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Illinois Natural History Survey Bulletin 



Vol. 23. Art. 5 



rels, the earliest and latest pregnancy 

 records were January 13 (one animal with 



2 fetuses averaging 4 millimeters in 

 length) and March 29 (one animal with 



3 fetuses averaging 15 millimeters in 

 length), table 16. Peak gray squirrel 

 pregnancy for the first season, based on 

 16 adult females, 9 of them pregnant, 

 came about the middle of February, table 

 15. The earliest and latest second-season 

 pregnancy records were June 19 and 



August 29 for fox squirrels, and July 5 

 and September 9 for gray squirrels, table 

 16. Fox squirrel females taken on August 

 15 and 29 each contained 2 fetuses; those 

 of the first averaged 20 millimeters in 

 length and those of the second 48 milli- 

 meters. Fig. 12 shows embryos at the age 

 of about 15 days in the uterus of a fox 

 squirrel. 



Gestation. — Previous writers have re- 

 ported difficulty in determining exactly the 



Fig. 12. — Uterus of pregnant fox squirrel. Right horn contains two normal fetuses and 

 one apparently in process of being resorbed, 



