Auk 
34 CHADBOURNE on Individual Dichromatism. Tan 
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 
(7. é., 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 even of 
the whole plumage, not only may, but has been proved to occur nor- 
mally without 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 
1 The ‘aptosochromatism’ of Coues (C/ Auk). 
2 The above was written in 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.— Epp. ] 
