INTRODUCTION. II 



with us is so meagre that it can almost be left 

 unnoticed ; the main features, however, remain 

 nearly the same. The fauna of both of these 

 islands is composed of a strong southern element, 

 of an eastern and a northern one, and in addition 

 we have here species whose ancestors lived in 

 Western Europe. 



Before investigating more minutely the problems 

 suggested by the composition of the faunas of these 

 insular and also of some continental areas, it is 

 necessary that we should thoroughly understand 

 all about the migrations of animals. One of the 

 principal objects of this work is to show how the 

 autochthonous animals of Europe, /.&, those which 

 have originated there, may be distinguished from the 

 immigrants, and to trace the latter to the home 

 of their ancestors. But in doing so, it is necessary 

 to refer to the many important geographical changes 

 which have occurred in Europe during the latest 

 geological epochs. The study of the geographical 

 distribution of the European fauna, as expounded in 

 this work, will in many instances confirm the theories 

 as to geographical changes based upon geological 

 foundations. But in every case the views herein 

 advocated are founded upon the geographical distri- 

 bution of living and extinct organisms alone. 



A terrestrial mammal like the deer can, under 

 ordinary circumstances, only reach one part of a 

 country from another by walking or running to it; 

 but a beetle, such as the cockchafer, has two different 



