288 University of California Puhlications in Zoology [Vol. 11 



TABLE XV 



Influence of Snail Juice Upon Reactions op Well-Fed Leeches to 

 Contact Stimulation. — Thirty Applications of Stimulus 



(c) Well-fed leeches. — The responses of the well-fed leeches 

 under the same conditions as those of the preceding experiments 

 are not essentially different from what was found to hold in 

 the normal individuals. Under the influence of contact stimulus 

 without the reinforcement of snail juice there is a somewhat 

 smaller number of positive responses than in the normal indi- 

 vidual. The same condition is true under the influence of the 

 snail juice. There is, however, a lowered responsiveness in the 

 well-fed individuals which would tend to lower the irritability 

 of the leech. This reduced irritability would tend to render the 

 responsiveness to light contact stimulation more nearly like that 

 of the normal individual which has not previously been excited 

 to a stage of activity. 



2. Light and Contact 



A dish sixteen by sixteen by thirty-one centimeters containing 

 three do^ns of leeches was placed over a 25-watt Mazda light 

 in a dark room, the di.sh being elevated on a tripod about eight 

 inches in height. With the light turned off a stone was placed 

 in the center of the dish, and underneath this within an hour 

 had accumulated ten of the leeches. The light was then turned 

 on, and the reactions of the leeches were carefully observed. At 

 first the stimulus produced in the leeches under the stone a state 

 of restlessness, indicated by side to side movements. In a few 



