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Show 82 MR. G. E. H. BARRETT-HAMILTON ON [Feb. 7, The interest pertaining to these two Mice, which undoubtedly represent local developments of Mus sylvaticus and Mus musculus, will be better appreciated if I briefly discuss the variations to which these two species are subject in other localities. I assume, however, from the outset that in neither case am I dealing with an animal which may have been recently introduced to the island. The great amount of variation from the type of a species which varies so little as Mus sylvaticus, as shown in the one case, and the evolution of a perfectly uniform and distinct type of coloration in one so variable as Mus musculus in the other, are both characters which would seem to have taken no inconsiderable time for their development. So that even if, as is probable, the presence of a Mus musculus-like species of Mouse on St. Kilda be due originally to a case of introduction, such an introduction could not have taken place at a very recent period in the history of the island, which is known to have been inhabited for at least several centuries. The distribution of Mus sylvaticus is almost coterminous with the limits of the Palaearctic Region, the species only just reaching the confines of the Oriental Region "in Grilgit, where it is.common from 5000 to 10,000 feet elevation " (Blanford, Faun. Brit. Ind., M a m m . p. 416). In the former region it is probably as widely spread as any other mammal, as it seems to be very regardless of the influence of temperature, and is found far up the slopes of the mountains. It is equally at home in all the countries (except probably the Arctic tundras and the great sandy deserts) from the eastern coast-line of China to the Atlantic. It has reached Morocco, Algeria, and Palestine, and has found its way to most of the Islands, such as those of the Mediterranean, the Channel Islands, Great Britain, Ireland, the Scotch Islands, the Shetlandsl, and even Iceland, where the local form (Mus islandicus Thien.) is said to be the only indigenous species of mammal. Its presence in such isolated, yet widely-separated, islands as Iceland and Corsica seems to mark it as a species which has for long maintained a wide area of distribution, and which had already occupied the greater part of its present range before these and the other islands where it is now found were finally separated from the continent as such, but still formed a part of the continuous Palaearctic land-area. And of its antiquity we have sufficient proof, for its bones have been found in numerous caves on the Continent and in the English Forest-bed (see E. T. Newton, Quart. Journ. Geol. Soc. vol. 1. pt. 2, no. 198 (May 1st, 1894), p. 195), and we have no trace of its ancestry, the Pleistocene species, Mus orthodon Hensel and abbotti E. T. Newton, being at least as specialized as itself. Not only is Mus sylvaticus of exceedingly wide distribution, but 1 A set of four from Dunrossness, for which I am indebted to Mr. Henderson, has recently reached me; I am unable to separate them from Mus sylvaticus of Western Europe and Great Britain, and the same remark applies to some specimens collected for me by Mr. W . Eagle Clarke on Alderney. |