That the secretion of the anterior pituitary is essential to gonadal function seems to be one of the most firmly established facts in the physiology of the reproductive system. With ablation of the anterior pituitary, follicles cease to develop and those with cavity formation undergo atresia. The uterus and vagina decrease in size and their cyclic changes cease. In the male the effects are equally pronounced. Pituitary implants restore gonad activity. In immature rats and mice, pituitary administration precociously develops the reproductive system, and in adults past the menopause it will induce estrus.Some recent work has shown that the pituitary sex hormone (or hormones) is secreted into the body fluids with almost amazing rapidity. This work at the same time has raised a question regarding the essentiality of the anterior pituitary in stimulating the growth of the corpus luteum. These results are so striking that we deemed it worth