1913] Gee: Behavior of Leeches 253 



are listed below. These responses were secured by stimulating 

 as nearly as possible the same region of the right side of the 

 anterior end of the body, though this is confessedly difficult to 

 do in as active a form as Dina microstoma. The stimulus was 

 that from a flexible bristle fixed rigidly into a split wooden handle, 

 the bristle being bent about the same degree at each application 

 of the stimulus. In this way there was secured, as nearly as is 

 practicable, fairly exact localization and an even intensity of 

 stimulation. 



The responses to stimulation in this way are as follows: 



1. A turn to the left and movement forward in that direction. 



2. A turn to the left, then to the right and forward movement. 



3. A turn to the right in the direction of the stimulus and 

 forward movement. 



4. A turn to the right, followed by a turn to the left and 

 forward movement. 



5. A release of hold on the substratum and forward movement 

 by the swimming reaction. 



6. Disregard of the stimulus except for local contraction, and 

 continued forward movement. 



7. Local contraction of the part stimulated, the animal hug- 

 ging the bottom of the dish. 



8. A lifting of the anterior end and execution of random 

 feeling movements. 



9. With posterior end attached, a complete reversal of direc- 

 tion by a sharp turn to the left, followed bj' swimming reaction. 



Many other combinations of these reactions might be men- 

 tioned ; for example, reactions number one, two, and three might 

 be performed as turns merely, not being accompanied by for- 

 ward movement. It will be observed, however, that though there 

 is a wide variation in degree and combination, the whole series 

 can be cla.ssified as follows: (1) turns to right or left or up 

 and down; (2) forward movements by looping or swimming; 

 and (3) local contraction of the part affected. "While it is a 

 difficult matter to explain the order of response in each case, 

 the knowledge of the mechanism of these reactions, as discussed 

 in the first part of this paper, serves to suggest many valuable 

 points toward this end. 



