THE SUB-KINGDOMS. I09 



vous system consists of a distinct brain and spinal cord, 

 and the latter is protected from injury by a more or less 

 weU - developed backbone or "vertebral column." The 

 limbs (when present) are never more than four in number, 

 and are turned away from that side of the body upon 

 which the main masses of the nervous system are sit- 

 uated. Examples of the sub-kingdom are the various 

 kinds of Fishes, the Newts, Frogs, and Toads ; the Tor- 

 toises, Snakes, Lizards, and Crocodiles ; the Birds; and 

 the numerous species of true Quadrupeds or Mammals. 



