156 The Scottish Naturalist. 



decidedly less numerous in the high-lying localities inhabited by 

 these insects. Their want of success in holding their own must 

 therefore, in part at least, be due to other causes. It is probable 

 that their vital constitutions are different from that of the species 

 which have supplanted them, and some of which even contest 

 with them their present habitats. In one respect their constitu- 

 tions must be hardy enough to sustain life at all in alpine and 

 arctic districts \ and it is probably not entirely (though in some 

 degree) the greater summer heat of low-lying localities that 

 makes such unsuitable for them, but the less severe and shorter- 

 lasting cold of winter. In the high altitudes or high latitudes 

 which they inhabit there is a continuous frost all through the 

 winter, and none of the alternate frosts and thaws, accompanied 

 by damp, that forms the winter of the northern lowlands, and 

 which we know is so much more destructive to insect-life than a 

 continuous low temperature. They are, moreover, protected at 

 this season by a thick covering of dry snow. 



Climate, therefore, is likely to have been an important factor 

 in the distribution of these species. It must be remembered, 

 however, that Anarta melaiiopa inhabits low elevations in the 

 Zetlands, whose climate is pre-eminently an "insular" one, and 

 where the mean winter temperature is comparatively high and 

 the summer temperature low. In Zetland, however, the com- 

 petition between species is much less than that in Britain. With 

 this exception oi Anarta melaiiopa., most of the species appear to 

 prefer a ''continental" climate to an " insular" one ; and this is 

 possibly the reason why more of them do not occur in Ireland, 

 where the influence of the Atlantic Ocean is greatest. While the 

 connection of Britain with continental Europe across the floor 

 of the German Ocean lasted, our climate was much more conti- 

 nentaP than at present, when we have what is termed an " insu- 

 lar" climate, reaching its maximum on our western shores. It 

 is to this insular climate that, I believe, the poorness of our 

 fauna, compared with parts of continental Europe situated much 

 further north of us, is partly due. For example, compare the 

 Butterflies of Finland with those of Scotland. Finland has 89 

 species, Scotland only about 36 (Britain altogether^ only 64); 

 and though Finland is situated to the north of any part of 

 Britain, yet many of its species are those which are — in Britain 



^ That is to say, the summer heat was greater and the whiter cold more 

 severe and continuous, — both due to a less humid atmosphere, caused by the 

 less near proximity of the sea. 



