CLASS AMPHIBIA: OKDEE URODELA. 



Fig. 310. Fly. 311. 



183 



/ riton crist&tus, Newt or Triton. 



SirMon lichenoides, Axolotl. 



Amphipneusta. The Double-breathing Amphibians 

 present anomalous forms, which are of interest on account 

 of the apparent permanency of their gills. Among Ihem are 

 the Siren, or Mud-eel, of the Carolina rice swamps, the Axo- 



Fig. 312. 



Profits anguinus. 



lot! of the Mexican lakes, and the Proteus, which inhabits 

 certain caves in Austria, and has only rudimentary eyes. 

 Recent investigations suggest a doubt whether they are not 

 merely the larvae of other animals whose life history is not 

 yet fully known.* 



furnish the most convenient means for observing the circulation of the blood. Plac- 

 ing the little creature in a vial, with a pocket-lens the globules may be seen chasing 

 one another as they go out through the arteries and return by the veins. 



* As they have tuft-like branchiae besides lungs, they have been thought to illus- 

 trate the general law that the " transient embryonic stages of the higher members of 

 any division of the animal kingdom are often represented by the permanent condi- 

 tion of its lower members."" 



