CHAP. XXII. LOXGEYITY OF SPECIES IN MAMMALIA. 441 



"We usually know nothing of the geographical varieties of the 

 post-pliocene and pliocene species, least of all, those suc- 

 cessive changes of form which they must have undergone in 

 the pre-glacial epoch between the upper miocene and post- 

 pliocene eras. Such being the poverty of our palffionto- 

 logical data, we cannot wonder that osteologists are at vari- 

 ance as to whether certain remains found in caverns are of 

 the same species as those now living; whether, for example, 

 the Talpa fossilis is really the common mole, the Meles mor- 

 reni the common badger, Lutra a7itiqua the otter of Europe, 

 Sciurus priscus the squirrel, Arctomys pranigenia the marmot, 

 Myoxus fossilis the dormouse, Schmerling's Felix Engihou- 

 lensis the European lynx, or whether Ursus spelceus and 

 Ursus priscus are not extinct races of the living brown bear 

 ( Ursus ardos). 



If at some future period all the above-mentioned species 

 should be united with their allied congeners, it cansot fail to 

 enlarge our conception of the modifications which a species 

 is capable of undergoing in the course of time, although the 

 same form may appear absolutely immutable within the 

 narrow range of our experience. 



Longevity of Species in the Mammalia. 



In the " Principles of Geology," in, 1833,* I stated that the 

 longevity of species in the class mollusca exceeded that in 

 the mammalia. It has been since found that this generaliza- 

 tion can be carried much farther, and that, in fact, the law 

 which o-overns the chano-es in or<j;anic beinc:s is such, that the 

 lower their place in a graduated scale, or the simpler their 

 structure, the more persistent are they in form and organi- 

 zation. I soon became aware of the force of this rule in 

 the class mollusca, when I first attempted to calculate the 



■■■■ 1st edit., vol. iii. pp; 4S and 140. 



