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Male rats castrated at 1, 5, 10, 20, 30, and 90 days of age and females ovariectomized at 90 days of age were compared as adults for female mating behavior when given estradiol and progesterone. The Day-1 and Day-5 castrates displayed more feminine behavior than those castrated after Day 5. When males castrated at similar ages received testosterone as adults, Day 1 and Day-5 castrates displayed fewer intromissions and ejaculations than Ss castrated later. The data support the hypothesis that the action of gonadal hormones on differentiating genital tracts and neural tissues is analogous. Feminization occurs in genotypic females or in either sex when gonads are absent. Masculinization occurs when androgen is present, regardless of genotypic sex.

The sexual behavior of 10 male rhesus monkeys was observed before and after castration and during replacement therapy with testosterone propionate. In 10 tests before castration, all of the males ejaculated at least once, and in Weeks 21-25 and 51-55 after castration, 50% and 30%, respectively, ejaculated at least once. In the 35 postcastration tests given over a 55-wk. period, 2 males did not ejaculate. Fifty percent of the males achieved intromission 1 yr. after castration. The percentage of castrated animals showing intromission and ejaculation and the frequency of these responses were higher than those reported for most nonprimate species but did not differ greatly from those reported for the dog. Within 1 wk. testosterone propionate restored whatever aspects of behavior were affecled to precastration levels.

The sexual behavior of a confined troop of 69 Japanese macaques was observed throughout its 5 months breeding season. Males 2 ¼ years of age and older mounted adult females but only males 4½ years and older ejaculated. All females 3 ½ years of age and older were sexually receptive and all but two of the adult females conceived. The frequency and intensity of mating was somewhat related to dominance in males, to age in both sexes and to the recency of an offspring in females. All males mated, some of the most active being low in rank; however, the most dominant males ejaculated more frequently. Middle-aged females were very active throughout the season; females with recent infants were least active. The frequency, the intensity, and the types of behaviors exhibited by females during the season showed no consistent cyclic fluctuations. The continued sexual activity of pregnant females, the higher numbers of ejaculations and the displays of high-ranking males, and the repeated mounting of mature females by nonejaculating males demonstrate the social nature and essentially nonprocreative functions of much breeding season activity. The interaction between hormonal and social factors must be considered in the approach to an eventual understanding of sexual behavior in primate species.