RHYTHMIC PULSATION 321 



pressure could be produced, the typical spouting movements also 

 occurred. Animals with the anterior end excised, however, 

 rapidly lost tone and, in the case of Stichopus, died within a day 

 or so. With Holothuria surinamensis, as appears also to be true 

 of Thy one (Scott, '14, p. 289), anal rhythm becomes slow and 

 weak soon after the amputation of the anterior end. This is 

 associated with a general loss of tone and a totally quiescent 

 condition, which is only removed upon the regeneration of a new 

 anterior end (Crozier '15 [?] ). The stimulus to 'spouting' is 

 therefore probably derived from a condition of general body 

 tension, resulting from the pumping of water into the interior 

 of the body when the muscular integument presents a volume 

 of definite size. The stimulus is not, necessarily at least, con- 

 ditioned by a state of tension in the respiratory trees alone, since 

 the eviscerated animals behaved in this respect as did the com- 

 plete ones. 



The muscles concerned in pulsation of the amputated cloacal 

 end have previously been enumerated. Experiments were carried 

 out to determine the significance of each of these. The results 

 may be briefly stated thus: 



Cutting out the cloaca, so that only the dermo-muscular tube 

 and sphincter remained, resulted in complete cessation of move- 

 ment. Scraping away the radiating muscles and connective- 

 tissue strands had the same effect. Cutting the radiating mus- 

 cles on only one side gave preparations which pulsated at normal 

 rates; but in these preparations the side of the cloaca and brim 

 on which the muscles were still intact closed and opened before 

 the other side, the rest of the cloaca lagging behind in such a way 

 as to give the impression of being "dragged along" with the 

 intact half. The anal brim when cut out by itself remained open 

 in sea water and did not pulsate, though it reacted, by a single 

 closure, to delicate mechanical stimulations and to small vol- 

 umes of various stimulating solutions. 



If preparations of this sort, i.e., isolated sphincters — pieces 

 deprived of the cloaca — or posterior ends in which all the radi- 

 ating muscles had been cut, were placed in solutions of unusual 

 Na/Ca content, they did exhibit rhythmic movement for some 



