PRELIMINARY CONSIDERATIONS. 57 



Glacial period ; and the present Central European 

 fauna had already become developed from the Plio- 

 cene in all its details of form and distribution before 

 the commencement of the Ice Age" (p. 162). "We 

 must draw the conclusion from the preceding remarks, 

 that the present (palaearctic) molluscan fauna in its 

 distribution is older than the Glacial period, and that 

 the latter produced merely a retreat of the fauna 

 from the most inhospitable regions of Europe with 

 a subsequent re-immigration, but did not cause its 

 destruction" (i., p. 169). 



A few attempts have also been made by naturalists 

 to trace the origin of the fauna of some smaller 

 European areas. Thus Riitimeyer, in dealing with 

 the mammalian fauna of Switzerland, remarks (p. 31) 

 "that it seems certain that, in spite of many local 

 disturbances, the continuity of generations was never 

 interrupted throughout the whole of the Tertiary 

 period until the present day." 



An even more interesting memoir is that of Mr. 

 Koppen on the origin of the Crimean fauna. It is 

 only recently, according to this author, that this pen- 

 insula has become connected with Southern Russia. 

 And it is for this reason that the Squirrel and a number 

 of other animals, and also plants, present in Russia, 

 are absent from the Crimea. Originally the latter prob- 

 ably formed a westward continuation of the Caucasus, 

 and at that time it was surrounded by the sea on 

 all other sides. " Much later," he continues, " after 

 and in consequence of a local subsidence, the country 



