I. ASTEROIDEA 



297 



ambulacral plate abuts against a small interamhulacral plate, bearing 

 usually movaljle spines. Beyond these come the less constant a(/amte/ac- 

 ral or mar^t^inal plates, and then those of the aboral surface. Each ambu- 

 lacral area terminates at the tip of the arm with an unpaired ocular plate. 



Fig. 2S8, — Asleriscus verrucidatus, aboral surface removed (after Gegenbaur). g, 

 gonads; h, hepatic cseca; i, stomach with anus. 



The organs lie in part in the coelom, in part in the ambulacral grooves. 

 The alimentary tract is in the coelom and extends straight upward from 

 the mouth to the aboral surface, where it ends with an anus or is entirely 



Fig. 289. — Section through ray and opposite interradius of a starfish (orig.). B 

 branchi;c; C, cardiac pouch of stomach; E, eye spot; G, gonad; H, ' liver'; .1/, mouth; 

 N , radial nen.'e; P, pyloric part of stomach; RC, ring canal; RD, radial canal of water- 

 vascular system; S, stone canal. 



closed (figs. 28S, 289). By a constriction it is divided into a larger, lower 

 cardiac portion and a smaller, upper pyloric division. From the latter 

 arise five hepatic ducts which connect with five pairs of hepatic glands 

 lying in the arms, while small ca.'ca arise from the intestine in some 



