DEEIVATION OF BEITISH COLEOPTEEA. 171 



other progressive species who have established a sort of 

 modus vivendi with civilization, readily adapt themselves 

 to those altered conditions which agriculture, among other 

 agencies, has imposed, and thrive under a new regime. 

 Such species we call common, and most of the others rare, 

 but the mystery of why one species of a genus can so 

 adapt itself, and another, so far as we can see, similar 

 physiologically, refuses to do so, is as impenetrable as 

 ever ; and to say that the fittest always survive only 

 restates the fact in other words, and does not explain it. 



However, the point is that those species which have 

 become fit, and are therefore common everywhere, are not 

 the slightest guide to us in our search for the causes and 

 methods of original distribution. Their facility for adap- 

 tation is so great, that whether they may have arrived 

 early or late, from the north, south, east, or west, it comes 

 to quite the same thing, that is, their present ubiquity 

 and the complete obliteration of all their past proceedings. 



We must thus eliminate at the commencement of our 

 enquiry all such quasi-domesticated Beetles as those of 

 the genera Dermestes, Pellio, Anthrenus, or Alphitobius, 

 and all such ubiquitous species as Nebria brevicollis, or 

 Harpalus ceneus, which appear to be equally abundant 

 from Cornwall to Caithness, and from the top of Ben 

 Nevis to below high-water mark. 



These exceptions, however, will be found to be but 

 trifling, and when we study the distribution of the great 

 bulk of our Coleopterous Fauna which will remain, we 

 shall, I think, discover that they can be, with more or less 

 precision, arranged in at least three groups, or rather, that 

 in their grouping we discover at least three diverse elements, 

 and this diversion will • be quite independent of genetic 

 affinities ; in fact, we shall be able to find in any of the 

 larger genera members belonging to each of them. 



