The work of various investigators indicates a relationship between the ovary and a successful pregnancy. The details of the relationship, however, appear to vary somewhat in the different species studied.The early work of Fraenkel ('03) in removing the ovaries and also burning out corpora lutea of rabbits, one to six days after coitus, prevented implantation of the ova and prcgnancy. Removal of one ovary or burning out of only some of the corpora lutea usually resulted in birth of young. He concluded there is a close relationship between the corpus luteum and occurrence of pregnancy, but that in later pregnancy both ovaries may be removed without disturbing the pregnancy. He maintained that the corpus luteum produces the only hormone of the ovary and that it exerts an influence on the generative functions throughout the reproductive period of the life of the animal, and that it causes heat, menstruation, implantation, and the formation of the placenta. These several functions attributed to the corpus luteum by Fraenkel have been disputed, in part, by Marshall and Jolley ('05), who, from the work on pregnant dogs and rats, consider that, "The ovary is an organ providing an internal secretion from the follicular, epithelial cells or by the iiiterstitial cells of the stroma. This secretion induces menstruation and heat. The corpus luteum provides a secretiou essential for the attachment and development of the early ' Contribution no. 97 of the

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