Again, all the great groups of the Ruminants, the _Bovidae, Antilopidae, Camelopardalidae_, and _Cervidae_, are represented in the Miocene epoch, and so are the Camels. The Upper Eocene _Anoplotherium_, which is intercalary between the Pigs and the _Tragulidae_, has only two or, at most, three toes. Among the scanty mammals of the Lower Eocene formation we have the perissodactyle _Ungulata_ represented by _Coryphodon, Hyra-cotherium_, and _Pliolophus_. Suppose for a moment, for the sake of following out the argument, that _Pliolophus_ represents the primary stock of the Perissodactyles, and _Dichobune_ that of the Artiodactyles (though I am far from saying that such is the case), then we find, in the earliest fauna of the Eocene epoch to which our investigations carry us, the two divisions of the _Ungulata_ completely differentiated, and no trace of any common stock of both, or of five-toed predecessors to either. With the case of the Horses before us, justifying a belief in the production of new animal forms by modification of old ones, I see no escape from the necessity of seeking for these ancestors of the _Ungulata_ beyond the limits of the Tertiary formations. I could as soon admit special creation, at once, as suppose that the Perissodactyles and Artiodactyles had no five-toed ancestors. And when we consider how large a portion of the Tertiary period elapsed before _Anchitherium_ was converted into _Equus_, it is difficult to escape the conclusion that a large proportion of time anterior to the Tertiary period must have been expended in converting the common stock of the _Ungulata_ into Perissodactyles and Artiodactyles.