22 Geographical Distribution of Animals. 



by the phenomena of the zone in which he lived and wander- 

 ed, and from which he extended farther, he took it for grant- 

 ed that all animals followed the same laws. But now that 

 we know the whole surface of our globe so satisfactorily, there 

 can no longer be a question about the difference between 

 animals and plants in the lower latitudes in all continents. 

 Besides, we see them equally striking in the southernmost 

 extremities of the three great continents, so that there can no 

 longer be any doubt about the primitive adaptation of these 

 various types to the continents where they live, as we do not 

 find a single one naturally diffused everywhere over all con- 

 tinents. Notwithstanding, therefore, the slighter differences 

 we notice between the animals of different continents in the 

 temperate zone, we are thus led step by step to ascribe to 

 them also a special origin upon those continents where they 

 now occur. 



But as soon as we rise to the highest latitudes, the uni- 

 formity becomes so close, that there is no longer any marked 

 difference noticed between the animals about the arctic regions, 

 either in America, Europe, or Asia ; and we are naturally 

 led to restrict the idea of a common centre of origin, or at 

 least of a narrow circle of primitive development, to those 

 animals which spread equally over the icy fields extending 

 around the northern pole upon the three continents which 

 meet in the north. The phenomena of geographical distri- 

 bution which we observe there among the terrestrial animals 

 are repeated in the same manner among the aquatic ones. 

 The fishes in the arctic seas do not materially differ on the 

 shores of Europe, Asia, and America, and through the north- 

 em Atlantic and through Behring's Straits they extend more 

 or less towards the colder temperate zone, or migrate into it 

 at particular seasons of the year, as do most birds of the 

 arctic regions also. But in the temperate zone we begin to 

 find more and more marked differences between the inhabi- 

 tants of different continents, and even between those of the 

 opposite shores of the same ocean ; as, for instance, the fishes 

 of Europe (some of the northern species excepted) are not 

 identical with those of the temperate shores of North America, 

 notwithstanding the very open field left for their uniform dis- 



