. The structure and life of birds. Birds; Evolution. VI FORM AND FUNCTION iji pulp, as it is called, is the same in the nestling down and the more lasting and stronger formation that follows it. The change, therefore, bears no resem- blance to the shedding of milk teeth and their re- placement by permanent ones. The early tooth is driven out by the later one ; the two are not in any way connected. After the first moult, the feathers develop without any nestling " downs " as precursors. Otherwise the process is not, in essential points, different. The cells of. Fig. 41.—(After Gad
. The structure and life of birds. Birds; Evolution. VI FORM AND FUNCTION iji pulp, as it is called, is the same in the nestling down and the more lasting and stronger formation that follows it. The change, therefore, bears no resem- blance to the shedding of milk teeth and their re- placement by permanent ones. The early tooth is driven out by the later one ; the two are not in any way connected. After the first moult, the feathers develop without any nestling " downs " as precursors. Otherwise the process is not, in essential points, different. The cells of. Fig. 41.—(After Gadow). Showing development of feather. AS, cells forming after shaft; d, cells forming barbs ; MS, cells forming main shaft; SH, horny sheath surrounding whole feather. the papilla, or rather of the epidermis over it, arrange themselves starwise. Two of the columns of cells which cause this starlike formation grow broader and longer than the rest, and go to make the rachis of the feather. Two on the opposite side form a secondary shaft, of which, as I have said, most feathers retain some trace. At the same time there is a growth inwards, so that in some cases the bone is reached. On the ulna the marks of the great wing feathers are easily discernible. The cap found on the top of young feathers is formed from the outermost cells of the epidermis, the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Headley, F. W. (Frederick Webb), 1856-1919. London, New York, Macmillan
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbirds, bookyear1895
