14 Jones — Nestling Feathers. 



The material which furnished the basis for Davies' studies of the de- 

 velopment of this "quill" was obtained from the canary embr^^o chiefly. It 

 is a strictly altricial bird. 



Figure 142, Plate IV, illustrates the passage of a down barb- 

 vane into three definitive feather barb-vanes where barbules are present 

 along the whole course of the vane. The lengthened barbules of the down 

 become shorter as the distal end of the definitive feather is approached 

 and these shortened barbules gradually assume the typical character 

 of pennaceous feather barbules. Figure 55 is a complete barbule taken 

 at 55 in Figure 142, Plate IV, and Figure 54 is the distal four-fifths of 

 another barbule taken from the region 54, Figure 142. Figure 52, Plate 

 IV, represents a normal down barbule. Since barbules are present 

 along the whole course of a barb of this sort there will be no interruption of 

 the normal development of the barb-vane ridge, and where a down barb is 

 continuous with a single definitive feather barb, instead of with several defini- 

 tive feather barbs, the only indication of the beginning of the definitive 

 feather barb will be the development of hooked barbicels, provided the 

 definitive feather is pennaceous in character. If the definitive feather 

 is plumulaceous in character no hooked barbicels will be developed. 

 It is common knowledge that the fluffiness of plumulaceous feathers, like 

 ostrich plumes, is due to long and slender barbules without hooks. Pen- 

 naceous feathers are provided with shorter and stiffer barbules upon which 

 some hooks are developed. 



The first feathers of the Anserine birds are mentioned as illustrating 

 the development of both shaft and quill in the first down. My 

 studies of the duck embryo prove that the first feathers begin to show as little 

 papillae on the skin surface on the fifth or sixth day of incubation ; that the 

 insinking of the proximal end of the down begins about the twelfth 

 day of incubation; and that no shaft rudiment makes its appearance until 

 about the twenty-second day of incubation. New barb-vane ridges are de- 

 veloped in the epidermal wall opposite to the shaft rudiment, as growth 

 continues, and the ridges next to the shaft rudiment become fused into 

 it laterally. The first feather continues to grow until the bird is nearly 

 full grown, w^hen a second feather begins to develop in the same papilla 

 at the base of the first feather. When the second feather begins to develop 

 a quill is formed at the proximal end of the first feather, but the proximal 

 end of the quill has not become cornified, so that a connection is established 

 between the proximal end of the quill of the first feather and the distal end 

 of the second feather (Figs. 90 to 96, Plate VII). The second feather thus 

 pushes the first feather out of the socket upon its tip. The connection be- 

 tween the two feathers is soon broken and the first feather falls off. 



The first feather of the duck is regarded as a stif¥ down feather. I have 

 failed to find any writer who regards it as in any sense a definitive feather, 

 or a feather of the second generation. The fact that it begins to appear upon 

 the skin surface on the fifth or sixth day of incubation, the time w^hen the 

 first down of other birds begins to show, indicates that there has been no short- 



