OX THE OBJECTS OF A COLLECTIOX OF INSECTS. 119 



Europe and Boreal America as now divides them ; the sea, 

 through a great part, must have been a shallow sea, and 

 somewhere, probably far to the north, there must have been 

 either a connexion or such a proximity of land as would ac- 

 count for the transmission of a non-migratory terrestrial and 

 a littoral marine flora." 



This does not strictly apply to Entomology, but it has 

 long been known that the summits of various mountains in 

 Europe, which agree in the vegetation, have also certain in- 

 sects in common which are not found in the surrounding: 

 countries. The fact of a very cold period having immedi- 

 ately preceded the present, offers us apparently an explanation 

 of the fact, which, again, on the other hand, may be con- 

 sidered to give us additional evidence of the truth of the 

 theory. For it is clear, that if the temperature of the plains 

 were then much lower than it is now, the little creatures in 

 question may have peopled the whole country, while, as the 

 climate grew gradually milder, they were driven up by de- 

 grees, until at length they only remained on the summits 

 where we now find them. 



So far all is very clear and satisfactory ; but another ex- 

 planation of the fact may be given. 



Thus Mr. Newman writes me word that, 



" Helobia nivalis ? brevicollis, 



" Agabus Snowdonius ? bipustulatus, 

 " Leistus montanus ? fulvibarbis, 



" Steropus iEthiops ? madidus, 

 " Patrobusseptentrionis? rufipes, 

 " and others, occur on the summits of Snowden, Helvel- 

 lyn, Ben Nevis, and other mountains ; but some eminent 

 Coleopterists regard these mountain insects as merely de- 

 pauperated forms of the commoner species whose names I 

 have placed in juxtaposition : certain it is that the Alpine 

 species never exists on the summit unless the corresponding 



