CLASSIFICATION. 405 



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 ani- 

 mal, I have always regarded as affording very clear indica- 

 tions 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 for- 

 merly 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 hav- 

 ing 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 physi- 

 ological 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 acknowl- 

 edged in the writings of almost every author. It will suffice 

 to quote the highest authority, Robert Brown, who, in speak- 

 ing of certain organs in the Proteacese, 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 Connaracese " 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 

 importance, though here, even when all taken together, they 

 appear insufficient to separate Cnestis from Connar^.s." To 

 give an example among insects : in one great division of the 

 Hymenoptera, the antennas, 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 antennas in these 

 ^wo divisions of the same order are of unequal physiological 



