But take him at his more ordinary figure—fifty to seventy feet or so—and what a gigantic monster he is! In appearance, from the point of the nose—where he seems to have been sawn through—to the middle of the back, he is like an enormous black tree-trunk. From here the body tapers, or rather slopes steeply, to the tail, where first a shape is observable—that, namely, with which we are familiar in the tail, or caudal fin, of almost every fish. Unlike the latter, however, the tail or “_flukes_” of the cachalot—as well as every other whale—lies flat-ways in the water, with its two points shooting out at right angles to the two sides, instead of to the back and belly of the creature. The difference is like that between the way a plank floats on the water, and the way in which the keel of a boat cuts through it. It seems curious that there should be such a difference here between the whale and the fish tribe, seeing that in each the tail has been gradually developed to meet the requirements of a similar mode of life. This being so, one might have supposed that the plan of the tail would have been the same in each, on the principle that one way—as represented by the whole class of fishes—must be better than any other. Apparently, however, this is not the case, since cetaceans, on the whole, swim as well and as swiftly as fish. The tail in their case, and not the two hinder limbs, as with seals, has been modified into a fin, and it is curious that in the beaver, where it has also been modified to a considerable extent, in this direction the expansion has likewise been lateral and not vertical. We see the same thing in the case of many crustaceans, and throughout nature this principle of attaining the same end by a variety of means is apparent. This should teach us that it is a great mistake to think, as people often do think, that the particular way in which any animal does a certain thing is the only, or best way, in which it might conceivably be done. Even a man—if a clever one—might think of some improvement in the structure of most animals, in relation to their habits of life. Only he could not carry out these improvements. Nature alone can do that, and in her own time and way she is always ready to do so.