ORIGIN AND CHARACTERISTICS 17 



In other of these contour feathers the barbs are 

 absent altogether, the rhachis being webless ; as 

 in the wing quills of the Cassowary, the rectrice 

 wires of certain Birds of Paradise, and in most 

 of the tail-feathers of the Lyre Bird ; whilst the 

 same remarks apply to the rictal or gape bristles 

 with which so many birds are furnished, and the 

 eyelashes of such birds that possess them, as the 

 Hornbills. In some species the tip of the rhachis, 

 as for instance in the neck hackles of certain 

 Galline birds, and in some of the wing and tail 

 feathers of the Waxwings, is expanded into 

 wax-like modifications or processes. The down- 

 plumes, as their name suggests, are softer in 

 texture than the contour feathers by which they 

 are hidden, are present in greater numbers, 

 but are smaller. In these feathers the booklets 

 (hamuli) are wanting, and the rhachis or shaft is 

 often absent, the barbs sprouting from a stunted 

 calamus. In connection with this type of feather 

 mention should be made of those highly curious 

 down -plumes known technically as ^^powder- 

 downs." They derive their name from the fact 

 that the slender tuft-like barbs and barbules of 

 which they are composed are continually dis- 

 integrating or crumbling at the tips into fine 



powder. Powder-downs in some birds grow 



B 



