XXVIU 



INTRODUCTION 



wing and tail quills. In some feathers, such as have 

 a loose, hairy texture, as in the body feathers of many 

 birds, these booklets are but feebly, if at aU, developed. 

 The loose feathers of the Ostrich tribe also lack them, 

 but even here they were at one period aU perfectly 



-C'?. 



Fig. 5. — Section through two rows parallel to the distal 



RADII or BARBULES. D.R., DISTAL RADII; P.R., PROXIMAL RADII 

 OR BARBULES. 



developed; when the birds ceased to fly, the feathers 

 degenerated, and the interlocking was lost. 



What are known as semi-plumous feathers are im- 

 perfectly developed or changed feathers. 



Down feathers differ considerably from "contour 

 feathers" in structure, having little or no shaft, all the 

 barbs arising from a common base. These barbs are, 

 further, very long, and have only very minute barb- 

 ules. In the Ducks and some other birds these 

 barbules take the form of triangular nodules ; while in 

 other birds again they are knot-like. 



The filo-plmnes have a long, slender shaft with a 

 minute vane at the tip. They are, apparently, a de- 

 generate form of contour feather, judging from the 

 fact tha;t during the earlier part of their development 



