XIII 
THE COLOURS OF BIRDS 
281 
modified both as to structure and pigmentation. 
The quill-feathers are mostly dull in colour, but a 
close examination shows that this relative dulness is 
due to the fact that, while the barbs are as before 
coloured with bright red zoorubin, the barbules contain 
a dull brown pigment, the result being to greatly 
diminish the brilliancy of colour. Certain of the 
quills have bright scarlet longitudinal bands at their 
edges ; this is due to the fact that here the barbules 
are absent and the bright red barbs have their full 
effect. 
It would be tedious to go on to discuss in detail 
the coloration of the rifle-birds, but we may briefly 
notice that here, associated with the development of 
a large amount of melanin and the loss of the lipo- 
chromes, we have also the loss of the tendency to 
suppression of the barbules; here these tend to become 
greatly specialised, and to develop metallic colour. 
In the elongated metallic feathers of the throat of 
e.g. Ptiloris magnified , we have further the develop¬ 
ment of those V-shaped bands of which we have 
already spoken. 
The examples given above have been taken from 
birds exhibiting bright pigmental colours or subjective 
structural colours ; perhaps we may be allowed further 
to give some illustrations with regard to the objective 
structural colours, like blue and green. A blue colour 
is always entirely confined to the barbs of feathers, 
and is often associated with a suppression of the 
barbules ; it only appears on exposed parts of 
feathers. 
