7 4 Chadbourne ou Individual Dichioinatisin. ft" 



of the spectral colors fail to reach the eye, the combination pro- 

 duces white. In addition, an almost endless variety of colors, 

 shades and tints are caused by mixtures of different ' pigments,' 

 much in the way we use different paints. The action of the 

 structure and form of the colored parts is, on the other hand, 

 purely physical ; for example, the lateral branches, forming the 

 vane, may have their surfaces so shaped, as to produce the effect 

 of a multitude of small prisms, by which the different colored 

 rays are made to diverge, only those of a certain color reaching 

 the eye ; perhaps, as believed by Gadow, slight movements bring 

 different kinds of rays successively to the eye, and iridescence is 

 the result. 



Color-change in the individual feather, — or, in a broader sense, 

 in the plumage as a whole, without adequate new feather-growth 

 (/. (?., without a so-called ' moult ')} seems to have received little or 

 no attention from ornithologists in this country during the past 

 quarter of a century or more.'^ Yet about 1850, when the theory 

 of " color-change without moult " was revived by Schlegel and 

 Martin independently, German ornithological literature teemed 

 with articles on this subject ; and it had been proved even prior 

 to this that the plumage might be completely altered in color 

 without feather-loss or new feather-growth. And such color- 

 change also seems to be normal, and probably recurs at regular 

 intervals in certain individuals and conditions among various 

 species. It has been shown in connection with the subject of the 

 ' Spring Plumage of the Bobolink,' ^ that feather-change and color- 

 change are two distinct processes ; but the point which concerns 

 us at present is that a change in the color of the feather^ or eveii of 

 the whole plumage^ tiot only may, but has been proved to occur nor- 

 mally ivithout increase of feather-loss. 



The color of my Owls was evidently due to pigmented matter, 

 and was practically independent of the physical action of the 

 structure of the part on the light rays. Morphologically, one 



' The ' aptosochromatism ' of Coues ( Cf. Auk). 



^ The above was written m 1894, before the recent articles of Allen, Chap- 

 man, Stone and others had appeared. 



3 'The Spring Plumage of the Bobolink.' Auk, Vol. XIV, pp. — . [The 

 publication of this paper is necessarily deferred till the April number. — Edd.] 



