. Elementary text-book of zoology. Zoology. WATER-VASCULAR SYSTEM. 273 called on account of the calcareous deposits in its walls, either hangs within the body cavity, whence it takes up fluid through the pores in its walls (Hoh>iln<- rians), or ends in a porous calca- reous plate, the madreporic plate, which is inserted in the external covering of the body, and through the pores of which the sea water percolates into the lumen of the canal system. The position of the madreporic plate varies con- siderably. In the Clypeastridea it is at the apical pole; in the Cidaridea and Spatangidea it
. Elementary text-book of zoology. Zoology. WATER-VASCULAR SYSTEM. 273 called on account of the calcareous deposits in its walls, either hangs within the body cavity, whence it takes up fluid through the pores in its walls (Hoh>iln<- rians), or ends in a porous calca- reous plate, the madreporic plate, which is inserted in the external covering of the body, and through the pores of which the sea water percolates into the lumen of the canal system. The position of the madreporic plate varies con- siderably. In the Clypeastridea it is at the apical pole; in the Cidaridea and Spatangidea it is interradial, and falls in the an- terior right interradius near the apex ; in the Asteridea it is also interradial and dorsal ; in the Eurycdidce and the Ophiuridce it lies on one of the five buccal plates. Some Echinoderms, , species of Ophidiaster and Eclii- naster echinites, possess several stone canals and madreporic plates. On the lateral branches of the five or more radial trunks are found the appendages known as the ambulacral feet (fig. 216). These are extensible tubes or sacs, which pass through pores and openings in the dermal skeleton and project on the surface of the body. They are capable of being swollen out, and are frequently r. 210.—Diagrammatic section through one of the arms of Asteracanthion (after W. Lange). JV, Nervous system ; P, ambulacralfeet; A, calcareous portions of integument; T, dermal. FIG. 215. — Diagramatic representation of the water-vascular system of a Star-fish. He, Circular vessel; Ap, ampulla3 or Polian vesicles ; Stc, stone canal; M, madreporic plate ; P, ambulacral feet connected with the side twigs of the radial canals; Aj>', the ampulla; of the 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 Claus, Carl, 1835-1899; Sedgwick, Adam, 1854-1913; Si
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
