Abstract
Tohoku hare, like other wild mammals, manifests periodical sexual activity according to the season. Minimal ovarian weight is observed during the season from November until January. Generally, gradual enlargement of size with increase in weight is seen from the end of Feburuary or from early March. During the breeding season, in spring and summer, the ovary is large in size and active. It undergoes rapid degeneration from September or sometimes from October. In the present experiment the effect of prolonged light exposure upon breeding was studied, with special reference to ovarian activity. From December 11, 1968, 25 mature females and 10 males in captivity were exposed daily to natural daylight from sunrise to 9a.m. and then artificial light was added until 9p.m. An increase in ovarian weight was observed from 50 days after the start of the experiment, namely from the end of January. However, a similar state of ovarian activity is not normally attained until late Feburuary or early March in the wild. Though the exposure experiment was ended on May 6, the ovary showed no signs of degeneration even on Apil 12. This year, the first pregnant female was captured in the wild on Feburuary 26 and one female gave birth to a litter of 3 on April 5. However, in the experiment a pregnant female was observed on January 30 and one female gave birth to a litter of one on Feburuary 22. The experimented animals continued to give birth until April 10. From April 11 to June 29 breeding seemed to be ceased but from June 30 it began again and continued until August 22. It is worthy to note that the ovaries, both of the wild animals or of the animals experimented, contained fully grown follicles at all seasons of the year.
