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A BOOK OF BIRDS 



us back to phases of development which belong to ancient types of 

 birds long since extinct, others carry us yet farther, and show, in a 

 way that makes contradiction mere stupidity, that the birds and the 

 reptiles have descended from the same common stock. 



Concerning Feathers, — Though feathers are so common, so 

 easily procured, yet but few people, even ornithologists, realise 

 what marvels of structural beauty, what wonders of mechanism, they 

 are ; nor is the peculiar fashion of their distribution over the body 

 even now generally recognised. Those who have spent their lives in 

 the study of live birds, as many of my readers have doubtless done,, 

 need not be told that the feathers of a bird are peculiar in that they 

 are not, as a rule, generally or evenly distributed over the body, after 

 the fashion of hairs on a dog, for instance, but, on the contrary, are 

 arranged in long and generally narrow bands, or " tracts," separated 

 by wide, bare, or sometimes down-clad spaces. 



The fact that these bands vary greatly in shape among birds was 

 first realised by a German naturalist named Nitzsch, who made a 

 long and careful study of the feather tracts of all the birds he could 

 get hold of. As a result of his patient work, he was able to show that 

 the variations in this arrangement followed certain definite lines, 

 each group of birds possessing a type peculiar to itself ; and, for the 

 purposes of convenient description, he gave these tracts distinctive 

 names, which, in the main, are followed to this day. 



Briefly, as a result of his work, he distinguished : (i) a head 

 tract, formed by the feathers clothing the head ; (2) a spinal tract, 

 extending from the head down the back of the neck, and along the 

 back to the tail ; (3) a ventral tract, running from the throat down 

 to the base of the neck, where it branches at the shoulders, to run 

 down over the breast and abdomen in the form of two bands, a broad 

 outer and a narrow inner band ; (4) a pair of humeral tracts, which, 

 crossing the upper arm, form the feathers known as the scapulars ; 

 (5) the wing tract, including the quills and wing-coverts ; (6) the 

 tail tract ; (7) the femoral tracts, which run across the thighs ; 

 (8) the leg tracts, which cover the legs below the knee. 



The most important of the variations which these tracts present 

 are to be found in the spinal and head tracts. Thus, in the first 

 named, the spinal tract in the Swifts encloses a bare space over the 



