. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. called on account of tlie calcareous deposits in its walls, either hangs within the body cavity, whence it talces up fluid through the pores in its walls {Ilolothu- 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 Cidarid
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. called on account of tlie calcareous deposits in its walls, either hangs within the body cavity, whence it talces up fluid through the pores in its walls {Ilolothu- 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 O^yhidiaster and Echi- naster echinites, possess several stone canals and madrepoi"ic 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 pro- vided with a sucking disc at their free extremity. Con- tractile ampullae are placed at the point of junction of the Lube feet Avith the side branch of the radial vessel; they force the 18 Fig. 215. — Diagramatic representation oC the water-vascular s:^ stem of a Star-fish. Re, Circular vessel ; Ap, ampullae or Polian vesicles ; Stc, stone canal; A', raartreporic plate ; P, ambulacral feet connected with the side twigs of the radial canals; Ap\ the ampullae of the Fig. 21G.—Diagrammatic eection through one of the arms of Anteracanfhion (after \V. Lange). ^'j Nervous system; P, ambulacral feet ; J, calcareous portions of integument; T, dermal Please note that these images are extra
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
