222 NAT0EAX 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 arc four- 

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



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. 

 V^Y'T. 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 j)rostrate 

 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- 



