Only two skeletons of this wonderful bird are known, and they were obtained, many years ago, from the Solenhofen, or Lithographic slates of Bavaria. The wing and tail-feathers are as perfectly developed as in modern birds. But these precious fossils present two characters which have long since been lost by birds. The first of these is the presence of well developed teeth in the jaws. The birds of to-day have horny beaks. The teeth bespeak the reptile. The second is the long, tapering tail, which is composed of a series of cylindrical bones, forming a lizard-like appendage. But each bone, be it noted, supported a pair of stiff, tail-quills, so that the tail of this ancient bird, in its general appearance, differs in a very striking way from that of a modern bird, wherein these feathers seem all to spring from a common base, fan-wise. But as a matter of fact this appearance is deceptive, for the large bone, or "pygostyle" which supports the tail feathers of the adult, is found, in the embryo, to be made up of a series of separate pieces, agreeing in number with those of the tail of the fossil ancestor, Archæopteryx. Each of these separate bones has, in fact, in the course of the ages, been shortened up to the condition of mere discs; and this "telescoping" of the vertebræ has brought the once separated feathers close up, so that their bases lie packed in like the 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.