272 COLOUR IN NATURE chap. 



pigment, while the barbs stand out as being of a dull 

 yellow colour, apparently produced by a mixture of 

 lipochrome and melanin. This type is seen in most 

 of the females and in the males of the inconspicu- 

 ously coloured species. Taking such a feather as a 

 starting-point, we may have divergence in two direc- 

 tions. In the first case, the lipochrome pigment 

 may increase greatly in amount, and colour the barbs 

 very deeply, while the dull barbules do not become 

 brightly coloured, but tend to become rudimentary 

 and disappear ; thus we get the bright red or yellow 

 patches formed. On the other hand, the lipochrome 

 may get swamped by the development of a large 

 amount of melanin, which occurs not only in the 

 barbs, but also in the barbules. At the same time, 

 the modified barbules near the ends of the barbs 

 progress further in the direction in which they have 

 begun to develop, become converted into completely 

 metallic barbules, and thus give rise to the band of 

 metallic colour seen at the ends of the general 

 contour - feathers of many males, e.g. Nectarinia 

 famosa. When, as in Cinnyris frenatus, the ventral 

 surface of the male has both metallic colour and 

 bright pigmental colour, it is possible to find in- 

 dividual feathers displaying both tendencies — that is, 

 with naked yellow barbs at the tip, then metallic 

 barbules placed on a dull-coloured region of the 

 barb, and then the covered unspecialised region of 

 the feather. 



In quill - feathers the tendencies as to colour 

 evolution seem slightly different. The quills of the 

 females, of the unspecialised species, and of the 

 wings of perhaps all species are a dull brownish 



