ELECTROTAXIS 59 
ments, trusting to luck to get it into a more favorable situa- 
tion. A comparatively large element of random movement 
may be combined with a tendency to turn directly away 
from the stimulus, as is apparently the case in planarians. 
The subject of orientation to heat rays has been little 
studied. With aquatic organisms it would be difficult 
to separate the reaction to heat rays and reaction to warmer 
or colder regions of the water. Of the effect of radiant 
heat alone on the movements of terrestrial organisms we 
have as yet very inadequate knowledge. 
ELECTROTAXIS 
Reactions to the electric current form no part of the be- 
havior of animals under natural conditions. Nevertheless, 
many forms respond to the electric current in a very precise 
manner. An attempt to review the rather extensive 
literature on this subject would lead to a considerable 
amount of technical discussion, and an adequate treatment 
would require much more space than can be devoted 
to it here. The subject is one, however, which has an 
important bearing on the general theory of tropisms, and 
we shall therefore describe briefly some typical cases of 
electrotactic response. 
An Ameba proteus placed in the pathway of a weak electric 
current assumes an elongated form and creeps toward the 
cathode. The protoplasm toward the end nearest the anode 
apparently contracts and with a stronger current may 
undergo a granular disintegration. Pseudopods are put out 
on the side toward the cathode and cause the flow of the 
protoplasm in that direction. 
When Parameecium is subjected to the action of the cur- 
rent it swims with a fairly accurate orientation of the body 
toward the cathode. If two poles of a galvanic battery are 
