352 W. J. CROZIER 



Since it was not practicable to employ a perfusion method, 

 experiments dealing with the action of the Ch- in solutions which 

 permitted the continuance of pulsation for some time were not 

 attempted, as it was found that such solutions were modified 

 in the direction of neutraUty by contact with the tissue for about 

 half an hour. 



It may be of interest to note that, although the function of 

 cloacal pumping is in part respiratory, no increase in pulsation 

 rate was induced by an increase in 0^. ; cloacal rhythm in Sticho- 

 pus thus resembles the (partly) respiratory movements of the 

 arms of barnacles (Roaf, '12). 



IX. SUMMARY 



The rhythmic pulsation of the cloacal chamber and anal 

 sphincter of Stichopus moebii is dependent upon the continuous 

 generation of stimuli within the cloaca, and particularly at its 

 anterior end. The mechanism whereby the radiating muscles 

 of the cloaca, the circular muscles of the cloaca and anal sphinc- 

 ter, the anal dilators, and the muscles of the body wall are brought 

 to act in orderly sequence in the pumping of water into the 

 respiratory trees is likewise locally contained. The aboral ends 

 of Stichopus moebii, Holothuria surinamensis, H. captiva, and 

 Cucumaria punctata continue to pulsate for many hours after 

 they have been amputated at the level of origin of the respiratory 

 trees. In such amputated parts a complete pulsation movement 

 begins with the opening of the anterior end of the cloaca ; a wave 

 of opening runs aborally along the cloaca ; the anal sphincter then 

 opens and afterward closes; a progressive constriction of the 

 cloacal chamber begins at the closed anal sphincter and runs 

 forward; at the termination of the pulsation the whole cloaca 

 is closed. 2'' 



Normally the pulsation of the cloaca is interrupted by two 

 means: (1) by complete constriction of the anal sphincter, in 

 response to sensory stimulation and during locomotion, and (2) 

 by holding the cloaca and anal sphincter open, during 'spouting.' 



-*' Doubtless the nervous arrangements for the production of this kind of 

 sequence in movements is similar to that involved in the use of the lantern in 

 the locomotion of Echinus (Gemmill, '12). 



