176 



it is doubtful whether they ever extend into the 

 southern hemisphere. 



How limited, then, are the journey ings of even 

 the most buoyant and the fleetest of creatures, 

 compared to the roamings of man over every 

 region of the habitable globe! Nevertheless, they 

 may have been quite sufficient, in conjunction 

 with the other causes already assigned, to effect 

 the distribution of animals from a single spot, 

 and a single pair of each species, over the whole 

 earth ; and to fix each particular species in the 

 locality and temperature best suited to its habits 

 and nature. The opposite opinion, that a suc- 

 cessive creation of animals has occurred, and 

 may still be going on, is as contrary to well esta- 

 blished facts as to revelation. Tribes of animals 

 which once existed may have become extinct ; 

 but there is no reason to believe that any new 

 tribes ever start up ; on the contrary, nature, 

 amid all her diversities of tribes, approaching 

 and blending into each other by almost imper- 

 ceptible shades, is ever careful to prevent a mul- 

 tiplication of species. Thus, animals in a state 

 of nature keep distinct the lion never mates 

 with the tigress, or the elephant with the rhino- 

 ceros ; the smallest wren is faithful to the partner 

 of its own kind, and the insignificant insect selects 

 its fellow for a mate ; and though occasionally, 

 from unnatural connections, some kinds of mixed 

 monsters are produced, they are happily, by a 

 beneficent law of nature, incapable of propaga- 



