186 



INTEODUCTOEY CHAPTEE. 



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

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

 object is apparently the same namely, that of connecting and 



Fig. 51. Fig. 52. 



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

 the aid of a small magnifying glass, in the quills of the Gfolden 

 Eagle, Aquila chrysaetus. 



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 any other 

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

 their curvature, tends to keep them closer together. 



