222 NATUEAL HISTORY. 



cause they have no ventral or belly fins. They have 

 long, snake -like bodies, covered with a soft skin, the 

 scales being very minute, often almost invisible. They 

 can live for some time out of the water, chiefly from a 

 peculiar arrangement of the gills. The gills have very 

 narrow openings, and are, therefore, so much sheltered 

 from the air that they do not readily become unfit for res- 

 piration in becoming dry (350). There is a similar ar- 

 rangement in the Lampreys, a class of Fishes of eel-like 

 shape, in some respects the lowest in organization of all 

 the Vertebrate animals. In these fishes there are four- 

 teen gill-openings, seven on each side, as seen in Fig. 175. 



Fig. 175. Lamprey. 



They are sometimes called Seven-eyes on this account. 

 The mouth is a singular apparatus. It is ring-shaped, 

 and is armed with numerous teeth, and there are also 

 two longitudinal rows of small teeth on the tongue. The 

 tongue moves backward and forward in the mouth, act- 

 ing as a piston, thus, by its suction power, enabling the 

 fish to hold on to any object that it pleases. 



377. In the rivers and ponds of Surinam and other 

 parts of South America there is found an Eel which is 

 armed with a true electric battery. It uses it in destroy- 

 ing the life of its prey, which it does instantaneously. It 

 can sometimes give a shock powerful enough to prostrate 

 a man. Humboldt describes the method adopted by the 

 natives in taking these animals. Having found a pool in 

 which they are, they drive in a troop of wild horses. Aft- 



