CHAP. XIII 



THE COLOURS OF BIRDS 



263 



feathers, we shall consider their characteristics in 

 detail. 



We shall take first a quill, such as one of the 

 primaries of the wing (see Fig. i). Such a feather 

 consists of a central axis or stem bearing on its upper, 

 portion a large number of lateral growths — the barbs. 

 The lower naked part of the axis forms the quill, 

 while the whole of the remainder of the feather is 

 known as the vane and consists of a central rachis 



Ni 



Fig. I. — Feathers of sun-birds to show i-elation between 

 colour and shape. The quill-feather was uniformly coloured 

 except for a slight edging of metallic colour at one side ; the 

 short feather shows three zones — a terminal metallic zone, a 

 median dark-coloured and slightly V-shaped zone, and a 

 downy basal zone. 



and lateral barbs. The barbs of the vane are closely 

 connected together, and on pulling them gently 

 apart, it is possible to see that they bear on either 

 side innumerable small processes, the barbules. The 

 barbs cling together because the barbules are locked 

 to one another in a manner presently to be described. 



