BEHAVIOR OF LOWER INVERTEBRATES 373 



on leaving the substrate on which they have been crawling, to 

 float up through the water, drawing behind them a thread of 

 mucus, on which, after the lung has been filled with air, they 

 descend. The spinning process in Physa is affected by the 

 food supply, by general activity, and by habitat. Its adaptive 

 aspect is not clearly made out. It cannot be related to need 

 of air, for if the snail's lung is not already full of air it will not 

 be light enough to ascend through the water, but must crawl 

 on a solid. In Section III food taking is discussed. Low tem- 

 perature decreases the snail's eagerness for food. Odorous foods 

 are more quickly found than odorless ones. The snail can sense 

 food at not over one centimeter away. "All parts of the head 

 and the first few mms. of the ventral surface of the foot were 

 found to be sensitive to food." Negative responses were ob- 

 tained to hydrochloric acid, onion juice, pieplant, and the juice 

 of a walnut husk. When mechanical and chemical stimulation 

 are combined the former is first effective ; a snail which in rapid 

 crawling comes in contact with food gives the negative response 

 first and then the feeding response. A well-fed snail has its 

 responses to the neighborhood of food decidedly weakened, while 

 a fasting snail will give the food reaction to mere mechanical 

 stimuli and even to chemical stimuli which ordinarily produce 

 a negative reaction. Part IV, on respiration, contains nothing 

 which calls for report here. The last section is entitled, "Some 

 Psychic Phenomena of Physa." A snail's reaction to stimula- 

 tion is much influenced by its previous experience, of being 

 handled, for example. A snail 'dropped into an aquarium where 

 it had been previously kept crawled at once to the surface as 

 though traversing a familiar path, while snails freshly taken 

 from the pond wandered about aimlessly on being dropped 

 into the same aquarium. On travelling several times to the 

 top of the water in an aquarium, the snails showed less aimless 

 wandering and exploratory tapping with the siphon. The fol- 

 lowing experiment indicates that Physa remembers the loca- 

 tion of the surface film. The vessel containing the snails was 

 covered with a glass plate resting directly on the water. The 

 snails came up for air and tapped their siphons on the glass, 

 behaving as they usually do at the surface film. Various other 

 evidences of the influence of past experience are noted. 



