252 LESSONS FROM NATUEE. [CHAP. VIII. 



The various groups into which animals and plants have 

 Natural cias- been divided are of this nature, i.e., are ideal 

 ^cation, entities with an objective basis. Classes, orders, 

 families, genera, and species exist as such only in a mind. 

 Objectively, there is nothing but individual animals and 

 plants. Nevertheless, the different biological groups also 

 exist objectively in those facts of structure which various 

 individual animals and plants present, and which serve for the 

 definitions of such different groups. What Mr. Lewes says * 

 (before quoted) of certain other abstractions applies here 

 with perfect correctness : &quot; They are realities in the sense 

 of being drawn from real concretes ; but they are not realities 

 existing apart from their concretes otherwise than in our con 

 ception ; and to seek their objective substitution, we must 

 seek the concrete objects of which they are the symbols.&quot; 



Natural classification, indeed, though formed by the mind, 

 does not depend on the mind. It is not arbitrary, but is 

 governed by the external realities of things. It is not that we 

 choose to separate bats and whales from birds and fishes re 

 spectively, and put them both in the same class as that which 

 contains also the lion and the antelope. We are compelled, 

 by the multitudinous facts of animal structure, so to separate 

 and so to class them. Moreover, such zoological classification 

 is only possible because different animals are found to have 

 like parts (parts alike as to their relations of position to other 

 parts) which can be compared and contrasted, and can, by 

 the agreements and differences they present, furnish us with 

 the determining and limiting characters of the different 

 natural groups. 



As it is with respect to the various groups of animals and 

 Of parts and plants, so it is with respect to the parts and organs 

 which together compose each individual animal or 

 plant. As the human mind surveys these parts and organs 

 in different lights, it finds different series of unlikenesses and 

 likenesses, extending along that line of thought which it 



* Op. cit. p. 281. 



