Sensory Discrimination : the Chemical Sense 7 * 



latter. In both cases the tentacles wind around the object, 

 contract, and direct themselves toward the mouth (291). 

 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 

 (207), showing that even within a genus the capacity for stim- 

 ulus discrimination may differ. In like manner one sea- 

 anemone, Actinia, will take filter paper soaked in acetic acid, 

 while another, Tealia, rejects it (127). 



Metridium, a common sea-anem- 

 one of our coasts, has its tentacles 

 covered with cilia which have a con- 

 tinual waving motion toward the tip 

 of the tentacle (Fig. 7). If particles 

 of an inedible substance are dropped 

 on a tentacle, no definite reaction 

 occurs, but the particles are carried 

 by the ordinary motion of the cilia 

 out to the tentacle tip, where they drop off. When a bit of 

 crab meat, or some meat juice, is dropped on a tentacle, the 

 latter contracts and curls over with the tip directed toward 

 the mouth. The ciliary movement continuing in its usual 

 direction now of course carries the food toward the mouth. 

 Applying food to the lips on either side of the mouth causes 

 a different response. The cilia on these lips ordinarily wave 

 outwards; when food is brought in contact with them their 

 motion is reversed, and the food is thus passed into the 

 mouth. In Metridium, then, there is no specific rejecting 

 reaction for inedible substances (303). 



Various instances of the effect of physiological condition 

 upon response to food stimulation in sea-anemones have been 

 noted. Adamsia loses the power to discriminate between edi- 



FIG. 7. Metridium. After 

 Parker. 



