126 PROCEEDINGS OF THE ACADEMY OF [1896, 



Gatke formerly repudiated, and oue which other advocates of the 

 " color-change " theory have generally left untouched, i. e., the theory 

 that simultaneously with the change in color there occurs a rebuild- 

 ing of the worn edges of the feathers which restores all the even 

 contours and gives them the appearance of newly molted feathers. 



The acceptance of the theory of color-change without molt or 

 abrasion, necessitates the adoption of some such theory as this, since 

 the bright spring feathers are generally much more perfect in outline 

 and often in striking contrast to the worn winter plumage from 

 which Schlegel and Gatke would have us believe they have been 

 produced. A slight knowlege of the development of feathers would 

 tend to show the absurdity of such a theory as this, since the barbs 

 of a feather do not continue to grow out from the shaft like the 

 limbs of a tree, but are really formed from the tip inward toward 

 the shaft. And once being unfolded from the sheath of the " pin 

 feather," no further structural development can possibly take place 

 in them. 



Too many writers have made arbitrary statements and then ques- 

 tioned the accuracy of the investigations of histologists because they 

 did not support them. In investigating these questions, we must 

 accept at the outset the testimony of physiologists and histologists, 

 that from the very nature of the structure of a feather it is incapable 

 of renewing its barbs or barbules, and that after the contents of the 

 quill have once dried up there is no connection between the vanes 

 of the feather and the life fluids of the bird. This at once precludes 

 the change of pigment, except by chemical action from without, and 

 it is difficult to see how this should only exert an influence during 

 a certain short period and have no effect at other times. 



It has been suggested that the presence of innumerable bubbles 

 of air would tend to obscure the pigment in a feather and cause it 

 to appear white, while the expulsion of air from a white feather 

 might bring out a dark pigment previously concealed. In the case 

 of the Motacilla, however, portions of the plumage turn white and 

 other parts black at the same time and it is hard to understand how 

 an external action could affect different feathei's in an exactly 

 opposite manner, and if there was proved to be exhalation from the 

 body into the feather, the structure of the feather would preclude 

 a passage of air into the barbs from the quill. It might further be 

 added, that the yellow feathers of Zanthopygia, which should accord- 

 ing to this theory contain a concealed dark pigment, have really no 



