INTRODUCTORY i i 



powder-down is luminous, and that the birds take advantage of 

 this luminosity by raising the contour feathers so as to shed 

 this light on the water wherein they may be fishing, and thereby 

 lure their prey to within striking distance. As these birds do 

 not fish by night, and the glow would be invisible by day, this 

 theory may be regarded as exploded. 



The feathers of nestling birds do not difTer structurally from 

 those of adults in any essential particular, but they are remark- 

 able for the very great range of degeneration which they dis- 

 play. On the varying number of successive plumages through 

 which nestlings pass before attaining to a dress which is structur- 

 ally equivalent to that of the adult much will be said later. 



The nestling down feathers, it should be remarked, are 

 known as " neossoptyles " to distinguish them from the " tele- 

 optyles," or adult feathers — terms coined by Dr. Hans Gadow 

 to serve a most useful purpose. 



The neossoptyles are made up (a) of feathers which im- 

 mediately precede the contour feathers of the adult ; and (/S) 

 of feathers which are later succeeded by down feathers. The 

 former are to be known as " pre-pennae," the latter as " pre- 

 plumulae ". 



The pre-pennae may further be divided into " protoptyles " 

 and " mesoptyles " ; and while the nestlings of some species 

 develop both, in others the protoptyles have become suppressed, 

 while the mesoptyles are degenerate, and may be represented 

 by little more than a few straggling, hair-like filaments, as in 

 young Pigeons, or the nestling may remain absolutely naked 

 until the appearance of the first " teleoptyles ''. 



Only in some species of Tinamous are the mesoptyles 

 really well developed, and here they very closely approach 

 teleoptyles in structure, but are peculiar in that the after 

 shaft is almost as large as the main shaft, a point wherein they 

 agree with the teleoptyles of the Emu and Cassowary. This 

 is a very remarkable and puzzling fact, because in the adult 

 Tinamou the after-shaft is either feebly developed or wanting, 

 and in the nestlings of the Emu and Cassowary, and the Ostrich 

 tribe .in general, the after-shaft is degenerate, or absent! In 

 the nestlings of certain Owls, e.g., Tawny and Eagle Owls, the 

 mesoptyle plumage is worn until the first autumn, at least in so 

 far as the trunk feathers are concerned, for the quill and tail 



