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.