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150 Degeneration in the Ostrich 



A casual examination of the surface of the body would fail to disclose 

 them, but farmers often remark upon their presence on the wings and 

 tail, and have some vague notion that a strong development is indicative 

 of a good plumage bird. They are usually more sparse on northern than 

 on southern birds, being almost absent from some individuals. 



As regards the individual feathers some are fully developed though 

 diminutive plumules, with quill, shaft, and flue, but by far the greater 

 number are imperfect and degenerate. In place of a single shaft, there 

 may be two or three imperfect ones; some are tufts of barbs provided 

 with barbules, like the natal down, only smaller; while others are 

 reduced to one or two hair-like barbs, with or without any barbules 

 (Fig. 2). But all intermediate stages between the extremes can be 

 observed, mingled together on the same bird. The remarks already 

 made in connection with the degeneration of the coverts as regards 

 the factorial changes involved apply with equal force to the down 

 feathers, though here complete feathers are rare, and the degenerative 

 processes largely concern the loss of the factors responsible for separate 

 structural parts. 



While usually restricted to the wings and tail, down is occasionally 

 found to extend over a wider area. Some birds display a sparse covering 

 of hair-like barbs over the whole of the hind part of the body, including 

 the broad lateral apteria. The upper part of the wings may also be 

 scantily provided, and in a few instances extremely degenerate down 

 has been observed over the inner naked part of the wing, where it 

 would least be expected, were it not for the evidence already presented 

 that this was at one time fully provided with coverts. 



All these occurrences strongly support the view that the ancestral 

 ostrich was clothed with an under-covering of down feathers over the 

 wings and body generally, in addition to the covering of large contour 

 feathers, after the fashion of most flying birds. Usually it is now re- 

 stricted to the area of the larger wing and tail feathers, but occasionally 

 it spreads over the more distant parts of the body, including both 

 pterylae and apteria. In addition, the individual feathers are now 

 rarely typical down, complete with quill, shaft, barbs and barbules; 

 they mostly exhibit the later stages of degeneration, ending in one or 

 two hair-like barbs and then complete loss. 



Two definite directions in the process of degeneration are thus 

 indicated which take place concurrently, namely, a reduction of the 

 area of the body provided with down, and a diminution and loss of 

 the constituent parts of the individual feather. When completed the 



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