Ovarian follicular activity increased sharply during the first 12 days of the luteal period, then ceased temporarily. Renewed follicle growth commenced towards pro-oestrus and terminated in ovulation. Although follicular activity decreased considerably during the period of anoestrus, relative large individual follicles were present in the ovaries. Following a period of active growth the corpus luteum attained maximum size and weight during the mid-luteal phase (Day 12) of the cycle. After Day 12 the corpus luteum began to regress and degeneration accelerated at the time of oestrus. In a large number of corpora lutea (28%) central cavities were observed, ranging in diameter from 1,9 to 8,9 mm (mean 3,7 mm).