84 VERTEBRATE REPRODUCTIVE CYCLES 



eliminates song, courtship display, and other mating 

 activities. This has been demonstrated in the case of the 

 ruff, 1^2 and of the turkey. ^^3, 177 However, such ex- 

 periments are sometimes complicated by unexpected 

 secondary effects. Perhaps the most surprising case wsls 

 that reported by Riddle, ^^^ who studied pigeons which 

 were congenitally without gonads and which neverthe- 

 less developed 'complete and emphatic masculine 

 behaviour'. This observation naturally led him to deny 

 that, in this species at least, male behaviour depends on 

 the state, or even the presence, of the gonads. However, 

 an explanation of this curious state of affairs is possible. 

 It will be remembered that in the absence of the gonads 

 the anterior pituitary gland tends to become over- 

 active, to which the adrenal cortex responds by abnormal 

 grov^h.121 It has already been remarked that, when 

 excessively active, the adrenal cortex exerts a male-like 

 influence which may easily account for the male behav- 

 iour and so rob the observations of their apparent 

 significance. 



Mention must also be made of mammals in which 

 castration sometimes fails, at least for a time, to prevent 

 or depress sexual activity. Occasionally such failure may 

 also be related to the induced hyper-activity of the 

 adrenal cortex, but there is a further complication which 

 arises in these animals, particularly if they are adult at 

 the time of operation. When the testes are removed from 

 adult mice or rats there is a lessening of the desire to 

 mate, but this effect does not become apparent until 

 weeks or even months have passed. In man this delay 

 may be much longer.21 The reason for this seems to be 

 that these animals, having experienced sexual activity 

 before the operation was performed, possess a clear 

 memory which, together with the strong, if unconscious, 

 desire to imitate the actions of others and to maintain a 

 position in the social group, is sufficient to preserve 

 sexual interest and activity for a considerable time. 

 Such a tendency is particularly strong in man. 



