The ostrich-tribe is peculiarly interesting, owing to the 

 fact that their wings present a really wonderful series of 

 degenerating stages. 



The wings of all differ conspicuously from those of other 

 birds in the great length and looseness of the texture of the 

 feathers. Those of the African ostrich arie the largest of all ; 

 but they are quite useless for the purpose of flight, though 

 they are used as aids in running. In the South American 

 ostrich, or rhea, they are also large, but again tiseless for flight, 

 for the " quill-feathers " are very weak, and have no " web," 

 such as one finds in the quills of flying birds. And besides, 

 the muscles of the wing have degenerated, the breast-muscles 

 having become reduced to mere vestiges. 



In both the African and South American ostriches, the 

 skeleton of the wing, compared with that, say, of a swan, 

 would seem, to the inexpert, to be quite normal. But with 

 the cassowary, the emu, or the apteryx matters are very 

 different. Here, at the first glance, it is apparent that the 

 process of decay is far advanced ; for the bones of the hand 

 have, as it were, shrunk up, so that a mere stump is all that 

 remains. The wing of the cassowary is further remarkable 

 for the fact that some of the forearm quills, or " secondaries," 

 are represented by long, stiff quiUs, resembling spines of 

 a porcupine ; the " vane " of the feather, which normally 

 runs down each side of the shaft, has vanished altogether. 



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