484 



COMPARATIVE ANATOMY 



CHAP. 



In the Echinasteridce 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, Brachial 

 diverticula of the stomach ; 2, gonads ; 3, base of the gonad, which corresponds with its aperture ; 

 4, stomachal sac ; 5, anus ; 6, rectal diverticnla ; 7, apical circular sinus and trunk ; 8, one of the 

 ten radial sinuses and trunks running 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 divertieula, whose number, arrange- 



