286 University of California Puhlications in Zoology ["Vol. 11 



considered previously in its relation to the feeding responses of 

 the animal. In studying the feeding reactions of the leech, it 

 was observed that these positive responses seemed to be accentu- 

 ated under the stimulating influence of the juices of a snail, its 

 favorite food. This point was made the subject of a series of 

 experiments on leeches in normal, starved, and well-fed condi- 

 tions. 



Specimens which had been in the laboratory for a few days 

 only were considered normal. One at the time, a half dozen of 

 these normal leeches were tested for the number of positive re- 

 sponses to thirty very light contact stimuli of the anterior end 

 in the manner above described. After the responses of a par- 

 ticular leech were thus secured in tap water, a considerable quan- 

 tity of juices extracted by macerating a Limnea was added to 

 the water in the dish. The number of positive responses to light 

 contact stimuli was determined under these conditions. The 

 results are indicated in the accompanying table (see table XIII). 

 By positive (-)-) response is meant the actual application of the 

 anterior sucker against the glass rod as a direct r&sult of the 

 stimulus; negative ( — ) indicates a direct turn away from the 

 stimulus; and indifferent (±) is a response such as local eon- 

 traction or a continued forward movement. The uniformity of 

 the results in the different individuals is rather striking. The 

 accentuation of the positive response under the influence of 

 diffusing snail juices is not great, but the increased amount of 

 indifference seems significant. This condition, while apparently 



TABLE XIII 



Influence op Snail Juice Upon Eeactions of Normal Individuals to 

 Contact Stimuli. — Thirty Applications of Stimulus 



