THE ALPINE FAUNA. 339 



removed from one another; but how different were 

 their paths of migration ! This, however, is not an 

 imaginary instance. Such a migration must have 

 actually taken place in a good number of instances 

 among the terrestrial invertebrates and also among 

 plants. 



The view still current among many zoologists and 

 botanists, that animals and plants were driven down 

 into the plain from the mountains of Europe during 

 the height of the Glacial period and there lived 

 together till the return of a more genial temperature, 

 when they retreated to their mountain homes, is a 

 very plausible one. During their sojourn in the 

 plain, the plants and animals say from Scandi- 

 navia intermingled with those from the Alps ; and 

 when the time of separation came, many Alpine 

 forms retired northward with the Scandinavians, 

 while many Scandinavians would go with the 

 Alpines to their home. In this way the similarity 

 between the Alpine and Scandinavian faunas and 

 floras is assumed to have been brought about. 

 These theories, first promulgated by Edward Forbes, 

 were hailed with general satisfaction by the scientific 

 world. Even Darwin says of them (p. 331), that 

 grounded as they are on the perfectly well- 

 ascertained occurrence of a former Glacial period, 

 they seemed to him to explain in a satisfactory 

 manner the present distribution of the Alpine and 

 Arctic productions of Europe. To the present day 

 this view meets with much favour among- naturalists. 



