CHAPTER II. 



PRELIMINARY CONSIDERATIONS. 



I INTEND to give in this chapter a general outline 

 of the subject which will be discussed in the 

 subsequent ones. This will include a brief history 

 of the great events, in recent geological times, which 

 have modified the evolution of the European fauna 

 by the influence which they have exerted on the 

 course of the successive streams of migration. 



The composition of the European fauna is the 

 first item which will have to be taken into con- 

 sideration. But not only must the existing species 

 of animals be dealt with : the extinct ones, too, 

 at least those which have lived in Europe during 

 late Tertiary times, will be useful for our inquiries. 

 A knowledge of the past faunas is a most important 

 factor in tracing the original home of the European 

 animals. 



Where a species first originated, whether this was 

 in one or several places, or, in other words, where 

 it first had its home, cannot be determined with 

 absolute certainty in the present state of our 

 knowledge, but as a rule it can be indicated 

 approximately with a fair amount of precision. In 



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