112 JEAN DAWSON 



project their siphons into long tentacle-Hke feelers and to tap 

 with them upon the bottom and sides much as a blind man taps 

 with his cane. This use of the siphon was not seen unless the 

 snail was in a disturbed condition as will be again shown in 

 later experiments. This tapping ceased as the snails reached 

 the film and was not resumed unless they were again disturbed. 

 If the snails, after .they had once filled their lungs at the 

 surface, were again picked out of the \\'ater and dropped back as 

 before, the process of reaching the film and the amount of tapping 

 with the siphons was much as it was in the first instance with, 

 perhaps, an appreciable diminution of time and in the amount of 

 tapping. This procedure was repeated eight or ten times within 

 an hour and a half, i.e., the snails, shortly after they had taken air, 

 were picked up and dropped back into the water. Each time they 

 came up to the surface, there was less aimless wandering and 

 siphon-tapping until, at the end of this time, they came up to the 

 film without hesitation and without groping about with the siphon. 

 The snails appeared to have " learned " the %^"ay, and behaved 

 in all respects as did the tame snails that were dropped back 

 into a familiar habitat. The shock that attended the experience 

 the first time gradually disappeared as it was repeated, and the 

 snails adjusted themselves to their new environment. These 

 experiments were repeated many times with snails fresh from 

 the ponil and always with the same result. It is also worthy 

 of note that the length of time that the snails were held in the 

 fingers and the roughness with which they were lifted from 

 their habitat increased the time that they wandered aimlessly 

 about tapping with their siphons. For example, Physa that 

 chanced to be upon stems of water plants could occasionally 

 be placed in a jar without taking them in the hand by trailing 

 the stem through the water so as to imitate wave motion. These 

 snails, while they usually expelled the air from their lungs, 

 got less of a shock than those that were handled, and came to 

 the surface much more directly and in much less time. Physa 

 that were living in a pond with shallow, sloping shores were 

 picked up and dropped back into the water again. They wan- 

 dered about in any direction for some time, but they invariably 

 at last turned toward the shore into the shallower water. Like 

 the snails from the pond that were placed in the jar, they appeared 

 to lose their sensitiveness to gravity and to reach the shore by 



