5 6 



ANIMAL BIOLOGY 



called the quill. 



of the shaft bearing 



by pressing together the two sides of a split in the "vane ? 



Does the web separate at the same place when pulled until 



it splits again ? 



The hollow part of the 

 shaft of a quill feather is 

 The part 

 the 



vane is called the racJiis 

 (ra-kis). The vane consists 

 of slender barbs which are 

 branches of the shaft (II, 

 Fig. 292). As the name 

 indicates (see dictionary), a 

 barb resembles a hair. The 

 barbs in turn bear second- 

 ary branches called bar- 

 bules, and these again have 

 shorter branches called bar- 



FIG. 292. I, CONTOUR FEATHER. 



II, III, PARTS OF QUILL FEATHER, 



enlarged. 



bicels (III, Fig. 292). These are sometimes bent in the 

 form of booklets (Fig. 292, III), and the booklets of 

 neighboring barbules interlock, giv- 

 ing firmness to the vane. When two 

 barbules are split apart, and then re- 

 united by stroking the vane between 

 the thumb and finger, the union may 

 be so strong that a pull upon the vane 

 will cause it to split in a new place 

 next time. 



There are four kinds of feathers, 



(1) the quill feathers, just studied; 



(2) the contour feathers (I, Fig. 292), 



which form the general surface of the body and give it its 

 outlines; (3) the downy feathers (Fig. 293), abundant on 



Sh, 



FIG. 293. A DOWN 

 FEATHER, enlarged. 



