THYROID AND GOXAD IX PLUMAGE. 22Q 



In post mortem examination of this bird, no trace of a definitive 

 ovary was seen. At the site of the latter, however, were certain 

 small fleshy nodules which revealed, on sectioning, masses of 

 tubules resembling testicular tubules in various stages of develop- 

 ment from sex cords, though lacking in definitive sex cells. 

 We have assumed no connection between this tissue and the 

 changes in pigmentation before us. Its significance appears to 

 lie in another direction; and its further consideration will be 

 deferred to another occasion. 



While barbule formation and melanin production are both 

 stimulated by thyroid feeding in the male, the presence of the 

 ovary in the thyroid fed female interferes with the second 

 without interfering with the first. Indeed, barbule formation 

 reaches its fullest expression in the female. Lacing, though 

 present in the hackles of the female to a limited extent, is an 

 elaborate and striking feature of those feathers in the male 

 that are especially associated with sex. 



The evidence is obviously not sufficient to warrant final 

 conclusions regarding the inhibitory effect of the ovary on 

 pigment formation stimulated by thyroid feeding. It is clear, 

 however, that males and females respond differently to thyroid 

 feeding. And that this difference is due in some measure to 

 the influence of the ovary seems equally true. As for the 

 measure of its influence and the nature of the mechanism by 

 which it is achieved, the matter is not so simple and must await 

 further investigation. 



III. 



Two classes of feather pigments have been distinguished: 

 lipochromes, which are soluble in alcohol and ether and are 

 red, rose brown, yellow and scarlet, and melanins, which range 

 from sepia to black. In our experiments, the extension of the 

 latter is correlated with the disappearance of the former. Cole 

 and Reid mention "an evident action toward the reduction of 

 red pigment." \Ve have no evidence of an actual replacement of 

 the one by the other, either by substitution or transformation. 

 It is quite consistent with our observations to assume for the 

 present that the former are merely concealed as the latter 

 advance. 



