FEATHEES. 187 



In the feathers of a large portion of birds there is a plumiform 

 formation, or small feather or plumule. This plumule is conspi- 

 cuous in gallinaceous birds — for instance, the Pheasants (Fig. 53) ; 

 it springs from the fore part of the tube, just at the commence- 

 ment of the shafts ; it gradually narrows, and is continued in the 

 form of a very delicate, thread-like fibre ; from! its side proceed 

 two series of barbs, and from the barbs two series of barbules, 

 extremely fine, entirely disunited, and very loose. This plumule 

 seldom exists among aquatic birds, but in gallinaceous fowls it 

 attains the length of two- thirds of the feather, and in the Emu 

 and Cassowary it equals it in length. 



Feathers may be divided into those specially employed as the 

 means of locomotion and those intended to protect the bird from 

 extreme cold. The former are much stronger, more compact, and 

 more elongated than the others. The row of feathers bordering 

 the wing behind is known as the alar quills, or wing-quills, and 

 those terminating the extremity of the tail, as caudal quills. From 

 the head, backwards to the tail, the feathers increase in strength 

 and size ; those on the face, or round the base of the bill, being 

 smallest, the tail-coverts longest. Immediately covering the base 

 of the wing-qunis 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, 

 and the more tropical the climate the more dazzling and brilliant is 

 the plumage. In many species the brilliant plumage is confined to 

 the males, while that of the females is dark and sombre. In other 

 cases it is the 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, in order to 

 put on a fresh dress. This is called moulting — a -change which 

 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 lively colours, which now rival the gayest flowers that 

 surround them. 



Among the gallinaceous birds, and especially among the 

 aquatic species, there exist over the coccyx certain receptacles 



