172 REPTILES AND BIRDS. 
more elongated than the others. The row of feathers bordering the 
wing behind is known as the a/ar guills, or wing quills, and those 
terminating the extremity of the tail, as caudal quills. From the 
head, backwards to the tail, the body feathers increase in strength 
and size, also alter in form ; those on the face, or round the base of 
the bill, being smallest (Fig. 53), the tail-coverts longest (Fig. 54). 
Immediately covering the base of the wing quills are a row of feathers 
on both surfaces of the wing ; these are the quill coverts. 
The most brilliant feathers are found in birds of warm climates. 
In many species the brillant plumage is confined to the males, while 
that of the females is dark and sombre. In other cases it is the 
Fig. 52.—Plumule. Fig. 53.—Neck covert. Fig. 54.—Tail covert. 
same in both sexes. The young of some species attain the adult 
appearance after the first moult ; others take several years to acquire 
their full splendour. 
Birds cast their feathers at least once a year. This is called 
moulting, and usually occurs in the autumn, but sometimes both in 
spring and autumn. During the moulting season Birds are dull, 
retiring, and silent; but when they emerge from this state they 
proudly display their brilliant plumage, which sometimes rivals the 
gayest flowers. 
Among the Gallinaceous Birds, and especially among the aquatic 
species, there exist over the coccyx certain receptacles which distil 
the oily substance with which they lubricate their plumage. These 
receptacles are known as the uropygial glands, On its lower surface 
