Abstract
The method of artificial insemination in the mouse, which has been used successfully only once previously (Mark and Long, 1911), has made it possible to collect exact data on the duration of life and the fertilising capacity of spermatozoa in the female genital tract. Earlier results concerning the conditions under which spermatozoa from the male genital tract attain their maximum activity (Merton, II) and the exact knowledge of the time of parturition (Merton, I) were helpful in carrying out artificial insemination during the following œstrous period.