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Page:Popular Science Monthly Volume 24.djvu/634

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THE POPULAR SCIENCE MONTHLY.

ming birds, in spite of their small size, possess a power of rapid flitting and of lightly poising themselves in front of flowers which makes them in some ways the very fullest existing embodiment of the avian ideal. To the same order belong also those most intelligent of all birds, the parrots, whose large heads and crafty eyes mark them at once as the opposite pole from the small-browed, dull-eyed, stupid cassowaries. With them must be ranked the toucans, the barbets, the king-fishers, the trogons, and whole hosts of other beautiful southern creatures, among which the feathers have been variously modified into the most exquisite ornamental devices. As for the birds of prey, the eagles, vultures, falcons, hawks, owls, and ospreys must suffice by way of example.

Even among these central groups of birds, which have varied most and developed farthest from the primitive reptilian character, there are many kinds which retain here and there some small and isolated peculiarities of the ancestral forms. For example, among the duck-like birds, as we have already seen, a single group, that of the mergansers, still keeps up some faint memory of the original sharp teeth in the shape of a few horny projections along the edge of the beak. The tooth-billed pigeon of Samoa, a close relation of that early and extinct form the dodo, has also some rudiments of horny teeth; and the South-American leaf-cutters, a primitive set of songless perchers, possess somewhat similar relics of the lost fangs. So, too, our earliest known bird, the archæopteryx, had three free claws on its fore-limb or undeveloped wing; and traces of such claws turn up in sundry unconnected birds even now, no doubt by reversion to the almost forgotten ancestral type. In all modern birds, one of the three fingers which make up the pinion still remains free; and in some species this finger supports an evident claw, sometimes used as a spur for the purpose of fighting. In many thrushes a rudiment of this claw may be perceived in the shape of a small tubercle or knob at the end of the wing, thus pointing back directly to some remote four-footed and claw-bearing reptilian ancestor. Several plovers have spurs, and so has the spur-winged goose; while the horned screamer has two on each wing, which he uses with great effect in battling with his rivals. The Australian brush-turkeys have also the rudiment or last relic of a primitive pinion-claw.

There is another way in which modern birds still partially recall the peculiarities of their reptilian ancestors, and that is in the course of their individual development within the egg. No adult existing bird has all the bones of the tail distinct and separate, like those of the archæopteryx; the last joints are all firmly welded together into a solid expanded piece, known from its queer shape as a plow-share-bone, such as the one which I am holding in my hand as the text for this discourse. The use of the plowshare-bone is to support the fan-like quill-feathers of the tail, and also to shelter the oil-