ORIGIN AND CHARACTERISTICS 15 



class of creatures as the most attractive of 

 organic beings ? Feathers, with the skin in 

 which they grow, form the integument of a bird, 

 and are classed with hairs, bristles, metatarsal 

 scales, spurs, claws, and bill sheaths as epidermal 

 structures. Probably many readers may think 

 that feathers grow from all parts of a bird's skin, 

 but such is not the case (with almost the sole 

 exception of the Penguins, Screamers, and Ratite 

 birds such as Ostriches). The feathers of a bird 

 grow in various tracts or well-defined patches, 

 technically called pterylae, the spaces between 

 these tracts, whether covered with down or 

 absolutely naked, being known as apteria. These 

 feather tracts are known as the pterylosis or 

 pterylographie of a bird, and as they vary a 

 good deal in their pattern or direction in the 

 several groups, their study is of some importance 

 to the ornithologist in his efforts to form a 

 natural classification of birds. Feathers not only 

 grow upon the newly formed chick, but at 

 certain intervals of time upon the adult bird, 

 when they are renewed either to replace acci- 

 dental loss, or at the seasons of the moult when 

 the old plumes are shed or pushed out by an 

 entirely new set. We may define feathers then 

 as horny products of the epidermal cells of the 



