spokes of a fan. As a result, a much more efficient tail for 
the needs of flight has come into being. And the tail, it must 
be remembered, plays, especially in some birds, an important 
part. But this is not all. We have now to consider the 
wing. In all essentials this agrees with that of living birds. 
And this agreement is strikingly close when it is compared 
with the embryonic and early nestling stages. A detailed 
account of these resemblances, and differences, would be 
out of place here. Suffice it to say that its closest modern 
counterparts are to be found in the wing of the nestling of 
that strange South American bird, the Hoatzin, and the 
“Game-birds,” such as of a young pheasant, or a young 
fowl. The evidence these can furnish in this matter of the 
evolution of the birds’ wing will be found in Chapter VI. 
For the moment it will be more profitable to discuss the 
broad outlines of the origin of flight, so far as this is possible. 
On this theme there are, as might be supposed, many 
opinions—some of them bearing little relation to fact. 
The feet of Archeopteryx, it is important to remember, 
bear a very extraordinary likeness to the feet of a “‘ perching ”’ 
bird, say that of a crow. They are without any semblance 
of doubt, the feet of a bird which lived in trees. Archeopteryx, 
then, was an arboreal bird. And this being so, the most 
reasonable hypothesis of the origin of flight is that it developed 
out of “ gliding ’’ movements, made for the purpose of passing 
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