226 BENJAMIN HORNING AND HARRY BEAL TORREY. 



as the hackles, saddles and sickles are longer and possibly more 

 highly colored. The plumage is more luxuriant, more masculine. 

 That it becomes more deeply pigmented with melanins as a result 

 of thyroid feeding, however, does not appear from our obser- 

 vations. 



In sharp contrast with the effect of thyroid feeding on the 

 coloring of the male bird is its effect on the normal female. 

 Our evidence on this point has been obtained first, from females 

 that had received a daily ration of thyroid approximately 

 i : 5000 body weight for at least a year, beginning with the second 

 to fourth week after hatching; second, from females approxi- 

 mately two years old that had been plucked in hackle and 

 saddle regions to stimulate the eruption of new feathers and 

 then placed on the same ration of thyroid as the others. 



In the first group, thyroid feeding produced no departure in 

 coloration from the controls. One conspicuous instance of this 

 absence of thyroid effect was supplied by three hens whose 

 parents as well as themselves had been on a thyroid ration 

 practically all their lives. When a year old, they were not 

 distinguishable from their controls. 



In the second group were five hens. In the new feathers 

 that appeared on the denuded areas during the period of thyroid 

 feeding there was little or none of the brown mottling charac- 

 teristic of the controls, and a correspondingly wider distribution 

 of dark pigmentation, less intense than in corresponding feathers 

 of thyroid males, but present in all the experimental birds. 



If these observations accurately represent typical conditions, 

 it may be said that the plumage of Brown Leghorn females 

 darkens under the influence of thyroid feeding, as indicated, but 

 not to the same degree as in males of the same age, and ap- 

 parently not at all in birds in their first year. 



A comparable difference in the effect of thyroid feeding on 

 the two sexes has also been observed among Barred Plymouth 

 Rocks. It is the male, rather than the female, whose plumage 

 darkens in the course of the early moults. 



These facts suggest a possible inhibitory influence of the 

 ovary in this connection, a view which receives strong support 

 from the following case. 



