282 THE THEORY OF THE GENE 



Sex Reversal in Birds. 



It has long been known that okl hens, and hens with 

 ovarian tumors, may develop the secondary plumage of 

 the male, and that they sometimes show characteristic 

 male behavior. It was also kno\\m (Goodale) that after 

 the complete removal of the single left ovary of a young 

 chick, the bird, when mature, develops the secondary 

 sexual characters of the male sex. Both effects may be 

 interpreted on the hypothesis that the normal ovary of 

 the hen produces some substance that suppresses the full 

 development of the plumage. When the ovary is diseased 

 or removed the hen then develops the full possibilities of 

 her genetic composition as seen ordinarily only in the 

 male. 



It is also known that hermaphroditic fowls occur in 

 which both ovaries and testes may be present, although 

 neither, as a rule, is fully developed, and it may or may 

 not be significant that in most of these cases the gonad 

 contains a tumor. There is some doubt here whether the 

 hermaphroditic condition came first, and the tumor later, 

 or, the ovary of a normal hen becoming tumorous, a testis 

 began later to develop. In none of these cases is there 

 evidence of sex reversal in the sense that the bird func- 

 tioned at one time as a female and later as a male. One 

 case has, however, been recently reported by Crew (1923) 

 in which a hen is said to have laid eggs and reared chicks 

 (from them?) and later to have become a functional male 

 that fertilized two eggs of a normal hen. Concerning the 

 second part of the story there seems to be no question, 

 since the results were obtained under controlled condi- 

 tions, but the previous history of this hen is not perhaps 

 above suspicion, since it was apparently an unrecorded 

 member of a small flock and no evidence by direct obser- 

 vation or by trap nesting is given that she was known to 



