"Further results obtained from the study of fossils have a bearing even on the deepest problems of Biology, namely, those connected with the nature of life itself. For instance, it is allowable to infer, from the statements already made, that the main factor in the evolution of organisms is some inherent impulse--the 'bathmic force' of Cope--which acts with unerring certainty whatever be the conditions of the moment." _E._ _Pedigree of the Horse._ Some recent evidence on this subject certainly does not clear away the difficulties set forth in the text. From _Nature_, Sept. 8, 1904, p. 474. "Professor Osborn (in a lecture before the British Association) mentioned that more than a hundred more or less complete skeletons of horses and horse-like animals had been found in North America. He thought he had established the fact that horses were polyphyletic, there being four or five contemporary series in the Miocene, but that the direct origin of the genus _Equus_ in North America was not established with certainty." Professor Sedgwick, _Student's Text Book of Zoology_, p. 599. "Much has been written on the ancestry of the horse. It has been maintained by many authors that a continuous series of forms connecting it with the four-toed, brachyodont Hyracothoridæ of the Eocene has been discovered, and that here if anywhere a demonstrative historical proof has been obtained of the doctrine of organic evolution. Without desiring in the smallest degree to impugn that doctrine, it may be permitted us here to examine rather closely the view that the series of forms which recent palæontological research has undoubtedly brought to light constitute that historical proof which has been claimed for them." [After an examination of the structural characters of these intermediate forms, viz., _Pliohippus_, _Protohippus_, _Desmathippus_, _Miohippus_, _Mesohippus_, _Orohippus_, and _Hyracotherium_, the author proceeds]: