484 



COM PARA TIVE ANA TOM Y 



In the Echiiiadeiida' and Asterinidw, the common tube swells into 

 a large sac. 



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



— - h 



Fio. 385.— Alimentary canal and genital organs of an Asteroid, diagvainmatic 1, Brachial 

 •liverticula of the stoinacli ; 2, gonads ; 3, base of tlie goiia<l, which corresponds with its aperture ; 

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

 ten radial sinuses and trunks running from tliis 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- 



