CHAPTER VII. 



CLASSIFICATION OF ZOOPHYTES. 



105. ZOOPHYTES constitute an order of the group or sub-kingdom 

 RADIATA. The limits of this sub-kingdom have of late been the 

 occasion of much discussion. In order to explain their relations to 

 other animals, a few remarks upon the general system of arrange- 

 ment in the animal kingdom are here offered. 



In Cuvier's Classification of Animals, the division Radiata includes 

 all invertebrate animals not comprised in either of the other sub-king- 

 doms, Articulata and Mollusca. Consisting thus only of refuse species, 

 and not limited by positive characters, as Owen states, we should 

 not expect that the group could be a natural assemblage. No line of 

 subdivision, however, has yet been made out, which has met with 

 general favour ; yet greater precision has been given to our views of 

 the affinities that run through the animal kingdom, by appealing to 

 the nerves, the seat of sensibility and sentiment, as a basis in classi- 

 fication ; and, in this manner, the subdivisions have been charac- 

 terized as follows by Dr. Grant. 



I. The Vertebrata, having a brain arid a spinal cord, constitute the 

 SPINI-CEREBRATA ; II. The Mollusca, having the nerves forming 

 generally a transverse series of ganglia disposed around the eso- 

 phagus, the CYCLO-GANGLIATA ; III. The Articulata, having no 

 proper brain, and the main cords, which run the length of the body, 

 double, the DIPLO-NEURA ; IV. The Radiata, having a radiate struc- 

 ture in the body, and the nervous ganglia arranged in a circle, 

 the CYCLO-NEURA. The orders of these sub-kingdoms are given as 

 follows : 



I. SPINI-CEREBRATA or VERTEBRATA. Mammalia, Aves, Reptilia, 

 Amphibia, Pisces. 



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