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 magnifica, 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. 



