410 DR. H. GADOW ON THE COLOUR OF FEATHERS. [May 2, 
Application of the Laws of Colours to Feathers. 
I. Pigment-cotours. The simplest case. It has long been a 
matter of discussion whether or not pigment exists in feathers on 
account of its never having been successfully extracted. Recently, 
however, various pigments have been discovered. What we know 
at present about pigment in feathers is almost entirely the result of 
the investigations of Bogdanow and Krukenberg. 
Pigment may produce the following colours :— 
Black, resulting from the presence of zoomelanin, a colouring- 
matter which is probably identical with the melanin of the Chori- 
oidea. This is the pigment most universally found in the animal 
kingdom, and almost every ‘‘ black”? feather owes its colour to this 
pigment. 
Brown. Zooxanthin, found in brown feathers. A mixture of this 
and the former pigment would of course give black-brown. 
Red. The best studied feather-pigment is the ¢uracin in the red 
quills of the Musophagidee. This very peculiar stuff has hitherto 
only been found in the Touracous. 
Another red pigment is the zooerythrin ; first extracted by Bog- 
danow from Calurus auriceps, and, as a pinkish matter, from Cotinga 
cerulea. The same matter produces the red in the wattle round the 
eye of the Black Cock (hence called by Wurm, its discoverer, tetraon- 
erythrin). Zooerythrin has been found in very different birds, 
which, like Phenicopterus, Cardinalis, Ibis, and Cacatua, have 
more or less red in their plumage; it is therefore very probable that 
red is generally produced by this pigment. 
Allied to the zooerythrin is the zoorudin, a red-brown matter in 
the feathers of Cicinnurus regius. 
Zoofulvin is a yellow to greenish-yellow pigment. 
Turacoverdin is found in the green feathers of the Touracous. 
In other green feathers no green pigment has hitherto been found, 
and the same applies to blue and violet. 
We may be almost certain that, wherever we have feathers with 
the various shades of black, brown, red, and yellow, if these feathers 
do not change their colour in different positions of the eye, their 
colour is merely due to a pigment. But there may be complication ;. 
if, for instance, the deeper strata contain a black, and the upper ones 
superimposed red pigment, the whole will appear dark red. Or if 
we take red with a superimposed yellow layer, the result will be 
orange. The richness of colours will often entirely depend on the 
amount of pigment, e.g. grey. 
II. By DIFFRACTION and REFLECTION we can explain the fol- 
lowing phenomena in feathers :— 
1. White. There is no white pigment or white objective colour in 
natural objects ; and wherever we have a white object, its colour is 
due to there being an innumerable number of interstices between its 
molecules, or air-cells in its substance. ‘The whole substance of a 
white feather, the ceratinine, is colourless, but its texture forms a 
fine network. 
2. Simple reflection of light. The gloss of feathers, independent of 
