On the (ieographical Bistrihutiun vf Insects. ■ 179 



If we deduct the three last mentioned regions, Asia, the 

 Indian Archipelago, and New Holland, the entomology of 

 which is not sufficiently known to enter into a very exact cal- 

 culation, we cannot fail to be struck with the rapidity with 

 which the genera proper to each region increase, the nearer we 

 approach the Equator. This is distinctly seen by comparing 

 Siberia, Europe, and Africa, with each other, and the propor- 

 tion is equally maintained in the New Continent. Genera, con- 

 sequently, are more endemical the more southern the region to 

 which they belong ; or, which is the same thing, their spora- 

 dicity diminishes from the Poles to the Equator ; and, as it 

 has been already shewn that the endemicity of species is in 

 dii'eet relation with that of genera, this conclusion extends 

 equally to them. This fact, it may be remarked, is not pecu- 

 liar to insects, but common to all other organised beings, for 

 they are much more tolerant of an increase than a diminution 

 of heat. We thus see the northern species, in general, ad- 

 vance much farther south than the intertropical kinds do in 

 an opposite direction. The exceptions to this are chiefly 

 found in the classes which nature has protected against the 

 changes of temperatiu-e by hair or feathers, and among such 

 as live in the water, which are less sensible of the extremes 

 of heat and cold. 



The table shews, besides, the immense superiority of South 

 America over the other regions, in respect to genera peculiar 

 to it ; and this holds true even with the C arabidse, of which it 

 possesses a much smaller absolute amount than Europe. If the 

 reader feel desirous to compare the Old and New Continent 

 in this point of view, the following table, which presents the 

 number of genera proper to each, as well as their common 

 genera, affords the means of doing so. It will be seen that 

 the first, although very inferior to the second in surface, yields 

 very little to it in the light we are now considering. The 

 pretty nmnerous genera, common to them both, almost all be- 

 long to the northern and temperate regions. 



