THEORY OF THE EARTH. 12 3 



tiff and a water-spaniel, and between a greyhound 

 and a pug-dog, are even more striking than be- 

 tween almost any of the wild species of a genus. 

 Finally, and this may be considered as the maxi- 

 mum of known variation in the animal kingdom, 

 some races of dogs have an additional claw on 

 each hind-foot, with corresponding bones of the 

 tarsus; as there sometimes occur in the human 

 species some families that have six fingers on each 

 hand. Yet, in all these varieties, the relations of 

 the bones with each other remains essentially 

 the same, and the form of the teeth never changes 

 in any perceptible degree, except that in some 

 individuals one additional false grinder occasion- 

 ally appears, sometimes on the one side, arid 

 sometimes on the other.* 



It follows from these observations, that animals 

 have certain fixed and natural characters, which 

 resist the effects of every kind of influence, whether 

 proceeding from natural causes or human inter- 

 ference ; and we have not the smallest reason to 

 suspect that time has any more effect upon them 

 than climate. 



I am well aware that some naturalists lay pro- 

 digious stress on the thousands of years which 

 they can call into action by a dash of their pens, 



* See, in the Annals of the Museum, XVIII. 333., a memoir by my 

 brother on the varieties of dogs, which he drew up at my request, 

 from a series of skeletons of all the varieties of dogs, prepared by me 

 expressly on purpose. 



