THE ARGUMENTS FROM CLASSIFICATION. 361 



Bidts a further reason for inferring that these have been 

 evolved. 



o 



125. There is yet another parallelism of like meaning. 

 We saw ( 101) that the successively-subordinate classes, 

 orders, genera, and species, into which zoologists and botan 

 ists segregate animals and plants, have not, in reality, 

 those definite values conventionally given to them. There are 

 well-marked species, and species so imperfectly defined that 

 certain systematists regard them as varieties. Between 

 genera, strong contrasts exist in many cases ; and in other 

 cases, contrasts so much less decided as to leave it doubtiul 

 whether they constitute generic distinctions. So, too, is it 

 with orders and classes : in some of which there have been 

 introduced intermediate sub- divisions, having no equivalents 

 in others. Even of the sub- kingdoms the same truth holds. 

 The contrast between the Mottuscoida and the Mollusca, is far 

 less than that between the Mollusca and the Annulosa ; and 

 there are naturalists who think that the Pertebrata are so 

 much more widely separated from the other sub-kingdoms, 

 than these are from one another, that the Fertebrata should 

 have a classificatory value equal to that of all the other sub- 

 kingdoms taken together. 



Now just this same indefiniteness of value, or incomplete 

 ness of equivalence, is observable in those simple and com 

 pound and re-compound groups, which we see arising by 

 evolution. In every case, the endeavour to arrange the 

 divergent products of evolution, is met by a difficulty like 

 that which would meet the endeavour to classify the 

 branches of a tree, into branches of the first, second, third, 

 fourth, &c., orders the difficulty, namely, that branches of 

 intermediate degrees of composition exist. The illustration 

 furnished by languages will serve us once more. Some dia 

 lects of English are but little contrasted ; others are strongly 

 contrasted. The alliances of the several Scandinavian tongues 

 with one another are different in degree. Dutch is much 

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