Chap. XIII. CLASSIFICATION. 381 



In confirmation of this view, let us glance at the classifica- 

 tion of varieties, which are believed or known to be descended 

 i'roin a sinu:le sjiecies. These are grouped under the species, 

 witli the sub-variclies under the varieties ; and in some cases, 

 as with domestic pigeons, several otlier grades of dilVerence are 

 requisite. Nearly the same rules are followed as in classifj-ing 

 species. Authors have insisted on the necessity of arranging 

 varieties on a natural instead of an artificial system ; we are 

 cautioned, for instance, not to class two varieties of the pine- 

 apple together, merely because their fruit, though the most 

 important part, happens to be nearly identical; no one puts 

 llie Swedish and conunon turnijjs together, though the escu- 

 h'nt and thickened stems are so similar. Whatever part is 

 found to be most constant, is used in classing varieties : thus 

 the great agriculturist Marsiiall says the liorns are very useful 

 loE this purpose with cattle, because they are less variable than 

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

 horns are nuicli less serviceable, because less constant. In 

 classing varieties, I apprehend that if we had a real pedigree, 

 a genealogical classification would be universally preferred ; 

 and it has been attempted in some cases. For we might feel 

 sure, wlicther there had been more or less modification, the 

 ])rinciple of inheritance would keep the forms together which 

 were alHed in the greatest number of points. In tundjler 

 ])igeons, tliougli some of the sul>varieties difler in the impor- 

 tant character of having a longer beak, yet all are kept togeth- 

 er, from having the common habit of tumbling; but the shoit- 

 faccd breed has nearly or quite lost this haljit; nevertheless, 

 without any thought on the sul)ject, these tumblers arc 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 lie includes in 

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

 enormously these sometimes dilh^r in the most important char- 

 acters, is known to every naturalist : scarcely a single fact can 

 be predicated in common of the adult males and hermajihro- 

 • lites of certain cirripedes, and yet no one dreams of sejiarating 

 ihem. As soon as the three Orchidean forms, Monachanthus, 

 -Myanthus, and Catasetum, which had jireviously been ranked 

 as three distinct genera, were known to bo sometimes pro- 

 duced on the same plant, they were inunediately considered as 

 varieties; and now 1 have been able to show that they are the 



