. The structure and life of birds. Birds; Evolution. IX YOUTH, MATURITY, AND AGE 289 nestling Hoatzin the hand is longer than the forearm ; gradually it grows shorter, while the other parts of the wing lengthen, till, in the fledged bird, the forearm surpasses it (Fig. 72 a, b). The feathers, too, adapt themselves to changing circumstances ; in the nest- ling the growth of the two outermost primaries is completely arrested, so that the use of the claws may not be impeded ; when it is fledged and can fly, they begin again to grow and attain their full. Fig. 72.—Wing of Hoatzin—{a) young, {U) ma
. The structure and life of birds. Birds; Evolution. IX YOUTH, MATURITY, AND AGE 289 nestling Hoatzin the hand is longer than the forearm ; gradually it grows shorter, while the other parts of the wing lengthen, till, in the fledged bird, the forearm surpasses it (Fig. 72 a, b). The feathers, too, adapt themselves to changing circumstances ; in the nest- ling the growth of the two outermost primaries is completely arrested, so that the use of the claws may not be impeded ; when it is fledged and can fly, they begin again to grow and attain their full. Fig. 72.—Wing of Hoatzin—{a) young, {U) mature—after Pycraft. length. With maturity, too, the claw on digit No. i grows small, while that on No. 2 is lost altogether. The pause made by the growing quills was first noticed by Mr Pycraft, and he has further pointed out that in the common chick we have traces of a similar development. There too we find the hand of the young bird longer, though only by a little, than the forearm ; the second digit has a claw only in the embryo stage; the first is much reduced, but retains U. 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
