The Field-mice and Wrens of St. Kilda and Shetland

IN his notice of Messrs. A. H. Evans and T. E. Buckley's "Fauna of the Shetlands" (NATURE, May 24, 1900, pp. 75 and 76), your reviewer regrets that the authors are silent in regard to the special characters of the Shetland field-mouse, in view of my own recent recognition of a peculiar representation of this type in St. Kilda. It may be interesting to point out that in a recent paper on geographical and individual variation in Mus sylvaticus and its allies (P.Z.S., 1900, p. 387), I found myself unable to separate the Shetland field-mouse (specimens of which I had fortunately been able to examine), at least at present, from that of Great Britain generally. I would not, however, therefore necessarily bind myself to follow your reviewer in his suggestion that the comparative distinctness of the local forms of wren and field-mouse may guide us in forming a decision as to the relative periods during which St. Kilda and the Shetlands have been separated from the mainland. So many factors seem to be brought into play in the evolution of a local race or subspecies that it is, I fear, unsafe to rely too much on such points, and I have a strong suspicion that the influence of the environment has been too little taken into account by recent writers. At all events the field-mouse of Iceland would, it might be thought, show remarkable deviations from the mice of Western Europe, yet the little that we know of it only shows us how closely allied it is to Mus sylvaticus proper.