CHAP. XIV.] 
THE NEOTROPICAL REGION. 
45 
The Palaearctic affinity of the South Temperate Carabidse 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 Carabidae of Squtli America, 
adapted to a warm, and probably forest-covered country. If, 
then, a further considerable elevation of the land 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 Carabidm 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 Rocky Mountains and Andes 
would obtain a population of northern forms, which would over- 
flow into Patagonia, and there, finding no competitors, would 
dev elope 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 from 
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 
