. A textbook in general zoology. Zoology. SPONGES 39 which these canals open outward, passes through fine open- ings in the walls of the former directly into the radial canals, from which it escapes into the cloaca and thence outward through the osculum. Body walls. —The body walls of Grantia are much thicker than those of the simple sponge, and the pores are longer. There are three layers of tissue similar to those of the simple sponge, already described. The inner layer, lining the radial canals, has its cells peculiarly modified in structure, and they are known as collar cells. Moreover, ea
. A textbook in general zoology. Zoology. SPONGES 39 which these canals open outward, passes through fine open- ings in the walls of the former directly into the radial canals, from which it escapes into the cloaca and thence outward through the osculum. Body walls. —The body walls of Grantia are much thicker than those of the simple sponge, and the pores are longer. There are three layers of tissue similar to those of the simple sponge, already described. The inner layer, lining the radial canals, has its cells peculiarly modified in structure, and they are known as collar cells. Moreover, each collar cell possesses a long vibratile flagellum. All of these flagella are constantly waving with lashhke vibrations and thus maintain cur- rents of water through the canals. Skeleton. — Like the simple sponge, Grantia has its body supported by a mass of interlaced spicules, composed of lime carbonate (Fig. 14). Two kinds of spicules are always to be found, — tri- radiate and needle- shaped. The tri- radiate spicules are interlaced and inter- ^• woven in the middle layer of the body walls so that they Fig. spicules. form a skeleton or supporting framework. The needle- shaped spicules are found projecting through the outer layer of cells all over the body. Method of feeding. — This sponge feeds upon micro- scopic bits of plant and animal organisms, floating in 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 Herrick, Glenn W. (Glenn Washington), 1870-1965. New York, Cincinnati [etc. ] American Book Company
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