Vol. XIV 
1857 CHADBOURNE on Individual Dichromatism. 33 
EVIDENCE SUGGESTIVE OF THE OCCURRENCE OF 
INDIVIDUAL DICHROMAT ISM” IN 
MEGASCOPS ASIO. 
BY ARTHUR P. CHADBOURNE, M.D. 
Plate L. 
(Concluded from Vol. XIII, p. 325-) 
As to the cause of the altered color:— The exclusive diet of 
liver seems to be the only unusual feature in the conditions under 
which my two Owls lived, compared with other birds of prey in 
captivity; or at least, it is the most noticeable one. We have 
already seen that the change in the female was first apparent 
after this food had been alone used for about three weeks, and 
also that the smaller Owl a little later showed signs of a similar 
change; while almost an equal length of time after the liver had 
been discontinued, there seemed to be a gradual loss of the red 
tint. Was this chance, or is it a hint, as to the cause of the red 
brown color? The liver is well-known to contain an extremely 
large amount of coloring matter, and to play an important part in 
the production of the majority of the different pigments of the 
organism, either directly or indirectly. Moreover, it is a fact that 
the color of the plumage can be altered by certain kinds of food — 
thus, some breeds of the Canary (the ‘ Yellow Norwich’ among 
others), change froma pure yellow to a bright orange, if red pepper 
is daily mixed with their food; and this too without any feather 
loss, as I have myself seen. Who can tell the effect of a continued 
diet of liver, until he has tried the experiment — on an Owl? 
The way in which the colors of feathers are produced can only 
be briefly mentioned here, but a few words on the subject may 
not be out of place. In general, feather-color is due (1) to pig- 
mented matter of one, or of several colors; (2) to the physical 
effect of the structure of the part on the light rays ; or (3) to both 
of the above combined. Pigment absorbs all kinds of light ex- 
cept that on which its color depends, thus in 2 brown feather the 
only unabsorbed light rays are those which produce the sensation 
of brown, and these alone reach the eye. Black results from the 
complete absorption, or deflection of all light rays; while if none 
5 
