18 GENERAL PRINCIPLES OF ZOOLOGY. 



mollusks, extended to the coelenterates, arthropods, and 

 vertebrates, living and fossil. He collected his extensive 

 observations into his two chief works " Le regne animal 

 distribue d'apres son organization" and " Lecons d'anato- 

 mie comparee." Of quite epoch-making importance was 

 his little pamphlet "Sur un rapprochement a etablir entre 

 les differentes classes dcs animaux," in which he founded 

 his celebrated type theory, and by which in 1812 was intro- 

 duced a complete reform of systemization. The Cuvierian 

 division, which has become the starting-point for all further 

 classifications differed, broadly speaking, from all the earlier 

 systems in this, that the classes of mammals, birds, reptiles, 

 and fishes were brought together into a higher grade under 

 the name, introduced by Lamarck, of " vertebrated ani- 

 mals" ; that further the so-called " invertebrated animals " 

 were divided into three similar grades, each equal to that 

 of the "vertebrated animals, viz., Mollusca, Articulata, 

 and Radiata." Cuvier called these grades standing above 

 the classes, provinces or chief branches (embranchements), 

 for which later the name Types was introduced by Blain- 

 ville. But still more important are the differences which 

 appear in the internal grounding of the system. Instead 

 of, like the earlier systematists, using in the division a 

 few various external characteristics, Cuvier built upon the 

 totality of internal organization, as expressed in the relative 

 positions of the most important organs, especially the 

 position of the nervous system, as determining the arrange- 

 ment of the other organs. " The type is the relative posi- 

 tion of parts" (von Baer). Thus for the first time was 

 Comparative Anatomy employed in the formation of a 

 natural system of animals. 



Finally the type theory established an entirely new 

 conception of the arrangement of animals. Cuvier found 

 as the prevalent view the theory that all animals formed 

 a single dependent series rising from the lowest infusorian 

 up to man ; within this series the position of each animal 

 was definitely determined by the height of its organiza- 

 tion. On the other hand Cuvier taught that the animal 



