180 ZOOLOGY. 
a nervous cord to the eye at.the end of the ray. It may be 
discovered by pressing apart the ambulacral feet along the 
median line of each arm. Fine nerves are sent off to each 
sucker, passing through the opening between the calcareous 
plates and extending to cach ampulla, thus controlling the 
movements of the ambulacral feet. 
Fig. 125.—Longitudinal section through the body and one arm of Astertas wulgaris. 
m, mouth; ¢, stomach; Z, lobe of stomach extending into the amy @, anus ; 27, ner- 
vous ring ; n, radial nerve; v7, water-vascular ring, sending a radial vessel (v) into the 
arm; mp, madreporic plate ;¢, stone canal; , hemal canal ; 0, oviduct ; 0, ovary ; 
am, ampulle, the ambulacral feet projecting below; 8, cceca or liver.—Drawn by 
A. F. Gray, under author's direction. 
The mouth (Fig. 125, m) is capacious, opening by a short 
esophagus into a capacious stomach (Fig. 125, s) with thin 
distensible walls, and sending a long lobe or sac (Fig. 125, 7) 
into the base of each arm; each sac is bound down by two 
retractor muscles attached to the median ridge lying be- 
tween the two rows of water-sacs (ampulle, see also Fig. 126). 
Fig. 126,—Diagram of the water-system of a star-fish. a, madreporic body; }. 
stone-canal; c, cireumoral water-tube; d, water-tubes to the arms; e, ampulles 
f, feet or suckers.—After Brooks. 
The stomach ends in an intestine. The intestine suddenly 
contracts and ends in a minute rectum situated in an angle 
between two of five fleshy ridges radiating from the centre. 
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