54 HISTORY OF THE EUROPEAN FAUNA. 



time, whilst the eastern forms (he calls them northern) 

 would swing southwards. The two migrations would 

 thus occupy, at different times of the year, the 

 same tract of ground (a, p. 1 13). From the mingling 

 of the remains of the Hyaena with those of the 

 Reindeer and Hippopotamus in the Kirkdale Cavern, 

 he infers that the former preyed upon the Reindecr 

 at one time of the year, and on the Hippopotamus at 

 another. He argues that in such a manner might 

 be explained the curious mixture of northern and 

 southern types which we find in the British pleistocene 

 and in cave deposits. 



Besides mammals, the only European animals 

 which have received some attention with a view to a 

 study of their origin, are the Butterflies and the Land- 

 Snails. The entomologists who have taken up the 

 problem have in so far scarcely produced satisfactory 

 results, as they all seemed to be bound down to the 

 hypothesis that practically all the butterflies had 

 been destroyed in Europe during the Glacial period. 

 Hofman, in his interesting little work, comes to the 

 conclusion (p. 50), that only in Greece and Spain 

 could a small remnant of the butterflies have survived 

 the extreme rigours of climate. Greece was at that 

 time connected with Asia Minor, and Spain with 

 North Africa ; and the author supposes that the semi- 

 alien fauna inhabiting these tracts was mainly re- 

 sponsible for the re-stocking of Southern Europe, but 

 that the main mass of our butterflies are post-glacial 

 Siberian immigrants. 



