316 W. J. CEOZIER 



not reversible experimentally, though sphincters which had ceased 

 to beat rhythmically in sea water would pulsate once in response 

 to a touch or to the local application from a pipette of a small 

 volume of a stimulating solution, and they could momentarily 

 be revived by immersion in sea water free of Ca; possibly the 

 mechanical stimulation involved in the last experiment was 

 responsible for part of the pulsation. 



A very significant fact about the pulsation exhibited by the 

 isolated cloacal ends, is that the rhythm was not interrupted at 

 intervals corresponding to the expulsion of the cloacal stream 

 in the intact Stichopus, but was indeed perfectly continuous, 

 unless complete contraction was induced by some especially 

 applied stimulus. This condition is intelligible in view of the 

 fact above noted that in the normal animal the edge of the 

 sphincter was observed to pulsate with faint amplitude during 

 spouting. It follows that the stimulus to spouting has its origin 

 outside the cloaca. 



The early parts of the exhaustion curves show a peculiarity 

 which must be noted. Immediately after amputation and im- 

 mersion in sea water, the contracted musculature of the cloaca 

 began to relax, and by two minutes, at most, had begun to open. 

 Very commonly it then remained wide open for some seconds, 

 and when pulsation was resumed the rate of sphincter movement 

 was very slow and closure incomplete. The rate of movement 

 was soon improved, however, coincident with the institution of 

 contractions and relaxations of the cloaca, which were of maximal 

 amplitude. It would seem that the coordination of the members 

 of the pulsating complex is disturbed by cutting this complex 

 away from the rest of the animal, and that some little time must 

 elapse before harmonious interaction can again be established. 

 The full amplitude of the pulsation was usually revived very 

 suddenly. 



Rhythmic pulsation in the isolated posterior ends was similar 

 in all essential respects to that in the intact animal. The time 

 relations of the several phases of movement are given in table 

 3, which may be compared with table 2, showing the normal 

 condition in the intact Stichopus. In the isolated pieces it could 



