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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