1^13] Gee: Behavior of Leeches 225 



The amount of direct turning in the responses of Dina micro- 

 stoma was tested in the following manner: A well-moistened 

 piece of filter paper was placed on a glass plate in turn resting 

 ujion a flat revolving disk. The leech was removed from the 

 aquarium and placed upon this piece of filter paper. The animal 

 was allowed sufficient time for its body to become straightened 

 out in forward movement. The disk was then turned so that 

 the body length was at right angles to the source of light, a 

 60-watt Mazda. These operations were performed by the aid 

 of the red light in a dark room, and when the body of the animal 

 had been properly oriented for the experiment the light was 

 turned on. The first turn of the body was carefully noted and 

 the light immediately turned off again. In the accompanying 

 table the turns toward the source of light are recorded as positive 

 ( + ) and those away from the light as negative ( — ). The 

 indifferent responses are those eases where the leech continued 

 its forward movement. However, the stimulus of the light was 

 allowed to continue acting on these eases until the leech had 

 turned either towards or away from the source of illumination. 



TABLE I 



Directive Influence op 60-Watt Mazda Light on Vina microstoma 



Light falling on right side of the leech 



Number of the leech 



Towards ( + ) 9 6 10 5 7 4 



Away (— ) 9 9 11 14 11 8 



(followed by ( + ) 13 13 3 5 



indifferent.^. ,-, 3 , , ^ ^ n n ^ . ^ 



^followed by ( — ) 6 7 3 3 4 8 



Light falling on left side of the leech 



Number of the leech 



12 3 4 5 6 



Towards ( + ) 6 7 5 4 8 2 



Away (— ) 10 16 15 15 11 15 



T .1-ff i (followed by ( + ) 3 14 3 



indifterent < r ,, :, , , ^ „ 



I followed by ( — ) 6 2 4 2 6 5 



None of the turns, except in a few cases, was so abrupt as 

 to cause a direct reversal of the direction of movement in the 

 leech. The light of the intensity used does not produce so 

 powerful an effect. The turns were comparatively slight, though 



