CHAP. XIV.] CLASSIFICATION. 343 



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." 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 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 service- 

 able 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 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 Pro- 

 teaceae, says their generic importance, "like that of all their parts, 

 not only in this, but, as I apprehend, in every natural family, is 

 very unequal, and in some cases seems to be entirely lost." 

 Again, in another work he says, the genera of the Connaraceae 

 " differ in having one or more ovaria, in the existence or absence 

 of albumen, in the imbricate or valvular aestivation. Any one of 

 these characters singly is frequently of more than generic import- 

 ance, though here even when all taken together they appear 

 insufficient to separate Cnestis from Connarus." To give an 

 example amongst insects : in one great division of the Hymen- 

 optera, the antennae, as Westwood has remarked, are most 

 constant in structure ; in another division they differ much, and 

 the differences are of quite subordinate value in classification ; 

 yet no one will say that the antennae in these two divisions of 

 the same order are of unequal physiological importance. Any 

 number of instances could be given of the varying importance for 

 classification of the same important organ within the same group 

 of beings. 



