September, 1945 



Brown & Yeager: Squirrels in Illinois 



483 



the more abdominal position of the testes, 

 the scrotum was less pendent. 



Oestrus. — The earliest evidence of 

 first-season or winter oestrus observed in 

 fox squirrel females was December 11 in 

 Alexander Count\^ (southern zone), tables 

 15, 16 and 17. The latest oestrus records 

 for the first season in the southern and 

 central zones were Januarj' 27 ; the two 

 observations were a year apart. In gray 

 squirrels the earliest evidence of winter 

 oestrus was December 16, and the latest 

 was February 11, both observations in the 

 southern zone. 



The external indication of oestrus, 

 commonly called "heat," is a swollen, pro- 

 truding condition of the vulva. During 

 oestrus the uterus is enlarged and con- 

 gested with blood, by w'hich the vulva is 

 commonly discolored. This condition is 

 easily observed in external examination. 

 Following copulation the congested con- 

 dition of the uterus clears. The uterus 

 becomes spongy and thick-walled, and 

 fetal nodes, 3 millimeters in length, appear 

 about 10 davs after successful coitus. 



Pregnancy. — An attempt was made 

 early in the survey to distinguish oestrus 

 and early pregnancy by the use of vaginal 

 smears, but this proved impractical under 

 conditions prevailing in the field. The 

 oestrual period thus was probably not dis- 

 tinguished as precisely as is desirable, and 

 perhaps an unknown number of very 

 early pregnancies were listed under the 

 heading of oestrus. Pregnancy could be 

 determined with some certainty by noting 

 the relaxed and perforated state of the 

 vulva and development of the mammae. 

 Somewhat advanced stages of pregnancy 

 (15 millimeter fetuses) could be detected 

 by palpating the lower abdomen. 



The earliest and latest first-season 

 pregnancy records for fox squirrels were 

 January 1 (one animal with 3 fetuses 

 averaging 6 millimeters in length) and 

 March 22 (one animal with 3 fetuses 

 averaging 19 millimeters in length), table 

 16. The first-season peak of fox squirrel 

 pregnancy, based on 43 adult females, 23 

 of them pregnant, table 15, came during 

 the first half of February. In gray squir- 



Fig. 11. — Glans penis and urethra of adult male squirrel, with Cowper's glands attached 

 in an uncoiled and in a nearly natural position in each case. Left, fox squirrel; right, gray 

 squirrel. Coles County, late January, 1944, 



