l T V 0 FIGURESStudies upon the effect of hypophysectomy on the survival of mature spermatozoa have not been reported, although a number of papers have appeared on the influence of castration on sperm motility and survival. The effects of the two types of operations are similar as regards certain features and might be expected to give a similar survival period of the sperm. The accessory organs after hypophysectomy undergo about the same degree of atrophy as after castration, and this atrophy is presumably the immediate cause for the decrease in the survival period of sperm which has been shown by a number of investigators.After hypophysectomy, however, there are certain effects which are not present after castration. Some of these might tend to further decrease the survival period of the sperm, whereas others might have the opposite effect. There is a profound systemic effect from hypophysectomy. Rats show varying degrees of cachexia, and certain organs which are not affected by castration undergo atrophy. The body temperature is lowered. Although an increased temperature has a deleterious effect upon sperm survival, the effect of a sub-= Submitted i n partial fulfillment of the requirements for the degree of Doctor