The 'Development of Nestling Feathers. 



INTRODUCTION. 



The purpose of this paper is to give a more complete account of the 

 development of the dovrn, or Neossoptile, than has been given by previous 

 writers and to show the true relation of this structure to the first definitive 

 feather. 



"The first clothing of the newly hatched bird consists of more or fewer 

 soft feathers, on the whole resembling the Downs of adult birds, but possess- 

 ing several characters which make it advisable to distinguish them, by the 

 name of 'Neossoptiles,' from those feathers which subsequently appear, and 

 may be called 'Teleoptiles,' the former being as it were the first generation 

 to which others follow in constant succession, so long as the bird lives. 



"Neossoptiles are characterized by (i) a very short calamus, (2) an 

 insignificant or ill-defined rachis — if there be one at all, (3) the almost 

 universal absence of cilia (barbules), (4) long and slender rami (barbs), 

 (5) absence of aftershaft, except in Dromaeus. To the combination of 

 these characters is due the soft or downy structure of these feathers. 



"Teleoptiles, whether Contour-feathers or Downs, are each originally 

 preceded by a Neossoptile, the base of which is in direct continuity with the 

 tips of the rami of its succeeding final feather, but, owing to a shortened 

 process of development of coenogenetic conditions, many, or even all Neos- 

 soptiles may occasionally be suppressed, so that the tips of the first feathers 

 to appear are actually those of the second generation." (A Dictionary of 

 Birds, A. Newton, p. 243.) 



Though a continuity between the nestling down ("Neossoptile") and 

 the nestling definitive feather ("Teleoptile") has been recognized, the former 

 has been regarded as a relatively complete and distinct feather. I shall at- 

 tempt to show that the "Neossoptile" is only a more or less differentiated 

 distal part of the first "Teleoptile." 



My attention M^as attracted to this relationship while studying the terns 

 {Sterna hirundo, S. dougallij and S. antillarum) , and the gulls {Larus atri- 

 cilla) which bred abundantly in the vicinity of Woods Holl, Mass., during 

 the summer of 1903. Further study of these birds at all ages, and of nu- 

 merous specimens of various species of birds, led to an examination of the 

 evidence for the accepted views. 



Under the stimulus of Professor C. O. Whitman's interest and encour- 

 agement the task of gathering the requisite material was carried forward. It 

 would have been difficult to carry on the necessary field studies and secure 

 the material from the terns and gulls but for the aid rendered by Dr. F. B. 



