5 34 CHORDATA 



existence in many feathers of a rudimentary feather, the hyporachis, 

 or after-shaft, attached to the scape below. 



In contour feathers the barbs are, to a great extent, united into a vane. 

 They lie close together and parallel, right and left of the shaft, each repeating in 

 miniature the entire feather, the barb having branches or barbnles, which, over- 

 lapping the barbules of adjacent barbs, give the vane its close texture. The 

 vane is held together by minute hooks on the barbules of one barb interlocking 

 with those of the next. Down feathers (plumes) differ from contour feathers in_ 

 the absence of hooks and the loose arrangement of the barbs. Since feathers 

 consist of cornined epithelium and these cells are held firmly (only in powder 

 down is there a gradual loss), they, like the scaly coat of the snakes and lizards, 

 must be molted yearly and replaced by new. 



Young birds or embryos have only down feathers. Later the contour 

 feathers arise in regularly arranged feather tracts, or pteryla, between which are 

 apteria in which no contour feathers appear (fig. 583). Since the contour 

 feathers overlap like shingles, they form a firm coat beneath which the down 

 and semiplumes .form a warm coat. Besides these covering feathers (coverts, 

 or tectrices, fig. 584, D) there are the longer feathers of the wing, the remiges, 

 and the tail feathers, or reel-rices (Sz). The larger remiges form the chief part 



FIG. 585. Wing skeleton of stork (from Gegenbaur). c, c', carpalia of first 

 row; h, humerus; m, fused metacarpals and carpals of second row; p-p", phalanges of 

 first three lingers; r, radius; u, ulna. 



of the wing; they spring from the part of the limb corresponding to the hand 

 (carpus, metacarpus, phalanges) and are known as primaries (HS), while the 

 secondaries (As), arising from the forearm, are shorter. These are overlapped 

 at the base by the coverts (D, D', D") and by the parapterium (SF) springing 

 from the shoulder. A few feathers arising from the first finger remain distinct 

 from the remiges and form the alula (EF). In the water birds especially the 

 feathers are oiled by the secretion of a pair of glands at the base of the tail 

 above the coccyx. 



Since the feathers are not only for protection, but give to most birds 

 the power of prolonged flight, they predicate a special mode of life, 

 under the influence of which all of the other organs exist. The character 

 of the skeleton, the respiratory organs, and in part the sense organs and 

 brain, are connected with the power of flight. 



As the feathers of the wings, like the fins, form what may be called a 

 paddle working as a whole, the skeleton of these limbs is simplified (fig. 

 585), first, by the reduction of the fingers, of which only three with a small 

 number of phalanges persist (p, p', p") ; second, by fusion of the corre- 



