Modification by Experience 255 



tentacle has stopped ; satiety ought surely to affect the 

 entire organism (374). Allabach, in the light of these re- 

 searches, 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 adapta- 

 tion to weak stimuli is shown by the fact that it may be 

 brought about by successive 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 considerable 

 quantity of mucus, the immediate supply of which is prob- 

 ably exhausted after a few reactions, and a short period of 

 rest is required (3). Parker (551) is still of the opinion that 

 adaptation is the proper explanation for the phenomenon. 



Another case of the cessation of reaction to a repeated 

 stimulus is reported by Wasmann of ants in an artificial 

 nest, which assumed the fighting attitude in response to 

 the movement of a finger outside the nest, but after two or 

 three repetitions of the motion were no longer disturbed 

 (762). Where animals as high in the scale as the ant and 

 spider are concerned, it is possible that this process of 

 getting used to a stimulus may involve rather a dulling of 

 emotion than a disappearance of sensation. This phe- 

 nomenon also is familiar in our experience, and may be 

 called emotional adaptation. 



That adaptation is itself adaptive hardly needs to be 



