The connection which in earlier geological periods had united Europe, Asia, Africa, and North America in the greatest homogeneous zoogeographical kingdom, the Arctogæa, was broken during the Tertiary and Drift Periods, so that several zoogeographical provinces were formed. The connection with North America was the first to be broken, so that even in the last two divisions of the Tertiary Period, the Miocene and Pliocene Epochs, the Old and the New Worlds stood in the relation of independent zoogeographical provinces to one another. Now, it is of the greatest importance to note that during the Drift Period North America again received some Northern immigrants from the Old World, according to Von Zittel “probably viâ Eastern Asia.” Consequently, during the Drift Period communication existed, at least temporarily, between Asia and North America in the region of Bering Strait, sufficient to allow the mammoth and some companions to migrate from the one continent to the other. In Kotzebue Sound mammoth remains are found in the “ground-ice formation,” together with those of the horse, elk, reindeer, musk-ox and bison. Mammoth remains are also known to have been found in the Bering Islands, St. George in the Pribylov group, and Unalaska, one of the Aleutian Islands. In that period the mammoth arrived in the New World as a colonist driven from the Old. It spread widely over British North America, Alaska, and Canada; it has also been found in Kentucky. A relatively recent union of the circumpolar regions of the Northern Hemisphere--of Europe, Asia, and North America--is also proved by the occurrence of animals that we recognise as companions of the mammoth, but which, surviving the Glacial Period, are still distributed over the whole region, such as the reindeer, elk, and bison. The absence in Asia of several animals specially characteristic of the European Drift (the hippopotamus, ibex, chamois, fallow-dear, wildcat, and cave-bear) explains also their absence in the North American Drift fauna. It is particularly strange that the cave-bear did not reach Northern Asia. It is otherwise the most frequent beast of prey of the Drift Period, and hundreds of its carcases often lie buried in the caves and clefts it once inhabited. In Southern Russia numerous remains of it are found, whereas in the English caves it is rarer, the cave-hyena predominating here. Apart from the exceptions just mentioned, J. F. Brandt considers North Asia and the high Northern latitudes to be the region in which the European, North Asiatic, and North American land fauna had concentrated during the Tertiary and Drift Periods, and whence their migrations and advances took place according as it grew older. As the northern fauna spread over more southern latitudes during the Drift Period, they took possession of the habitats of the species there belonging to the Tertiary Period, drove them back into tropical and subtropical regions,