(l) Trials involving a total of 18 Japanese Corriedale ewes were conducted in an attempt to gain several lambs under artificial light treatment over three out-of-seasons. (2) Artificial lighting and black-out treatments for controlling the breeding season of ewes were tried in a light-proof pen. (3) The hours of exposure to light were allowed daily for an actual day light to keep a gradually increasing light rhythm until the total light length corresponded to summer solstice, and then it was changed over from increasing to decreasing light by artificial lighting and darkness. When the light length was corresponded to winter solstice the constant light length was kept up. In the second and third seasons, the rhythmical changes of light were designed to elapse more rapidly. (4) All of ewes under light treatment came in oestrus for 40-50 days' intervals after the change-over from increasing to decreasing light. It may, therefore, be considered that there are some constant intervals in Corriedale ewes to come in oestrus under short day treatment. And it is of some interest to say that these intervals will be in accordance with natural intervals, if there may probably be a silent heat before onset of oestrus under normal condition. (5) 13 out of the 16 oestrous ewes became pregnant as a result of induced mating after one cycle interval. Several of 14 lambs which were produced in the present experiments were born weak. It may be necessary for further investigations to set such questions at rest.
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The authors wish to express grateful thanks to the Ministry of Education for grants in aid and to Mr. H. MORITA, Mr. K. MURAKAMI, Mr. T. HORIKAWA, Mr. K. HASEGAWA, Mr. T. MOTOTANI, Mr. M. MASUNISHI, and Mr. K. SHIMAKAWA for general assistance.