AN ANALYSIS OF THE LEARNING PROCESS IN THE SNAIL 81 

 TABLE XII-A 



Summary of tests in which a mechanical stimulus was used in connection with 

 electric shock. 



Snail Snail Snail Snail Snail Snail 



No. No. No. No. No. No. 



9 10 13 19 21 22 



Total number of trials 147 173 121 141 174 174 



Per cent of choices correct by 



chance 51 48 51 55 59 45 



Per cent of choices correct by 



association 23 13 12 24 12 13 



Per cent of incorrect choices. . 26 39 37 21 29 42 



Table XII shows that in a total of 930 trials on six individuals 

 of Physa, 51.2% were correct by chance, that is, the correct 

 path was chosen without contact with the warning stimulus. 

 In 15.6% of the trials the correct path was chosen after contact 

 with the warning stimulus, but without punishment, showing 

 that a weak association had been formed between the two 

 stimuli. In 32.5% of the trials, the warning stimulus was dis- 

 regarded and punishment received. This shows that the behavior 

 of the snails tested was modified during the experiments inas- 

 much as they apparently learned to recognize the warning 

 stimulus and turned back before receiving the electric shock. 

 The snails profited by experience. The slightly downward 

 tendency of the jagged ctirves based on these records (figs. 

 23-28, Plate VIII) shows an erratic decrease in error, weak asso- 

 ciation and limited associative memor3^ 



7. Summary of Observations 



1. All observations and experiments were made on the snail 

 Physa gyrina Say while in tap water at room temperature and 

 under uniform lighting conditions. 



2. When the air is pressed from the lung of Physa and the 

 snail is placed in the water at the base of a U-shaped labyrinth 

 supported on an upright stem, it crawls up the stem and along 

 the arms of the U to the surface of the water. Fig. 14, Plate IV. 



3. Experiments to test right or left preference : first series. — In 

 a series of 24 trials in which three individuals of Physa were 

 deprived of air and placed on the bottom near the wall of a 

 glass dish filled with water, and allowed to crawl unhindered 

 to the surface of the water, the path chosen deviated from a 



