HABITS AND REACTIONS OF SAGARTIA DAVISI. 213 



size was swallowed in three minutes, and a half-cube of heavy 

 drawing paper, of about the same size, was also swallowed, 

 though more slowly. Tiny bits of glass were frequently swal- 

 lowed. 



I can say definitely that these objects were, not carried in by 

 the beat of the cilia covering the siphonoglyphs and producing 

 an insetting current, but by cilia covering the lips and oesophagus 

 between the siphonoglyphs and producing a current which ordi- 

 narily sets outward. It would seem, then, that chemically inert 

 substances, if small enough to be taken easily into the mouth 

 and thus brought into direct contact with the ciliated cells lining 

 the oesophagus, are ingested under some conditions. Other ex- 

 periments show that one of these conditions, probably the most 

 important, is the degree of hunger of the polyp. Starving polyps 

 were always more ready than well fed individuals to swallow 

 chemically inert substances. Some explanation of this fact may 

 be derived from the further fact that hungry polyps are in gen- 

 eral unusually sensitive to both chemical and mechanical stimuli. 

 Increased sensitiveness means increased effectiveness of a given 

 stimulus ; this is equivalent to saying that the stimulus is more 

 intense. 5". davisi, then, responds only to certain intensities of the 

 same stimulus, so far as the ciliated cells of the lips and oesoph- 

 agus are concerned. Under mechanical stimulation of a given 

 intensity, the cilia do not reverse their beat ; an increase in the 

 intensity or, if you will, effectiveness of the stimulation may 

 produce this reversal. To chemical stimuli, or to mechanical 

 which are above a certain degree of intensity (i. e., when the 

 stimuli polyp is starving), the response is usually positive ; 

 to a weakened mechanical stimulus there is less likelihood of 

 any response. 



The positive response to mechanical stimuli is undoubtedly 

 advantageous to the polyp. It is apparent that substances with 

 even a very small food value must be of some importance to a 

 starving polyp although they would not be desirable as food 

 for a well nourished animal. For the latter they would come 

 into the category of useless substances, which the ciliary cur- 

 rents on (Esophagus, lips and tentacles are admirably adapted 

 to remove. 



