RHYTHMIC PULSATION 313 



before evisceration. The general tonal depression of the animal 

 involved some decrease in pulsation amplitude. 



The stimulus to spouting, then, does not necessarily originate 

 from a state of tension in the full respiratory trees. 



b) Effects of a7n'putation. The cloacal end of Stichopus when 



amputated at the level a a (fig. 1) contracted firmly. But 



if it was then put into sea water, or into one of a variety of salt 

 solutions subsequently to be described, it very shortly opened up 

 and continued to pulsate rhythmically, though with a gradually 

 decreasing frequency and amplitude, for as much as thirty 

 hours. The duration of pulsation depended upon the size of the 

 excised piece, the volume and composition of the surrounding 

 solution, and the existing temperature. 



About one minute after excision the cut edges of the body wall 

 began to bend inward (fig. 12 B). The cut edge of the cloaca 

 itself was flared outward, while its lumen was closed by the con- 

 traction of a powerful circular muscle about midway between 

 respiratory trees and anus. The radiating muscle-strands near 

 the plane of the cut were relaxed, but they contracted when 

 pinched. The flared anterior end of the cloaca was then pulled 

 toward the anus, while the cut edge of the body wall was bend- 

 ing inward. These processes, tending to close the remnant of 

 the coelom, had a highly protective appearance. Some three to 

 four hours after the inbending of the edge of the cut, the body 

 wall in this region became flabby and relaxed, and a progressive 

 degeneration, which involved swelling and mucoid disintegration, 

 began at the cut edge. After about five to six hours the inter- 

 radii became sunken inward, so that a cross section of the pul- 

 sating piece had the appearance shown in figure 13; in addition, 

 the previously inturned edges of the body wall were now relaxed. 

 At this time, that is after about six hours' isolation in sea water, 

 the excised cloacae looked like the one sketched in figure 14. 



Tlie history of individual preparations, made in the way de- 

 scribed in the preceding paragraph, was followed under various 

 conditions until they ceased to live. I shall refer here merely to 

 the performance and fate of cloacal pieces contained in one liter 

 of sea water. The time required for the execution of 10 rhythmic 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY. VOL. 20, NO. 3 



