224 On the Geographical Distribution of Insects. 



Oases are not fertile spots in the midst of a sandy plain, biit 

 depressions in the lofty table-land of Africa, where, by the re- 

 moval of the superincumbent limestone sti-ata, the water has 

 the power of rising to the sm-face : nor is the desert a dreary 

 plain of sand, as some have imagined, which has overwhelmed 

 a once fertile country, whose only traces are the isolated gar- 

 dens of the Oases. 



-iTHrr: "" 



bn the Geographical Distribution of Insects. (Concluded from 



page 183.) 



Of Entotnological Begions. — In the same manner as when 

 viewed in a physical or political aspect, the surface of the globe 

 is susceptible of being divided, zoologically, into many regions, 

 characterised by the animals found there : but very diflFerent 

 methods may be taken to effect this division. 



The method adopted by Fabricius, who was the first that 

 made the attempt in relation to insects, is too well known to 

 require repetition in this place ; and the same thing may be 

 said of the improved plan of Latreille. These two systems are 

 founded on data inherent in the globe itself ; but others may 

 be established solely dependent on insects themselves. There 

 is nothing to prevent us characterising a region according to 

 the families, genera, or species which inliabit it, and even ac- 

 cording to a single remarkable species, foimd there exclusive- 

 ly. This method, however, is likewise attended with incon- 

 venience. In truth, one or more families may predomuiate 

 in two coimtries very remote from each other, in which case 

 it would be very difficult to distinguish these countries ; or 

 there may be families so uniformly spread over the globe, that 

 they cannot afford the means of distinguishing any one coun- 

 try in particular. Finally, if we employ only one species to 

 the exclusion of others, we wiU convey so vague a notion of 

 the region so characterized, that it will be impossible to form 

 a real idea of its entomology. These difterent modes of pro- 

 ceeding may each have its merit in some pai-ticular cases, but 

 they cannot serve as a general groundwork, far geogrj^phujai 

 entomology, ^jj ^^j .vd-iiyJ Jvl f J ^^luhtoooa .ha^imQ-sx) aJ 



