THE ENGLISH SPARROW. 219 



Observe a longitudinal groove on the under side of the 

 rhachis. Place a needle point in this groove, and push 

 it along toward the calamus until it enters a small hole 

 (umbilicus). Trace the vanes downward to their origin. 

 Where is there another hole leading to the interior of the 

 calamus ? 



Examine the vane with a lens. The thin, narrow linear 

 plates of which it is made up are called barbs. Observe 

 that each barb is fringed with similar smaller plates, called 

 barbules, which, by their interlacing, form a true web, ana 

 give capacity for much resistance to very weak filaments. 

 If a piece of the vane be soaked for a time in strong alco- 

 hol, to remove air, a microscopic examination of its bar- 

 bules will discover little hooks (hamuli) along a portion of 

 their margins. 



Pluck one of the small rictal bristles from just above 

 the corner of the mouth. Examine it with lowest power 

 of microscope, to make out calamus, rhachis, and partial 

 vanes. 



There is one other part present in many feathers. It 

 may be found in one of the surface feathers of the breast 

 or back. Examine one of these with a lens. Make out 

 calamus, rhachis, and vanes, and find in addition an after- 

 shaft arising from the summit of the calamus, behind the 

 rhachis. Compare the aftershaft with the parts already 

 studied. 



The three feathers examined, together with nearly all 

 others that are exposed on the surface, and that make up 

 the contour of the bird, are contour feathers. The great 

 variation seen in these is but an intimation of what may be 

 expected in feathers of this class. 



Down feathers lie beneath and between the contour 

 feathers. Pluck the contour feathers one by one from 

 a small space on the body, and the down feathers will 

 remain. Examine one of them with a lens. Compare its 



