STRUCTURE OF COMMON STAR-FISH. 181 
of the aboral disk. The anus (Fig. 125, 2) is minute and 
difficult to detect, being situated between the short spines, 
and is evidently not used in the expulsion of fecal matter 
unless the urinary secretions, if there be such, pass out of 
it. It would seem as if the opening were rudimentary and 
that the star-fish had descended from Echinoderms like the 
Crinoids, in which there is a well-marked external terminal 
opening of the digestive tract. Appended to the intestine 
are the ‘‘coca”’ or “‘liver” (Fig. 125, 6), 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 stem. The two main ducts unite to form a 
short common opening into the intestine. The cceca are 
usually dark, livid green, and secrete a bitter digestive 
fluid, representing probably the bile of the higher animals. 
The star-fish is bisexual, but the reproductive glands are 
much alike, the sexes only being distinguishable by a micro- 
scopic examination of the glands. The ovaries (Fig. 125, 0). 
are long racemose bodies lying along each side of the in- 
terior of the arms, and the eggs are said to pass out by a. 
short narrow oviduct (ov) through an opening between two- 
plates on each side of the base of the arms, the opening be- 
ing small and difficult to detect. 
The water-vascular system consists of the madreporie: 
body, the ‘‘ stone-canal ”’ (Fig. 125, 7), the ring or circumoral 
canal (vr), and the radial vessels (v) ending in the water- 
sacs (am) and ambulacral feet. The stone-canal begins 
at the outer and under side of the sieve-like madreporic 
body, passing directly forward and downward in a sinuous 
course to the under side of the circumoral plates. The 
madreporic body (md) is externally seen to be perforated by 
linear apertures radiating and subdividing toward the pe- 
riphery. The sea-water in part enters the body-cavity 
through the fissures in the madreporic body, while most of 
it enters the stone-canal, which is a slender tube scarcely 
one fourth the diameter of the entire madreporic body. 
The water entering the stone-canal (Fig. 125, 4) passes di- 
rectly into the water-vascular ring (Fig. 125) and then into. 
the ten Polian vesicles and the five radial canals, whence 
