2/4 SOME RESULTS OF OSTRICH INVESTIGATIONS. 



t 



chick and adult. Allowing for such an adaptive correlation, we 

 still have to attempt an understanding from a germinal and 

 factorial basis. Do the feather-producing factors naturally lose 

 their potency with the late chick stages, or are they inhibited by 

 some other physiological influences appearing in the chick? 



Down. 



In most flying birds a covering of down feathers or plumules 

 occurs beneath the ordinary contour feathers of the body and 

 wings, and a number of small, hair-like feathers or filoplumes 

 may also be present. Accounts of the plumage of the ostrich 

 refer to the absence of these additional small feathers, yet on 

 close examination every Nigerian and Cape bird is found to 

 <lisplay them around the base of the larger feathers on the wings 

 and tails, the degree of development varying much with the 

 individual. A casual examination of the surface of the body 

 would fail to disclose them, but farmers often remark u])on their 

 presence on the wings and tail, and have some vague notion that 

 their strong development is indicative of a good plumage bird. 

 They are usually more sparse on northern than on southern birds. 



As regards the individual feathers, some are fully developed, 

 though diminutive down, provided with quill, shaft, and flue, 

 Init by far the greater number are imperfect and degenerate. In 

 place of a single shaft, many have two f)r three imperfect ones, 

 others are tufts of barbs with barbules, while others are reduced 

 to one or two hair-like barbs without any barbules. But all inter- 

 mediate stages between the extremes can be observed on the 

 same bird. 



While the down is usually restricted in its distribution to the 

 neighbourhood of the large wing and tail ]^lumes. it is occasionally 

 found to extend over a larger area. Some birds display a sparse 

 covering of the hair-like barbs over the whole of the hind ;iart 

 of the body, including the broad lateral apteria ; 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 the 

 under part of the wing was at one time fully provided with contour 

 coverts. 



All these occurrences lend strong support to the view that the 

 ancestral ostrich was clothed with an under covering of down 

 feathers over the body generally, in addition to the covering of 

 large contour feathers, after the fashion of most flying birds. 

 Usually it is now restricted to the region of the larger wing and 

 tail feathers, but occasionally it spreads over other parts of the 

 body. In addition, the feathers are now rarely tvt)ica! down, 

 complete with quill, shaft, barbs, and barbules. The shaft is 

 usually imperfectly developed ; sometimes there is only a tuft of 

 barbs with barbules ; and again one or two hair-like barbs, 

 without any barbules, may alone persist. In other cases it is 

 found that individual feather degeneration follows the same 



