SEX BIOLOGY AND PSYCHOLOGY 143 



are affected by a certain type of tumour, the bird stops 

 laying, her comb and wattles enlarge to the size of a 

 cock's, her spurs grow, she begins to crow, her plumage 

 changes at the moult and becomes cock-like, and finally 

 she becomes indistinguishable from a male. Indis- 

 tinguishable, even in behaviour : her years of feminine 

 routine in laying and brooding are forgotten : the 

 secretion of the altered ovary now apparently re- 

 sembles that of a testis and stimulates centres of 

 the brain which would otherwise have remained per- 

 manently dormant. She struts and crows, fights and 

 mates, and the memory of the previous part of her 

 life is for all practical purposes lost, since the centres 

 for female activity are no longer stimulated at all. 



Various workers have even experimentally produced 

 a state of hermaphroditism in mammals by simultaneous 

 grafting of portions of testes and ovary : the be- 

 haviour here oscillates between male and female.^ 



It is quite clear from these and other facts that in 

 higher vertebrates there are present in every individual 

 of either sex the nervous connections which give the 

 possibility of either male or female behaviour ; but 

 that normally only one of these two possibilities is 

 realized, since for the potentiality of action given by 

 the nervous connections to become actual as be- 

 haviour it is necessary for the nervous system to be 

 activated by the secretion of one or other of the 

 reproductive organs. Castrated animals fail to realize 

 * See Lipschiitz, '19J Goldschmidt, '23. 



