PRELIMINARY CONSIDERATIONS. 43 



Finally, animals have also reached us from the north, 

 and in the fourth chapter the history of that remark- 

 able migration will be fully discussed under the title 

 of the Arctic element of the European fauna. 



It is generally believed that Africa played an im- 

 portant role in the peopling of our continent, but 

 this is quite a mistake. The eminent Swiss palae- 

 ontologist Riitimeyer was quite right in saying (p. 

 42) that it is much more probable that Morocco, 

 Algeria, and Tunis were stocked with animals by way 

 of Gibraltar, and perhaps also by Sicily and Malta, 

 from Europe, than the South of Europe from Africa. 



I have already referred to what are known as 

 "centres of dispersion" of animals, but before con- 

 tinuing to explain the general outline of this book, 

 it will be necessary to make a few additional remarks 

 on the subject. 



Since every animal naturally tends to spread in 

 every direction from its original home that is to 

 say, from the place of its origin the latter should 

 correspond with the centre of its range. And in 

 any particular group of animals the maximum 

 number of species should be formed in the area or 

 zone which is the centre of its distribution. In the 

 great majority of instances this is probably the case, 

 in the higher animals perhaps less so than in the lower; 

 still the rule must hold good that the original home 

 of a species is generally indicated by the centre of 

 its geographical distribution. 



Take for example our familiar Badger (Meles taxus). 



