(vi.) Worthy of notice also is "the remarkable circumstance that in the line of evolution culminating in the modern Horse, a parallel series of generically identical or closely allied forms occurs in the Tertiaries of both Europe and North America, from which it has been suggested that on both continents a parallel development of the same genera has simultaneously taken place."[291] And, as we have seen, while the American pedigree must have been entirely different from the European, it terminates equally in both continents with the genus _Equus_, if not actually with _Equus caballus_.[292] But, on any mechanical system of evolution, it is impossible to suppose that developments conducted along separate roads could thus be brought to meet in one terminus.[293] Mr. Darwin did not conceive it possible that the same species should be produced twice over, "if even the very same conditions of life, organic and inorganic should recur,"[294] and the production of genuine horses, not only in widely diverse circumstances, but through totally different ancestors, must appear still less conceivable. Consequently, says Mr. Mivart,[295] "it follows from this generic identity, that classification will be no longer Darwinian, but one more Aristotelian, and will regard, not the origin but the _outcome_ of development, whether of the individual or the species." (vii.) There is, however, another consideration more serious than any of the above. In order to set the theory of genetic Evolution upon a sound and substantial basis, it is not sufficient to show that the last ungulate is lineally descended from the first,--_Equus_ from _Eohippus_, _Hyracotherium_, _Phenacodus_, or _Hippops_,--but that this first ungulate himself--whichever it was--has been, or at least may have been, similarly developed from a non-ungulate Mammalian ancestor, the common parent of all the protean forms assumed by his progeny. To develop all these from one original, through a graduated series in each case, by the infinitesimal process of descent with modification, would require a period of time inconceivably long--immensely longer than that required to change one ungulate into another. Ungulates, as has been said, are a highly specialized type of Mammals, and although they walked on the nails of five digits instead of only one, a vast amount of Evolution would be required to bring them even to this point, from that whence all Mammals are said to have started. There must also have existed, while this development was in progress, a teeming and multitudinous mammalian life, as raw material for its operations--and of this at least _some_ trace should remain.