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Show 424 CLASSIFICATION. CHAP. XIII. in the important character of having a longer beak, yet all are kept together from having the common habit of tumbling; but the short-faced b~eed has nearly. or quite lost this habit; nevertheless, Without any reasoni~g or thinking on the subject, ~hes~ tumblers are k~pt ~n the same group, because allied In blood and ahke m some other respects. If it could be proved that the Hottentot had descended from the Negro, I think ho would be classed under the Negro group, however much he might differ in colour and other important characters from negroes. With species in a state of nature, every naturalist has in fact brought descent into his classification ; for he includes in his lowest grade, or that of a species, the two sexes; and how enormously these sometimes differ in the most important characters, is known to every naturalist: scarcely a single fact can be predicated in common of the males and hermaphrodites of certajn cirripedes, when adult, and yet no one dreams of separating them. The naturalist includes as one species the several larval stages of the same individual, however much they may differ from each other and from the adult · as he likewise ineludes the so- called alternate genera' tions of Steenstrup, which can only in a technical sense be considered as the same individual. He includes monsters; he includes varieties, not solely because they closely resemble the parent-form, but because they are descended from it. He who believes that the cowslip is descended from the primros~, or conv~rsely, ranlrs them together as a single species, and g1ves a single definition. As soon as three Orchidean forms (Monochanthus, Myanthus, and Catasetum), which had previously been ranked as three distinct genera, ":ere known to be sometimes produced on the same sp1~ce, they were immediately included as a single specws. CIIAP. XIII. CLASSIFICATION. 425 But it may be asked, what ought we to do, if it could be proved that one species of kangaroo had been produced by a long co~rse of n1o~ification, from a bear? Ough~ we to rank this one speCies with bears, and what should we do with the other species ? The supposition is of course preposte~·ous; and I might answer by the argumentum ad hom'tnem, and ask what should be done if a perfect kangaroo were seen to come out of the womb of a bear? According to all analogy, it would be ranked with bears; but then assuredly all the other species of the kangaroo family would have to be classed under the bear genus. The whole case is preposterous; for where there has been close descent in common there will certainly be close resemblance or affinity. ' As descen~ h~~ universally been used in classing together the Individuals of the same species, though the ~ales and females. and larvoo are sometimes extremely d1~erent; and as It has been used in classing varieties whiCh have undergone a certain, and sometimes a considerable amount of modification, may not this same eleme~t of d~scent have been unconsciously used in grouping specie~ under genera, and genera under higher groups, though In these cases the modification has been greater in degree, and has taken a longer time to complete? I believe it has thus been unconsciously used· and only thus can I understand the several rules ancl g~ides which have been followed by our best systematists. \!ole have no written pedigrees; we have to ~ake o~t community of descent by resemblanees of any Ind. Therefore we choose those characters which as far ~s we .can judge, are the least likely to have b~en mod1fied 1n relation to the conditions of life to which each species has been recently exposed. Rudimentary s~ructures on this view are as good as, or even sometimes better than, other parts of the organisation. vV e |