232 STUDY OF NATURAL HISTORY. 



the animal kingdom, and examine the question 

 more closely. 



(161.) The thick-skinned or pachydermatous tribe 

 of quadrupeds comprise the genera of the elephant, 

 rhinoceros, megatherium, and hippopotamus : these 

 are well known as the most gigantic of all animals. 

 We have ascertained, by analysis, that they form a 

 circular group, and that the rank of this group is 

 equivalent to that of a tribe. Yet, in regard to the 

 number of objects it comprises, this is the most 

 scanty tribe in the animal kingdom. It does not 

 contain, in fact, as many individuals as are found 

 in a single genus of parrots. Whence, therefore, 

 arises this disparity ? How are we to account for 

 the wide intervals between the different Pachyder- 

 mata, and the very small ones between the genera 

 of parrots ? To this we should answer, first, that 

 many of these forms, which once existed, are lost ; 

 and, secondly, that their paucity, so far from dis- 

 turbing the harmony and regularity of nature's 

 system, tends to show it in a light directly the re- 

 verse. First, then, the extinction of numerous forms 

 of Pachydermata rests on well known and incon- 

 trovertible facts. Not only are the fossil remains 

 of hippopotami, of elephants, and of rhinoceroses, 

 belonging to extinct species (and very probably to 

 intermediate gradations of form), found in nume- 

 rous and various parts of the world, and in consi- 

 derable quantities, but modern geology has brought 

 to light a whole family of these quadrupeds, repre- 

 sented by the megatherium, which are now so com- 

 pletely exterminated from the earth, that not a single 

 living example exists to testify the creation of such 



