104 NATURAL HISTORY 



sour, it corrupt the water. They will also 

 feed on the water-plant called lemna (duck's 

 meat), and also on small fry. 



"When they want to move a little they 

 gently protrude themselves with \he\v pinncB 

 pectorales\ but it is with their strong mus- 

 cular tails only that they and all fishes shoot 

 along with such inconceivable rapidity. It 

 has been said that the eyes of fishes are 

 immoveable : but these apparently turn 

 them forward or backward in their sockets 

 as their occasions require. They take little 

 notice of a lighted candle, though applied 

 close to their heads, but flounce and seem 

 much frightened by a sudden stroke of the 

 hand against the support whereon the bowl 

 is hung ; especially when they have been 

 motionless, and are perhaps asleep. As 

 fishes have no eyelids, it is not easy to 

 discern when they are sleeping or not, be- 

 cause their eyes are always open. 



Nothing can be more amusing than a 

 glass bowl containing such fishes : the dou- 

 ble refractions of the glass and water repre- 

 sent them, when moving, in a shifting and 



