THYROID FEEDING AND SEX CHARACTERS. 



373 



To a less but still striking degree, the hackles of the thyroid-fed 

 males tended to assume the aspect of female hackles. Compare, 

 with this in mind, Fig. 6, a, b, with Fig. 6, e,}, g, h. And note also 

 that, in this series of feathers, the hackles of the female, which 

 are here exceptionally male in structure, are modified in the same 

 direction. 



To a still less degree than the hackles do the saddle feathers of 

 thyroid-fed males approximate the saddles of normal females: 

 yet here too the changed shape of the feather and the added 

 barbules and consequent diminished lacing suggest the female 

 type. 



a be 



FIG. 7. Saddle feathers from R. I. R. birds about seven months old: b, from a 

 normal male; a, c, from a thyroid-fed male. 



By way of summary it may be said that when male Rhode 

 Island Red chicks were fed desiccated thyroid in daily doses 

 increasing with their weight, two general effects were observed: 



1 . Their plumage appeared precociously but differentiated later 

 than usual, so that at the age of 12 weeks they were feathered like 

 females. It was to this effect that our earlier observations 

 referred. 



2. Their adult plumage, though prevailingly male in type, 

 exhibited characteristics of form and structure, especially in the 



