Department of Biology, Wmhington Square College of Arts a d Sciences, New York University lNTRODUCTION
I n previous studies on induced ovulation in the frog it was stated (Rugh, '35) that the ovary of Rana pipiens did not respond to the anterior pituitary hormone in vitro. It was believed that the anterior pituitary gland stimulation was mediated through either the nervous or the circulatory system or both. Excised ovaries kept in sterile media and exposed to pituitary and to other endocrine organs of the frog did not respond-by ovulation. However, recently Heilbrunn, Daugherty and Wilbur ( '39), while studying the initiation of maturation of the frog's egg, took issue with this statement of Rugh by reporting successfully induced ovulation in vitro, in the same species. Grant ('40) also reported inducing ovulation in vitro in Rana pipiens. Ryan and Grant ('40) stated that they had followed exactly the methods of Heilbrunn, Daugherty, and Wilbur and had similarly achieved in vitro ovulation.
McPhail and Wilbur ('43), in studying the potentiating action of colchicine on the action of the anterior pituitary gland in inducing ovulation, used this in vitro method for assaying the experimental procedures.
I n view of the fact that the above discrepancies existed it became important that the matter be re-investigated under the most critical conditions. This paper is a report of the results of this investigation.