44 ELIZABETH LOCKWOOD THOMPSON 



1. At no time during these experiments did the snail appear 

 to make any effort to obtain air except at the surface of the 

 water. Inasmuch as the depth of the water in the experimental 

 tank was greater than that in the home aquarium, the observa- 

 tions conflict with those of Dawson (1911) which refer, how- 

 ever, to young snails. 



2. The touching of the tentacles to the surface of the dish, 

 at intervals, on either side of the path of the snail appeared 

 in no case to alter the direction of the path. 



3. There appeared to be no effort on the part of the snail 

 under observation in these experiments, to re-distribute its weight 

 by shifting the shell from side to side. Such shifting of the 

 shell might exert a pull upon the body of the animal, strong 

 enough to turn it in one direction more than another. 



In the second scries of preference tests the U-shaped labyrinth 

 was used. Both of the upright arms reached the surface of the 

 water so that a choice of either did not result in punishment. 

 Six snails were used. They were divided into two groups of 

 three each and tested on alternate days. This division was 

 made because six snails could not be worked each day during 

 the time at the disposal of the operator, and it was deemed 

 advisable to have records from more then three snails. Each 

 snail in each group of three was given ten trials per day. Enough 

 fresh tap water at room temperature was placed in the experi- 

 mental tank to reach the top of the arms of the U apparatus 

 resting in the center of the dish. The snail was taken from the 

 bacteria dish, in which it was kept at room temperature, and 

 held in the hand while the body was gently pressed back into 

 the shell by means of a dull metal seeker. In this way the 

 snail was compelled to expel air from its lung. The animal, 

 now negatively geotropic, was placed on the base of the U, E 

 (fig. 14, Plate IV) by means of long forceps. The apex of the 

 shell rested on base E while the opening of the shell touched the 

 stem D. Thus when the snail came out of its shell, which it 

 usually did almost immediately, it at once started to crawl up 

 the stem D to the surface. At the top of D it turned either 

 to the right or left on the cross bar C and then moved up either 

 arm A or B to the surface of the water where it was permitted 

 to obtain air. It was then lifted off with the hand as gently 

 as possible and returned to its individual di.sh where it was 



