. Outlines of zoology. Zoology. WATER TASCULAR SYSTEM. 233 The stone canal leads into a water ring round about the mouth. From this circiimoral ring are given off nine glandular bodies (Tiedemann's bodies), and five radial tubes, one for each of the arms. Considerations of symmetry suggest that there should be ten glandular bodies, Ijut the stone canal has taken the place of one. In many starfishes there are five or ten little reservoirs (Polian vesicles) opening into the circumoral ring, but in Asterias rithens these are hardly distinguishable from the first ampulk^ of the radial vessels. Alo
. Outlines of zoology. Zoology. WATER TASCULAR SYSTEM. 233 The stone canal leads into a water ring round about the mouth. From this circiimoral ring are given off nine glandular bodies (Tiedemann's bodies), and five radial tubes, one for each of the arms. Considerations of symmetry suggest that there should be ten glandular bodies, Ijut the stone canal has taken the place of one. In many starfishes there are five or ten little reservoirs (Polian vesicles) opening into the circumoral ring, but in Asterias rithens these are hardly distinguishable from the first ampulk^ of the radial vessels. Along each arm, then, there runs a radial vessel. It lies in the ambulacral groove beneath the shelter of the rafter-like ossicles. From it branches are given off to the bases of the tube feet, but from each of these bases a canal ascends between each pair of ambulacral ossicles, and expands into an ampulla or reservoir on the dorsal or more internal side. The fluid in the system may pass from the radial vessels into the tube feet, and from the tube feet it can flow back, not into the radial Fig. 76.—Diagrammatic cross section of starfish arm. (After LunwiG.) «., radial nerve ; /'.7'., radial blood vessel according to Ludwig, sep- tum in blood vessel according to others; 7c'.7'., radial water vessel; a?n., ampulla; f/., tube foot; , a pyloric caecum cut across ; a calcareous spine ; ^., a slcin gill ; lac., spaces in the skin ; go., ova in ovary ; , ambulacral ossicle. but into the ampullce. There are muscles on the walls of the tube feet, ampuHa;, and vessels. At the end of each arm, there is a long unpaired tube foot, which seems to act as a tactile tentacle, and has also olfactory significance. To recapitulate, the madreporic plate leads into the stone canal, this passes into the ring round the mouth with its nine vesicles, from the ring radial vessels run along the arms, they give off branches to the tube feet, and the base of each tube foot communic
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
