Oe NATURAL 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 
aman. 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- 
