212 The Animal Mind 



have found that these cease or turn into negative responses 

 when the animal is satiated ; although Pieron indeed reports 

 that while the responses of Actinia equina and A. rubra to 

 mechanical stimulation cease on repetition of the stimulus, 

 those to food stimulation continue indefinitely (327). If the 

 change from food-taking to negative reaction has a conscious 

 accompaniment, this might naturally be thought of as a 

 change from pleasant to unpleasant affective tone. One 

 very interesting case of such a change in the feeding reaction 

 occurs in the sea-anemone. Nagel observed that if a ball of 

 filter paper soaked in fish juice were placed upon one of the 

 tentacles of Adamsia, it was seized as eagerly as a ball of fish 

 meat, but that when this deception had been several times 

 repeated, the ball was held for a shorter period each time, and 

 was finally rejected as soon as offered. Nagel is inclined to 

 think that this is learning by experience, and points out that 

 the psychic life of Adamsia must possess little unity, for the 

 "experience" of one tentacle does not lead other tentacles to 

 reject the paper balls at once (291). Parker finds similar 

 behavior in Metridium, and explains it by saying that the 

 filter paper offers but a weak food stimulus, and that " the suc- 

 cessive application of a very weak stimulus is accompanied by 

 ... a gradual decline in the effects, till finally the response 

 fails entirely" ; in other words, that we have adaptation to a 

 food stimulus (303). Jennings fed Aiptasia alternately with 

 pieces of crab meat and with filter paper soaked with meat 

 juice, the result being that the fifth piece of filter paper was 

 rejected but so was the crab meat thereafter. Jennings 

 came to the conclusion that the phenomenon is due simply 

 to loss of hunger on the animal's part, and that where Parker 

 found that the crab meat would be taken after the filter paper 

 was refused, it was because the latter was a weaker stimulus 

 and naturally was the first to call forth the effects of 



