VERTEBRATA. 295 
Subkingdom VerRTEBRATA. 
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 25,000 living spe- 
cies, widely differing among themselves in shape and hab- 
its, yet closely allied in the grand features of their organi- 
zation, 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 cay- 
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 sys- 
tem. This ventral, or 
heemal, cavity corre- 
sponds to the whole 
bod f Tniver Fie. 270.—Ideal Plans of the Subkingdoms. V, 
O ¥ oO an nverte- transverse section of vertebrate type; v, the 
- é Bh - same, invertéd. M, transverse section of mol- 
brate oo hile the dor- luscous type; and Md, of molluscoid. A and 
sal, or neural. is entire- <4¢, transverse sections of articulate type, high 
s ? and low. C, longitudinal section of celente- 
ly extra. rate type; a, alimentary canal; c, body-cavity. 
In the other figures, the alimentary canal is 
Vertebrates are also shaded, the heart is black, and the nervous 
distinguished by an in-, °° Pen ngs. 
ternal, jointed skeleton, endowed with vitality, and capa- 
ble of growth and repair. During embryo-life if is rep- 
resented by the notochord; but this is afterward replaced 
