JDEEIVATION OF BRITISH COLEOPTERA. 169 



such introductions in the British Fauna, and more in the 

 flora than the fauna of most islands. By non-natural, I 

 mean introductions which are in any way directly or 

 indirectly due to the appearance of humanity on the 

 scene. Cases of the sort, of course, do occur, and impress 

 one by the rapidity of their advance. There is, for 

 instance, the oak-gall fly, Gynips kollari, which produces 

 our familiar oak apple, and this insect appears to have 

 been first introduced into Devonshire and restricted to 

 that county not much more than half a century ago — now 

 every oak tree in the country testifies to the extent of its 

 present range. The deplorable ubiquity of the common 

 cockroach is another case in point among the insecta. 



On the other hand, among mammals we have the poor 

 success which has attended all attempts to introduce our 

 common English hare into Ireland, whose native form is 

 a closely allied but distinct species the Arctic or moun- 

 tain hare. Here some unknown influence seems to resist 

 the establishment of a new species in an area which appears 

 to be perfectly suitable to its maintainence. Generally 

 speaking the adjustment between existing species and 

 their environment in any region is so close and so exact 

 that there is no room, not the least chink of an interstice, 

 into which a new arrival can thrust itself, and the nearer 

 genetically such a would-be immigrant may be to forms 

 already existing, so much the more difficult is its entrance 

 made. 



Where we do find such introductions is where the 

 environment itself has been changed by man, and among 

 the.Coleoptera there are perhaps 40 or 50 species, quasi- 

 domesticated, the Beetles of granaries and bakeries and 

 grocers shops. These we must eliminate in any considera- 

 tion of the natural distribution of the group. 



But, considering the matter a little further, we discover, 



