THE BEHAVIOR OF INFUSORIA; PARAMECIUM 87 



mal turns toward the aboral side, as it does under other stimuli. But 

 in certain positions (from d to /, Fig. 63) it turns directly toward the oral 

 side, a result not producible by other stimuli. 



If the direction of the electric current is frequently reversed, certain 

 peculiar effects are produced. If the reversal occurs at the moment 

 when the anterior end has become directed toward the cathode, then the 

 animal continues to turn toward the aboral side till the anterior end is 

 pointed toward the new cathode. By repeated properly timed rever- 

 sals, the animals can be caused to spin round and round, — always 

 toward the aboral side.' If the intervals between the reversals of the 

 current are made less, so that the animal has not yet become pointed 

 toward the cathode, it swings back over the space through which it has 

 turned. Thus the animals may be made to swing back and forth or turn 

 round and round, remaining in the same spot, like animated galva- 

 nometers, — the anterior end pointing out the direction of the current. 



If the rate of reversal is much increased,^ so that the animals have 

 scarcely time to begin swinging in a certain direction before a new re- 

 versal occurs, then certain other phenomena result; these have been 

 described by Statkewitsch (1903, 1903 a). The Paramecia which are 

 swimming toward one electrode when the current is closed usually con- 

 tinue to swim in the same direction for a time, as if reacting to only one 

 of the current directions. Those not already pointed toward one of the 

 electrodes usually take quickly the transverse position. Thus, soon after 

 the beginning of the experiment, part of the animals are swimming 

 toward the electrode at the right, part toward that at the left, while the 

 rest are transverse. Soon those not transverse have reached the region 

 of the electrode toward which they are swimming. Thus the Paramecia 

 are now divided into three groups, — a group at the right swimming 

 toward the right electrode, another at the left swimming towards the 

 left electrode, and a central group swimming athwart the current (Fig. 

 64). After a time the transverse position is assumed also by those 

 directed toward the electrodes, especially if the current is made stronger 

 or the rate of reversal is increased. Thus at a later stage all or nearly 

 all are transverse ; they swim across the current, some toward one side 

 of the preparation, some toward the other. 



The reason for taking the transverse position when the current is 

 rapidly reversed seems to be as follows: We have seen above that to 



' As soon as a specimen has made a half revolution on its long axis, as may happen, it 

 of course seems to spin in the opposite direction, because the aboral side has taken up a 

 new position. 



" The strength of the current remaining the same in both directions, not varying as in 

 ordinary induction shocks. 



