THE TRANSMUTATION OF SPECIES. 239 



philosophical arrangement. He recognised, however, that 

 the very merits of the natural classification render it 

 difficult of use by beginners. A natural arrangement can- 

 not be employed without difficulty for the mere purpose 

 of identifying an unknown species. On the other hand, 

 an artificial system, like that introduced into botany by 

 Linnaeus, can be used with the utmost ease in the identi- 

 fication of species, though it has the philosophical demerit 

 of associating together forms which have no real relation- 

 ships to one another. The method employed by Lamarck 

 in the ' Flore Frangaise ' was a sort of combination of 

 the natural and artificial methods of classification. The 

 ' dichotomous ' or analytical method consists, in fact, in a 

 classification of natural objects by means of positive and 

 negative characters, the characters selected being always 

 obvious and easily recognised. In the identification of a 

 species, therefore, the choice is always restricted to one of 

 two opposite characters, and the method proceeds by 

 constantly dividing and subdividing by two. The dicho- 

 tomous method of classification, as adopted by Lamarck 

 in botany, has been used also in natural history. When 

 one has to deal with very large groups of nearly allied 

 species, such, for example, as the different groups which 

 constitute the order of the Beetles, or in the case of the 

 different species of a single large genus, the dichotomous 

 method is sometimes extremely useful. It is, however, 

 distinctly an artificial method, and labours under the 

 inherent weakness that a group defined by a negative 

 character only must be artificial in principle, and is hardly 

 likely to prove in actual practice to be natural even by 

 accident. 



