The Scottish Natiwalist. 157 



■ — only found in those parts which have a more continental (or a 

 less insular) climate, and are insects which do not reach Scotland 

 or the north of England. ^ 



That many species, now confined to a few localities in the 

 south of England, had at one time a much wider range in 

 Britain, is extremely probable ; and it is equally probable that 

 perhaps many other European species once inhabited this coun- 

 try, but failed to survive the change to a more insular climate. 

 On the other hand, we possibly owe to our insular climate (and 

 situation) many of the curious varieties of Lepidoptera that are 

 found only in Britain. 



One more point in connection with our mountain Lepidoptera 

 merits attention, and that is, their comparative age as species, as 

 well as the probable place where they originated. 



There seems great reason to believe that the countries of the 

 north temperate hemisphere, and even the north circumpolar 

 lands, were the regions where many of the species of plants and 

 animals at present in existence were evolved, and that the last 

 and other glacial periods were very instrumental in dispersing 

 these species over the earth's surface. We have proofs that 

 many species now only existing in a living state in the warmer 

 temperate regions once flourished near the North Pole, in com- 

 pany with other species now extinct, but which seem to have been 

 the more immediate ancestors of certain living species. Prob- 

 ably very many other species (including many living now) once 

 flourished along with these, but from their more fragile nature 

 have left no remains. 



To go no further back than the last glacial period, it is easy 

 to understand how the change of climate of that epoch acted as 

 a dispersing agent, driving the plants and animals before it step 

 by step, and, doubtless, utterly destroying many species that 

 failed to make good their escape to more genial climes. We 

 must not think of this change of climate, and its accompanying 

 phenomena of ice-sheets and heavy snows, as having occurred 

 suddenly. It would happen gradually — probably very gradually 

 — and possibly, had any naturalists been then existent to study 

 the change induced in the fauna and flora, it would have required 

 the observations of many generations before such changes be- 

 came established — or, rather, admitted — facts. 



1 Amongst other species may be noticed Papilio Machaon, Thecla betiihs 

 ^xidi primi, Melitiea cinxia, Argynnis Latonia, (Sic. &c. 



