CriAr. XIII. CLASSIFICATION. 375 



zation is concerned with special habits, the more important it 

 becomes for chissilication. As an instance — Owen, in speak- 

 inf];' of the dufjonp:, says : " The generative or<^ans, Ijein^r those 

 wiiich are most remotely related to the habits and food of an 

 animal, I have always regarded as alTordinti; very clear indica- 

 tions of its true airmities. We are least likely in the modifi- 

 cations 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 tlieir nutrition and life de- 

 ]icnd, are of little signification ; whereas the organs of repro- 

 duction, with their product tlie seed and embr^'o, are of ])ara- 

 mount importance ! So, again, in formerly discussing morpho- 

 logical dilleronces M'hich are not jihysiologically important, we 

 have seen that they are often of the highest service in classifi- 

 cation. Tliis depends on their constancy througliout many 

 allied groups ; and the constancy depends chiefly on any shght 

 deviations of structure in such parts not having been pre- 

 served and accumulated by natural selection, wliich acts only 

 on useful characters. 



That tlie mere jihysiological 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 w^e have 

 every reason to suppose, has nearly the same physiologi- 

 cal value, its classificatory value is widely difltM-ent. No 

 naturalist can have worked at aily 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 aulhorily, Kobert ]}ro'\\Ti, who, in speaking of certain 

 organs in the Proteacere, says, their generic importance, " like 

 that of all their parts, not only in this, Init, as I apprehend, in 

 every natural familv, is verv unequal, and in some cases seems 

 to be entirely lost." Again, in another work, he says, the 

 genera of the Connaracea? " differ in having one or more 

 ovaria, in the existence or absence of albumen, in the imbri- 

 cate or valvular rcstivation. Any one of these characters 

 singly is fref|uently of more than generic importance, though 

 here even when all taken together they a])pear insufficient 

 to separate Cnestis from Connarus." To give an example 

 among insects: in one great division of the Ilymenoptera, 

 the antenna?, as Westwood has remarked, arc most constant 

 in structure ; in another division they differ nuich, and the 

 differences are of (juitc subordinate vahie in classification ; yet 

 no one will say that the antennif in these two divisions of the 



