. The elementary nervous system. Nervous system; Nervous system -- Coelenterata. 110 THE ELEMENTARY NERVOUS SYSTEM sphincter muscle and the nerve-net are not coextensive. In Aurelia the sphincter forms a continuous circular band. In RTiizostoma, on the other hand, it is composed of a suc- cession of sixteen muscle fields, a pair between each pair of the eight marginal bodies (Fig. 33). These muscle fields are partly separated from each other by areas of interven-. FIG. 33.—Diagram of a portion of the bell of Rhieostoma seen from the oral side; m, muscle field; n, area covered by the nerve-net
. The elementary nervous system. Nervous system; Nervous system -- Coelenterata. 110 THE ELEMENTARY NERVOUS SYSTEM sphincter muscle and the nerve-net are not coextensive. In Aurelia the sphincter forms a continuous circular band. In RTiizostoma, on the other hand, it is composed of a suc- cession of sixteen muscle fields, a pair between each pair of the eight marginal bodies (Fig. 33). These muscle fields are partly separated from each other by areas of interven-. FIG. 33.—Diagram of a portion of the bell of Rhieostoma seen from the oral side; m, muscle field; n, area covered by the nerve-net but devoid of muscle. (Modified from Bet he. 1909.) ing non-muscular tissue over which, however, the nerve- net extends. Consequently, it is possible to cut prepara- tions from Rliizostoma in which one muscle field with an attached marginal body is connected with its neighbor only by an area of nerve-net (Fig. 34). When such a prepara- tion is stimulated through its marginal body, not only does the immediately adjacent muscular field contract but also the more distant one. It is, therefore, clear that in this case transmission from one muscle field to the next is accomplished by the nerve-net and not by the muscle fibers. Another piece of evidence bearing on this question has been advanced by Mayer (1906, 1908). Cassiopea is a jellyfish that possesses considerable powers of regenera-. 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 Parker, George Howard, 1864-1955. Philadelphia, London J. B. Lippincott Company
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