C II A P T E \l THIRD. 



NOTICE OF THE PRINCIPAL SYSTEMS OF ZOOLOGY. 



SECTION I. 



GENERAL KEJLAUKS UPON MODERN SYSTEMS. 



Without attempting to give an historical account of the leading features of all 

 zoological systems, it is proper that I should here compare critically the practice 

 of modern naturalists with the principles discussed above. With tliis view, it 

 would hardly be necessary to go back beyond the publication of the "Animal 

 Kingdom," by Cuvier, were it not that Cuvier is still represented, by many naturalists, 

 and especially by Ehrenberg,' and some other German zoologists, as favoring the 

 division of the whole animal kingdom into two great groups, one containing the 

 Vertebrates, and the other all the remaining classes, under the name of Inverte- 

 brates, while in reality it was he, who first, dismissing his own earlier views, 

 introduced into the classification of the animal kingdom that fourfold di^•ision which 

 has been the basis of all improvements in modern Zoology. He first showed that 

 animals differ, not only by modifications of one and the same organic structure, 

 but are constructed upon four different plans of structure, forming natural, distinct 

 groups, which he called Radiata, Articulata, Mollusca, and Vertebra ta. 



It is true, that the further sulidivisions of these leading groups have under- 

 gone many changes since the publication of the "Regno Animal." Man}- smaller 

 groups, even entire classes, have been removed from one of his " embranchments " 

 to another; but it is equally true, that the characteristic idea which lies at the 

 bottom of these great divisions was first recognized by him, the greatest zoologist 

 of all times. 



* EiinENiiEiiG, (C. G.,) Die ConiUonthiere dcs rotlien Mccrcs, liurlin, 1834, 4to., p. 30. 



