and peculiar of all. Strangest among them is the kiwi or apteryx of New Zealand, that almost wholly wingless bird who may be seen any morning at the Zoo, gravely stalking up and down, like an important political prisoner, within the small inclosure to which tyrannical circumstances have temporarily confined him. The kiwi has feathers which closely resemble hair in texture, and his wings are so very rudimentary that they can only be properly observed at a post-mortem examination. His bones have no air-canals, and some of his internal anatomy is very abnormal. The cassowaries of the Papuan district are somewhat more bird-like in type, but they also preserve many antique features, especially in the relative smallness of the head and brain compared with the general size of the whole body. The Australian emus approach more closely to the true ostriches, and their feathers are far more feathery than those of the cassowary. In both these classes, however, the small and functionless wings are destitute of plumes, which are only represented by a few stiff, horny shafts. The true ostriches, including both the familiar African species and the South American rheas, have real wings with real feathers in them, though they can only use them to aid them in running, and not for the purpose of flight. They are therefore the most bird-like of their order, with small wings and very feathery plumes. We may fairly regard all these keelless and often almost wingless birds—the kiwis, cassowaries, emus, and ostriches—as the last survivors of a very ancient group, immediately descended from ancestors not unlike the toothed hesperornis, and never forced by circumstances to develop into the full avian type represented by the swallows, hawks, and herons. All of them are strictly terrestrial in their habits; none of them can fly in even the slightest degree; and the feathers of the most developed among them invariably lack the tiny barbules or small hooks which bind together the cross-barbs in the feathers of the flying bird, so as to form a compact and resisting blade. It is this looseness of the cross-barbs which gives ostrich-plumes their light and fluffy appearance; while, pushed to an extreme in the cassowary and the kiwi, it makes the plumage of those ugly birds approximate in character to the hair of mammals. Though from the human and decorative point of view we may admire the fluffiness of ostrich-plumes, it is obvious that, looked upon as a question of relative development, such loose, floating barbs are far less advanced in type than the firm and tightly interlocked quill-feathers of a goose or a raven, with which alone sustained flight is possible.
Except in such isolated countries where higher mammals do not, or did not till lately, exist, the power of flight, once acquired, was sure to be developed in a high degree. For the possession of feathers gives birds an advantage in this respect which enables even the little sparrows to hold their own in the midst of our crowded cities. Hence all other modern birds, except these lingering, ostrich-like creatures,