381 



and flora, the limit of the former being oftentimes determined, 

 so far as terrestrial animals are concerned, by the extent of 

 the latter. 



624. Animals are endowed with instincts and faculties 

 corresponding to the physical character of the countries they 

 inhabit, and which would be of no service to them under other 

 circumstances. The monkey, which is a frugivorous animal, 

 is organized for living on the trees from which he obtains his 

 food. The reindeer, on the contrary, whose food consists of 

 lichens, lives in cold regions. The latter would be quite out 

 of place in the torrid zone, and the monkey would perish with 

 hunger in the polar regions. Animals which store up provi- 

 sions are all peculiar to temperate or cold climates. Their 

 instincts would be uncalled for in tropical regions, where the 

 vegetation presents the herbivora with an abundant supply of 

 food at all times. 



625. However intimately the climate of a country may be 

 allied with the peculiar character of its fauna, we are not to 

 conclude that the one is the consequence of the other. The 

 differences observed between animals of different faunas are 

 no more to be ascribed to the influences of climate, than their 

 organization is to the influence of the physical forces of 

 nature. If it were so, we should necessarily find all animals 

 precisely similar, when placed under the same conditions. We 

 shall find, by the study of the different groups in detail, that 

 certain species, though very nearly alike, are nevertheless 

 distinct in two different faunas. Between the animals of the 

 temperate zone of Europe, and those of the United States, 

 there is similarity, but not identity ; and the particulars in 

 which they differ, though apparently trifling, are yet constant. 



626. Fully to appreciate the value of these differences, it 

 is often requisite to know all the species of a genus or of a 

 family. It is not uncommon to find, upon such an examina- 

 tion, that there is the closest resemblance between species 

 dwelling far apart from each other, while species of the same 

 genus, living side by side, are widely different. This may 

 be illustrated by a single example. The Menopoma, Siren, 

 Amphiuma, Axolotl, and the Menobranchus, are batrachians 

 which inhabit the rivers and lakes of the United States and 

 Mexico. They are very similar in external form, yet differ in 

 the fact that some of them have external gills at the sides of the 

 head, in which others are deficient ; that some have five toes, 



