CHAP. XIV.] THE NEOTROPICAL REGION. 45 



The Palsearctic affinity of the South Temperate Carabida^ may 

 be readily understood, if we bear in mind the great antiquity of the 

 group, and the known long persistence of generic and specific 

 forms of Coleoptera ; the facility with which they may be trans- 

 ported to great distances by gales and hurricanes, either on land 

 or over the sea ; and, therefore, the probability that suitable 

 stations would be rapidly occupied by species already adapted 

 to them, to the exclusion of those of the adjacent tracts which 

 had been specialised under different conditions. If, for example, 

 we carry ourselves back to the time when the Andes had only 

 risen to half their present altitude, and Patagonia had not 

 emerged from the ocean (an epoch not very remote geologically), 

 we should find nearly all the Carabidse of South America, 

 adapted to a warm, and probably forest- covered country. If, 

 then, a further considerable elevation of the laud took place, a 

 large temperate and cold area would be formed, without any 

 suitable insect inhabitants. During the necessarily slow pro- 

 cess of elevation, many of the tropical Carabidse would spread 

 upwards, and some would become adapted to the new conditions ; 

 while the majority would probably only maintain themselves by 

 continued fresh immigrations. But, as the mountains rose, 

 another set of organisms would make their way along the 

 highest ridges. The abundance and variety of the North 

 Temperate Carabidse, and their complete adaptation to a life on 

 barren plains and rock-strewn mountains, would enable them 

 rapidly to extend into any newly-raised land suitable to them; 

 and thus the whole range of the Eocky Mountains and Andes 

 would obtain a population of northern forms, which would over- 

 flow into Patagonia, and there, finding no competitors, would 

 develope into a variety of modified groups. This migration.was 

 no doubt effected mainly, during successive glacial epochs, when 

 the mountain-range of the Isthmus of Panama, if moderately 

 increased in height, might become adapted for the passage of 

 northern forms, while storms would often carry insects I'rom 

 peak to peak over intervening forest lowlands or narrow 

 straits of sea. If this is the true explanation, we ought to find 

 no such preponderant northern element in groups which 



