The effects of castration upon the cytological picture of the rat hypophysis has been described by Addison ( '17). This author has shown that the basophiles enlarge markedly following gonadectomy, this enlargement finally attaining the so-called 'signet-ring' condition. Engle ( '29) and Evans and Simpson ( '29) consider this enlargement as indicating the storage of the gonad-stimulating hormone, because they were able to show that the hypophyses of gonadectomized rats are more potent than glands from normal animals in their capacity to stimulate the immature ovary. However, Emery's ('32) demonstration that the hormone occurs in the blood of castrated rats-a condition not present in normal animalsindicates that the gonad-stimulating factor is not confined to the hypophysis in castrated animals.These studies, as well as a number of others, especially those of Moore and Price ('32), are evidence for the existence of a reciprocal relationship between the gonads and the m t erior hypophysis. Thus the gonads are stimulated through the agency of the pituitary hormone, but the gonadal hormones exercise an inhibitory influence on the hypophysis. Removal of the pituitary causes gonadal regression, but gonadectomy permits abnormal pituitary activity.Inasmuch as gonadectomy in the male removes all of the testicular elements, it becomes of interest to inquire into the gonad-pituitary relations of animals in which only certain National Research Council Fellow 241