Geographical Distribution of In-sects. 105 



manner as latitude, they produce the same eflFects on insects 

 as the latter. It often happens that a species which frequents 

 plains in northern regions, only reciurs among mountains in 

 countries farther south, without existing at all in the inter- 

 mediate districts. Thus the Parnassus Apollo, whose special 

 native country is Sweden, when it frequents plains and hills 

 of inconsiderable elevation, is again found among the heights 

 of the Alps, the Pyrenees, and even the Himalayas. For the 

 same reason Carabus auratus^ which inhabits the plains of 

 France, is not met wdth in Italy, except on the highest moun- 

 tains. 



These latter, it must be observed, have also their peculiar 

 species, which are arranged in a certain gradation over these 

 declivities after the manner of plants, but without the same 

 regularity as these, in consequence of the power of locomotion 

 which they all enjoy in a gi'eater or less degree. 



Finally, mountains, when they form continuous chains like 

 the Andes in America, and the Himalaya in India, present 

 an almost insuperable barrier to the diffusion of insects. 

 Their locomotion being infinitely less powerful than that of 

 mammiferous animals and birds, does not enable them to sur- 

 mount such natural obstacles. It is thus that Mendoza, si- 

 tuate at the foot of the Andes on the east side, has scarcely 

 a single species in common with Santiago in Chili, which lies 

 under the same parallel, and is not fifty leagues distant in a 

 direct line. 



The running waters which traverse continents have but an 

 inconsiderable influence on the progress of insects, since the 

 largest of them, such as the Amazon, La Plata, and Missis- 

 sippi, are by no means of sufficient breadth to produce an ef- 

 fect of this kind. If the species of the opposite banks are 

 dissimilar, as sometimes happens, the explanation must be 

 sought for in other causes, particularly those influencing the 

 vegetation. At the same time it must be admitted that the 

 aquatic insects of a country will be numerous in proportion 

 to the abundance of its waters. 



lujliienre of Organised Beings. — Certain mammiferaj and 

 entire families of birds, live at the expense of insects. Their 

 multiplication has consequently a powerfiU influence on that 



