336 



ECIIINODERMA. 



The organs lie in part in the coelom, in part in the ambulacra! 

 grooves. The alimentary tract is in the ccelom and extends 

 straight upward from the mouth to the aboral surface, where it 

 ends with an anus or is entirely closed (figs. 313, 314). By a 



FIG. 314. Section through ray and opposite interradius of a starfish (qrig.). B, 

 branchiae; (7, cardiac pouch of stomach; .E 1 , eye spot; G, gonad; //, 'liver'; M % 

 mouth; N, radial nerve; P, pyloric part of stomach; RC, ring canal; RD, -radial 

 canal of water-vascular system ; tf, stone canal. 



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. The cardiac division gives origin to five gastric pouches 

 which can be protruded from the mouth or retracted by appro- 

 priate muscles. The gonads are five pairs of racemose glands lying 

 in the basis of the arms and opening interradially between the 

 arms. Lastly, the stone canal, extending from the aboral madre- 

 porite to the ring canal, and the lymphoid gland lie in the coelom. 

 The radial nerve, canal, and blood-vessel lie in the roof of the 

 ambulacra! groove between the ambulacra. The nerve ends at the 



FIG. 315. Longitudinal section of eye of Asterias. (Orig.) 



tip of the arm in a compound eye spot colored with red or orange 

 pigment which experiment shows is sensitive to light. A second 

 nerve has been described lying in the ccelom of the arm. The 

 ambulacral system corresponds with the foregoing description 



