CLASSIFICATION 453 



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, 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 charac- 

 ters ;" 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 organisation 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 re- 

 lated 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 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 reproduction, 

 with their product the seed and embryo, are of paramount 

 importance ! So again in formerly discussing certain mor- 

 phological 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 accumu- 

 lated 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 physiolog- 

 ical value, its classificatory value is widely different. Xo 

 naturalist can have worked long at any group without being 

 struck with this fact; and it has been fully acknowledged in 

 the writings of almost every author. It will suffice to quote 

 the highest authority, Robert Brown, who. in speaking of 

 certain organs in the Proteacea;, says their generic impor- 



