ClIAP. I. 



GRADATION OF STRUCTURE AMONG ANIMALS. 



27 



most classes should be characterized, and what is their respective standing; since 

 every day brings dissenting views, respecting the details of classification, nearer 

 together, the supposition that all animals constitute one continuous gradated series, 

 can be shown to be contrary to nature. Yet the greatest difficulty in this inquiry, 

 is to weigh rightly the respective standing of the four great branches of the whole 

 animal kingdom ; for, however plain the inferiority of the Radiata may seem, when 

 compared with the bulk of the Mollusks or Articulata, or still more evident when 

 contrasted with the Vertebrata, it must not be forgotten, that the structure of most 

 Echinoderms is for more complicated than that of any Bryozoon or Ascidian of the 

 type of Mollusks, or that of any Helminth, of the type of Articulata, and, perhaps, 

 even superior to that of the Amphioxus among Vertebrata. These facts are so well 

 ascertained, that an absolute superiority or inferiority of one type over the other 

 must be unconditionally denied. As to a i-elative superiority or inferiority however, 

 determined by the bulk of evidence, though it must be conceded that the Vertel)rata 

 rank above the three other types, the question of the relative standing of Mollusks 

 and Articulata seems rather to rest upon a difference in the tendency of their whole 

 organization, than upon a real gradation in their structure ; concentration being the 

 prominent trait of the structure of Mollusks, while the expression ' outward display ' 

 would more naturally indicate that of Aj-ticulata, and so it might seem as if Mollusks 

 and Articulata were standing on nearly a level with one another, and as much 



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