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. 
This is certainly a very remarkable feature, but it gains an 
added interest from the fact that it has a parallel in the history of 
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