. Zoology : for students and general readers . Zoology. 183 ZOOLOGY. The mouth is situated on a disk {lophophore, Fig. 137, B), bearing the tentacles, wliich are liollow i^rocesses of the body-walls, comnmnicating witli the body-cavity, tire blood flowing into them, there being aerated, while tliey are exter- nally ciliated. They serve both to catch food and for respir- ation as makeshift gills. Hyatt states that the tentacles are used not only to catch the prey, but for a multitude of other offices. They are each cajsable of in- dependent motion, and may be twisted or turned in any direction
. Zoology : for students and general readers . Zoology. 183 ZOOLOGY. The mouth is situated on a disk {lophophore, Fig. 137, B), bearing the tentacles, wliich are liollow i^rocesses of the body-walls, comnmnicating witli the body-cavity, tire blood flowing into them, there being aerated, while tliey are exter- nally ciliated. They serve both to catch food and for respir- ation as makeshift gills. Hyatt states that the tentacles are used not only to catch the prey, but for a multitude of other offices. They are each cajsable of in- dependent motion, and may be twisted or turned in any direction ; bending inwards, they take up and discard objectionable matter, or push down into the stomach and clear the ossophagus of food too small to be acted upon by the parietal muscles. They are also employed offensively in striking an intrusive neighbor, and their tactile power, sensitive to the slightest unusual vibration in the water, warns the polypide of the ap- proach of danger. The digestive canal hangs free in the body-cavity, only attached by the mouth and anus to the walls of the body. It consists of a pharynx, a large stomach, and an intestine which lies by the side of the pharynx, since the canal has a simple deep dorsal flexure, the vent being situated on the dorsal or cardiac side, near the mouth. Usually the stomach is tied by a sort of ligament {funiculus) to a point on the body-walls, near the mouth. The nervous system is rep- resented by a double ganglion form- ing a single mass situated between the mouth and vent; it is highly contractile and changeable in form. There is no heart nor any circulatory apparatus. The sexes are united in a single polypide, and form cellular masses growing ou. Fig. 127.—Organization of a Polyzoou. A, Palud-ieella Eh- renhergii. B, Plumatellafru- ticoaa. bi\ tentacular branchise of lophophore ; ffi, ossophagns ; y, stomach ; r, intestine ; a, anus ; i, cell ; x, posterior, x'^, anterior cord, at the insertion of which into the body th
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
