The palæontologist, for example, traces the descent of the horse, which, until its reintroduction by the Spaniards was unknown in the New World, through a variety of intermediate forms, to the genus Orohippus occurring in Eocene deposits in Utah and Wyoming. This animal was no larger than a fox, and possessed four separated toes in front, and three behind. Domestic cattle he refers to the Bos primigenius, and many existing Carnivora to Tertiary forms such as the cave-bear, cave-lion, sabre-tiger, and the like. The zoologist groups the existing fauna into distinct provinces, and demands, in explanation of the anomalies which these exhibit, the reconstruction of large areas, of which only small outlying districts remain at the present date, in many instances widely separated by oceans, though once forming parts of the same continent; and so, for the simile readily suggests itself, the workers in another branch of science, Philology, argue from words and roots scattered like fossils through the various dialects of very distant countries, a mutual descent from a common Aryan language: the language of a race of which no historical record exists, though in regard to its habits, customs, and distribution much may be affirmed from the large collection of word specimens stored in philological museums. Thus Mr. Sclater, on zoological grounds, claims the late existence of a continent which he calls Lemuria, extending from Madagascar to Ceylon and Sumatra; and for similar reasons Mr. Wallace extends the Australia of Tertiary periods to New Guinea and the Solomon Islands, and perhaps to Fiji, and from its marsupial types infers a connection with the northern continent during the Secondary period. Again, the connection of Europe with North Africa during a late geological period is inferred by many zoologists from the number of identical species of mammalia inhabiting the opposite sides of the Mediterranean, and palæontologists confirm this by the discovery of the remains of elephants in cave-deposits in Malta, and of hippopotami in Gibraltar; while hydrographers furnish the supplemental suggestive evidence that an elevation of only fifteen hundred feet would be sufficient to establish two broad connections between the two continents--so as to unite Italy with Tripoli and Spain with Morocco, and to convert the Mediterranean Sea into two great lakes, which appears, in fact, to have been its condition during the Pliocene and Post Pliocene periods. It was by means of these causeways that the large pachyderms entered Britain, then united to the continent; and it was over them they retreated when driven back by glacial conditions, their migration northward being effectually prevented by the destruction of the connecting arms of land. Some difference of opinion exists among naturalists as to the extent to which zoological regions should be subdivided, and as to their respective limitations.