SEXUAL BEHAVIOUR 85 



Ovary removal in the female has similarly depressing 

 effects on mating behaviour. If the operation is carried 

 out when the animal is young the appearance of sexual 

 activity is prevented altogether, and if it is carried out 

 when the animal is adult then such activity disappears 

 completely in the great majority of cases. The effect is 

 more clearly defined than that obtained by castration in 

 the male, and it has been demonstrated in all vertebrate 

 classes. Even in the case of the mammals the effect is 

 clear cut, and, again unlike the male, it develops imme- 

 diately after the operation instead of appearing gradually. 

 However, as usual, the case is confused in the human by 

 psychological and social factors, so that the removal 

 of the ovaries results in little if any loss of sexual 

 activity. 2 r 



Before leaving this subject, a curious reaction which 

 sometimes follows the removal of the ovaries of birds 

 must be mentioned. Most birds possess only the left 

 ovary, and, when this is taken away, interesting be- 

 haviour changes may follow. In a hen, the first reaction 

 is normal with a loss of interest in the nests, the cessation 

 of cackling, and the disappearance of the normal female 

 reactions when approached by a cock.^' Later, however, 

 the bird may start to develop male plumage and a comb, 

 and to crow and otherwise show male behaviour. This 

 result was baffling until it was found to be associated 

 with the development of the rudimentary right gonad. 

 Apparently, when the left ovary is removed the 

 secretion rate of gonadotropic hormone from the 

 anterior pituitary rises unchecked to a maximum to 

 stimulate the growth of this normally quiescent organ. 

 In these circumstances, for reasons which have not yet 

 been fully explained, the growth is commonly bisexual 

 and results in the appearance of both oocytes and 

 spermatic tubules to form an ovo-testis. It is when the 

 spermatic tubules appear that the male behaviour de- 

 velops and the bird crows regularly. 



This introduces the interesting subject of sex reversal, 



