412 CLASSIFICATION. 



viously been ranked as three distinct genera, were known to 

 be sometimes produced on the same plant, they were imme- 

 diately considered as varieties ; and now I have been able 

 to show that they are the male, female, and hermaphrodite 

 forms of the same species. The naturalist includes as one 

 species the various larval stages of the same individual, how- 

 ever much they may differ from each other and from the 

 adult, as well as the so-called alternate generations of 

 Steenstrup, which can only in a technical sense be con- 

 sidered as the same individual. He includes monsters and 

 varieties, not from their partial resemblance to the parent- 

 form, but because they are descended from it. 



As descent has universally been used in classing together 

 the individuals of the same species, though the males and 

 females and larvae are sometimes extremely different ; and 

 as it has been used in classing varieties which have under- 

 gone a certain, and sometimes a considerable, amount of 

 modification ; may not this same element of descent have 

 been unconsciously used in grouping species under genera, 

 and genera under higher groups, all under the so-called 

 natural system ? I believe it has been unconsciously used ; 

 and thus only can I understand the several rules and guides 

 which have been followed by our best systematists. As we 

 have no written pedigrees, we are forced to trace community 

 of descent by resemblances of any kind. Therefore, we 

 choose those characters which are the least likely to have 

 been modified, in relation to the conditions of life to which 

 each species has been recently exposed. Rudimentary 

 structures on this view are as good, or even sometimes 

 better than other parts of the organization. We care not 

 how trifling a character may be — let it be the mere inflec- 

 tion of the angle of the jaw, the manner in which an 

 insect's wing is folded, whether the skin be covered by hair 

 or feathers — if it prevail throughout many and different 

 species, especially those having very different habits of life, 

 it assumes high value ; for we can account for its presence 

 in so many forms with such different habits, only by inherit- 

 ance from a common parent. We may err in this respect 

 in regard to single points of structure, but when several 

 characters, let them be ever so trifling, concur throughout a 

 large group of beings having different habits, we may feel 

 almost sure, on the theory of descent, that these characters 

 have been inherited from a common ancestor ; and we know 

 that such aggregated characters have especial value in 

 classification. 



