ECHINODERMATA — THE (JCELOMIC CAVITIES 



443 



In certain Clijpcadroida {Echinodiscus biforis, PeroncUa orhicularis) small inter- 

 radial, thin-walled, vesicular outgrowths of the lantern membrane, on the base of 

 the lantern itself, have been called Stewart's organs. Two of these occur in each 



Fig. 370.— Viscera of Asthenosoma (after F. and P. Sarasin). 1, Gonads ; -i, constrictiou in a 

 Stewart's organ ; 3, Stewart's organ ; 4, nmscle lainellie ; o, radial canal of tlie water vascular 

 system ; 6, tip of a Stewart's organ ; 7, forked radius of the Tnasticatory framework ; S and 

 !i, ujijier and lower coils of the intestine ; 10, Polian vesicle ; 11, intestine. 



intcn-adius, but are generally wanting in that interradins in which the intestine in 

 ascending lies upon the lantern. 



3. Ophiuroidea. — Two circular membranes, one above the other, 

 found round the cesophagus, and traversing the body caA'ity, connect 

 the cesophagus Avith the oral skeleton. They thus cut off two very 

 small perioesophageal sinuses from the general body cavity. 



