72 ELIZABETH LOCKWOOD THOMPSON 



series a possible tendency to prefer the rough side. The punish- 

 ment had no apparent effect upon this tendency. It seemed as 

 though this might be due to the fact that owing to the con- 

 struction of the apparatus the punishment (shock) was delayed 

 too long after the warning stimulus (roughness) had been received, 



6. Experiments With Y-Shaped Labyrinth: Mechanical Stimulation 

 AS Warning Signal 



The results treated in Table XI and in the group of figures 

 (19-22, Plate VII) show no indication of learning. It is believed 

 that the large percentage of error might have been lowered in a 

 greater number of tests, but this would probably not account 

 for the type of curve obtained. It was then suggested by Dr. 

 John F. Shepard that while the snails were unable to solve the 

 labyrinth they might nevertheless be able to form a simple 

 association under the conditions of the labyrinth experiments. 

 They might show on the labyrinth a capacity equal to that 

 developed under tests with simultaneous stimuli. A series of 

 tests was therefore carried out, using the Y apparatus with the 

 electric shock punishment but modified as follows: 1. In place 

 of roughness on the shock side a mechanical warning stimulus 

 was used which could be observed to affect the snail. 2. The 

 wrong arm of the labyrinth was shortened so that the shock 

 followed immediately on the warning stimulus. The time rela- 

 tion of the two stimuli was similar to that in Yerkes' experi- 

 ments (1912), with earthworms and approached that of the method 

 of simultaneous stimuli. The Y apparatus just described was 

 used in a slightly modified form. All traces of the sand and 

 metal were removed. The long arm of the Y was shortened 

 to 3 cm. in order to bring the reward nearer the point of diver- 

 gence of the paths, while the short arm was reduced to 1.5 cm. 

 in length in order to bring the punishment nearer to the point 

 of the path which necessitated choice on the part of the snail. 

 The snail was placed at the base of the path in the usual way. 

 If at the top of the stem the short arm was chosen, as soon 

 as the turn was made the tentacles and head were stroked 

 with a hair. This was fastened to the end of a small stick so 

 that it could be handled by the operator. This tactile stimulus 

 was immediately followed by the usual electric shock. The fact 

 that the tentacles were withdrawn and that the animal recoiled 



