WATER VASCULAR SYSTEM OF ECHTNUS 69 



many specimens of Echinus were kept in fresh sea water 

 coloured with methyl blue*. The animals were opened at 

 intervals of one to five days, and every specimen showed colour 

 in the axial sinus ; many had the axial organ stained very 

 deeply, two had a doubtful suggestion of colour in the stone 

 canal directly under the madreporite, but not a single specimen 

 showed any colour at all in the stone canal beyond this point. 

 On another occasion an Echinus was kept in methyl blue and 

 sea water for two days, then opened. The stone canal and 

 polian vesicles were bright blue ; there was no colour at all 

 present in the axial organ. 



These experiments seem to prove that there is no con- 

 tinuous current in either direction in the madreporic system. 

 That fluid passes in through the madreporite seems certain, 

 but apparently it passes sometimes into the axial sinus, some- 

 times into the stone canal. GemmeDf found, by cutting thin 

 sections of fresh madreporites, that " the cilia on the surface 

 of the madreporite act tangentially, and tend to sweep away 

 any foreign particles. No pore- canal system as a whole has 

 its cilia acting oralwards, but in each pore-canal there is a 

 short superficial segment which shows the converse condition." 

 Our observations agree with this report exactly, but do not 

 throw very much light on the apparently erratic action of the 

 whole system as shown in Experiment 6 above. From work 

 on Asterias and Solaster, Gemmell found that the ciliation of 

 the axial sinus is in an aboral direction. Whether this is 

 true or not for Echinus also has not been ascertained to my 

 knowledge. But be that as it may, the ciliation of the madre- 

 poric system clearly does not account for our observed facts. 

 Probably, as Cuenot,MacBride and Gemmell have suggested, the 



* Methyline blue is useless for this experiment owing to the fact that living 

 tissue reduces it to a colourless leucobase. 



t Dr. J. F. Gemmell. London, Phil. Trans. Roy. Soc, Series B., Vol. CCV, 

 pp. 213-294 (1914). 



