i6 A BOOK OF BIRDS 



Yet another form of feather is that which is found fringing 

 the mouths of birds like Flycatchers and Nightjars. Bristle-like, 

 there will yet be found about the bases of many a few weak 

 barbs ; the eyelashes of many birds, like the Ostrich, the Ground- 

 hornbill, and some other birds, are similarly fringed with these 

 peculiar bristle-like feathers. 



The down which covers the nestlings of many birds, such as Fowls 

 and Ducks, answers to the contour feathers of the adult, but is of 

 a simpler structure ; indeed, it differs in character among different 

 species of the same group. In its most completely developed form 

 it recalls the contour feathers, having a shaft and barbs with weak 

 barbules, but those last have no distinct hooklets, hence the general 

 loose character of down plumage ; while in its more degenerate 

 form the shaft is absent, as in a true down feather. 



Where down is present in the adult, it will be found in the nestling 

 just before the feathers begin to appear. In some birds, as in the 

 Hoatzin, indeed, and young Hawks, these early down-feathers, or 

 '* pre-plumulae," attain to so large a size that they eventually play 

 a more prominent part than the typical nestling-down, or '' pre- 

 pennae," so-called because preceding the pennae, or feathers. In 

 young Cormorants the nestling-down is wholly made up of these pre- 

 plumulae, which are succeeded later, not by contour feathers, but 

 by down feathers. 



Nestling-down in its most degenerate form may be seen in young 

 Pigeons, and the young of most of the Song-birds ; while in others it 

 is altogether wanting, as in young Sparrows, and those of the Crow 

 tribe. 



Only in the nestling-down of the Game-birds, Ducks, and the 

 Ostrich tribe is there found an *' after-shaft." This, by the way, is 

 a conspicuous feature in the adult feathers of the Emeu and Cassowary 

 (fig. II, p. 29), where it forms a sort of duplicate of the main-shaft, 

 equalling it in size ; while among the higher birds it is never very 

 large, except in the Game-birds (fig. 7, p. 17), but even here it is 

 downy in texture, and is always shorter than the main shaft. 



As touching the growth of feathers, but little can be profitably 

 said here. The earliest traces of feathers must be sought for in the 

 embryo, where the first rudiments of the coming nestling-down 



