Abstract
SUMMARY: Oestrous cycles, as judged by vaginal smears, persist for a variable time after X-ray sterilization of the ovaries, but their phases do not synchronize with the growth and rupture of surviving Graafian follicles and the formation of corpora lutea. Cyclical fluctuations in the size of the uterus and the histological appearance of the vagina occur during but not after the first two oestrous periods following sterilization.