The great majority of species of the large genus _Microtus_ (_Arvicola_) are Asiatic, and there can be little doubt that it has originated in that continent. There is one species of Vole (_Microtus nivalis_) which occurs in the high Alps, and which has been supposed to be a typical Alpine form. It is known, however, to occur also in North Italy and in Bohemia, while _Microtus leucurus_ of the Pyrenees is identical with this species. But its range is by no means confined to Europe, for it has also been discovered in Syria and Palestine, while a closely allied form exists in the Himalayan Mountains. This shows clearly that the species has migrated to the Alps from Asia Minor. That this migration may have taken place at an early period--at a time when Sardinia and Corsica were still connected with Southern Europe--is indicated by the occurrence of an extinct Vole (_Microtus brecciensis_) in Sardinian and Corsican pleistocene (?) deposits. All the Alpine species mentioned except the Chamois can be easily traced to their former Asiatic home. But even it has its nearest relations in Asia. I might also refer to another Vole (_Evotomys Nageri_) which is practically confined to the Alps and Northern Italy, and which has probably originated there, though most of its nearest relations are either Asiatic or North American species. But besides these Asiatic immigrants and their modified descendants we have a small truly native Alpine mammalian fauna. _Sorex alpinus_--the Alpine Shrew--occurs only in the Alps, the Harz Mountains, Pyrenees, and Carpathians. The genus has been found in European eocene strata,--in vastly older deposits in our own continent than elsewhere,--so that it is extremely probable that it has originated there. It may then have developed a new centre of distribution in the newly-formed Alps where both _Sorex alpinus_ and _S. minutus_ (_pygmæus_) have their home. From there they again spread--perhaps already in miocene times--to Asia and North America, where a large number of new species originated. It seems to me even probable that one of these Asiatic species of _Sorex_, viz. _S. araneus_ (_vulgaris_), subsequently migrated towards the old home of its forefathers, since we find it more or less confined to Central and Northern Asia and Northern Europe.