OF ANIMALS. 105 



the interior of Africa, a third in the New World, and another again 

 in the great islands of Australia. It is much more natural to sup- 

 pose that every species was placed, from the beginning, by the 

 Author of all things, in the region where it was destined perma- 

 nently to live, and that by extending from a certain number of 

 these distinct centres of creation, different animals have spread 

 throughout tfoose portions of the globe now forming the domain 

 of each kind. In the present condition of the earth, it is impos- 

 sible to recognise all those zoological centres : for we can con- 

 ceive the possibility of exchanges so multiplied between two 

 regions, the faunrc of which were primitively distinct, that they 

 present species common to both, and nothing now points out to 

 the eyes of the naturalist their original separation ; but when a 

 country is inhabited by a considerable number of species which 

 are not seen elsewhere, even where local circumstances are most 

 similar, we are warranted in the supposition that this region was 

 the theatre of a peculiar zoological creation, and we must regard 

 it as a distinct region. 



What the naturalist should ask, is, not how different portions 

 of the earth have come now to be inhabited by different species, 

 but how animals could be so far extended over the surface of the 

 globe, and how nature placed variable limits to this dissemination 

 according to species. The latter question especially presents 

 itself to the mind when we consider the unequal extent now occu- 

 pied by this or that group of animated creatures : for example, 

 the ourang-outang is confined to the island of Borneo and the 

 neighbouring lands ; the musk-ox is colonized in the most northern 

 part of America, and the lama in the elevated regions of Peru 

 and Chile, while the wild-duck is seen everywhere, from Lapland 

 to the cape of Good Hope, and from the United States to China 

 and Japan. 



The circumstances which favour the dissemination of species 

 are of two kinds : the one pertains to the animal itself, and the other 

 is foreign to it. Among the first is the development of the loco 

 motive power, all things being equal in other respects ; the species 

 which live attached to the earth, or which possess only imperfect 

 instruments of locomotion, occupy a very limited extent of the 

 earth's surface, compared to those species whose moving powers 

 are rapid and energetic : among terrestrial animals, birds present 

 us with most examples of cosmopolite species, and, among aquatic 

 animals, the ceta'ceans, and fishes. Reptiles, on the contrary, 

 are restricted to narrow limits, and the same is true of most 

 mollusks and crusta'ceans. The instinct possessed by certain 

 animals to change their climate periodically, also contributes to 

 the dissemination of species ; and this instinct exists in a great 

 number of these creatures. 



