AX ANALYSIS OF THE LEARNING PROCESS IN THE SNAIL 7 



TABLE I — {Continued) 



Total time of observation • 32 . 75 hrs. 



Total number of reactions 38 



Total number of reactions, no visible cause 17 (44 . 73%) 



Total number of reactions, mucous stimulation 21 (55 . 26%) 



Average number of reactions per hour 1 . 16 



Average number of reactions, no visible cause, per hour 0.51 



This table shows that when six snails were kept under obser- 

 vation for nearly thirty-three hours (about five and a half hours 

 each) in filtered tap water onty 38 mouth reactions were observed, 

 an average of 1.16 per hour. If we allow for each reaction 1.25 

 seconds (Table 11, p. 8) the duration of the i'& reactions is 47.50 

 seconds. Of the 38 reactions 21 or 55.26% were observed to be 

 due to mucous stimulation and the remainder were probably 

 due to the same cause. Owing to the fact that the mucus is 

 colorless, and as it occurs on the surface of the water, trans- 

 parent, it is exceedingly difficult to determine its presence at 

 all times. Any attempt to bring it into view by the addition of 

 pigment such as powdered carmine would only serve to make 

 it more eft"ective as a stimulus. The reactions which did occtir 

 can then be accoiuited for. The mouth reactions of Physa may 

 then be regarded as a true reflex, an " luilearned response " 

 (Watson, 1914), which occtirs normally as the result of external 

 stimulation of the mouth or the region immediately surrounding 

 it. For experimental purposes we may say that the reaction 

 occurs only as the result of external stimulation. If now, the 

 snail were placed in water freed from microscopic particles by 

 filtration and the mouth reactions were practically alwa^^s in- 

 duced by bringing food directly into contact with the mouth, 

 the reactions must be regarded as reflexes, that is, involuntary. 

 Such a series of reactions then might be interpreted as an " un- 

 conditioned reflex " (Pawlow, 1904). The ntimber of reactions 

 and the duration of the series should then prove an available 

 substitute for the measurements of saliva in inquiries into the 

 behavior of a group of animals widely separated from mammals. 



B. Number and duration of reactions in the normal jood- 

 stimulus response. — The snails that were used in all of the re- 

 maining tests had been fed upon lettuce while in the laboratory; 

 for this reason lettuce was used as a food stimulus in all the 

 experiments. A small piece taken from a fresh leaf was applied 

 to the normally inactive mouth of the snail by means of forceps 



