VERTEBRATA. 239 



CHAPTER XV. 



VERTEBRATA. 



Thus the seer, 



With vision clear, 



Sees forms appear and disappear, 



In the perpetual round of strange 



Mysterious change 



From birth to death, from death to birth, 



From earth to heaven, from heaven to earth ; 



Till glimpses more sublime 



Of things unseen before, 



Unto his wondering eyes reveal 



The Universe, as an immeasurable wheel 



Turning for evermore 



In the rapid and rushing river of Time. 



LONGFELLO \V. 



i. THE type, or sub-kingdom, Vertebrata, (vertebra, a 

 joint of the back, from vertere, to turn,) is characterized 

 by the separation of the greater part of the nervous sys- 

 tem from the general cavity of the body. A transverse 

 section of the body exhibits two cavities, or tubes ; the 

 dorsal, or neural, tube, containing the cerebro-spinal 

 nervous system, and the ventral, or haemal tube, inclos- 

 ing the alimentary canal, heart, lungs, and a double chain 

 of ganglia belonging to the sympathetic system of nerves. 

 The ventral cavity, with its contents, corresponds to the 

 whole body of an Invertebrate animal, while the dorsal 

 tube is distinctly typical.* 



Vertebrates have an internal, jointed skeleton, capable 



* See Frontispiece. 



