1^2 
Jeffries on the Colors of Feathers. 
All the above pigments seem to be blended and used in gaudily 
colored birds much after the manner of paints by artists. So that 
a great variety of colors may be produced from a few pigments 
by the skilful hand of nature. 
Metallic feathers, properly speaking, are those which partake 
of the characters shown by the red crests of the Woodpeckers. 
The metallic appearance is limited to the barbs, the barbules not 
showing this peculiarity, and being quickly shed. If a feather 
from the crest of a Woodpecker, say Picus pubescens , be exam- 
ined, it will at once be noticed that the red barbs have few 
if any barbules, and that the barbs themselves are enlarged. 
Such barbules as are present, are not red but black, and only 
Serve to diminish the effects of the red parts. They would seem 
accordingly to be properly classed among useless hereditary 
organs. That the red color is due to a pigment is proved by 
dissolving it out and by its persistence when examined by trans- 
mitted light. But what causes the brilliancy which has led to 
their being called metallic? This is due to the extreme smooth- 
ness of the barbs, the horn-cells of which they are composed 
being; fused together and solid. Thus the unabsorbed rays of the 
beam of light which strikes them are reflected as a whole, instead 
of being sent in every direction by the walls of the cells as in 
most cases. The metallic feathers differ from ordinary feathers 
in the same way that window or glass paintings differ from ordi- 
nary pictures. They simply give off' much more light, and thus 
produce more marked effects on our eyes. 
The colors of metallic feathers seem to be limited to the red 
end of the spectrum, the colors varying from yellow or orange to 
red ; blue, green or purple feathers constructed on this principle 
do not seem to abound. 
So far we have only had to deal with pigments, and all has 
been plain sailing, but the various accidental colors shown by 
feathers are far more difficult of explanation. Not only are the 
parts extremely small, but the entire subject of accidental colors 
as regards organic structures has been in large part dealt with 
from a theoretical point of view. The question has not been 
how is the feather part made, but what kinds of structures will 
produce such color effects. Accordingly divers opinions have 
been expressed on the subject, the most probable of these we 
shall now endeavor to sketch out. 
