MOUSE, in its original sense probably the name of the semi-domesticated house-mouse (Mus musculus), the type of the genus Mus and of the family Muridae. Zoologically, there is no distinction between mice and rats; these names being employed respectively for most or all of the smaller and larger “mouse-like” and “rat-like” representatives of the Muridae, whether they belong to the genus Mus or not. It is true indeed that in zoological nomenclature some of these are distinguished as “voles” (see Vole), but this is not in accord with popular usage, where such creatures come under the designation either of water-rats or field-mice. The distinctive characters of the typical mice (and rats), i.e. those included in the genus Mus, are dealt with in the article Rodentia. With the exception of Madagascar, the genus Mus ranges over practically the whole of the Old World, having indigenous representatives even in Australasia; while the house-mouse, with man’s involuntary aid, has succeeded in establishing itself throughout the civilized world. The following is a brief notice of the species of true mice (that is to say, those generally included in the genus Mus) inhabiting the British Isles. These are three in number, M. musculus, the house-mouse, originally a native of Central Asia, the wood or long-tailed field-mouse, is a species common in many parts of England, often taking to barns and out-houses for shelter during the winter. It is of about the same size and proportions as M. musculus but of a bright reddish-grey colour, with a pure white belly. M. minutus, the harvest-mouse, is the smallest of the European mice, seldom exceeding 212 or 3 in. in length; and of a yellowish-red colour, with comparatively short ears and tail. It lives entirely away from houses, commonly taking up its abode in wheat or hay fields, where it builds a round grass nest about the size of a cricket-ball, in which it brings up its young. Its range extends from England to Japan. In regard to the first it is noteworthy that house-mice isolated on a small sandbank near Dublin have developed a special colouring of their own; also that distinct local varieties, M. musculus muralis and M. faeröensis, inhabit respectively St Kilda and the Faeroes. In Central Asia there exists a wild mouse (M. bactrianus), and likewise a second species (M. wagneri), allied to M. musculus; while there is third kind (M. gentilis), also nearly related, in the deserts of North Africa. According to Major G. E. H. Barrett-Hamilton it is probable that M. bactrianus and M. musculus are respectively desert and house modifications descended from some Central Asian ancestor more or less nearly allied to M. wagneri. As regards the other two British species, it must suffice to say that there are several local races of each; Mus sylvaticus being represented by several in the British Isles, although there is but one representative of M. minutus. It may be added that by some naturalists both M. sylvaticus and M. minutus are separated from Mus as Micromys.
See G. E. H. Barrett-Hamilton, “Note on the Harvest-Mice of the Palaearctic,” Annals and Magazine of Nat. History (April 1899); “On the Species of the genus Mus inhabiting St Kilda” Proc. Zool. Soc. (London, 1899); “On Geographical and Individual Variation in Mus sylvaticus and its Allies,” op. cit. (1900); W. E. Clarke, “On forms of Mus musculus with Description of a New Subspecies from the Faeroe Islands,” Proc. Roy. Phys. Soc. (Edinburgh, 1904), vol. xv. (R. L.*)