EVOLUTION. 11 



the latter consists to a large extent of boughs and twigs, 

 while that of the former is composed more of juicy leaves, 

 fruits, and roots, the necessity of a more complicated 

 masticating apparatus in the one than in the other is 

 apparent. 



In modern elephants, the six molar teeth on either side 

 of each jaw are all that are ever developed. This is, 

 however, by 110 means the case with some of the earlier 

 elephants, and with most of the mastodons. In these 

 animals, when the second and third molars became worn 

 out, they were succeeded vertically by much smaller teeth, 

 from which we learn that the first three molars of the 

 modern elephants really correspond to the milk-teeth of 

 other mammals, which, as we all know, are succeeded 

 vertically by some of the teeth of the permanent series. 

 This succession of the teeth shows us, therefore, another 

 point in which mastodons tend to connect modern 

 elephants with ordinary Ungulates. 



We might go further and enter upon the consideration 

 of some of the structural peculiarities presented by the 

 soft parts of elephants. Enough has, however, been 

 stated to show that while these animals have preserved 

 a very ancient type of structure in their limbs, they 

 have acquired a very special modification in the structure 

 and mode of succession of their teeth. And it is highly 

 probable that it is owing to this particular specialization 

 that elephants have survived to our own day, while all 

 the other plantigrade and five-toed primitive Ungulates 

 have completely passed away ; while it is almost certain 

 that it is this feature alone which has enabled them to 

 attain the gigantic bulk which forms one of their most 

 striking features. In regard to their evolution, perhaps 

 no group shows more clearly than that of the elephants 

 how exceedingly important is the study of fossils to eluci- 

 date the relations of existing animals. Had we only the 

 two living species of elephants to deal with, we should 

 never have had the least inkling of the manner in which 

 they were related to other Ungulates, imperfect as our 

 knowledge of the relationship still is. Moreover, from 

 the distribution of these two species, it would have been 



