362 ESSAY ON CLASSIFICATION. 



cotyleclones, and the four classes of Pisces, Amphibia, Aves, 

 and Mammalia, to his Hypocotyledones. He compares 

 his primary divisions to the Dicotyledones, Monocotyle- 

 dones, and Acotyledones of the vegetable kingdom. But 

 he overlooks that the Cephalopoda are not Allocotyledones, 

 and that any group of animals which unites Mollusks, 

 Worms, and Radiates in one great mass, cannot be 

 founded upon correct principles. As to his classes, I can 

 only say, that, if there are natural classes among animals, 

 there never was a combination of animals proposed since 

 Linnseus less likely to answer to a philosophical idea of 

 what a class may be, than that which unites the Tunicata 

 with the Polyps and Acalephs. In his latest work, Van Bene- 

 den has introduced in this classification many important 

 improvements and additions. Among the additions, the 

 indication of the orders (which are introduced in brackets 

 in the diagram above) deserves to be particularly noticed. 

 The changes relate chiefly to the Mollusks and Polyps, 

 the Tunicata and Bryozoa being removed from the Polyps 

 to the Mollusks. The Acalephs and Polypi, however, are 

 still considered as forming together one single class. 



The comparison instituted by Van Beneden between 

 his classification of the animal kingdom and that of plants, 

 as now most generally adopted, leads me again to call 

 attention to the necessity of carefully scrutinizing anew 

 the vegetable kingdom, with the view of ascertaining how 

 far the results at which I have arrived concerning the value 

 of the different kinds of natural groups existing among 

 animals, 1 apply also to plants. It would certainly be 

 premature to assume that, because the branches of the 

 animal kingdom are founded upon different plans of struc- 

 ture, the vegetable kingdom must necessarily be built also 



1 See Chap. II. 



