5O H. D. GOODALE. 



in different groups. In a given species, castration remodels the 

 secondary sexual characters of only one sex. The case of the 

 stylopized Andrenidae recorded by Perez, in which reciprocal 

 modifications took place, seems in the light of present knowledge 

 to be somewhat doubtful (Wheeler) . At present, then, the effects 

 of castration, so far as it affects the secondary sexual characters, 

 agree with breeding experiments in indicating that one sex only 

 is heterozygous for sex. 



The view that the male in birds owes his secondary sexual 

 characters to the addition of something to the female type, is 

 not supported by these experiments on ducks, for it is quite 

 clear that the female owes her color to the ovaries or something 

 associated with them, which previous to castration, suppressed 

 the male characters and which insured the development of her 

 own type of plumage. The female's plumage is obviously a 

 protective adaptation. From an evolutionary standpoint, it is 

 quite as conceivable, that selection should operate to pick out the 

 inconspicuously colored females, as that the greater vitality of the 

 male, or a selection of the more brilliantly colored males by the 

 females, should bring about an addition to the female's type of 

 plumage. 



For the present, I think it makes little difference whether we 

 assume that the ovaries themselves or a modifier always trans- 

 mitted with the ovaries, prevents the development of the male 

 characters. The evidence of the possible presence of a modifier, 

 however, renders possible a somewhat different suggestion re- 

 garding the mode of sex-limited inheritance than has previously 

 been expressed. 1 It involves also a number of possibilities re- 

 garding the inheritance of sexual dimorphism of plumage. 



The Brown Leghorns are highly sexually dimorphic in plumage. 

 In cross breeding it is found that the female transmits this 

 color to her male offspring only, though the male transmits it 

 to all his offspring. Barring, likewise dimorphic though in less 

 degree, is transmitted is the same way. But that this is a 

 universal rule for poultry with sexually dimorphic plumage ap- 

 pears to be somewhat doubtful. The penciling of the Dark 



^ex-limited inheritance appears to occur in ducks. A paper on this subject 

 in preparation. 



