SEXUAL BEHAVIOUR 83 



gonad size and sexual activity,2i» 56 but it is sufficient to 

 say here that no exceptions are known. 



However, while the activities of most vertebrates 

 may be closely associated in this way with the state of 

 the reproductive system, in the higher mammals, and 

 particularly the great apes, the connexion, though 

 present, becomes a little less obvious. It is clear enough 

 at puberty when the gonads mature and sexual activity 

 becomes intense, but once it has started this activity is 

 maintained almost without intermission until the onset 

 of old age. In the female the significance of the oestrous 

 period is reduced or even lost, although in more primitive 

 primates such as the lemur, Galago senegalensis mohli, 

 the female is said to permit copulation only during 

 oestrus in the manner of rats and mice.^^s However, in 

 the rhesus monkey, while the female is most ready to 

 accept the male just before ovulation, copulation may 

 occur at other times as well,2i and in the chimpanzee the 

 female will receive the male at any phase of the ovarian 

 cycle. 1^9 Conditions similar to those in the chimpanzee 

 are also found in man, the course of the ovarian cycle 

 having little if any effect on behaviour. 



The question of the relation between the gonads and 

 behaviour has also been tackled on an experimental 

 basis and the earliest of such experiments, involving the 

 removal of the gonads, were carried out in pre-historic 

 times, perhaps originally as a reprisal against conquered 

 enemies. It is now known that the results of gonad 

 removal vary with the species, the sex, and also the 

 time at which the operation is performed. In males it is 

 generally true to say that if the testes are removed during 

 immaturity there is a complete prevention of all sexual 

 activity, but that if they are removed from an adult the 

 results are variable. In the lower vertebrates the castra- 

 tion of adults usually eliminates or greatly depresses 

 sexual activity, and many examples from the fishes, 

 amphibians, and reptiles are listed by Beach.^i 



In birds, too, it is known that castration disrupts or 



