64 Transactions Tennessee Academy of Science. 



tive behavior would result in encircling movements as illustrated 

 in figures 2 and 3. 



This tendency to move in a straight path is not very strong, as 

 might be expected ; but when external stimulation is not very 

 strong or is not definitely localized, the tendency to move in a 

 straight path is stronger than the tendency to change the direc- 

 tion of movement in accordance with some external or internal 

 stimulus. When the tendency to move straight ahead is of about 

 the same strength as that to react to some external stimulus, en- 

 circling movements result. It is possible that this tendency to 

 move straight ahead is found in other animals. Some of the ex- 

 perimental data obtained by other investigators seem to indicate 

 that it may be present in other protozoa, but it would probably be 

 necessary to carry on experiments especially to prove the pres- 

 ence of this factor. But if it should prove to be present in other 

 forms, it must be regarded as an essential factor in movement, 

 a factor which must not be overlooked in investigations touching 

 any phase of movement. 



