VERTEBRATA. 



305 



Subkingdom VIII. VKRTEBRATA. 



This grand division includes the most perfect animals, 

 or such as have the most varied functions and the most 

 numerous and complex organs. Besides the unnumbered 

 host of extinct forms, there are about twenty-five thousand 

 living species, widely differing among themselves in shape 

 and habits, yet closely allied in the grand features of their 

 organization, the general type being endlessly modified. 



The fundamental distinctive character of Vertebrates 

 is the separation of the main mass of the nervous system 

 from the general cav- v 



ity of the body. A 

 transverse section of 

 the body exhibits two 

 cavities, or tubes the 

 dorsal, containing the 

 cerebro- spinal nervous 

 system; the ventral, in- 

 closing the alimentary 

 canal, heart, lungs, and MI 

 a double chain of gan- 

 glia, or sympathetic 

 system. This ventral, 

 or haemal, cavity corre- 

 sponds to the whole 



j * T FIG. 2T8. Ideal Plans of the Subkingdoms. 



DOdy 01 an Inverte- transverse section of vertebrate type; v, 



hntp- whllp thp dor 



Sal, Or neural, is added. 



7 



Vertebrates are also 

 , . . . . , , . 



distinguished by an in- 



ternal, jointed skeleton, 

 endowed with vitality, and capable of growth and re- 

 pair. During embryo -life it is represented by the noto- 

 chord ; but in the higher forms this is afterwards replaced 



20 



r, 

 the 



same, inverted. 3f, transverse section of mol- 

 luscous type ; and Md, of molluscoid. A and 

 Ad, transverse sections of articulate type, high 

 and low. C, longitudinal section of ccelente- 

 rate type; o, alimentary canal; c, body-cavity. 

 In the other figures, the alimentary canal is 

 shaded, the heart is black, and the nervous 

 cords are open rings. 



