GONADECTOMY IN RELATION TO THE SECONDARY SEXUAL 

 CHARACTERS OF SOME DOMESTIC BIRDS.^ 



INTRODUCTION. 



It has been long known that an intimate relation exists between the 

 primary sexual organs of certain animals and their secondary sexual 

 characters. Until recent years, however, there has been considerable 

 doubt as to the interpretation of many of the effects of castration — 

 I. e., as to whether the effect tended toward the appearance of char- 

 acters belonging to the opposite sex. In particular, there has been a 

 dispute as to whether certain characters, such as the small comb of the 

 capon, were to be considered juvenile or female. In birds the occur- 

 rence of individuals with the plumage and other characters of the male, 

 but having the sexual organs of the female, have attracted a great deal 

 of attention. Recently, Guthrie (1910) has described a hen with male 

 plumage following ovariotomy, while Fitzsimons (1912) has reported 

 like results in the ostrich. 



Very often, and perhaps always, the records state that the ovaries of 

 male-plumaged females occurring in nature have degenerated to a 

 greater or less degree, and from this it has been inferred that the occur- 

 rence of the male plumage was in some way or other associated with the 

 degeneration of the ovary. On the other hand, the sporadic occur- 

 rence of birds with the external characters of the female and the internal 

 sexual organs of the male is relatively uncommon in races such as 

 pheasants or domestic fowl. As a rule such males, whose primary 

 sexual organs are perfectly normal, exhibit only one or two female 

 characters, the remainder of their secondary sexual characters being 

 those of the normal male. Female characters may also be normal to 

 the juvenile male. Moreover, it has been shown in the case of hen- 

 feathered males of the domestic fowl that this character is inherited in 

 a definite fashion. The occurrence of male birds with the secondary 

 sexual characters of the female, where these characters are distinct 

 from those of the juvenile male, are extremely rare. It seems highly 

 probable that, except in the very rarest of instances, female-feathered 

 males are in an entirely different category from male-feathered females. 

 (However, cf. Morgan, 1915.) Nevertheless, races exist, such as the 

 bobolink, in which the males may become nearly or quite indistin- 

 guishable from the females at certain seasons of the year. 



^This paper is based on work done at the Station for Experimental Evolution of the Carnegie 

 Institution of Washington, while the author was a member of the staff at that station. It has 

 been necessary, however, to include some observations made at the Massachusetts Agricultural 

 Experiment Station, which relate either to matters of detail or confirm results previously obtained. 



