BTRnCTXTRB OF STAU-FISR 
each sac is bound down by two retractor muscles attached to the 
median ridge lying between the two rows of water-sacs (ampullae, see 
also Fig. 38). The stomach ends in a short intestine, the limits be- 
tween the two not distinctly seen. The intestine suddenly contracts 
and ends in a minute rectum situated in an angle between two of 
five fleshy ridges radiating from the centre of the disk. Appended 
to the intestine are the "coeca" or " liver" (Fig. 37, b), consisting of 
two long, tree-like masses formed of dense branches of from four to 
six pear-shaped follicles, connecting by a short duct with the main 
Fig. 38.— Diagram of the water-system of a star-fish, a, madreporic body; 6, 
stone-canal; c, circumoral water- tube; c2, radial water-tubes; e, ampullae; /, 
feet or ambulacra. After Brooks. 
stem. The two main ducts unite to form a short common opening 
into the intestine. The coeca are usually dark, livid green, and 
secrete a bitter digestive fluid, representing probably the bile of the 
higher animals. 
The ovaries (Fig. 37, o) are long racemose bodies lying along each 
side of the interior of the arms, and the eggs are said to pass out by 
short narrow oviduct (ov) through an opening between two plates on 
,each side of the base of the arms, the opening being small and diffi- 
cult to detect. 
The water-vascular system consists of the madreporic body, the 
" stone-canal " (Fig. 37, i), the ring or circumoral canal (vr), and the ra- 
