MAMMALIAN AFFINITIES 223 



able, partly from palaeontological evidence, and partly from 

 other methods of reasoning. That most of them trace their 

 origin in America or Europe to the former existence of a 

 direct land bridge across the mid-Atlantic seems also obvious. 

 Yet many geologists are very strongly opposed to a theo- 

 retical bridging of the Atlantic. Nothing short of a well- 

 marked mammalian affinity between the two areas alluded to 

 will satisfy them. We can produce little of such evidence, be- 

 cause most groups of mammals have changed very rapidly 

 during the course of the Tertiary Era. A few, however, 

 such as the rodents, appear to have the faculty of preserving 

 their ancestral characters for longer periods, and some, 

 apparently, have undergone little change since remote times. 



There are two instances, one among the voles, the other 

 among the hare family, that seem to point to the existence of 

 the land connection just discussed, and these cases may pos- 

 sibly throw more light on the age of the land bridge than the 

 invertebrates or reptiles can do. Professor Tullberg * con- 

 tends that the meadow voles (Arvicola^Microtus) only entered 

 Europe in Pliocene times from Asia, where they had already 

 existed for some time previously. He also expressed the 

 opinion that these voles subsequently crossed over to America 

 from Europe by a north- Atlantic land connection, which I 

 presume must be the Scotland-Greenland-Labrador bridge. 

 We know very little of fossil meadow voles. If Professor 

 Schlosser is correct in his assertion that only geological re- 

 searches can give us any clues as to former changes of 

 land and water, and that zoogeography cannot do so, the 

 meadow voles can teach us very little. 



Yet if we examine the present range of one of the sub- 

 genera of meadow voles, such as Pitymys, we find it very 

 remarkable and instructive. One species lives on the Mont 

 d'Or in France, at a height of over 4,000 feet, another on one 

 of the southern Alpine spurs, at a height of 6,000 feet. De 

 Selys long ago described a species (Pitymys incertus) from 

 the St. Gothard mountain, a locality which is over 7,000 

 feet high ; another related form inhabits the Pic du Midi in 

 the Pyrenees, and still another a mountain in Sicily. Quite 



* Tullberg, T. " System der Nagetiere," p. 499. 



