BIOEOGY OF PHYSA 115 



they had been dropped back into the new aquarium three or 

 four times, they ceased to tap as they came to the surface, 



Physa accustomed to living in a cyHndrical vessel, were trans- 

 ferred to a globe aquarium having water of the same depth 

 and temperature. They immediately came up the side but 

 soon after crawling on the curved surface, began to tap with 

 their siphons. After they had been dropped back and made 

 to crawl up to the surface five or six times, they ceased to tap 

 with the siphon and gave no further indication that they sensed 

 a change in the sides of their aquarium. 



Physa that were accustomed to live in a beaker were trans- 

 ferred to a bottle of the same size, with the same temperature 

 and depth of water. The bottle, near the top, had shoulders 

 which curved toward the neck. The snails came up the sides 

 without tapping until they reached the rounded surface and then 

 they felt about with their siphons. After they had been dropped 

 back into the bottle five or six times they ceased to tap as they 

 crawled over the shoulder of the bottle. 



Tamed snails that had been living for weeks in water an 

 inch deep in a cylindrical aquarium dish were made to expel the 

 air from their lungs and were dropped back into the dish after 

 it had been filled with water of the same temperature. They 

 came up the sides of the dish without tapping until they had 

 passed by about one-half inch the level at which they were 

 accustomed to get air; then they began to tap with the siphons. 

 They repeated this behavior if dropped back three or four 

 times, but after that they came up to the surface without tapping 

 at all. Since the snail can not see objects and the surface of 

 the vessel was smooth, the snail could neither see nor feel " land 

 marks," but must have formed an associated memory of the 

 space over which it had passed from the time it left the bottom 

 to the time it reached the film. Hence, we may conclude that 

 the tapping in this case was due to association with the level 

 at which the snail was accustomed to get air. 



Physa that were tamed and had been kept in a bacteria 

 dish for some time were removed to another bacteria dish whose 

 sides were coated with vaseline and the water in which was of the 

 same depth and temperature. The snails began immediately 

 to crawl up the sides of the dish but upon encountering the 

 vaseline, they projected their siphons and felt about and even 



