70 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



action of the cilia lining the stone canal serves to keep up the 

 pressure in the ambulacral system. If the pressure in this 

 system is high no fluid will be able to enter the stone canal 

 through the madreporite in spite of the action of its ciliary 

 lining. 



Cuenot has also suggested that fluid may enter the body 

 cavity through the permeable axial organ, and this view seems 

 to be supported by these experiments. There is no evidence 

 to prove that excess fluid does not also leave both ambulacral 

 system and body cavity through the madreporic system. 



Apparently the whole question is one of balance between 

 internal and external pressures. 



