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[Reprinted from Biological Bulletin, Vol. XX., No. i, December, 1910. 



SOME RESULTS OF CASTRATION IN DUCKS.^ 



H. D. Goodale. 



Introduction. — The present paper is largely in the nature of a 

 first report and will be followed by others as the experiments 

 warrant. In addition to a brief review of some other studies on 

 castration, I have considered, also very briefly, some problems 

 relating to sexual dimorphism, sex-limited inheritance and the 

 determination of sex. 



It is a matter of rather common knowledge that females of 

 birds and mammals, which have become sterile from any cause, 

 may assume the plumage and other secondary sexual characters 

 of the male. On the other hand, the male when castrated, often 

 does not develop his usual trappings. This has often been inter- 

 preted as a development of the female characters. It has, 

 however, been pointed out that castration of the j'oung male 

 causes rather a retention of his own youthful characters. 



Castration, besides its effect on the secondary sexual charac- 

 ters, may lead to certain specific changes in the organism, not 

 correlated with secondary sexual characters. Thus the capon 

 grows larger than the cock and is more sluggish. Tandler and 

 Grosz found in man, among other things, that there was a ten- 

 dency for fat to develop in certain regions, and either a failure, 

 or poor development of body, axial, and pubic hairs. 



The present paper deals almost w^holly with the effect of cas- 

 tration on the secondary sexual characters. 



The breed known as Rouens was selected for this work, largely 

 because they are strongly sexually dimorphic in plumage.^ 



The Rouens are probably derived from the mallard, Anas 

 boschas. Coues says, "nearly everywhere domesticated, being 

 the well known original of the barnyard duck." In some respects 

 the Rouens differ from the mallard. The latter are much smaller. 



'For the suggestion of studying the effects of castration in ducks, I am indebted 

 to Professor T. H. Morgan. 



2The individuals used in these experiments were reared from eggs secured from 

 the White Birch Poultry Farm, Bridgewater, Mass. 



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