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 
