THE BEHAVIOR OF INFUSORIA; PARAMECIUM 89 



other. The behavior thus becomes uncoordinated, lacking unity. The 

 animal seems to strive to perform two opposite actions at once. The 

 anterior cilia drive the animal backward, the posterior cilia forward. In 

 certain positions (Fig. 63, /) part of the cilia tend to turn the animal to 

 the right, others to the left. The action of the current is more local and 

 direct than that of other stimuli, producing opposed reactions in dif- 

 ferent parts of the body. The whole secret of this extraordinary be- 

 havior lies in the cathodic reversal of the cilia. If this cathodic effect 

 were non-existent, the behavior under the action of the electric current 

 would probably be the same as under other stimuli. The reaction due 

 to the anodic stimulation is, as we have seen, the same as that due to 

 other strong stimuli, and in the constant current the anodic cilia strike 

 backward in the usual way. If the anodic stimulation alone existed, 

 the animal would doubtless become directed to the cathode by the method 

 of trial and would swim in that direction. But as the behavior actually 

 occurs, there is nothing like a trial of different positions. The cathodic 

 reversal of the cilia forces the animal directly into a certain orientation. 

 The reaction is not due, like that to chemicals, to the change in condi- 

 tions as the animal passes from one region to another. It is not due to 

 a tendency to collect about the cathode, for, as we have seen, if it is 

 possible, the animals go beyond the cathode. Moreover, in a strong 

 current there is no movement to the cathode, and in a still stronger 

 current the movement is away from the cathode, though the orientation 

 remains the same in both cases. All these peculiarities in the behavior 

 are due to the cathodic reversal of the cilia. 



What is the cause of this fundamental feature of the reaction to the 

 electric current, — the cathodic reversal? Many theories have been 

 proposed to account for the reaction to electricity, though often these 

 do not touch this fundamental feature in any way. It will be better to 

 reserve an account of these theories until we have examined the behavior 

 of other infusoria under the action of electricity (see Chapter IX). 



2. OTHER METHODS OF REACTION IN PARAMECIUM 



In Paramecium there are certain methods of reacting to stimuli which 

 we have not yet described. These are, first, local contractions of the 

 ectosarc, and second, discharge of trichocysts. Neither of these seem to 

 play any important part in regulating the relation of the organism to 

 the surrounding conditions. 



Slight local contractions of the ectosarc occur in response to many 

 stimuli. Since the ectosarc of Paramecium is not known to contain con- 

 tractile elements, the way in which these are brought about is unknown. 



