AN ANALYSIS OF THE LEARNING PROCESS IN THE SNAIL 3 



cholog^^ as a means to the intensive study of the mental Hfe of 

 a hmited number of mammals." (Yerkes and Morgulis, 1909.) 

 Theoretically, however, this method is applicable to any organism 

 that responds to a stimulation by a specific, measurable reflex 

 of muscles or glands. Such reflexes occur in many of the lower 

 forms. The mouth movement of Physa is an example. 



It was decided then to study; 



(1.) The character of the response following a single appli- 

 cation of a food stimulus to the mouth parts of the snail. Such 

 a response consists of one or more reactions. A single complete 

 movement — one reaction — may be compared to the secretion 

 of a drop of saliva in the Pawlow experiments. A determination 

 of the number of reactions per response was deemed comparable 

 to Pawlow's measurements of the salivary secretion induced by 

 food alone or resulting from an " unconditioned " stimulus. 



(2.) Following this the application of two stimuli together, 

 that is, food to the mouth parts and pressure at a fixed .distance 

 from the mouth, would, it was believed, correspond to Pawlow's 

 " conditioned " stimulus. The number of reactions constitut- 

 ing each response would correspond to his measurements of 

 saliva under such conditions. 



(3.) It was then planned to apply the associated or auxiliary 

 stimulus alone in the absence of food, in order to determine 

 from the presence or absence of reactions, whether or not an 

 association had been formed between the two stimuli. 



2. Material and Methods 



The snails* used in the experiments were collected in an 

 oxbow pond that had been completely cut oft' from a small 

 creek. Several hundred were brought into the laboratory and 

 placed in large glass aquaria containing water plants such as 

 Elodea and Spirog\Ta. An effort was made to have the environ- 

 ment in these aquaria as nearly like the natural habitat as pos- 

 sible. Besides the water plants upon which snails usually feed, 

 fresh lettuce was placed in the aquaria. The\^ ate this in com- 

 paratively large quantities, and seemed to prefer it to other plant 

 food. 



* The author is indebted to H. B. Baker and Harold Cummins for the identifica- 

 tion of the snails used in the experiments. 



