the adult stage of the wing of the ancient Archzopteryx. 
This bird could have been but a poor flier, and probably 
during the time it was moulting its quills it was absolutely 
flightless, so that it needed a permanent finger-tip, and claw, 
beyond the margin of its wing-surface. 
This matter of ‘‘ moulting,” by the way, needs, at least, 
passing comment. All birds renew their plumage at least 
once: the body plumage often twice in the year. The old 
feathers fall out, and their places are taken by new ones. 
But their growth is slow. In geese and ducks, and some other 
birds, the wing-quills are moulted all at once, so that flight, 
for a week or two, is impossible. But they can escape from 
their enemies while thus at a disadvantage, by taking to the 
water. In all other birds the quills are moulted, and renewed, 
in pairs: so that at no time are they left flightless. 
But this by the way. Let us revert, for a moment, to the 
hoatzin’s wing. The appearance of the outermost quills of 
the hand, it will be remembered, is delayed till the inner 
, 
feathers have grown long enough to “ flutter,” at least for a 
short distance, then the growth of the complete series proceeds 
apace. This has been called an “ Adaptation” to enable 
these youngsters, active from the moment they leave the 
egg, to move about in comparative safety. But it is more 
than this. It is a survival of an ancient order of things 
which takes us back to the first known birds. 
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