VERTEBRATA. 
305 
Subkingdom VIII. —Vertebrata. 
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 
a double chain of gan¬ 
glia, or sympathetic 
system. This ventral, 
or haemal, cavity corre¬ 
sponds to the whole 
body of an Inverte¬ 
brate; while the dor¬ 
sal, or neural, is added. 
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 
Fig. 2.78.—Ideal Plans of the Subkingdoms. F, 
transverse section of vertebrate type; v, the 
same, inverted, ill, 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; a , 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. 
