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Society Proceedings (122). 



This appearance of cock-feathering in normally hen-feathered 

 males after castration is now familiar to us. It is the purpose of 

 this paper to call attention to experiments that have led to a 

 similar transformation but in just the opposite direction, namely, 

 to the appearance of hen-feathering in cock-feathered males of 

 ordinary breeds. 



We had begun a series of preliminary experiments upon the 

 physiological correlations of certain of the ductless glands. Eighty 

 Rhode Island Red chicks were under observation. They were 

 of the same hatch. They had been divided into four lots of 

 twenty each. 



All the birds in two of the lots, both males and females, had 

 been castrated between two and four weeks after hatching. 

 Those in the other two lots were unaltered. 



Four weeks after hatching, one lot of castrated birds and one 

 lot of normal birds had begun to receive daily doses of dried thyroid 

 (Armour and Company, containing 0.2 per cent. I) by mouth. 

 The initial individual dose was 50 mg. It was increased from 

 time to time. At the end of fifteen weeks it had become 330 mg. — 

 a dose the birds were able to take without any disturbance of 

 their normal health. 



There is a striking difference between the sexes of this breed 

 of fowls with regard to the time at which the tail coverts make 

 their appearance. These feathers began to show themselves in 

 some of our birds six weeks after hatching. Five weeks later, 

 they were well developed on the normal females, in both thyroid 

 and control lots. But they had not yet appeared on the control 

 males, either normal or castrated. This absence of tail coverts 

 provided a ready recognition mark of the male. Less conspicuous 

 at this time, but nevertheless unmistakably present on the neck, 

 were the hackles characteristic of the male bird only. 



In sharp contrast with these hackled and tailless males were 

 the thyroid-fed normal males. Though the latter were upstanding 

 birds with well-developed comb and wattles, and unquestionably 

 male in carriage and instincts, they were as unquestionably female 

 in plumage, owing to the absence of hackles and the presence of 

 well-developed tail coverts. All doubt as to the sex of these 

 birds was removed when they were killed four weeks later. At 



