INSECTS IN GENERAL. 91 



are at the foot of those monntains. If, in the same country, 

 the temperature of its low-lying situations, or even of those 

 upon a level with the horizon, be modified by certain local 

 circumstances, we may observe a corresponding modification 

 in the species of insects there to be found. For instance, 

 if the mean temperature is lowered, the species are the same 

 as those to be found a little more northwards ; if raised, we 

 shall find the same species as exist a little more to the south. 



M. Latreille would divide the old and new continents into 

 zones, extended successively in the direction of the meridians, 

 and the breadth of which is measured by a portion of a 

 circle, parallel to the equator. The species proper to one of 

 these zones disappear gradually, and give place to those of 

 the following zone, so that from interval to interval, the 

 dominant, or even the entire of the species^ shall cease to be 

 the same. These changes he compares to the series of hori- 

 zons discovered by the traveller in proportion as he recedes 

 from the point whence he originally set out. 



Sweden has many insects peculiar to itself, some of which 

 are located in its most northern provinces, as in Lapland. 

 In the southern, as in Scania, are found, though in small 

 number, many insects of Germany. France, even towards 

 the forty-fourth and forty-fifth degrees of latitude, has many 

 which are to be found in the former countries. But it would 

 appear that the Rhine and its eastern mountains form, with 

 regard to some other species, a frontier which they have not 

 passed. The first of those which are proper to the warm 

 countries of western Europe begin to shew themselves to- 

 wards the lower course of the Seine, precisely at the point 

 where the vine begins to flourish in the open plain without 

 the assistance of any local circumstances. This is still more 

 remarkable at Fontainbleau, and in the neighbourhood of 

 Orleans. 



But these insects are only the forerunners of those which 



