Chap. XIV. Classification. 365 



an artificial method of enunciating, as briefly as possible, general 

 propositions, — that is, by one sentence to give the characters 

 common, for instance, to all mammals, by another those common 

 to all carnivora, by another those common to the dog-genus, and 

 then, by adding a single sentence, a full description is given of each 

 kind of dog. The ingenuity and utility of this system are indispu- 

 table. But many naturalists think that something more is meant 

 by the Natural System ; they believe that it reveals the plan of the 

 Creator ; but unless it be specified whether order in time or space, 

 or both, or what else is meant by the plan of the Creator, it seems 

 to me that nothing is thus added to our knowledge. Expressions 

 such as that famous one by Linnasus, which we often meet with in 

 a more or less concealed form, namely, that the characters do not 

 make the genus, but that the genus gives the characters, seem to- 

 imply that some deeper bond is included in our classifications than 

 mere resemblance. I believe that this is the case, and that commu- 

 nity of descent — the one known cause of close similarity in organic 

 beings — is the bond, which though observed by various degrees of 

 modification, is partially revealed to us by our classifications. 



Let us now consider the rules followed in classification, and the 

 difficulties which are encountered on the view that classification 

 either gives some unknown plan of creation, or is simply a scheme 

 for enunciating general propositions and of placing together the 

 forms most like each other. It might have been thought (and was 

 in ancient times thought) that those parts of the structure which 

 determined the habits of life, and the general place of each being 

 in the economy of nature, would be of very high importance in 

 classification. Nothing can be more false. No one regards the 

 external similarity of a mouse to a shrew, of a dugong to a whale r 

 of a whale to a fish, as of any importance. These resemblances,, 

 though so intimately connected with the whole life of the being, 

 are ranked as merely " adaptive or analogical characters ; " but to 

 the consideration of these resemblances we shall recur. It may 

 even be given as a general rule, that the less any part of the organ- 

 isation is concerned with special habits, the more important it 

 becomes for classification. As an instance : Owen, in speaking of 

 the dugong, says, " The generative organs, being those which are 

 most remotely related to the habits and food of an animal, I have 

 always regarded as affording very clear indications of its true affini- 

 ties. We are least likely in the modifications of these organs to 

 mistake a merely adaptive for an essential character." With plants 

 how remarkable it is that the organs of vegetation, on which their 

 nutrition and life depend, are of little signification ; whereas the 



