56 The Bird 
have numerous little ridges extending down the sides, 
and in some way, by reflection, these change the yellow 
or black to blue. If we take a parrot’s feather and 
pound the blue portion, that colour will disappear and 
the vane will become black. 
It is surprising to see how the colours of many beau- 
tiful feathers will vanish when we hold them between 
our eye and the light. When we look at feathers under 
the microscope, and see their horny rays, we forget, for 
a time, the delicacy and fluffiness which the bird’s plumage 
as a whole exhibits, and we are constantly reminded of 
the scales of reptiles. And in colour we have another 
similarity between the two: lizards have both pigment 
and prisms, and the scales of large snakes glow like opals 
when the sunlight falls on them. 
White never exists as a pigment in the feathers of 
birds, but is always due to innumerable air-spaces in the 
substance of the feather, by which the rays of light are 
reflected and deflected until, as in snow or foam, all 
colour is lost and white results. 
In any one Order of birds there may often be found 
a series of species with colour patterns grading into each 
other and connecting two extremes, perhaps very diverse 
in appearance. But it is seldom that we can examine 
such a series at once, and, except in a large collection of 
birds’ skins in a museum, these wonderful life-chains, or 
twig-tips of the tree of evolution seldom appeal to us 
very forcibly. But in a feather it is different. We may 
find on one bird a most delicately graduated series, show- 
ing every step in the process by which simple unicoloured 
