"It is a well-known and universally acknowledged fact that we can choose two portions of the globe of which the respective fauna and flora shall be so different that we should not be far wrong in supposing them to have been the result of distinct creations. Assuming, then, that there are, or may be, more areas of creation than one, the question naturally arises how many of them are there, and what are their respective extents and boundaries; or, in other words, what are the most natural primary ontological divisions of the earth's surface?" Mr. Sclater's answer was that there are six great regions; Neotropical, Nearctic, Palæarctic, Ethiopian, Indian, and Australian, and his answer, with minor alterations and the addition of a great wealth of detail, has been accepted by zoölogy. Two years later, however, Darwin gave a new meaning and a new importance to Sclater's work, by the new interpretation he caused to be placed on the words "centres of creation." Sclater's facts and areas remained the same; Darwin rejected the idea of separate creations in the older sense of the words, and laid stress on the impossibility of accounting for the resemblances within a region and for the differences between regions by climatic differences and so forth. He raised the questions of modes of dispersal and of barriers to dispersal, of similarities due to common descent, and of the modifying results produced by isolation. He gave, in fact, a theory of the "creations" which Mr. Sclater had shewn to be a probable assumption. It was in the nature of things that Huxley should make a contribution to a set of problems so novel and of so much importance to zoölogy. In 1868, in the course of a memoir on the anatomy of the gallinaceous birds and their allies, he made a useful attempt, nearly the first of its kind, to correlate anatomical facts with geographical distribution. Having shewn the diverging lines of anatomical structure that existed in the group of creatures he had been considering, he went on to shew that there was a definite relation between the varieties of structure and the different positions on the surface of the globe occupied at the present time by the creatures in question. He made, in fact, the geographical position a necessary part of the whole idea of a species or of a group, and so introduced a conception which has become a permanent part of zoölogical science.