MUTUAL AFFINITIES OF ORGANIC BEINGS 373 



most alike, and for separating those which are most unlike; or 

 as an artificial method of enunciating, as briefly as possible, gen- 

 eral 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 in- 

 disputable. But many naturalists think that something more is 

 meant by the Natural System; they beheve 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 knowl- 

 edge. Expressions such as that famous one by Linnaeus, 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 community 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 classi- 

 fication either gives some unknown plan of creation, or is simply 

 a scheme for enunciating general propositions and of placing to- 

 gether the forms most like each other. It might have been thought 

 (and was in ancient times thought) that those parts of the struc- 

 ture 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, of a whale to a fish, as of any importance. These re- 

 semblances, though so intimately connected with the whole life 

 of the being, are ranked as merely "adaptive or analogical char- 

 acters:" 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 organization 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 affinities. We are least likely in the modi- 

 fications of these organs to mistake a merelv adaptive for an 



