AN ANALYSIS OF THE LEARNING PROCESS IN THE SNAIL 13 



described apparatus was applied without food to the upturned 

 ventral surface of the foot. It was placed upon the animal 

 in such a way that the food hook was just above the mouth. 

 Pressure was thus applied to the same part of the foot that would 

 receive it if the double stimuli, food and pressure, were being 

 applied together. In the total of 120 trials 4 responses occurred 

 (3.33%) and these were probably due to mucous stimulation. 

 Pressure alone, as applied with the apparatus used is followed 

 by response in so small a percentage of the trials that its occur- 

 rence does not vitiate the experiments which foll9w. 



C. Experiments to determine response to the conditioned food 

 stimidus: first food and pressure series. — By means of the food- 

 pressure apparatus food and uniform pressure were next applied 

 simultaneously in a long series of trials. Both stimuli were 

 immediately withdrawn and the number of reactions of the mouth 

 counted and recorded as before. Table III shows the record 

 obtained in this attempt to form an association between two 

 dissimilar stimuh applied simultaneously. 



TABLE III 



Showing the number of reactions of the mouthsof two individuals of Physa gyrina 

 Say, resulting from the simultaneous application of two dissimilar stimuli, food and 

 pressure. The tests were made in filtered tap water on alternating days. The 

 snails had been starved for 24 hours preceding the tests. 



