288 



THE STUDY OF ANIMAL LIFE CHAP. 



songs. They love much and 

 joyously, and live a life re- 

 markably free and restless, 

 qualities symbolised by the 

 voice of the air in their 

 throat, and by the sunshine 

 of their plumes. There is 

 more than zoological truth 

 in saying that in the bird 



FIG. 93. ONE OF THE WING- 

 FEATHERS OF A GOLDEN EAGLE ; 

 THE VENTRAL SURFACE is 

 SHOWN. 



The student should carefully 

 verify all the points and study other 

 kinds of feathers, e.g. down. 



The axis of the feather consists 

 of a hollow cylindrical calamus (C) 

 or quill, and of a solid, rather quad- 

 rangular rachis (f?) which carries 

 the barbs composing the vane. The 

 barbs are linked together by visible 

 barbules and by microscopic bar- 

 bicels. The dorsal surface of the 

 rachis is convex ; the ventral sur- 

 face has a groove. 



As long as the feather is growing, 

 blood enters by a minute hole (IU) 

 the inferior umbilicus at the 

 base of the quill. The base is em- 

 bedded in a pit or feather follicle 

 in the skin. 



At the upper end. of the quill 

 there is an unimportant slit (SU) 

 called the superior umbilicus, and 

 near this there is a tuft of barbs, 

 called the aftershaft (AS). In some 

 birds, such as the emu, the after 

 shaft is as long as the shaft. 



" the breath or spirit is 

 more full than in any other 

 creature, and the earth 

 power least," or in thinking 

 of birds as the purest em- 

 bodiments of Athene of the 

 air. 



But just as there air 

 among mammals feverish 

 bats with the power of true 

 flight, and whales somewhat 



