i 5 6 



ANIMAL BIOLOGY 



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 

 called the quill. The part 

 of the shaft bearing the 

 vane is called the rachis 

 (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- 

 bides, and these again have 

 shorter branches called bar- 

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

 form of hooklets (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 



FIG. 292.--!, CONTOUR FEATHER. 



II, III, PARTS OF QUILL FEATHER, 



enlarged. 



-Sh. 



FIG. 293. A DOWN 

 FEATHER, enlarged. 



