^6 The Bird 



have numerous httle ridges extending down the sides, 

 and in some way, by reflection, these change the yeUow 

 or black to bkie. If we take a parrot's feather and 

 pound the bhie 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 flufhness 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 

 colom- 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 



