266 POPULAR HISTORY OF THE AQUARIUM. 



and thus drawing themselves back to the point which they 

 had quitted. 



" A LimncPM stagnalis had glided its way along a voiing 

 and short leaf of the Vallisneriaj whicli terminated below 

 the surface of the water^ and^ having reached the extremity, 

 launched itself off from it ; after moving about with a sort 

 of swimming and rolling motion in a horizontal direction 

 for some time, it lowered itself gradually, and in effecting 

 this the long flexible leaf of the Vallisneria was bent with an 

 undulating motion, corresponding exactly with every move- 

 ment of the Snail, showing clearly that it had a firm attach- 

 ment to the extremity of the leaf. On another occasion a 

 L. glutinosa gradually rose from the surface of a piece of 

 submerged rock, and, when at the distance of about three or 

 four inches from it, stayed its progress, floating about in a cir- 

 cumscribed horizontal direction for some time ; at last it 

 rose suddenly and rapidly to the surface, evidently from the 

 rupture of its thread of attachment. The most convincing 

 proof however of this fact that I can perhaps adduce, and 

 one tliat I have often repeated with all the before-mentioned 

 Limnccce, is that when the Snail has been some inches distant 

 from the supposed point of attachment, a rod or stick has 

 been carefully introduced and slowly drawn on one side, be- 



