SEXUAL CHARACTERS OF SOME DOMESTIC BIRDS. 7 



The terms primary, accessory, and secondary sexual characters have 

 been used in their usual significance — i. e., the primary organs are the 

 testes in the male, the ovary in the female. The accessory characters 

 are the vasa deferentia and the penis or papillae in the male, the oviduct 

 in the female. The secondary sexual characters include in a broad 

 sense all the other characters in which the sexes differ. No attempt, 

 however, has been made to cover so wide a field, but attention has been 

 limited to the more obvious characters. There are many details of 

 interest that thus far it has been impossible to study thoroughly and 

 which will have to be left for the future. 



In describing results, the words "male" and "female" have often 

 been used in a purely descriptive sense. Thus, "male" feathers in a 

 female means of course that such feathers are indistinguishable from 

 similar feathers found in males, and so on. No impUcation is made 

 as to the actual nature of the feathers. 



THE MATERIAL. 



During the course of the work, experiments have been performed on 

 both pure-bred and cross-bred birds of both sexes, a majority of which 

 have been pedigreed. The cross-bred ducks were derived originally from 

 Rouen and Pekin crossed reciprocally. The cross-bred fowl were mostly 

 from a White Plymouth Rock and Brown Leghorn cross. The results 

 obtained from the cross-breds have agreed in a general way with those 

 obtained from pure-bred birds. In detail, however, their use intro- 

 duced some complications which are discussed in the body of the paper. 

 For the pure breeds, Rouen ducks and Brown Leghorns were selected, 

 not only because they represent the acme of sexual dimorphism among 

 easily available domestic birds, but because they offered an opportunity 

 to determine whether or not the male assumes female characteristics as 

 a result of castration or whether the so-called female characters are in 

 reality j uvenUe . Moreover, it seemed wise in the case of the fowl to have 

 birds that were relatively homogeneous in respect to the size and form of 

 comb, particularly for the work with the male. Previous observers of 

 the effects of caponization, so far as I have had access to their papers, 

 have not usually paid sufficient attention to the variety of fowl used. 

 As it happens, the variety of birds used for capons, at least in this 

 country, are mainly the small-combed breeds. Hence, at best, the 

 capons would have relatively small combs. The Leghorns, however, 

 have large combs in each sex, a feature which might affect the size of 

 the capon's comb. Moreover, in heredity, the small comb is at least 

 partially dominant over the large — i. e., the offspring of a cross between 

 a small-combed and a large-combed race approximated in size that of 

 the small-combed parent.^ 



'Unpublished data. 



