in dealing with the affinities of the Archeopteryx. Finally, as Vogt points out, there is a complete affinity betwixt the scale of the reptile and the feather of the bird. The feather is, in fact, the further modification of the scale; and we may, therefore, "imagine the ancestors of the Archeopteryx as lizard-like terrestrial reptiles, having feet with fine, hooked, free digits, showing no modification in

ᏤᏤᏤᏤᏤᏤᏤᏤᏤᏤᏤᏤᏤᏤᏤ

FIG. 81.

their skeleton, but having the skin furnished at different points with elongated warts, downy plumes, and rudimentary feathers, not yet fitted for flight, but susceptible of further development in the course of generations."

But that this odd relic of the Oolite leads us decidedly in the direction of the reptiles by its tail and its hand there can exist no reasonable doubt. Scepticism may exist on this latter point, but the doubt is neither of a learned nor of a scientific kind. We may not say that Archæopteryx actually leads us from any one bird to any one group of

8 reptiles. It rather stands inter-
mediately and alone; but even
in its solitary position it certainly
makes the gulf betwixt the two
classes seem less formidable.

ᏤᏤᏤᏤᏤᏤᏤᏤ

Next in order from the aviary of the geologist may be produced evidence of the existence of reptilelike birds in a most interesting series of fossils obtained from the Chalk of Western America by Professor A Marsh. About 1871 a headless bird skeleton was discovered in the HESPERORNIS Upper Chalk of Western Kansas. JAW. This bird evidently resembled our living divers, and was duly christened Hesperornis regalis. Like our living ostriches, emeus, and their allies, this extinct bird possessed no keel on its breast-bone. It had the merest rudiments of wings; and certain reptile-like resemblances seen in its haunch-bones made geologists naturally anxious for the realisation of their hopes in the discovery of a complete skeleton. In 1872 fresh discoveries rewarded the patient and indefatigable search of Professor Marsh. Not only were the missing parts of the Hesperornis duly obtained, but the remains of another and still more remarkable species (Ichthyornis dispar) of extinct birds, were duly brought to

FIG. 82. ICHTHYORNIS JAW.

light. By the new discovery both Hesperornis and Ichthyornis were found to possess teeth; the former (Fig. 81) having its curved teeth (B) set in a common groove in the jaw-bones; whilst Ichthyornis (Fig. 82) makes a further advance towards perfection in dental apparatus, in that its twenty or so teeth of each jaw were lodged in distinct sockets. The importance of these facts as bearing on true reptile-like characters in birds may be readily imagined. No living bird possesses even the semblance of teeth, if we except the horny ridges of the Merganser's bill. Prior to Marsh's discoveries, no fossil bird was known to have been provided with true teethalthough indeed, in certain bird-remains, described by Owen, from the London clay (Eocene) of Sheppey, under the name of Odontopteryx (Fig. 83), the jaws were provided with bony projections. These projections, however, are not true teeth-which, as many readers may know, do not resemble bones, either in development or structure, being developed from the "gum" or lining membrane of the mouth, and not from cartilage, as true bones usually are. Doubtless these bony projections aided Odontopteryx to catch its finny prey, as the horny ridges

of the Mergansers enable them to retain the fishes they so dexterously capture. One curious bird (Phytotoma), a South American Leafcutter, certainly possesses a double row of bony projections on its palate. But even this novel and unusual addition to the list of birdpossessions bears but a faint resemblance to the bony teeth of Odontopteryx, as these latter in turn are an entirely different and relatively modern feature of the bird-type, when compared with the true teeth of their "American cousins" of the Western Chalk.

The Ichthyornis, moreover, diminishes the distance betwixt birds and reptiles in yet another fashion-the joints of its spine (Fig. 82, B.) were concave at either end (c), a conformation familiar to us in the joints of the fish-backbone, utterly unknown in living birds, but common enough in reptiles. This character alone, in the eyes of the naturalist, becomes invested with an importance hardly to be over-estimated as regards its reptilian relationships; and in Hesperornis, also, certain features in addition to those already noted show unmistakable marks of affinity to the reptile type. The teeth of this latter bird, set, as

M

already remarked, in a common groove, strongly remind one of the manner in which the teeth of certain lizards are fixed in their jaws. Some of the teeth of this curious bird also exhibit the manner in which one series of teeth was replaced by another-for, as most readers know, reptiles and fishes possess an unlimited supply and a continual succession of teeth. The old teeth are ousted from their sockets by new teeth which are developed at their bases; and in the jaws of Hesperornis such a manner of tooth-formation, exactly imitating a common reptilian mode of renewal, is to be plainly seen. The tail of this great diver of the Chalk seas was, lastly, like that of the Archæopteryx of the Oolite epoch, and exhibited a very different structure from the caudal appendage of existing and of other fossil birds. At its middle and under parts the joints of the tail present long projections of flattened shape, which strongly suggest the idea of the tail having been a rigid unyielding member in so far as a side movement was concerned, but, like that of the beaver, being probably mobile in a vertical direction, and being thus of use in the diving movements of its possessor. The last joints of the tail were massed together, but in a fashion different from that in which the "ploughshare-bone" of living birds is formed.

In so far as the birds themselves have rendered an account of their past history, it is clearly seen that their affinities to reptiles become very strongly marked in various directions, especially in the structure of the spine, and in the possession of true teeth. Ichthyornis, in the matter of its hollowed spine-bones (Fig. 82, B, c), and in that of its socket-implanted teeth, is a more modified and more truly reptilelike bird than Hesperornis. This latter again, approaches much nearer reptiles than Odontopteryx (Fig. 83) of the London Clay, which latter, as becomes its nearer approach to the existing order of affairs, presents a less marked relationship with "the dragons of the prime."

FIG. 84.
RESTORATION OF COMPSOGNATHUS.

But what evidence, we may lastly ask, do the reptiles afford on their side of any tendency towards the bird type? Have the reptiles remained as passive to advance and evolution, as they would appear at first sight to remain to-day; or does their history but repeat the changes and variations exhibited by their bird-neighbours? Let the history of the reptile class in the past answer these

queries. A considerable number of fossil reptiles are ranked to form a distinct order or division, marked by various near approaches to the structure of birds. A single example of this curious group will suffice to show the intermediate nature of its included forms. Once again the Lithographic Slates of Solenhofen yield a rich reward to geological investigation, and present us with the fossil skeleton of an animal which in the flesh attained a length of about two feet. This is the Compsognathus (Fig. 84) of the geologist-a long-necked reptile, possessing a small head, the jaws of which, however, were armed with teeth. Its fore limbs were short, its hind limbs being long and birdlike. Like that of birds, its thigh-bone (Fig. 85, B, fe) is shorter than its leg-bone. As in birds (Fig. 85 A), the upper half of the anklebone of Compsognathus (Fig. 85, B, as, ca) unites with the lower part of the leg; but the lower half of the ankle (td) was not, as in birds, united with the instep-bones, or metatarsals (1, 2, 3, 4), which are three or four in number, long and slender, and which, in Compsognathus, support the second, third, and fourth toes. A mere trace of the instep-bone of the fifth toe exists, and the first or great toe is of small size. In all birds the fifth toe is entirely wanting. Looking at the structure of Compsognathus, and of its fossil allies, such as Iguanodon, little or no doubt can be entertained that these reptiles were capable of resting on their hind limbs, in bird-like fashion, and of walking, or hopping, after the fashion of the feathered bipeds, to

FIG. 85. (A) Hindlimbs of Bird; (B) Extinct Reptile; and (C) Crocodile.

which indeed, by a use of the imagination, strictly scientific, we may regard this reptilian group as having in due time given origin. Ít is unquestionably to the struthious birds, that is, to the ostriches and

their allies, that this curious reptile bears the closest resemblance; and a comparative glance at the hinder extremities of the crocodile, bird, and its reptilian neighbour (Fig. 85), will suffice to show the marked resemblances and gradation which connect, and at the same time distinguish, this curious series of forms. The Compsognathus limb stands intermediate betwixt the saurian (Fig. 85, c) and the bird (A); and, strictly judged, is comparable most nearly to that of the unborn chick. Those "dragons of the prime" known as Iguanodon and Megalosaurus, from the Chalk and Oolite, are near relations of Compsognathus. When we think of the size of these reptiles, which attained a length of from forty to sixty feet, and of the probability that, like their diminutive neighbour, they may have walked on two legs, the origin of the giant footprints (Figs. 78 and 79) of the Triassic Sand-stones would appear to present no special difficulties in the way of satisfactory solution.

Mention must here be made of the curious Pterodactyls (Fig. 86), or those extinct reptiles of the Lias, Oolite, and Chalk, in which a wingmembrane or fold of skin, similar to that seen in bats, stretched from an outer and enormously elongated finger of each hand to the fore-limb,

FIG. 86. SKELETON OF PTERODACTYL. (The wing membrane in black.

sides of the body, and hind limbs, and between the hind limbs and tail. By aid of this wing-membrane these literal "flying dragons" must have winged their way through the air with ease and speed. Their breast-bone was keeled like that of the bird (Fig. 76, f, g); their shoulder-girdle was bird-like; and their bones, as in birds, were hollow, and were filled with air in place of marrow. The Pterodactyl brain was essentially bird-like, but the hind limbs and pelvis were rep