Modification by Experience 213 



satiety. The objection to the hunger hypothesis is that 

 other tentacles of the same animal will react after one 

 tentacle has stopped; satiety ought surely to affect the 

 entire organism (207). Allabach, in the light of these 

 researches, made a careful study of Metridium. She dis- 

 poses of the psychic learning by experience theory of Nagel 

 by saying that the only experience upon which the animal 

 could reject the filter paper must be experience that it is not 

 good for food. This could be learned only by swallowing it ; 

 but the failure of the reaction occurs just as well when the 

 animal is prevented from swallowing the filter paper. That 

 the phenomenon is not one of adaptation to weak stimuli 

 is shown by the fact that it may be brought about by succes- 

 sive feedings with meat which is not allowed to be swallowed. 

 It cannot be due to loss of hunger, for this is experimentally 

 shown to affect all the tentacles at once. Allabach concludes 

 that it is simply a case of local fatigue of the tentacles. The 

 taking of food by a tentacle involves the production of a con- 

 siderable quantity of mucus, the immediate supply of which 

 is probably exhausted after a few reactions, and a short period 

 of rest is required (3). 



This explanation seems, however, not precisely adapted to 

 the most recently published experimental results bearing upon 

 the point ; those of Fleure and Walton. They tested Actinia 

 with a scrap of filter paper once every twenty-four hours, 

 placing it on the same tentacles, which usually carried it to 

 the mouth, where it was swallowed and later ejected. After 

 from two to five days the mouth would no longer swallow the 

 fragment, and in two more days the tentacles refused to take 

 hold of it. Other tentacles could be "deceived" at least 

 once or twice after this, but very soon manifested the inhibi- 

 tion, indicating that a nervous connection and not merely 

 local fatigue was involved. All traces of the "learning" 



