64 



NOTE ON SOME EXPERIMENTS ON THE 

 WATER VASCULAR SYSTEM OF ECHINUS. 



By Ruth C. Bamber, M.Sc. 



[Read December 10th, 1920.] 



In 1887, Professor Marcus Hartog* published a paper on 

 " The True Nature of the ' Madreporic System ' of Echino- 

 dermata, with Remarks on Nephridia," in which he put forward 

 the view that " we must needs regard the madreporic system 

 and the ' vasal ' part of the vasoperitoneal sac as constituting 

 a left nephridium, the right having failed to receive a duct." 

 Previous to this, the generally accepted view was that 

 water enters the water vascular system through the madre- 

 porite, and is probably lost gradually by passing out through 

 the walls of the tube feet, etc. 



Hartog supports his view by experiments which seem to 

 prove that there is an ouhvard current through the madreporite, 

 as would be expected if the water vascular system is an 

 excretorv organ. Fresh specimens of Echinus were opened and 

 the madreporic canals removed and slit longitudinally on one 

 side : they were then examined in the perivisceral fluid and he 

 reports a strong inrush of particles through the slit, and a 

 corresponding outward flow through the cut end towards the 

 madreporite. The madreporite of an Echinus and of several 

 starfishes, with part of the stone canals attached, were removed 

 and examined in sea water with powdered charcoal in suspen- 

 sion. No particles ever settled on the madreporites. Normal 

 and eviscerated specimens of Antedon were examined disc 

 upwards in sea water, with charcoal in suspension. No 

 particles were observed to settle on the discs except along the 

 imperforate ambulacral grooves. 



* London, Ann. Mag. Nat. Hist., 1887, pp. 321-326. 



