Abstract
Meriones unguiculatus Kurauchii Mori were bred, and their duration of pregnancy, size of litters and some postnatal developmental changes of the young were examined. The principal results may be sum-marized briefly as follows :
1. The duration of pregnancy was found to be 24 to 26 days.
2. Average number of a litter was 4.8±0.9. The value of the first litter was the lowest.
3. The growth curve of the body weight was nearly S-shaped and in general, the female was slightly inferior to the male.
4. The tail ratio was lower than that of rats at the time of birth, but it increases remarkably during maturation.
5. As for the external developmental changes, the opening of the ear auricle and the eruption of the lower incisors occured in the period similar to rats or mice, while the opening of the eyelids was observed few days later than that of latter animals.
6. The testis descended in average on the 36 th days of age, while the vagina opened in average on the 49 th day.
