. A textbook in general zoology. Zoology. 92 STARFISH, SEA URCHIN, BRITTLE STARS and wrapped around the victim, which is then dissolved and digested, after which the stomach is withdrawn into the body. The water vascular system. — The madreporite, of which we have already spoken, is the cover to a short canal, the stone canal, that runs downward and opens into a ringlike canal that encircles the mouth. Five long canals, one for each arm, radiate from the ring canal about the mouth. Each of these long radiating canals is provided with many short side branches to which are at- tached the tube fe
. A textbook in general zoology. Zoology. 92 STARFISH, SEA URCHIN, BRITTLE STARS and wrapped around the victim, which is then dissolved and digested, after which the stomach is withdrawn into the body. The water vascular system. — The madreporite, of which we have already spoken, is the cover to a short canal, the stone canal, that runs downward and opens into a ringlike canal that encircles the mouth. Five long canals, one for each arm, radiate from the ring canal about the mouth. Each of these long radiating canals is provided with many short side branches to which are at- tached the tube feet (Fig. 45). Each tube foot is connected, by a slender tube that passes through a minute pore between the ossicles, with a water bulb in the body cavity. The bulb and the tube foot are both contractile. This whole system of tubes is called the water vascular system (Fig. 45). The tubes are filled with a watery fluid composed largely of sea water that flows in through the madreporite. Locomotion of the starfish. —When the starfish desires to move, it compresses the water bulb connected with each tube foot and forces the water out into the latter organ. This greatly elongates each tube foot which is then directed forward in the direction the animal wishes to go. After. Fig. 45.—-Diagram of the water vascular sys- tem of a starfish : S, stone canal; C, circular canal; R, radial canal; T, tube feet; A, am- pullae. After Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Herrick, Glenn W. (Glenn Washington), 1870-1965. New York, Cincinnati [etc. ] American Book Company
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