BIOLOGY OF PHYSA 111 



habitats are in a similar physiological state and react alike to 

 objects of a similar character, stationary or moving, and that 

 the more varied the experience a snail has, the more readily it 

 adjusts itself to new experiences. 



III. Reaction of Physa to a new experience. 



A snail that was accustomed to being handled was taken from 

 its aquarium and, after being compelled to empty its lung, by 

 pressing upon its foot with a pencil, was dropped back into the 

 same aquarium. It lay upon the bottom for a moment and 

 then began to crawl about until it reached the sides of the aqua- 

 rium. No sooner had its head and tentacles touched the sides 

 of the vessel than it began to crawl up to the surface of the 

 water with as much apparent purpose and directness as though 

 it were traveling a famiHar path. Repetition of this experiment 

 always brought about like results, unless repeated until the snail 

 was exliausted . Physa from the pond north of the campus were 

 lifted from the water and placed directly in a glass jar, pre- 

 viously filled with water from the pond to the depth in which 

 the snails were living up to the time of the experiment. They 

 were handled as little and gently as possible; nevertheless they 

 quickly expelled the air from their lungs and retreated into their 

 shells, — the usual reaction of Physa resulting from an experience 

 to which they are unaccustomed. In a short time they crawled 

 about on or near the bottom of the jar for a relatively long 

 time. Some of the snails ascended the sides in an aimless way 

 and were liable to turn and go back even though they were within 

 a few mm. of"the film. They reacted like the higher animals that 

 are lost or suddenly deprived of their sense of sight, and appeared 

 from their aimless wanderings to be no longer sensitive to gravity. 

 They reached the film finally, apparently by chance and required 

 from five minutes to an hour or more. This was in sharp contrast 

 to the apparently direct, purposeful reaction of the tame snail. 

 After the snails had once found the film, they seemed to recover 

 their sensitiveness to gravity and seemed to experience no further 

 difhculty in orienting themselves in their new habitat if left undis- 

 turbed. 



IV. Adjustment of Physa to a new experience. 



During the time that the snails were wandering about in the 

 jar in the aimless fashion just described, they were seen to 



