Sensory Discrimination: The Chemical Sense 73 



Fig. 7. — Metridium. 

 Parker. 



After 



contraction without the winding seizure of the object. 

 Touched by the same object "handed on" to it by a tentacle 

 nearer the mouth than itself, it seizes the paper and passes 

 it on to the tentacle beyond it. The cause of this differ- 

 ence in behavior seems to lie in the 

 processes that have been taking 

 place just previously. Nagel does 

 not hesitate to say that a psychic 

 process must be involved, but its 

 details are not easy to construct 



(S2l). 



Another sea-anemone, Aiptasia, 

 has but one ring of tentacles, and 

 like Tuhularia crocea, instead of 

 showing different responses to contact stimulation alone 

 and to contact plus food stimulation, it merely reacts with 

 greater emphasis to the latter. In both cases the tentacles 

 wind around the object, contract, and direct themselves 

 toward the mouth (521). Again the question arises whether 

 the possible accompanying sensations differ in quality or 

 only in intensity. One species of Aiptasia, A. annulata, 

 however, does react differently to filter paper soaked in crab 

 juice and to plain filter paper (374), showing that even 

 within a genus the capacity for stimulus discrimination 

 may differ. In like manner one sea-anemone, Actinia, 

 will take filter paper soaked in acetic acid, while another, 

 Teaha, rejects it (228). 



Metridium, a common sea-anemone of our coasts, has 

 its tentacles covered with cilia which have a continual 

 waving motion toward the tip of the tentacle (Fig. 7). 

 If particles of an inedible substance are dropped on a ten- 

 tacle, no definite reaction occurs, but the particles are 

 carried by the ordinary motion of the cilia out to the ten- 



