THE ARGUMENTS FROM CLASSIFICATION. 363 



in its organization, Dr Carpenter remarks, that it " furnishes 

 an apt illustration of another important fact, that it is by 

 the lowest rather than by the highest forms of two natural 

 groups, that they are brought into closest relation.' ' What 

 are the faint traces of community between the Annuhsa and 

 the Mollnsca? They are the thread-cells which some of 

 their inferior groups have in common with the Goelenterata. 

 More decided approximations exist between the lower 

 members of classes. In tracing down the Crustacea and 

 the Arachnida from their more complex to their simpler 

 forms, zoologists meet with difficulties : respecting some of 

 these simpler forms, it becomes a question which class they 

 belong to. The Lepidosiren, about which there have been 

 disputes whether it is a fish or an amphibian, is inferior in the 

 organization of its skeleton, to the great majority of both 

 fishes and amphibia. Widely as they differ from them, the 

 lower mammals have some characters in common with birds, 

 which the higher mammals do not possess. 



Now since this kind of relationship of groups is not ac- 

 counted for by any other hypothesis, while the hypothesis of 

 evolution gives us a clue to it ; we must include it among the 

 evidences of this hypothesis, which the facts of classification 

 furnish. 



§ 127. What shall we say of these several leading truths 

 when taken together ? That naturalists have been gradually 

 compelled to arrange organisms in groups within groups; 

 and that this is the arrangement which we see arises by 

 descent, alike in individual families and among races of men, 

 is a striking circumstance. That while the smallest groups 

 are the most nearly related, there exist beween the great 

 sub-kingdoms, structural contrasts of the profoundest kind ; 

 cannot but impress us as remarkable, when we see that where 

 it is known to take place, evolution actually produces these 

 feebly-distinguished small groups, and these strongly-dis- 

 tinguished great groups. The impression made by these two 



