But I need not multiply proof of the functional identity of organic nature in all ages. It may, however, be inquired, how this identity, as well as that of anatomical structure, is reconciled with the great anomalies, both in size and form, which have confessedly prevailed among ancient animals. Compare the plants and animals which now occupy the northern parts of the globe with those which flourished there in the remote periods of geological history, and can we believe them to be portions of one great system of organic nature? Compare, for instance, the thirty or forty species of ferns now growing to the height of a few inches, or one or two feet, in Europe and this country, with the more than two hundred species already dug out of the coal mines, many of which were forty to forty-five feet in height; or the diminutive ground pines, and equiseta, now scarcely noticed in our forests, with the gigantic lepidodendron, sigillaria, calamites, and equiseta, of the carboniferous period; and who will not be struck with the great difference between them? Or go to Germany, and imagine the bones of the dinotherium to start out of the soil, and become clothed with flesh and instinct with life. You have before you a quadruped eighteen feet in length, and of proportional height, much larger than the elephant, and with curved tusks reaching two or three feet below its lower jaw, while no other living animal would be found there larger than the ox, or the horse--mere pygmies by the side of such a monster, and evidently unfit to be his contemporaries. Again. Let the megatherium be brought back to life on the pampas of South America, and you have an animal twelve feet long and eight feet high, with proportions perfectly colossal. Its fore feet were a yard long, its thigh bone three times thicker than that of the elephant, its width across the haunches five feet, its spinal marrow a foot in diameter, and its tail, where it was inserted into the body, two feet in diameter. What a giant in comparison with the sloth, the anteater, and the armadillo, to which it was allied by anatomical structure! Still more unequal in size, as compared with living batrachians, was the labyrinthidon, once common in England and Germany, if, indeed, the tracks on sandstone were made by that animal. It was, in fact, a frog as large as an ox, and perhaps as large as an elephant. Think of such animals swarming in our morasses at the present day! But coming back from Europe, and turning our thoughts to the animals that trod along the shores of the estuary that once washed the base of Mount Holyoke, in New England, we shall encounter an animal, probably of the batrachian family, of more gigantic proportions. It was the _Otozoum Moodii_, a biped, with feet twenty inches long, more than twice the size of those of the labyrinthidon; yet its tracks on the imperishable sandstone show that such a giant once trod upon the muddy shore of that ancient estuary.