228 ESSAY ON CLASSIFICATION. Part I. 



are not Allocotyledones, and that any group of animals which unites MoUusks, 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 Linnoeus, less likely to 

 answer to a j^hilosophical idea of what a class may be, than that which unites 

 Tunicata with Polyps and Acalephs. In his latest work. Van Beneden 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, deserve to be particularly noticed. These 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 the plants most generally adopted now, leads me to 

 call again attention to the necessity of carefully scrutinizing anew the vegetable 

 kingdom, with the view of ascertaining how far the results I have arrived at 

 concerning the value of the diffei'ent kinds of natural groups existing among 

 animals,^ ^pplj fil^'o to the plants. It would certainly be premature to assume, 

 that because the branches of the animal kingdom are founded upon different plans 

 of structure, the vegetable kingdom must necessarily be built also upon different 

 plans. There are probably not so many different modes of development among 

 jjlants as among animals ; unless the reproduction by spores, by naked polyem- 

 bryonic seeds, by angiospermous monocotyledonous seeds, and by angiospermous 

 dicotylodonous seeds, connected with the structural differences exhibited by the 

 Acotyledones, Gymnospermes, Monocotyledones, and Dicotyledones, be considered as 

 amounting to an indication of different plans of structure. But even then these 

 differences would not be so marked as those which distinguish the four branches 

 of the animal kingdom. The limitation of classes and orders, which presents com- 

 paratively little difficulty in the animal kingdom, is least advanced among plants, 

 whilst botanists have thus far been much more accurate than zoologists in charac- 

 terizing families. This is, no doubt, chiefly owing to the peculiarities of the two 

 organic kingdoms. 



It must be further remarked, that in the classification of Van Beneden the 

 animals united under the name of Allocotyledones are built upon such entirely 

 different plans of structure, that their combination should of itself satisfy any 

 unprejudiced observer that any principle which unites them in that way cannot 

 be true to nature. 



1 See Chap. II., p. 137 to 178. 



