Nevertheless, as a rule, they probably live long lives, till their teeth are worn, or their whalebone frayed and broken, and their blubber wasted away; and then, it may be after eighty or one hundred years of life, they die a natural death. Therefore they probably share with the elephant the longest term of life of any of the warm-blooded animals; and though their existence cannot certainly be said to be an exciting one, yet, when undisturbed by man, it is at least peaceful, sociable, and full of family love. It may perhaps seem strange that we should have taken these ocean-dwellers last in our glimpses of animal life; but in the first place, how was it possible to show how they are truly related to the land mammalia until we understood the structure of these last? And in the second place, we have as our object to see how the backboned family have won for themselves places in the world, and surely there are none which have done this more successfully or in a more strange and unexpected way than the whales, which, while retaining all the qualities of warm-blooded animals, have won themselves a home in the ocean by imitating the form and habits of fish, and so adapting themselves to find food in the great oceans, where their land relations were powerless to avail themselves of it. [Illustration: WHEN THE COLD HAS PASSED AWAY] CHAPTER XII. A BIRD’S-EYE VIEW OF THE RISE AND PROGRESS OF BACKBONED LIFE. We have now sketched out, though very roughly, the history of the various branches of the great backboned family, and we have found that, as happens in all families, they have each had their successes and their downfalls, their times of triumph, and their more sober days, when the remaining descendants have been content to linger on in the byways of life, and take just so much of this world’s good as might fall to their share. We have seen also that, as in all families of long standing, many branches have become extinct altogether; the great enamel-plated fish, the large armour-covered newts, the flying, swimming, and huge erect-walking reptiles, the toothed and long-tailed birds, the gigantic marsupials, the enormous ground-loving sloths, and many others, have lived out their day and disappeared; their place being filled either by smaller descendants of other branches of the group, or by new forms in the great armies of fish, birds, and milk-givers which now have chiefly possession of the earth. Still, on the whole, the history has been one of a gradual rise from lower to higher forms of life; and if we put aside for a moment all details, and, forgetting the enormous lapse of time required, allow the shifting scene to pass like a panorama before us, we shall have a grand view indeed of the progress of the great backboned family.