GALVANOTROPISM 



43 



a current goes through a trough containing Paramcecia 

 the animals will all move toward the cathode. The mech- 

 anism of the reaction was discovered by Ludloff. 817 The 

 locomotion of Paramecium is brought about by cilia. 

 As a rule the cilia are directed backward (Fig. 14), and in 

 their normal movement they strike 

 powerfully backward and are retracted 

 with less energy to their normal posi- 

 tion. Since their powerful stroke is back- 

 ward the animal is pushed forward in the 

 water. Ludloff and Bancroft 17 ' ls show 

 that if a Paramecium is struck sidewise 

 by the current, the position of the cilia 

 on the cathode side is reversed inasmuch 

 as they are now turned forward. On the 

 anode side they continue to be directed 

 backward (Fig. 15, a). Instead of 

 striking symmetrically on both sides 

 of the animal, the cilia on the cathode side strike for- 

 ward powerfully while those on the anode side strike 

 powerfully backward. The animal is thus under the 

 influence of a couple of forces which turn its oral pole 

 toward the cathode side. As soon as it is in this condition 

 the symmetrical cilia are struck at the same angle by the 

 parallel current lines and they must assume a symmetri- 

 cal position which is as in Fig. 15, b, namely the cilia are 

 pointed forward toward the cathode at the oral end, and 

 backward toward the anode at the aboral end. As long 

 as the current is not too strong, the oral region, where 

 the cilia are pointing forward, is rather small and there- 

 fore the action of those cilia prevails which are in the 

 majority and which are pointed backward. As a result 

 the organism moves slowly forward to the cathode. 



Fig. 14. — Paramet- 

 rium under normal 

 conditions. Cilia all 

 pointing toward aboral 

 pole. 



