CLASSIFICATION 373 



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, 

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

 blances, 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 have to 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 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 modifications of these organs to 

 mistake a merely adaptive for an essential character.' 

 So with plants, how remarkable it is that the organs of 

 vegetation, on which their whole life depends, are of 

 little signification, excepting in the first main divisions ; 

 whereas the organs of reproduction, with their product 

 the seed, are of paramount importance ! 



We must not, therefore, in classifying, trust to resem- 

 blances in parts of the organisation, however important 

 they may be for the welfare of the being in relation to 

 the outer world. Perhaps from this cause it has partly 

 arisen, that almost all naturalists lay the greatest stress 

 on resemblances in organs of high vital or physiological 

 importance. No doubt this view of the classificatory im- 

 portance of organs which are important is generally, but 

 by no means always, true. But their importance for 

 classification, I believe, depends on their greater con- 

 stancy throughout large groups of species ; and this 

 constancy depends on such organs having generally been 

 subjected to less change in the adaptation of the species 

 to their conditions of life. That the mere physiological 

 importance of an organ does not determine its classi- 



