ZOOLOGICAL CLASSIFICATIONS. 191 



necessity is in the direct ratio of the number of object* 

 observed. An abstract type must represent every group. 

 Thus we speak of man in general, the horse, the oak, mean- 

 ing no man in particular, no horse, no oak ; and to this- 

 ideal representative we give the name of man, horse, oak. 

 But we do not stop here. Generalizing still higher, we re- 

 present by the word bird a vast group of living beings ; and 

 the terms animal or plant embrace a still higher range of 

 generalization ; and thus, from the remotest antiquity, men 

 have divided all natural bodies into three kingdoms^ namely, 

 minerals, vegetables, and animals ; have spoken in a general 

 way of fishes, reptiles, &c. ; and have given to each species a 

 proper name. 



360. As science grew in its dimensions, the language of 

 naturalists of necessity became more precise ; for without a 

 precise definition there could be no science. To write the 

 natural history of animals, it became necessary not only to 

 form a great catalogue, in which each being should be designated 

 by its proper name, but also to indicate for each of them the 

 characters by which they could be recognised and distinguished 

 from all others. Now it was evident that, from the conforma- 

 tion alone of these beings could such characters be drawn, 

 those alone being constant. But there is no animal which 

 can be recognised by a single character, but by a reunion 

 of several a reunion not to be found in any other. But the 

 number of animals being immense, the definition soon de- 

 generated into a description of the animals, to which no 

 memory was equal; and if we possess not the means of 

 arriving at this end by an easier route, the study of natural 

 history would for ever remain in its infancy. By establishing 

 among animals divisions and successive subdivisions, which 

 themselves are named and characterized, a great part of this 

 difficulty is overcome. With the assistance of a small num- 

 ber of characters and names, we so circumscribe the field of 

 comparison, that to distinguish the object before us we have 

 only to observe its differences from those most allied to it. 



And this, in fact, is what naturalists have done. They 

 have divided the animal kingdom into a certain number of 

 groups of the first degree, each characterized by certain pecu- 

 liarities of structure. They next divide each of these groups, 

 and characterize the secondary groups thus formed in the 

 same manner. These secondary groups are in their turn 

 divided, and the sections multiplied as required, until at last 



