56 SECRETS OF ANIMAL LIFE i 
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 Lockwood Thompson (Behaviour Mono- 
graphs, vol. iti, 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, 
Ivan 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 
