I: 



256 ' The Animal Mind 



emphasized. As Jennings suggests, if the sea-anemone 

 'that contracts at the first ray of light were to remain con- 

 tracted in steady illumination, it would lose all chance of 

 getting food under the new conditions (374). The negative 

 reactions ordinarily involve interruption of the food-taking 

 process, and it is important that they should not be 

 continued in response to stimulation that is relatively 

 permanent. Hargitt thinks that the loss of reaction to re- 

 peated shadows which he observed in marine worms may 

 be an adaptation to the varying illumination caused by 

 ripples at the surface of the water (285). 

 /a very important psychological question concerns the 

 ' permanence of the effects of adaptation. Sensory adap- 

 tation and lapse of attention to repeated or continuous 

 stimuH, as these phenomena are met in our own experience, 

 are not considered phenomena of learning at all. The 

 J former is purely temporary in its effects : the person who 

 \ has become so used to an odor that he cannot smell it shows 

 ^^o effects of this experience half an hour later. The effect 

 of fanaiharity on emotion and on attention is more lasting : 

 one's loss of attention to a clock ticking in one's room may 

 persist despite more or less prolonged absences from the 

 room, although a sufficiently long absence, during which 

 one encountered no ticking clocks, would cause the sound 

 to be noticed again. The loss of emotional response to a 

 /familiar stimulus may persist for some time. Emotional 

 I adaptation and lapse of attention to continued stimuli 

 limay fairly be termed learning in proportion as their effects 

 \are more than temporary. 



/ In many cases, the effects of adaptation on animal re- 



[ actions last over a considerable interval between the stimuli. 



\ This seems to be increasingly the case, the higher the animal. 



Thus Hydra, which is only a ccelenterate, if it is allowed to 



