CLASSIFICATION. 431 



mined the habits of life, and the general place of each 

 being in the economy of nature, would be of very high im- 

 portance 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 resemblances, though so inti- 

 mately 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 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 at!in- 

 ities. We are least likely in the modifications of these 

 organs to mistake a merely adaptive for an essential char- 

 acter.^' With plants how remarkable it is that the organs 

 of vegetation, on which their nutrition and life depend, 

 are of little signification; whereas the organs of reproduc- 

 tion, with their product the seed and embryo, are of para- 

 mount importance! So again, in formerly discussing cer- 

 tain morphological characters which are not functionally 

 important, we have seen that they are often of the highest 

 service in classification. This depends on their constancy 

 throughout many allied groups; and their constancy 

 chiefly depends on any slight deviations not having been 

 preserved and accumulated by natural selection, which 

 acts only on serviceable characters. 



That the mere physiological importance of an organ 

 does not determine its classificatory value, is almost 

 proved by the fact, that in allied groups, in which the 

 same organ, as we have every reason to suppose, has nearly 

 the same physiological value, its classificatory value is 

 widely different. No naturalist can have worked long at 

 any group without being struck with this fact; and it has 

 been fully acknovvledged in the writings of almost every 

 author. It will suffice to quote the highest autliority, 

 Robert Brown, who, in speaking of certain organs in the 

 Proteace^e, says their generic importance, ^Mike that of all 

 their parts, not only in this, but, as I apprehend in every 



