500 ZOOLOGY. 



influence of a fixed temperature. Thus the apes which crowd 

 tin- tropical regions almost always die of phthisis (pulmo- 

 nary consumption) when they an- exposed to the cold and 

 humidity of our climate : whilst the reindeer, formed to support 

 tin- rigors of a long and rude Lapland winter, suffers from 

 heat at St. Petersburg, ami in general sinks quickly under 

 the influence of a temperate climate. From this it results 

 that, in a great number of cases, difference* in climate alone 

 are found to be sufficient to arrest the march of speeie> fn.-m 

 high latitudes towards the equator, or from equatorial regions 

 towards the poles. The influence of temperature on the ani- 

 mal economy explains to us also why certain species remain 

 cantoned in a chain of mountains without beingable to spread 

 abroad into analogous localities. We know, in fact, that the 

 temperature decreases by reason of the elevation of the soil, 

 and that in consequence animals which live at considerable 

 elevations could not descend into the low plains to reach 

 other mountains, without traversing countries where the tem- 

 perature isj much superior to that of their ordinary habita- 

 tion. The llama, for example, abounds in the grassy coun- 

 tries of Peru and of Chili, situated at an elevation of four or 

 five thousand metres (from four to five thousand yard-) 

 above the level of the sea, and, extending to the south as far 

 as the extremity of Patagonia ; but it is to be found neither in 

 Brazil nor Mexico, because it could not arrive there without 

 descending into regions too hot for its constitution. 



The nature of the vegetation and of the pre-existing fauna 

 in a region of the globe equally influences its appropriation by 

 exotic species. Thus the dispersion of the silkworm is 

 limited by the disappearance of the mulberry above a certain 

 degree of latitude; the cochineal cannot spread itself ln-yond 

 a region where grows the cactus; and the large carnivora, 

 unless they live on fish, cannot exist in the polar regions. 

 where the vegetable productions are too scant to support a 

 considerable number of herbivorous quadrupeds. 



634. It were easy for us to multiply examples of these 

 necessary relations between the existence of an animal species 

 in a given locality, and the existence of certain climaterie. 

 phytological, or zoological conditions; but we want space for 

 >ueh details, and the considerations we have ju>t given appear 

 to us sufficient to give an idea of the manner by which nature 

 ha> accomplished the repartition of animal species over dif- 

 ferent points of the surface of the globe; and to attain the 



