SEX BIOLOGY AND SEX PSYCHOLOGY 143 



seen in fowls. Here nature makes a number of ex- 

 periments, which have recently been studied by Dr. 

 Crew of Edinburgh. When the ovaries of a hen 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 plum- 

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

 finally she becomes indistinguishable from a male. 

 Indistinguishable, even in behaviour: her years of 

 feminine routine in laying and brooding are forgot- 

 ten : the secretion of the altered ovary now apparently 

 resembles 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 pro- 

 duced a state of hermaphroditism in mammals by 

 simultaneous grafting of portions of testes and 

 ovary: the behaviour here oscillates between male 

 and female.^ 



It is quite clear from these and other facts that in 

 higher vertebrates there are present in every indi- 

 vidual of either sex the nervous connections which 

 give the possibility of either male or female be- 

 haviour; but that normally only one of these two 

 possibilities is realized, since for the potentiality of 

 action given by the nervous connections to become 



8 See Lipschiitz, '19; Goldschmidt, '23. 



