CLASSIFICA TION 215 



be more false. No one regards the external similaiity of 

 a mouse to a shrew, of a dugoug 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 

 characters"; but to the consideration of these resem- 

 blances 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 afford- 

 ing very clear indications of its true affinities. We are 

 least likely in the modifications of these organs to mis 

 take a merely adaptive for an essential character." With 

 plants how remarkable it is that the organs of vegetation, 

 on wliich 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 

 morphological characters which are not functionally im- 

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

 service in classification. This depends on their con- 

 stancy 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 



