138 ANNALS OF SCOTTISH NATURAL HISTORY 



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 Hy. 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 I 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 musciilus 

 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 sylvaticns. Still it has never, I 

 believe, been asserted that the species is anything but an introduction 

 into Western Europe, including the British Islands. 



Light or yellowish varieties of Mus musculus have from time to 

 time received names such as M. hortulanus, Nordmann, M. nord- 

 manni, Keys, and Blasius, M, flavescens, Fisher, and M. flaviventris, 

 Lataste ; the last two preoccupied by names applied to 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 world wild forms of Mice which, though differing to a more 

 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, Brants, which are 

 widely distributed in the deserts respectively of Asia and N. Africa, 

 and M. wagneri, Eversm. ( = M. pachycercus, 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 characterised 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 propinquity to 

 the typical Mus musculus, as was 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. 

 We know, however, that almost everywhere where there are deserts 



