296 



CHAPTER III 



TABLE 9. Circumpolar Carabidae, 45 species {vide table 8). Western limit in 

 Europe plotted against eastern limit in North America. 



W. limit in Europe 



If the extension of area is primarily dependant on powers of dispersal, it is to 

 be expected that a species occurring far east, in Newfoundland or Labrador, in 

 North America, is usually at the same time among those which have spread farthest 

 west, to the British Isles or Scandinavia in Eurasia. This is confirmed by the follow- 

 ing simple arrangement (table 9). 



Though circumpolar Carabids are thus, generally speaking, characterized by 

 well developed powers of dispersal, they by no means constitute a homogenous 

 group in this respect. A division of the species of each vegetational zone according 

 to the development of wings, into macropterous (flying, or probably flying), 

 brachypteroiis (flightless), and dimorphic forms (as in table 8), gives the following 

 picture: — 



Circumpolar Carabidae 



species macropt. brachypt. dimorph. 



total 



Total 45 



29 = 64 % 9 = 20 % 



The decreasing number of flightless circumpolar species in the direction north- 

 south is very striking. The explanation is probably that selection on the wind- 



