Abstract
Sex ratio in rats, especially their total and seasonal changes, were studied with 6, 155 animals of the Wistar-Imamichi strain. Data were collected over a period from December, 1970 to February, 1972. Analysis on sex ratio was performed by the same method as described in the previous report for the determination of sex ratio in swine2). The classes which showed a shift of sex ratio to either sex were cited mainly in tables. The results obtained are summarized as follows.
In a total, the sex ratio was 49.8 (male percent) and insignificant. Shifts of sex ratio were seen in the monthly sex ratios, both primary and secondary. There was no shift in the seasonal secondary sex ratio. In the primary sex ratio, however, a shift to female was seen in winter. There was a shift of sex ratio to female in the first winter (from December, 1970 to February, 1971) of the present investigation. No shift of sex ratio to either sex was recognized in the next winter (from December, 1971 to February, 1972). Taking the results mentioned in the previous report1) into consideration, the sex ratio for the three winters as a whole exhibited a shift to female.
