, fig. 5. Follow- 

 ing the mating season, in June or later, 

 the scrotum lost this rubbed, blackened 

 appearance through sloughing of the skin 

 and replacement of hair and underfur in 

 the molting process. The new skin of the 

 sac was of lighter pigmentation, as in juve- 

 nile males, fig. 5. In "old squirrels, the 

 loose saclike condition of the scrotum pre- 

 vailed, whereas in juveniles, because ofi 



