382 CLASSIFICATION. Chap. XIII. 



male, female, and hermaphrodite forms of the same species. 

 The naturalist ineludes as one species the various larval stages 

 of the same individual, however much they may differ from 

 each other and from the adult, as Avell as the so-called alter- 

 nate generations of Stcenslrup, which can only in a technical 

 sense be considered 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 fe- 

 males and larvfc are sometimes extremely different ; and as it 

 has been nscd in classing varieties which have undergone a 

 certain, and sometimes a considerable amount of moditication, 

 may not this same element of descent have been unconsciously 

 used in grouping species under genera, and genera imder 

 higher groujis, all under the so-called natural system? I be- 

 lieve it has been unconsciously used; and thus only can I im- 

 derstand the several rules and guides which have been fol- 

 lowed by our best systematists. We have no written pedi- 

 grees ; Ave have to make out community of descent by resem- 

 blances of any kind. Therefore Ave choose those characters 

 Avhich, as far as Ave can jucige, are the least likely to Ikia'C been 

 modified in relation to the conditions of life to Avhich each spe- 

 cies has been recently exposed. Rudimentary structures on 

 this vicAV are as good as, or CA'en sometimes better than, other 

 ]")arts of the organization. We care not hoAV trilling a charac- 

 tcn- may be — let it be the mere inflection of the angle of the 

 jaAv, the manner in Avhich an insect's Aving is folded, Avhet'licr 

 the skin be covered b}' hair or feathers— if it prevail thn^ugh- 

 out many and different species, especially those haA'ing very 

 different habits of life, it assumes high A'alue ; for Ave can ac- 

 coimt for its presence in so many forms Avith such different 

 habits, only by inheritance from a common ]iareut. A\^e may 

 err in this resjiect in regard to single points of structure, but 

 Avhen scA'eral characters, let them be eA'cr so trifling, concur 

 throughout a large group of beings haA'ing different habits, aa'C 

 may feel almost sure, on tlieory of descent, that these charac- 

 ters have been inlierited from a common ancestor. And aa-g 

 knoAV that such correlated or aggregated charactei's haA'e es 

 jiecial value in classification. 



We can understand Avhy a sjiecies or a group of sjiecies 

 may depart, in several of its most important characteristics, 

 from its allies, and yet be safely classed Avith them. This may 



