37 



on the low sandy shores and sheltered sea-cliffs of more 

 temperate regions, finds its position here only on the 

 summits of the loftiest mountains. It is true that the 

 aberration from the typical state is not in the present 

 instance very considerable ; yet when the circumstances 

 producing it are taken into account, I am persuaded 

 that the difference is exactly of that nature on which too 

 great stress cannot possibly be placed, when discussing 

 the general question of geographical distribution as 

 having a tendency, more or less directly, to affect both 

 colour and form. It is well known to naturalists that a 

 multitude of insects from the New World, receding from 

 their European analogues merely in certain excessively 

 minute characters, have usually been pronounced at once 

 as new to science, first because those differences are con- 

 stant, and secondly because the specimens have been 

 received from the other side of the Atlantic. And yet 

 in instances like the present one, — in an island which, 

 while it belongs artificially to Europe, is yet naturally 

 sufficiently distinct from it as to form at any rate a 

 stepping-stone to the coast of Africa and the mountains 

 of Barbary, — species similarly circumstanced are not 

 necessarily received as new (and rightly so, I apprehend), 

 though in every respect affording differences not only 

 analogous to those already mentioned, but in many in- 

 stances positively identical with them. If, however, a 

 specific line of demarcation does of necessity exist be- 

 tween the creatures of the Old and New Worlds, the 

 problem yet remains unsolved, so long as intermediate 



