RHYTHMIC PULSATION 



305 



"time for ten pulsations;" where less than 10 successive pulsa- 

 tions could be timed, the observation was repeated two or three 

 times; closely agreeing times were always obtained in successive 

 determinations. 



When the cycle of movements comprising a single pumping 

 operation had been carried out some 6 to 10 times in succession, 

 an interruption occurred, in the form of a wide opening of the 

 anus persisting for some seconds (table 2), during which the water 

 previously pumped in was forced out of the respiratory trees. 

 The ratio of the number 'of inspirations to an expiration varied 

 directly with the size of the animal.^ This expiration, or 'spout- 

 ing,' was accompanied by retraction of the tentacles, constriction 



TABLE 2 

 Stichopus moebii; occurrence of spouting in relation to the number of cloacal pulsa- 

 tions between each expulsion of water; / indicates an expulsion of water 



of the buccal sphincter, and a general body contraction. The 

 interesting point in this connection, however, is that when the 

 central edge of the anal sphincter was watched closely it was 

 seen that the sphincter continued to pulsate at a normal rate, 

 though with greatly reduced amplitude, in spite of the fact that 

 it was being held wide open by the body-wall muscles and the 

 strongly contracted radiating strands. The first inspiration suc- 

 ceeding a spouting act was usually of greater vigor than the 

 following ones. 



The pumping movements also ceased, the oral sphincter con- 

 tracting firmly, when the posterior end of the animal was stimu- 

 lated tactually, especially when the papillae were touched. 

 Stimuli of various kinds applied to the animal's surface resulted 

 in reactions which included the temporary constriction of the 



^ A similar observation was made by Hcrouard ('89, p. 689). 



