If we could only get the birds to tell us how they have learned the routes they take, and by what rules they are guided! One thing we know, that each kind of bird makes its nest in the coldest region which it visits, and where, at the time its young brood are ready, insect and other life is abundant; so that while the wild duck and goose, the woodcock, snipe, and field-fare, go to the far north to lay their eggs, and come to us in the sharper weather to feed when there is nothing but ice and snow in the home they have left, the swallow, the cuckoo, the swift, and the wheatear, on the other hand, visit us in the spring to build, and when autumn comes on take their flight to Africa and the East; and even many of the song-thrushes and robin-redbreasts which remain with us in England start off from Germany to warmer climates. Others, again, such as some of the Reed-warblers, the Stint, and the Ortolan Bunting, only make our island a house of call between the arctic regions where they breed in the summer when mosquitoes are swarming there, and the south where they winter after flying thousands of miles.

It would take too long to discuss here why and how they go, even if we knew it with certainty; but it is most probable that their ancestors first learned the routes now taken when Europe and Africa had not so wide a sea between them, and we can see that it must be a great advantage to be able to travel from climate to climate, so as to find a plentiful table spread at all times of the year; while they may return to the north to breed, not merely because there is food there, but also because in still earlier times, when the northern countries were much warmer than they are now, they doubtless lived there altogether, and, though now obliged to go south, have never lost the tradition of their old home.

Thus the birds, with their feathery covering and powerful wings, have left their early friends, the reptiles, far far behind. Taught by their many dangers, many experiences, and many joys, they have become warmhearted, quickwitted, timid or bold, ferocious or cunning, deliberate as the rook, or passionate as the falcon, according to the life they have to lead; or, in the sweet tender emotions of the little song-birds, have learned to fill the world with love and brightness and song. If mere enjoyment were all that could be desired in life, where could we expect to find it better than in the light-hearted skylark as she rises in the early summer morning to trill forth her song of joy, or in the happy chuckle of the hen as her little ones gather around her.

Yet we cannot but feel that, happy as a bird’s life may be, it still leaves something to be desired; and that, with their small brain and their front limbs entirely employed in flying, they cannot make the highest use of the world. The air they have conquered; and among the woods and forests, over the wide sea, and above the lofty mountains, they lead a busy and happy existence, bringing flying creatures to their highest development, and showing how Life has left no space unfilled with her children. Yet, after all, it is upon the ground, where difficulties are many, conditions varied, and where there is so much to call for contrivance, adaptation, and intelligence, that we must look for the highest types of life; and while we leave the joyous birds with regret, we must go back to the lower forms among the four-footed animals, in order to travel along the line of those that have conquered the earth and prepared the way for man himself.

--- HOME OF THE EARLIEST KNOWN MILK GIVERS

CHAPTER VIII. THE MAMMALIA OR MILK-GIVERS. The Simplest Suckling Mother, the Active Pouch-bearers, and the Imperfect-Toothed Animals.

Our backboned animals have now travelled far along the journey of life. The fish, in many and varied forms, have taken possession of the seas, lakes, and rivers; the amphibia, once large and powerful, now

in small and scattered groups, fill the swamps and the debateable ground between earth and water; the reptiles, no longer masters of the world, but creepers and skirmishers still holding their own in many places either by agility, strength, or the use of dangerous weapons, swarm in the tropics, and even in colder countries glide rapidly along in the warm sunshine, or hide in nooks and crannies, and sleep the winter away. And the birds,—the merry, active, warmhearted birds,—live everywhere, making the forests echo with their song, rising into the heights of the clear atmosphere, till the world lies as a dim panorama below them, crowd the water’s edge with busy fluttering life, and even wander for days and weeks over the pathless ocean, where nothing is to be seen but sky and water.

Yet still the great backboned division is not exhausted; on the contrary, the most powerful if not the most numerous group is still to come; that group which contains the kangaroos and opossums, the dreamy sloths, the night-loving moles and hedgehogs, the gentle lemurs and the chattering monkeys, the whales, seals, and walruses for the water; the herds of wild cattle and antelopes, of noble elephants and fleet horses, for the forests, mountains, and plains; and the ferocious beasts of prey, which make these gentler animals their food; while last, but not least, comes man himself, the master and conqueror of all.

Where, then, shall we look for the beginning of this vast multitude of warm-blooded, hairy, and four-limbed animals? If we turn back to the past, we get but little help; for though in that early time, when huge reptiles overran the world and swam in the waters, we find small animals (see Fig. 48), probably of the marsupial or pouched family, living in the forests, yet even if these were the earliest of their race, which is not at all likely, they would tell us very little about the beginning of the milk-givers, since only their lower jaws remain, and we can only guess at their relationship by these having that peculiar inward bend which we still find in all pouched animals.

Fig. 48.

A, Jaw of Dromatherium; B, Tooth of Microlestes; both milk-givers, probably marsupials, found in beds of the same age as those containing the ancient swimming lizards.

No! for the few scattered facts about the lowest mammalia or milk-giving animals we must inquire of our own day, to learn something as to the causes of their success in life. And first let us notice two important changes which give them an advantage over other backboned creatures. We have seen that, as we have gradually risen in the scale of Life, parents have taken more and more care of their eggs and their young ones. Among the boneless animals which we studied in Life and her Children, it was not (with very few exceptions) till we reached the clever, industrious, intelligent insects, that we found them taking any thought for the weak and helpless infants. There we did find it, for insects in their own peculiar line stand very high among animals; when, however, we turned back again to

begin with the first feeble representatives of the backboned family, we found the fish casting their eggs to the bottom of the sea, or on the pebbly gravel of a flowing stream, and, as a rule, taking no more thought of them. The tiny stickleback with his nest, and the lumpsucker watching over his young ones, were quite exceptions among the finny tribe. So it was again with the frogs, so with the reptiles (the turtles, lizards, and snakes), whose eggs, even when carefully buried by the mother, are often devoured by thousands before the little ones have a chance of creeping out of the shell. But when we come to the birds, there, as with the insects, we find parental care beginning—the nest, the home, the feeding, the education in flying, in singing, in seeking food, the warm-hearted love which will risk death sooner than forsake the little ones.

Yet still these same little ones have many perils to run even before they break through the shell. In spite of their parents’ care, more eggs probably are eaten by snakes or weasels, field-rats, and other creatures, than remain to be hatched; while, even if they escape being devoured, the eggs must not be allowed to grow cold; and should the parents be too long away or be scared off the nest by some enemy, or should a damp cold season spoil the warm dry home, the young bird is killed in the egg before it has ever seen the light.

It is not difficult to see, therefore, that if the mother could carry the egg about with her till the little bird was born, as we found our little common lizard doing (see p. 105), it would be much safer than when left in the nest exposed to so many dangers.

Now something of this kind takes place with all that great group of animals we are going to study. The cat and the cow, as we all know, do not lay eggs as birds do; but the mother carries the young within her body while they are going through all the changes which the chicken goes through in the egg. Thus they go wherever she goes, the food which she takes feeds them, and they lie hidden, safe from danger, till they are born, perfectly formed, into the world. Nor is this all; for when at last her little ones see the light, the mother has nourishment ready for them; part of the food which she herself eats is turned into milk, and secreted by special glands, so that the newly-born calf or kitten is suckled at its mother’s breast till it has strength to feed itself.

These two advantages, then,—namely, that the young have no dangerous egg-stage, but are sheltered by their mother till they are perfect, and that their mother has milk to give them for food,—at once divide the Mammalia or milk-giving group of animals from the rest of the backboned family.

But how will this help us to learn where that great group begins? Is it possible that such creatures as these can have anything in common with reptiles and birds? To answer these questions we must travel to a part of the world which has long been separated from the great continents of Europe, Asia, Africa, and America, and where the low and feeble milk-giving animals had a chance of still keeping a place in the world.

Take a map and look at Australia, New Guinea, and Tasmania, and you will see that they are separated by a number of scattered islands from the great continents, which are not only large in themselves, but are all nearly joined together, with only narrow straits dividing them. Moreover, Australasia stands even more alone than appears at first sight; for Mr. Wallace has pointed out that a very deep sea separates New Guinea and Australia on the one hand from Borneo and China on the other; so that the land might rise several thousand feet, and yet the Australasian islands would not be joined to the great continents.

Now, if the milk-givers once had feeble beginnings, and gradually branched out, as the ages went on, into all the many forms now living, it is clear that on the great battlefield of Europe, Asia, Africa, and America, the first poor weak forms would gradually be destroyed by the stronger ones that overran these great continents. They would be crushed out, as so many of the reptiles and newts and fishes had been before them; and only their bones, if any remained, would tell us that they had once lived. But if some of them could find a refuge in a domain of their own, where after a time they had a good open sea between them and their stronger neighbours, they might have a chance of living on and keeping up the old traditions.

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