ON THE NESTLING FEATHERS OF THE MALLARD. 609' 



34. The Nestling Feathers of the Malhird, with Observations- 

 on the Composition, Origin, and History of Feathers. 

 By J. CossAR EwART, M.D., F.R.S., F.Z.S., Eegins 

 Professor of Natural History, University of Edinburgh. 



[Received March 7, 1921 : Read March 22, 1921.] 

 (Plates I.-X. ; Text-figures 1-14.) 



I. The Nestling Feathers of the Mallard {Anas boscas). 



In a recent paper in ' The Ibis ' it is pointed out that " there 

 is no branch of ornithology that has remained so long neglected 

 as the study of nestling birds, nor is there one in which so many 

 problems await solution" (1), That the study of nestling feathers 

 has been neglected will be admitted when it is mentioned that up 

 to 1906 it was not realized that the true feathers (pennse) may be 

 preceded by two generations of nestling feathers (prepennse), that 

 ornithologists have not yet made up their minds whether the 

 familiar coat worn by newly-liatched chicks and ducklings corre- 

 sponds to the first (protoptile) or to the second (mesoptile) 

 nestling coat of Penguins, and that morphologists have not yet 

 ascertained whether nestling and other feathers originally con- 

 sisted of one shaft or of two complete shafts like the nestling and^ 

 adult feathers of the Emu. 



True or definitive feathers vary greatly in size and structure ; 

 nevertheless, they may be said to belong either to a plumose 

 (metaptile) or to a pennaceous (teleoptile) type. The plumose 

 true feathers are characterized by barbules which may possess 

 cilia but never have booklets (hamuli) ; in pennaceous feathers 

 some of the barbules are armed with booklets, by means of which 

 the barbs are "woven" into a web — in the wing-quills of flying 

 birds we have highly specialized teleoptiles ; in the plumose 

 feather from a Mallard represented in PI. I. fig. 1 we have an 

 example of a simple metaptile, bearing a protoptile. 



In Penguins all the true feathers are probably preceded by 

 both protoptiles and mesoptiles (text-fig. 3), but in many birds 

 there is only one nestling coat — the mesoptiles have either been 

 completely suppressed or are represented by inconspicuous and 

 barely recognizable vestiges. 



In most birds there are numerous hair-like feathers associated 

 with, and intimately related to, the true feathers. As these 

 hair-like feathers are preceded by minute prepennse — are, in fact, 

 degenerate pennse, — they might be known as filopennse. 



Further, in many birds there appear between the true or 

 contour feathers (pennae) true down feathers (plumulfe). In all 

 the Ducks, Geese, and Penguins examined the plumulse are 

 preceded by preplumulse. 



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