438 CLASSIFICATION. 



an artificial system; we are cautioned, for instance, not to 

 class two varieties of the pine apple together, mereh'' be- 

 cause their fruit, though the most important part, happens 

 to be nearly identical; no one puts the Swedish and com- 

 mon turnip together, though the esculent and thickened 

 stems are so similar. Whatever part is found to be most 

 constant, is used in classing varieties: thus the great agri- 

 culturist Marshall says the horns are very useful for this 

 purpose with cattle, because they are less variable than the 

 shape or color of the body, etc. ; whereas with sheep the 

 horns are much less serviceable, because less constant. In 

 classing varieties, I apprehend that if we had a real pedi- 

 gree, a genealogical classification would be universally pre- 

 ferred; and it has been attempted in some cases. For we 

 might feel sure, whether there had been more or less modi- 

 fication, that the principle of inheritance would keep the 

 forms together which were allied in the greatest number of 

 points. In tumbler pigeons, though some of the sub- 

 varieties differ in the important character of the length of 

 the beak, yet all are kept together from having the common 

 habit of tumbling; but the short-faced breed has nearly or 

 quite lost this habit: nevertheless, without any thought on 

 the subject, these tumblers are kept in the same group, 

 because allied in blood and alike in some other respects. 



With species in a state of nature, every naturalist has in 

 fact brought descent into his classification; for he includes 

 in his lowest grade, that of species, the two sexes; and how 

 enormously these sometimes differ in tlie most important 

 characters is known to every naturalist: scarcely a single 

 fact can be predicated in common of the adult males and 

 hermaphrodites of certain cirripedes, and yet no one 

 dreams of separating them. As soon as the three Orchi- 

 dean forms, Monachanthus, Myanthus, and Catasetum, 

 which had previously been ranked as three distinct genera, 

 were known to be sometimes produced on the same plant, 

 they were immediately 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, however much they may differ from each other 

 and from the adult, as well as the so-called alternate gen- 

 erations of Steenstrup, which can only in a technical sense 



