THE ENGLISH SPABROW 3T'.t 



and serving to carry the great flight feathers. The hinder 

 appendages, used as legs, I)ear four toes, whose great spread 

 serves to increase the base of support for the relatively large 

 body. 



Body Covering. — The feathers are of two general sorts, 

 those which form a relatively close covering over the body 

 of the bird and serve to maintain its high temperature, and the 

 great quill feathers which are the main organs of flight. Those 

 which are borne on the fore limbs serve to propel the bird 

 through the air, whereas those which arise from the tail may, 

 by their change in position, control the direction of flight. 

 The earhest feathers of the young pigeon are called " down " 

 feathers, and consist of a cylindrical base which breaks up into 

 many branches above the skin (Fig. 350 C) . Among the main 

 body-feathers of the adult there are found hair-like feathers 

 which break up into several branches at the tip (Fig. 350 B). 

 These feathers serve as connecting links to show the real 

 relations between feathers and hair. The remaining feathers 

 of the adult plumage are, however, much more comi^licated 

 (Fig. 350 A). They consist of a central shaft which passes 

 into the quill below the level of the skin. Outside the skin, 

 however, the shaft bears on each side a row of " barbs," 

 which, taken all together, make up the " web " of the feather. 

 The barbs cling together so that the web acts as a unit, and as 

 the web is concave toward the downward stroke and convex 

 toward the upward stroke, the air is held better in the down 

 stroke, and this is therefore the more effective in lifting the 

 bird than the upward stroke is in depressing it. When a single 

 barb is removed from the web, it will be seen to bear two rows 

 of microscopic organs which are the interlocking apparatus 

 (Fig. 351). The organs on that side of the barb facing the tip 



