INTRODUCTION xxix 



many more barbs are present than are to be found in 

 the fully grown filo-plume. 



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 these last have no 

 distinct booklets, 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 ap- 

 pear. In some birds, as in the Ducks, indeed, and 

 young Hawks, these early down-feathers, or "pre- 

 plumulas," attain so large a size that they eventually 

 play a more prominent part than the typical nestling- 

 doAvn, or "pre-pennae," so-called because preceding the 

 pennse, or feathers. In young Cormorants the nest- 

 ling-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 you»g Pigeons, and the young of most of the 



