NOTES ON THE DISTRIBUTION OF THE BRITISH COLEOPTERA. 177 



study of the physiological characteristics of these species will make 

 clear to us that in this, as in all the other orders of Insecta, its 

 members naturally fall into two more or less definitely separated 

 groups, which we may call the adaptables and the non-adaptables, or 

 if we prefer, the progressives and conservatives, that is species which 

 are common everywhere, and species which are either generally rare 

 or abundant only very locally ; in other words, that there are a 

 certain number of forms which have successfully solved the problem 

 of the continual adjustment of themselves to an ever-changing 

 environment, and those which, failing to do so, perish when their own 

 particular environment ceases to be. Now, it must further be noted 

 that this cleavage follows no distinct lines of phylogenetic affinity. In 

 nearly every large genus we find a minority of adaptables, a majority 

 of non-adaptables, a majority attached to the sandy wastes of the 

 shore, to marshes, forests, heaths, and mosses, and when we replace 

 our sandhills by docks and golf-links, drain our fens and mosses, cut 

 down our forests, and cultivate our desert wildernesses, then the non- 

 adaptables, the conservatives of the feral population of such places, 

 pass to return no more ; they are, in fact, incapable of the necessary 

 adaptations. Hence it is that inasmuch as the physical characteristics 

 of this country are continually changing, and that in an increasing 

 ratio, the extinction of many of our rarer species is merely a matter of 

 time. This process may not perhaps be very obvious among the 

 coleoptera, but it is certainly noticeable among such a group as the 

 diurnal lepidoptera, is in full progress among the birds, and has nearly 

 completed itself among the mammals. The further problem of why 

 one species of a genus — why for instance in \ebria, N. brevicollis 

 should be everywhere one of our most abundant beetles, and the other 

 three members of the genus strictly limited in distribution, or in 67.s, 

 why we should find ( '. bnlcti almost everywhere where grows sufficient 

 Boletus to support it, and all the other species which apparently subsist 

 on the same food and are nurtured under the same environment only 

 rarely and sporadically — this is a problem which eludes our solution. 

 Probably the causes of a disparity so striking depend on factors too 

 complex or too subtle for our apprehension, for to say the fittest survive 

 is only to restate the fact in other words, and not to explain it. How- 

 ever this nuiy be, the point germane to the present enquiry is that 

 these conservative species are the only ones which can be of any 

 service in our endeavour to trace the derivation of any of them. 

 The others, the 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 

 adaptation being 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. Having thus eliminated from our survey 

 all such coleoptera as are not found apart from the habitations or 

 operations of mankind, and all such indiscriminately abundant species 

 as Harpalns aenetis, Tacln/porus li!/])itonnii, or Aiiabiis bipiistulatus, we 

 still find we have abundant material for consideration. A further 

 scrutiny, however, reveals the evidence of some of these witnesses as 

 not absolutely admissible, for there are certain parasitic and semi- 

 parasitic species attached to various hymeuopterous hosts, as Melo'e, 



