THE ARGUMENT'S FROM CLASSIFICATION. 859 



explained on the supposition of a genealogical tree by which 

 all organisms are affiliated. If, wherever we can trace 

 direct descent, multiplication, and divergence, this formation 

 of groups within groups takes place ; there results a strong 

 presumption that the groups within groups which constitute 

 the animal and vegetal kingdoms, have arisen by direct 

 descent, multiplication, and divergence that is, by evolu- 

 tion. 



124. Strong confirmation of this inference is furnished 

 by the fact, that the more marked differences which divide 

 groups, are, in both cases, distinguished from the less 

 marked differences which divide sub-groups, by this, that 

 they are not simply greater in degree, but they are more 

 radical in kind. Objects, as the stars, may present them- 

 selves in small clusters, which are again more or less aggre- 

 gated into clusters of clusters, in such manner that the in- 

 dividuals of each simple cluster, are much closer together 

 than are the simple clusters composing a compound cluster : 

 in which case, the kinship that unites groups of groups 

 differs from the kinship that unites groups, not in nature, 

 but only in amount. But this is not the case either with 

 the groups and sub-groups which we know have resulted 

 from evolution, or with those which we here infer have re- 

 sulted from evolution. Among these, we find the highest 

 or most general classes, are separated from one another by 

 fundamental differences that have no common measure with 

 the differences that separate small classes. Observe the pa- 

 rallelism. 



We saw that each sub-kingdom of animals is marked ofl 

 fi'om the other sub-kingdoms, bv a total uulikeness in its 

 plan of organization : that is, the members of any sub-kingdom 

 are bound together, not by some superficial attribute which 

 they all have, but by some attribute determining the general 

 nature of their organizations. While, contrariwise, the 

 members of the smallest groups are united together, and se- 

 parated from the members of other small groups, bv modi- 



