STUDIES IN ANIMAL LIFE. S3 



through, forms which were permanent in the lower 

 animals. This idea Cuvier always opposed. He 

 held that the four types were altogether distinct; 

 and by his arrangement of them, their distinctness 

 certainly appears much greater than would be the 

 case on another arrangement. But, without dis- 

 cussing this question here, it is enough to point out 

 the fact of the enormous superiority in intelligence, 

 in sociality, and in complexity of animal functions 

 which insects and spiders exhibit when compared 

 with the highest of the mollusks, to justify the re- 

 moval of the mollusca, and the elevation of the ar- 

 ticulata to the second place in the animal hierarchy. 

 Nor is this all. If we divide animals into four 

 groups, these four naturally dispose themselves into 

 two larger groups: the first of these, comprising 

 Vertebrata and Articulata, is characterized by a 

 nervous axis and a skeleton ; the second, comprising 

 Mollusca and Eadiata, is characterized by the ab- 

 sence of both nervous axis and skeleton. It is ob- 

 vious that a bee much more closely resembles a 

 bird than any mollusk resembles any vertebrate. 

 If there are many and important differences be- 

 tween the vertebrate and articulate types, there are 

 also many and important resemblances ; if the nerv- 

 ous axis is above the viscera, and forms the dorsal 

 line of the vertebrate, whereas it is underneath the 

 viscera, and forms the ventral line in the articulate, 

 it is, nevertheless, in both, the axis of the body, and 

 in both it sends off nerves to supply symmetrical 



