484 



COM PARA TIVE ANA TOM Y 



CHAP. 



In the Ecliinasteridce and Asterinidce, the common tube swells into 

 a large sac. 



At the point where the stomachal sac narrows to form the short 



FIG. 385. Alimentary canal and genital organs of an Asteroid, diagrammatic. 1, Braclual 

 diverticula of tin.- stomach ; -, gonails ; IS, base of the gonacl, wliicli corresponils with its api-rtun- ; 

 4, stomachal sac ; 5, anus ; 6, rectal diverticula ; 7, apical circular sinus and trunk ; S, one of the 

 ten radial sinuses and trunks nmiiini; from this latter to the gonads; 9, stone canal in the axial 

 sinus; 10, madreporite. 



rectum, i.e. high up in the apex of the disc, it is once more provided 

 with diverticula. These rectal diverticula, whose number, arrange- 



