WATER VASCULAR SYSTEM OF ECHINUS 65 



Hartog concludes, " the above experiments show clearly 

 that the perforations of the madreporite in Echinus and 

 Asterias, and of the disc in Comatula, are purely excretory, 

 and serve to eliminate the excess of water taken up by the 

 body." These experiments and the view they seem to support 

 met with much criticism. 



Cuenot* claimed that ciliary action on the madreporite 

 would give Hartog's results, without any outward current. 

 He considered " qu'il n'y avait ni courant d'entree, ni courant 

 de sorti ; tout ce que Pou peut admettre, a la regueur, c'est 

 qu'il se produit une diffusion lente au contact des pores madre- 

 poriques entre le liquide des cavites environnantes et l'eau de 

 mer ballotee en tors sens par les cils." He did not support 

 this view by experiment. Laterf, he suggested that the cilia 

 lining the stone canal keep up the pressure in the water vascular 

 system by constantly tending to produce an inward current. 



LudwigJ brought forward experimental evidence to prove 

 that there is an inward current through the madreporic pores. 

 He examined different adult Echinoderms, also Auricularia 

 larvae, in perivisceral fluid, with or without particles added, 

 and reported a distinct inward current through the madreporite 

 and down the stone canal. 



MacBride§ also claims that the current is inwards. After 

 keeping Amphiura squamala living for several days in sea water 

 with carmine or lamp black in suspension, he found, on cutting 

 sections, that some particles were present in the pore canals. 



In 1913, Mr. Burfield and myself, working at the Port Erin 

 Biological Station, repeated some of Hartog's experiments and 

 added others, as follows : — 



Experiment 1. The madreporite, with the stone canal 



* Cuenot, L. Leipzig, Zool. Anz., Vol. XIII, pp. 315-318 (1890). 



t Cuenot, L. Bruxellbs, Arch. Biol., Vol. II, pp. 313-680 (1891). 



\ Ludwig, H. Leipzig, Zool. Anz., Vol. XIII, pp. 377-379 (1890). 



§ MacBride, E. W. London, Quart. Journ. Micros. Sci., Vol. XXXVIII, 

 pp. 339-411 (1896). 



