INTRODUCTION. 33 



character of the faunas and floras of oceanic islands; 

 and I believe that the normal mode in which islands 

 have been peopled, has been by direct continuity with 

 the land at some former period, or by contiguity so 

 close as to be equivalent to junction " (p. 15). " That 

 a slight intermixture," he continues, "due to Mr. 

 Darwin's colonisation, occurs in many (probably in 

 all) I am ready to admit ; and from instances to be 

 afterwards noticed, I am disposed to reckon the pro- 

 portions of such intermixtures in the flora, in the 

 most favourable circumstances, at not more than two 

 per cent. In the fauna I think it must be much less." 



Mr. Murray's views, though they relate only to 

 oceanic islands, are likewise applicable to continental 

 islands such as our own. I think we might take the 

 admixture in the British fauna due to occasional, 

 including human introduction, as amounting to five 

 per cent. It is better to take a high estimate, so as to 

 include all the species about whose native land there 

 might be some reasonable doubt. Now of what 

 importance, after all, is this five per cent? The 

 remaining ninety-five per cent, of the species of 

 animals belonging to the British fauna undoubtedly 

 migrated to these islands in the normal way by land. 



It is of great importance, in dealing with the 

 question of the origin of the British fauna, to 

 thoroughly grasp this conclusion that ninety-five 

 per cent, of the animals have reached us by land. 

 We can afford in fact to ignore the five per cent, 

 altogether. It is an insignificant factor. As regards 



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