Feathers 



33 



The two lines of barbs which grow out on each side 

 of the quill are very elastic and so intimately hooked to 

 each other that they will bend some distance before sepa- 

 rating. If we ever tried to force our way through a 



FIG. 21. Model showing interlocking barbules and barbicels of feather, 

 greatly enlarged. 



bramble of sweet-brier or blackberry- vines, we can more 

 readily appreciate how these barbs and the interlocking 

 barbules clutch each other. The thorns in the bramble 

 catch our clothes and, when we move, the elasticity of the 

 long stems tends to make them hold the tighter. 



We notice that one line of barbs that along the 

 inner curve of the quill is much longer than that on the 

 outer curve and we might think the air would force this 



