336 



ECIIINODEUMA. 



The oi-gaiis lie in jiart in the ccelom, in jiart in the ambulacral 

 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 interradium of a starfish forig.). B, 

 branchi£e ; C, cardiac pouch of stomacla; J?, eye spot; (r, gonad; H, 'liver': J/, 

 mouth; N, radial nerve; P, pyloric part of stomach ; BL\ ring canal: RB, radial 

 canal of water-vascular system ; 6', 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 piairs of hepatic glands Mng 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 niadre- 

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

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

 ambulacral groove between the ambulacra. The nerve ends at the 



FiQ. 31,5.— Longitudinal section of eye of Asterias. (Orig.l 



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

 pigment which experiment shows is sensitive to light. A second 

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

 ambulacral system corresponds with the foregoing description 



