CHAPTER II. 



GENERAL CHARACTERS OF VERTEBRATED ANIMALS. 



GO. THE Vertebrated sub-kingdom, including the classes of 

 Mammals, Birds, Reptiles, Batrachians, and Fishes, is charac- 

 terised by the presence, in all its members, of an internal skele- 

 ton, composed of bone or cartilage, and forming an envelope to 

 the nervous centres. In the Articulated classes, there is no 

 vestige of any such structure ; and the only Mollusca (some of 

 the Cuttle-fish tribe) in which there is the least approach to it, 

 are sufficiently distinguished by other characters. It is true that, 

 among many of the Radiata, such as a few of the .Jelly-fish 

 tribe, and a large proportion of the Polypes, there is an internal 

 skeleton, sometimes composed of a horny or cartilaginous tissue, 

 and sometimes possessing even a stony hardness ; but this gives 

 equal support to the whole fabric, and is not arranged in such a 

 manner as to give the least degree of peculiar protection to the 

 nervous centres ; so that, although it may be fancifully regarded 

 as a kind of sketch, or shadowing-forth, in this lowest group, of 

 the plan of structure which is characteristic of the highest, it 

 cannot be said to have any real correspondence with it. 



61. The animals of the Vertebrated series are, of all sentient 

 beings, those whose faculties are the most varied and the most 

 perfect. The principle of the division of labour is carried out in 

 them to its highest degree ; every function to be performed 

 having its own separate organ, whose operations are limited to it 

 alone ; consequently, the Vertebrata are, of all animals, those in 

 which the distinct organs are the most numerous and the most 

 complicated. "We may encounter many, among the lower tribes, 

 in which the number of parts is as great, or even greater j but> 



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