NATURAL HISTORY. 201 



" The heavenly bodies (as growne now lesse strong) 

 Doe seeme more stalke (as weary of their race) 

 All cliniats still new temperatures embrace, 

 What strange effects must follow them ere long ! " STIRLING. 



distribution. But it may not be unreasonable to assume that at 

 the beginning of the actual geological period, the various species 

 were limited to narrow regions, and that by degrees they afterwards 

 spread to a distance, so as to occupy a more or less considerable 

 portion of the surface of the globe. 



603. The circumstances which favour the dissemination of species are of two 

 kinds. The first is connected with or dependent on the nature of the animal ; the 

 second, with causes foreign to it. In the number of the first, the development of 

 the locomotive power holds an important place. All things being equal, the species 

 which live fixed to the soil, or which possess but imperfect instruments for 

 locomotion, occupy but a restricted portion of the surface of the globe, compared 

 with the species whose movements of translation are rapid and energetic. Thus, 

 birds have a most extended area, whilst reptiles, on the contrary, are generally 

 confined to narrow limits. 



604. IVTiy do differences of climate serve to arrest the march 

 of animals from' one region to another ? 



Because there are throughout all nature, mutiuil adaptations of 

 animate and inanimate existences of organic and inorganic forms. 

 This is seen in the growth of vegetables, as well as in the 

 development of animals. 



605. Apes, which crowd the tropical regions, almost always die of pulmonary 

 consumption when they are exposed to the coldness and humidity of our climate ; 

 while the rein-deer, formed to support the rigours of a long and rude Lapland 

 winter, suffers from heat at St. Petersburg, and in general sinks quickly under the 

 Influence of a temperate climate. 



Man and the dog are the only species that can support the two extremes of 

 arctic cold and tropical heat. 



The influence of temperature on the animal economy explains to us why certain 

 species remain cantoned in a chain of mountains, without being able to spread 

 abroad into analogous localities. We know 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 temperature is much superior 

 to that of their ordinarv habitation. 



