On the Geographical Distribution of Insects. 225 



rn' It appears the most expedient course to employ none of 

 these two methods exclusively, but to combine them, keeping 

 the first in subordination to the second : in other words, the 

 insects ought to characterize the region, and not the region 

 the insects. No doubt we shall thus. obtain very unequal ter- 

 ritorial divisions, since we shall often be obhged to form a 

 distinct region of an island, for example, of very limited extent, 

 or to imite immense tracts of country ; but by this method, 

 we shall at least approach as nearly as possible to the distri- 

 bution of nature, which has not placed species in regular com- 

 partments. The regions which we shall in this way form, will 

 be the more natural, since they will possess in themselves a 

 greater number of species, and particularly of genera. In those 

 which follow, this proportion is often found to amount to one- 

 half, and sometimes nearly three-fourths. 



It is not to be concealed that, what method soever may be 

 adopted, much that is arbitrary must always exist in the esta- 

 blishment of these regions, and that they can only be regarded 

 as such in a relative light. We may, therefore, either strictly 

 confine ourselves to the eight which have been made use of on 

 a former occasion ; or, if it were desirable, even such a country 

 as France might be divided into several. It is best to fix on 

 a medium between these two extremes, without attempting t 

 attain an exactness, which, in such a case, is impossible. 



Acting on this view, we find, that there are not fewer than 

 forty regions, one of which is common to both continents, 22 

 peculiar to the Old, and 17 to the New. 



1. Begion common to the Two Continents. i ; 



1st, Arctic Begion. — This comprehends all the parts of the 

 two continents which lie within the northern polar circle. Its 

 entomology is yet but little known, except in relation to that 

 portion of Lapland included in it. The investigations of M. Zet- 

 terstedt have shewn, that the latter is richer than might have 

 been supposed. It is probable that this is likewise the case with 

 the northern parts of Asia, although we are scarcely accpiaint- 

 ed with one species from that quarter. Iceland would like- 

 wise appear not to be so poor as was for a long time supposed. 

 In Greenland, according to Mr Kii'by, all tlie orders have 



