THEORIES OF ORGANIC EVOLUTION 



conclude that the ancient and now extinct species were 

 as permanent in their forms and characters as those 

 which exist at present ; or, at least, that the catastrophe 

 which destroyed them did not leave sufficient time for 

 the productions of the changes that are alleged to have 

 taken place. 



" In order to reply to those naturalists who acknowl- 

 edge that the varieties of animals are restrained by 

 nature within certain limits, it would be necessary to 

 examine how far these limits extend. This is a very 

 curious inquiry, and in itself exceedingly interesting 

 under a variety of relations, but has been hitherto 

 very little attended to. 



" Wild animals which subsist upon herbage feel the 

 influence of climate a little more extensively , because 

 there is added to it the influence of food, both in re- 

 gard to its abundance and its quality. Thus the ele- 

 phants of one forest are larger than those of another; 

 their tusks also grow somewhat longer in places where 

 their food may happen to be more favorable for the 

 production of the substance of ivory. The same may 

 take place in regard to the horns of stags and reindeer. 

 But let us examine two elephants, the most dissimilar 

 that can be conceived, we shall not discover the small- 

 est difference in the number and articulations of the 

 bones, the structure of the teeth, etc. 



11 Nature appears also to have guarded against the 

 alterations of species which might proceed from mixt- 

 ure of breeds by influencing the various species of 

 animals with mutual aversion from one another. Hence 



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