1913] Gee: Behavior of Leeches 227 



The responses of the leeches to light appear fundamentally 

 the same as those recorded by Parker and Arkin (1901), Adams 

 (1902), Holmes (1905), and Harper (1905) in the case of the 

 earthworm. There is combined a certain degree of direct turning 

 with a large degree of random movement, the path of the leech 

 away from the source of light representing the resultant of these 

 two factors. 



6. Effect of Currents 



As has been previously pointed out, the specimens of Dina 

 used in this work were secured from a fresh-water pond located 

 in among the foothills of the Coast Range Mountains. Except 

 in the rainy season, no currents are likely to be produced in the 

 pond, which contains in its deepest part only a few feet of water. 

 It was rather intere.sting to note that specimens reared under 

 these conditions, even the young, only a couple of months old 

 at the most, which had not passed through a rainy season, showed 

 a distinct positive rheotaxis. 



Allee (1912) has pointed out the fact that Allen found the 

 current set up in a circular pan by stirring not to be straight, 

 but that of a diverging spiral. Comparison of the responses of 

 isopods in the straight and spiral current showed in his tests 

 only negligible differences. In the ease of Dina microstoma, 1 

 found the rheotactic responses under the stimulus of a straight 

 current to be even more markedly positive than they were in 

 the circular current. This result is perhaps to be explained as 

 due to the fact that the circular current induced was very much 

 stronger than the straight current used. The circular current, 

 as the most convenient, was adopted in the following experiments 

 on rheotaxis. 



Five individuals which had been in the laboratory only about 

 three days were subjected to a current induced in a glass dish 

 25 cm. in diameter, containing about 6 cm. depth of water. The 

 leeches were tested one at a time for twelve trials of a minute 

 each. The current was produced by briskly pushing a glass rod 

 1 cm. in diameter around near the edge of the dish for eight 

 times. The accompanying table (Table II), the column indi- 

 cated (-)-) denotes the number of seconds of the minute period 



