40 ESSAY ON CLASSIFICATION. 



the respective standing of Radiata, Polyps would be 

 placed lowest, Acalephs next, and Echinoderms highest. 

 A similar arrangement of Mollusks would bring Acephala 

 lowest, Gasteropoda next and Cephalopoda highest. Arti- 

 culata would appear in the following order : Worms, 

 Crustacea and Insects. Vertebrata with the Fishes lowest, 

 Reptiles and Birds next, and Mammalia highest. I 

 have here purposely avoided every allusion to contro- 

 verted points. Now if Mollusks were to follow Radiata in 

 a simple series, Acephala should join on to the Echino- 

 derms : if Articulata, Worms would be the connecting 

 link. We should then have either Cephalopoda or Insects 

 as the highest term of a series beginning with Radiata, 

 followed by Mollusks or by Articulates. In the first case, 

 Cephalopoda would be followed by Worms : in the second, 

 Insects by Acephala, Again, the connection with Verte- 

 brata would be made either by Cephalopods, if Articulata 

 were considered as lower than Mollusks, or by Insects, if 

 Mollusks were placed below Articulata. Who does not 

 see, therefore, that in proportion as our knowledge of the 

 true affinities of animals is improving, we accumulate 

 more and more convincing evidence against the idea that 

 the animal kingdom constitutes one simple series ? 



The next question would then be: Does the animal 

 kingdom constitute several, or any number of graduated 

 series 1 In attempting to ascertain the value of the less 

 comprehensive groups when compared to one another, the 

 difficulties seem to be gradually less and less. It is already 

 possible to mark out with tolerable precision the relative 

 standing between the classes, though even here we do not 

 yet perceive in all the types the same relations. Among 

 Vertebrata there can be no doubt that the Fishes are 

 lower than the Reptiles, these lower than Birds, and that 



