The distribution of a genus (except of course when the genus is represented only by a single form) is very generally more extensive than that of a species; and this may be markedly the case when there are only some two or three species in a genus. In genera, moreover, we meet with what is known as discontinuous distribution, that is, where the distributional area of one or more species is totally separated from that of others. The best instance of this occurs in the case of the Tapirs, where we find one species inhabiting the Malayan Peninsula, and no others anywhere in the world, with the exception of South America. The explanation of such an apparently anomalous feature in distribution is to be found in the past history of the globe, which shows us that Tapirs once existed in China, Europe, and North America, and, therefore, indicates that the existing isolated species are the sole survivors of a group once spread over a large portion of the earth’s surface. In regard to generic distribution it must, however, be mentioned that this depends to a great extent on the limits which we are disposed to assign to genera themselves. As the distributional area of a genus generally exceeds that of a species, so that of a family, or group of genera, is larger than that of a single genus; and similarly the distribution of an order, or assemblage of families, usually occupies a larger area than that of a single family. Thus, for instance, the genus _Thylacinus_, represented only by the so-called Tasmanian Wolf or Thylacine, is now entirely restricted to Tasmania; but the family _Dasyuridæ_, to which that genus belongs, ranges all over Australia, while the order Marsupialia, which includes the _Dasyuridæ_, is found both in Australia and America, and in past epochs was probably spread over the entire globe. A remarkable feature in connection with the distribution of the terrestrial Mammalia is the circumstance that, with the exception of certain species introduced by human agency, and small forms which can easily have been transported on floating timber or other similar means, they are totally absent from what are known as oceanic islands—that is islands arising from great depths in the ocean, mainly composed of coral or volcanic rocks, and showing no signs of having ever been connected with the existing continents, or the larger and so-called continental islands. The obvious explanation of this feature is, that from their total isolation these islands have never been able to receive a mammalian fauna from the great continental areas on which mammalian life was probably first developed.