TEETH AND THEIR VARIATIONS. 215 



Horses fed on the hard substances given to them in Euro- 

 pean stables will often live to at least five-and-twenty 

 years of age, and it is perfectly evident that this com- 

 paratively long duration of life could never be attained 

 if these animals were not furnished with the long- 

 crowned teeth we have just described, since the short- 

 crowned and simple teeth of a Tapir would be entirely 

 worn away by such a diet at a very much earlier period. 



We see, then, in the Horse an animal which, in the 

 structure of its teeth and limbs, has attained, so to 

 speak, to the same platform of specialisation as that 

 on which the Deer and Antelopes stand, but has 

 reached it by a totally different ladder. It is, indeed, 

 as if two engineers had, after many intermediate steps, 

 at last perfected two machines, each equally well fitted 

 for the same purpose, and each resembling one another 

 to a certain extent in their general plan of construc- 

 tion, but yet differing very decidedly in details. And 

 it cannot be too strongly impressed upon the reader 

 what a powerful argument this gradual evolution of the 

 teeth in two allied stocks of animals, towards the same 

 relative perfection of structure, affords to the doctrine 

 of a general evolution of the whole animal kingdom. 



Our last illustration of the gradual increase in the 

 complexity of the structure of the grinding teeth in 

 the Ungulate order, as we proceed from the old extinct 

 generalised types (and some allied ones which still 

 survive) to the specialised forms characteristic of the 

 world of to-day, will be derived from the peculiar 

 group of Elephants. At the present time, it need 



