INTEODUOTOEY CHAPTEE. 



to it (Figs. 51, 52). The barbules themselves frequently throw- 

 out filaments in the same manner, which are called barbkels, whose 

 object is apparently the same — namely, that of connecting and 



Fig. 51. Kg. 53. 



retaining the barbules in position. These may be observed, by 

 the aid of a small magnifying glass, in the quiLls of the Golden 

 Eagle, Aquila chrymetus. 



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

 the webs ; the webs being the barbs furnished with barbules, some- 



Fig. 53. Fig. 54. Fig. 55. 



times barbicels. They are convex above, and are thus enabled to 

 resist flexion or fracture better from beneath than from anjr other 

 direction. They are also elastic ; and this property, together with 

 their curvature, tends to keep them closer together. 



