. Animal biology. Zoology; Biology. Rac//(f/ ccrncf/ chamber Incurrent \/y^ '^ Oscu/un? ?^ ^ Gcistral cav/'-f-y. A B C Fig. 51.—Diagrams of canal systems of sponges. ^4, ascon type. B, sycon type. C, rhagon type. (From Wieman, ''General Zoology," A and B after Minchin, and C modified from Parker and Haswell, by the courtesy of McGraw-Hill Book Company, Inc.) The gastral epithelium is shown by heavy black, the dermal epithelium by a light line. Arrows show water currents. forming cells are sderoblasts. The spicules may be straight rods with one axis, the monaxon type; or they may have thre
. Animal biology. Zoology; Biology. Rac//(f/ ccrncf/ chamber Incurrent \/y^ '^ Oscu/un? ?^ ^ Gcistral cav/'-f-y. A B C Fig. 51.—Diagrams of canal systems of sponges. ^4, ascon type. B, sycon type. C, rhagon type. (From Wieman, ''General Zoology," A and B after Minchin, and C modified from Parker and Haswell, by the courtesy of McGraw-Hill Book Company, Inc.) The gastral epithelium is shown by heavy black, the dermal epithelium by a light line. Arrows show water currents. forming cells are sderoblasts. The spicules may be straight rods with one axis, the monaxon type; or they may have three rays in one plane and be triradiate; or four rays lying in four planes, in which case they are known as tetraxon. They may have six rays, the ends of three axes, in which case they are triaxon; or they may have numerous rays and be polyaxon (Fig. 52). Many modifications of each type occur. 153. Histology.—There are in the bodies of sponges a number of different types of cells. In the outer, or so-called dermal layer, are flat epithelial cells, contractile cells, gland cells which secrete the material that attaches the animal to its support, and the cells which form the skeleton. In the middle layer are reproductive cells and wandering cells, the latter capable of ameboid movement. The cells of the gastral layer are flat epithelial cells or collar cells. These cells, however, do not work together to the same degree as do the cells in higher animals. The whole is really a great colony of semi-independent cells, and individuality is so little evident that zoologists have not agreed upon what constitutes an individual. H. V. Wilson has found it possible, by gently squeezing sponges through the meshes of fine silk cloth, to separate them into individual cells. These cells will then gather together in small groups. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illus
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