If the great master who laid the foundations of palæontology could revisit the scene of his former labours, he would find that many strange things had happened since the appearance of his _Ossemens Fossiles_. He would perhaps be stupefied at first to discover how little is now made of the Revolutions of the Earth, the proofs of which had seemed to him unimpeachable, while the conjectures about the development of new races, which in his own day had been almost negligible, have proved to be anticipatory of fundamental biological truths. The first shock over, one can imagine the zest with which he would strive to combine the familiar facts into a body of new doctrine. The ungulates, recent and fossil, would of course interest him particularly. He would recognise the gradations of structure which run through the whole order, branching and crossing in all directions; gradation in the number of the toes, in the rearing of the body more and more upon the toe-tips, in the progressive complication of the teeth. One chain of examples would lead from the shallow, tuberculate molar of the pig to the molar of the horse or ruminant, deep and massive, with crescentic enamel-folds; another would illustrate the gradual development of tusks from ordinary incisors or canines; a third series would show the steps by which the primitive ungulate dentition became reduced to the dentition of the elephant, with only a single pair of incisors, enlarged into tusks several feet long, with no canines but molars of great weight, complicated by extreme folding. It would surprise and delight him to compare the almost insensible steps by which his own Palæothere can be seen to pass into the modern horse. Then we can imagine how our regenerate Cuvier would draw nearer and nearer to the common ancestor of the whole group, a five-toed, plantigrade ungulate, with the full dentition of forty-four unspecialised teeth, and how readily he would admit that Phenacodus, both in its structure and its geological horizon, was just the common ancestor that theory required. The proofs of intermediate stages between ancient and modern ungulates which he had once called for in vain, he would now find ready to his hand. It might well seem that the history of the ungulates, with all its modern expansions, would suffice to occupy even his unparalleled energy. He would see with delight how the palæontology which he had been the first to treat as a science has enlarged the comparative anatomy of which also he was so great a master. He would cheerfully admit that both yield proofs of that doctrine of descent with modification which a hundred years ago seemed to him so questionable.