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Show 86 MR. G. E. H. BARRETT-HAMILTON ON [Feb. 7, " The possibility of the shells haA'ing been brought as bait, for the lines of the fishing-boats visiting the bank is, I think, disposed of by the mixed character of the deposit, some of the shells being unsuitable for such a purpose. It would be interesting to trace out the area occupied by these dead shells, and, possibly, to search in a similar manner for the lost land of H y Brassil on the Porcupine Bank, but the time at our disposal only gave us the chance for one dip into this deposit." Turning to Mus musculus we have to deal with a very different species, and I do not in this case attempt to prove that this animal has reached St. Kilda without the help of man. That it must have existed there for a considerable time, perhaps for hundreds of years, is, however, as 1 hope to show, very probable. Well known and widely spread in almost all regions where the habitations of man afford it a refuge, it is impossible to state what is the native home of the species. Not only is the domestic form of Mus musculus widely spread and readily susceptible of introduction into the houses of its unwilling protector, man, but its variability is as remarkable as is the constancy to type of Mus sylvaticus. Still it has never, I believe, been asserted that the species is anything but an introduction into Western Europe and the British Islands. Light or yelloAvish varieties of Mus musculus have from time to time received names, such as M. hortulanus Nordmann, M. nord-manni Keys. & Blasius, M. fiavescens Fisher, and M. fiaviventris Lataste; the last two names preoccupied by other species of the genus. In addition, however, to these almost domestic members of the Mus-musculus group of Mice, we have in many parts of the Avorld wild forms of Mice which, though differing to a greater or less extent in their size, length of tail and colour, cannot be distinguished from Mus musculus in their skull and teeth. Such Mice are M. bactrianus Blyth and M. gentilis Brauts, which are widely distributed in the deserts respectively of Asia and N.Africa, and M. wagneri Eversm. ( = M. pachycereos Blanford) of Central Asia, the latter a true House-Mouse, often found inhabiting houses, and differing in no cranial characters from Mus musculus proper. Lastly we have a set of Mice also of varied colours, size of body, and proportion of tail, but mostly characterized by the possession of a white belly, which are found in many of the regions where typical Mus musculus occurs. Such are M. spretus Lataste, of the Barbary States, and M. spicilegus Petenyi, of Hungary, France, Portugal, and Western Europe. These mice may occur in close proximity to the typical Mus musculus, as Avas found by Mr. Oldfield Thomas in Portugal and by myself in Morocco. Among all these perplexing forms it is indeed difficult to assign a proper place to M, muralis, and more so to hazard even a guess as to the possible origin of the domestic races of Mus musculus. W e know, however, that almost wherever there are deserts there a bactrianus-like Mouse is found, so that M. bactrianus is perhaps as widely distributed in deserts as is Mus musculus |
