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. 1). 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 
J 
Fig. i.—F eathers of sun-birds to show relation 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. 
