56 SECRETS OF ANIMAL LIFE 



and a few instances of profiting by experience 

 (e.g. the effective behavior of water-snails dropped 

 into an aquarium in which they had previously 

 lived), there has hitherto been little basis for an 

 answer to the question: "Can a snail learn?" 

 But a satisfactory answer has now rewarded a series 

 of exceedingly careful experiments made by Miss 

 Elizabeth Lock wood Thompson (Behaviour Mono- 

 graphs, vol. Hi, No. 3, 1917, Cambridge, Mass.), 

 and it is encouraging to learn that the answer is in 

 the affirmative. Even a worm will turn; even a 

 snail will learn. Who shall set limits to education? 

 Miss Thompson studied the learning process in a 

 common water-snail, Physa gyrina by name, which 

 is wont to glide about in ponds, mouth and creeping 

 sole upwards, suspended to. the surface film. The 

 method of the research was a distinctly ingenious 

 modification of a well-known experiment associated 

 with the name of the famous Russian physiologist, 

 Mvan Petrovich Pavlov. A dog's mouth waters at 

 the sight or smell of food, and it is possible to 

 measure the quantity and quality of the secretion. 

 With the primary stimulus of food Pavlov associ- 

 ated some sound or color, and after a time the dog 

 mastered or registered the association so thoroughly 

 that the sound or color served of itself to evoke 

 the mouth-watering. The shadow, so to speak, 

 worked like the substance somewhat in the same 

 way as the sight of a menu-card may, within limits, 

 serve as an appetizer. Miss Thompson observed 

 that when the immediate neighborhood of the 



