Fig. 31.

Common English viper (Pelias berus), with poison-fangs showing in the open mouth, and the soft harmless tongue outstretched to feel.

We see, then, that it is not without some struggle that these cold-blooded reptiles have held their own

in the world, nor is it to be wondered at that only these four types—tortoises, lizards, crocodiles, and snakes—should have managed to find room to live among the myriads of warm-blooded animals which have filled the earth. These four groups have made a good fight of it, and many of them even make use of warm-blooded animals as food. The tortoises, it is true, feed upon plants, except those that live in the fresh water, and feed chiefly on fish, snakes, and frogs, while most of the lizards are insect-feeders. But the crocodile, as he lurks near the river’s edge, and the snake, when he fastens his glittering eye on a mouse or bird, are both on the look-out for animals higher in the world than themselves.

It is, perhaps, natural that we should shrink from cold-blooded creatures, especially as they seem to show very little affection. Yet lizards, tortoises, and snakes can all be made to know and care for those who are kind to them; while, as we have seen, the fierce crocodile watches over and feeds her young, and the python coils herself over her eggs, and will take no food till they are hatched. Moreover, we can scarcely look at the quaint shell-covered tortoise, or examine the heavily-mailed coat of the alligator, or the poison-fangs of the snake, without admiring the curious devices by which these animals have managed to survive in a world which once belonged to their ancestors, before our present swarm of warm-blooded animals multiplied and took possession of their kingdom.

--- THE EARLIEST KNOWN WATERBIRDS

CHAPTER VI. THE FEATHERED CONQUERORS OF THE AIR. Part I.—Their Wanderings over Sea and Marsh, Desert and Plain.

It is a warm sunny day in early spring, one of those few bright days which sometimes burst upon us in April, just after the swallows have come back to us, searching out their old nooks under the eaves, or their old corners in the chimneys, to build their

new nests. There they are, clinging with their sharp claws to the edge of the cottage thatch, while the impudent little sparrow, which has remained hopping about all the winter long, chirrups at them from a neighbouring apple-tree. Upon the grass-plot near a blackbird is pecking at a worm, and from the wood beyond a thrush trills out his clear and mellow song, accompanied from time to time by the distant cry of the cuckoo calling to his mate. For it is the love-time of the birds; and as we watch them flying merrily hither and thither in the bright sunshine, we ask ourselves whether we must not have made a great leap on leaving the cold-blooded snakes and tortoises, since now we find ourselves among such merry, warm-hearted, passionate little beings, with their beautiful feathery plumage, their light rapid flight, their love for each other, their skill in nest-building, and their patient care for their little ones.

And, indeed, we have come into quite a new life, for now we are going to wander among the conquerors of the air, who have learned to rise far beyond our solid ground, and to soar, like the lark, into the clouds, or, like the eagle, to sail over the topmost crags of the mountains, there to build his solitary eyrie.

Even the little sparrow, which flits about by the roadside, can laugh at us with his impudent little chirp, as he flies up out of reach to the topmost branch of a tree. And yet a glance at his skeleton will show us that he has the same framework as a reptile, only it is altered to suit his mode of life.

Fig. 32.

The Sparrow.

With wings raised, as in the skeleton on next page.

True, his breastbone (b, Fig. 33) is deep and thin instead of flat, and those joints of his backbone which lie between his neck and tail are soldered firmly together, more like those of the tortoise, and he stands only upon two feet. Yet this last difference is merely apparent, for if you look at the bones of his wings you will find that they are, bone for bone, the same as those in the front legs of a lizard, only they have

been drawn backwards and upwards so as to work in the air.

Fig. 33.

Skeleton of a Sparrow (from a specimen).

q, Quadrate bone, peculiar to reptiles and birds and some amphibia; b, breastbone; m, merrythought or collar bone; c, coracoid bone, over which the tendon works to pull up the wing; p, ploughshare bone, on which the tail grows.

Wing bones—a, upper arm; e, elbow; fa, fore arm; w, wrist; t, thumb; ha, hand.

Leg bones—th, thigh bone; k, knee; l, lower part of leg; h, heel; f, foot.

There is the upper arm (a) answering to the same part of the lizard’s front limb (p. 103); there is the elbow (e); then the two bones of the fore-arm (fa); then the wrist (w), and a long hand (h), which has

lost almost all trace of separate fingers, except the little thumb (t), which carries some feathers of its own, known as the “bastard” wing. Now when the sparrow is resting he draws back his elbow, folds his wrist joint, and brings the whole wing flat to his body. But when he wishes to fly he stretches his arms out and beats the air with them, and as his hand moves over most space, it is there that you will find the longest quill feathers, which stretch right to the tip of his wing; then next to these follow the feathers of his fore-arm, while those of the upper arm are short and close to his body, and over all these are the rows of covering feathers, which make the whole wing thick and compact.

Here, then, we have the lizard’s front legs turned into a wonderful flying machine in the bird, and this in quite a different way from the flying lizards which lived long ago, and which had only a piece of membrane to flit with, like bats. And now what has happened to the hind legs, the only ones used as legs by the birds? Look at the sparrow as he clasps the bough with his toes, and you will, perhaps, be puzzled why the first joint of his leg turns back like an elbow and not forward like a knee. Ah! but that joint is his ankle, and the knob behind is his heel (h), for the bones of his foot have grown long and leg-like; and he always stands upon his toes, the rest of his foot forming a firm support to hold his body up in the air. Look at the skeleton and you will find his true knee (k) up above; and if you go to the Zoological Gardens and watch the Adjutant birds, you will often find them resting their whole foot upon the ground (see Fig. 34), and comical as it looks, it will help to explain the curious foot and leg of a bird.

Fig. 34.

The Adjutant Bird.

Showing the foot resting from heel to toe upon the ground.

Already, then, we see that the bird is using the same bones as a reptile, though he uses them in a different way; and besides these resemblances between the skeletons of birds and reptiles there are two special ones easy enough for us to understand. We saw in

the snakes and the lizards that they have a separate bone (9, Figs. 23 and 26) joining the lower jaw on to the head; now you will find this same bone in the sparrow and in all birds (see Fig. 33), but in quadrupeds this bone is not to be found, the part representing it being changed into one of the bones of the ear. Again, the sparrow’s skull is joined to his backbone by a single half-moon-shaped knob, which fits into a groove in the first joint or vertebra. This also we find in reptiles, while all higher animals have two such knobs, so that although they can nod the head upon these, they cannot turn it upon them, and consequently the first joint turns with the skull upon the second vertebra.

These, then, are some of the reasons why Professor Huxley tells us that though frogs and reptiles look in many ways so like each other, yet in truth the frogs must be grouped with the gill-breathing and fish-like animals;[88] while the cold-blooded reptiles, when we come to look closely into them, are linked with such different looking creatures as the bright and merry birds.[89] But we have also another and stronger reason for thinking that reptiles and birds are distant connections; for in those far bygone times (see p. 92), when the huge land-lizards browsed upon the trees, the birds living among them were much more like them in many ways than they are now. From their skeletons and feathers which we find, we know that the strange land birds[90] which then perched on the trees had not a fan-shaped tail made of feathers, growing on one broad bone as our

Footnote 88. Ichthyopsida—ichthys, fish; opsis, appearance.

Footnote 89. Sauropsida—sauros, lizard; opsis, appearance.

Footnote 90. Archœopteryx, see picture-heading, Chapter VII.

birds have now (p, Fig. 33), but they had a long tail of many joints like lizards, only that each joint carried a pair of feathers, and like lizards too they had teeth in their jaws, which no living bird has. They must have been poor flyers at best, these earliest known birds, for their wings were small and the fingers of their hand were separate more like lizard’s toes, two of them at least having claws upon them, while their long hanging tail must have been very awkward compared to the fan-shaped tail they now wear. For some time they were the only birds we know of, but later on we come upon the bones of water-birds[91] telling the same story. For some about the size of small gulls,[92] though they flew with strong wings and had fan-shaped tails, still had teeth in their horny jaws, set in sockets like those of the crocodile, while their backbones had joints like those of fishes rather than birds; and with them were other and wingless birds[93] rather larger than our swans, but more like swimming fish-eating ostriches, for their breastbones were flat, not thin and sharp like the sparrow’s, and they had scarcely any wings, short tails, long slender necks, and jaws full of teeth, this time set in grooves like those of lizards and snakes.

In these and many other points the early birds came very near to the reptiles—not to the flying ones, but to those which walked on the land. And now, perhaps, you will ask, did reptiles then turn into birds? No, since they were both living at the same time, and those reptiles which flew did so like bats, and not in any way like the birds which were their

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