38 ESSAY ON CLASSIFICATION. 



is still more accurately known how 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, graduated 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, although the inferiority of the Eadiata may 

 seem plain when they are compared with the bulk of the 

 Mollusks or Articulata, or still more evident when they are 

 contrasted with theVertebrata,it must not be forgotten that 

 the structure of most Echinoderms is far more complicated 

 than that of any Bryozoon or Ascidian, of the type of Mol- 

 lusks, or that of any Helminth, of the type of Articulata, and 

 perhaps even superior to that of the Ampliioxus among 

 the Vertebrata. These facts are so well ascertained, that 

 an absolute superiority or inferiority of one type to the 

 others must be unconditionally denied. As to a relative 

 superiority or inferiority, however, determined by the 

 bulk of evidence, though it must be conceded that the 

 Vertebrata rank above the three other types, the question 

 of the relative standing of Mollusks and Articulata seems 

 to rest rather 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 dis- 

 play' would more naturally indicate that of Articulata; 



by W. J. BURNETT, Boston, 1854. Cambridge, 1856, 2 vols. 8vo. CA- 



BERGMANN (C.) und LEUCKART (R.), RUS (J. V.), Icones Zootomicae, mit 



Vergleichende Anatomie und Physi- Original-beitragen von G. J. Allman, 



ologie; Stuttgardt, 1852, 1 vol. 8vo. C. Gegeubauer, Th. II. Hayley, Alb. 



fig. VAN DER HOEVEN (F.), Hand- Kolliker, H. Miiller, M. S. Schultze, 



book of Zoology, translated from the C. Th. E. von Siebold und F. Stein, 



Dutch by the REV. WILLIAM CLARK; Leipzig, 1857, fol. 



