FEATHERS. 



171 



by the aid of a small magnifying glass, in the quills of a Golden 

 Eagle. 



Feathers, then, consist of three parts — the tube, the shaft, and 

 the webs (Figs. 48, 49, 50) ; the webs being the barbs furnished with 

 barbules, sometimes barbicels. They are convex above, and are thus 

 enabled to resist flexion or fracture from beneath better than from 

 any other direction. They are also elastic ; and this property, com- 

 bined with their curvature, tends to keep them closer together. 



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



Fig. 48.— Tube. Fig. 49.— Shaft. Fig. 50.— Web. 



Fig. 51. — Plume. 



formation (Fig. 51). The plumule is conspicuous in gallinaceous birds 

 ; — for instance, the Pheasants (Fig. 52) ; it springs from the fore part 

 of the tube, just at the commencement 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 



