306 
COMPARATIVE ZOOLOGY. 
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 
v from the general cav¬ 
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 ven¬ 
tral, or haemal, cavity 
corresponds to the 
Fig. 280.—Ideal Plans of the Subkingdoms. F, * 
transverse section of vertebrate type ; v, the whole body of an In- 
same, inverted. M, transverse section of mol- , , ... , 
luscous type; and Md, of molluscoid. A and Vertebrate ; While the 
Ad, transverse sections of articulate type, high J nr{J i -nmiral ic 
and low. C, longitudinal section of ccelente- UUI or “CUrai, IS 
rate type; a, alimentary canal; c, body-cavity, added. 
In the other figures, the alimentary canal is 
shaded, the heart is black, and the nervous Vertebrates are also 
cords are open rings. .. J . . . , , 
distinguished by an in¬ 
ternal, jointed skeleton, endowed with vitality, and capa¬ 
ble of growth and repair. During embryo-life it is rep¬ 
resented by the notochord; but this is afterwards replaced 
