60 ELIZABETH LOCKWOOD THOMPSON 



TABLE X-A 

 Summary of Left-Right Discrimination Tests 



Snail Snail Snail 



No. No. No. 



1 2 3 



Total number of trials 282 307 299 



Per cent of incorrect choices 52 62 62 



Table X shows that in a total of 888 trials on three individuals 

 of Physa, in a series of tests offering a choice of right and left 

 paths, with a reward for the correct choice (left), the incorrect 

 path (right) was followed in 58.8% of the trials. The graphs 

 (figs. 16-18, Plate VI) show very great irregularity in the time 

 distribution of the right and wrong choices. There are days 

 when the record is perfect, other days when all choices are 

 wrong. Between these is every intermediate condition. A 

 slight excess of incorrect choices is to be expected on account 

 of the possible tendency to turn to the right shown in the right- 

 left preference tests. TJicsc records shoiv no indication of learning. 



5. Experiments With the Y-Shaped Labyrinth: Roughness of Path as a 

 Warning Sign: Electric Shock Punishment 



It seemed either that the problem itself was too dififictilt or 

 that the immediate demand for air (punishment) was not great 

 enc^ugh to force its solution. In its natural habitat the snail 

 often depends on plant stems as a means of reaching the surface 

 of the water when a fresh supply of oxygen is needed. The 

 stems must frequently be too short. The problem is then 

 familiar to the snail and should be eas3^ To make the problem 

 still easier it was decided to determine whether or not the snail 

 cotild form a simple association between two stimuh upon a 

 labyrinth that it had failed to solve. The labyrinth was changed 

 as follows: 1. A Y-shaped labyrinth was ttsed so that the 

 snail could make a choice immediately upon reaching the top 

 of the stem of the Y. The Y was made of glass tubing. 2. The 

 snail was not confined to one side of it. Owing to the spiral 

 course followed by the ascending animal, there was no right and 

 left choice. vS. One side of the Y was made rough and the other 

 left smooth. The training series had shown that the snail feels 

 the delicate pressure on the foot of the three-pronged pressure 

 fork of the food-pressure apparatus (fig. 1, Plate I). It should 



