82 MB. G. E. H. BARRETT-HAMILTON Olf [Feb. 7, 



The interest pertaining to these two Mice, whicli undoubtedly 

 represent local developments of Mus sylvatieus and Mas muscuJios, 

 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 w^hich varies so little as 3[us sylvaticus, as shown in the 

 one case, and the evolution of a perfectly uniform and distinct 

 type of coloration in one so variable as Mas muscitlus 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 3Ius musculus-hke species of Mouse on 

 yt. Kilda be due originally to a case of introduction, such an 

 introduction could not have taiien place at a very recent period 

 in the history of the island, which is known to have been in- 

 habited for at least sevei-al centuries. 



The distribution of Mus si/lvaticus is almost coterminous with 

 the limits of the Palaearctic Kegion, the species only just reaching 

 the confines of the Oriental Kegion " in Grilgit, where it is common 

 from 5000 to 10,000 feet elevation " (Blanford, Faun. Brit. Ind., 

 Mamm. 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 Shetlands ^, 

 and even Iceland, where the local form (Mus islandicus Thien.) 

 is said to be the onlj' 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 x-ange 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 

 Paljearctic 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. Xewton, 

 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 ahhotti E. T. Newton, being at 

 least as specialized as itself. 



Not only is Mus sylvaticus of exceedingly wide distribution, but 



' A set of four from Dunrossness, for which I am indebted to Mr. Henderson, 

 has recently reached nie ; 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. \^^ Eagle Clarke on Alderney. 



