. Electro-physiology . » t Hydra, furnished with a flagellum, also possess basal muscular fibrils. A similar but more complicated arrangement exists in the Actinia. We are still in every case dealing with muscles of epithelial origin, epithelial miiscle-cells, which take part in the external or internal limitation of the body-surface, or lie deep down—their epithelial origin being always, however, unmistakable. In the simplest case, a transverse section through the endoderm shows, as in Hydra, a single row of shining granules, lying under a single layer of cylindrical, epithelial cells, which
. Electro-physiology . » t Hydra, furnished with a flagellum, also possess basal muscular fibrils. A similar but more complicated arrangement exists in the Actinia. We are still in every case dealing with muscles of epithelial origin, epithelial miiscle-cells, which take part in the external or internal limitation of the body-surface, or lie deep down—their epithelial origin being always, however, unmistakable. In the simplest case, a transverse section through the endoderm shows, as in Hydra, a single row of shining granules, lying under a single layer of cylindrical, epithelial cells, which it divides from the mesenchyme (Fig. 2, «.). Here again, as we learn from isolated preparations, we have a cross-section of muscle-fibrils (bundles of fibrils ?) which must be regarded as a differentiation product of the epi- thelial cells. The cell-bodies are cubical, cylindrical, or filiform, according to the state of contraction of the body- wall ; they carry cilia, or a solitary flagellum, at their free ends, while muscle-fibrils are differentiated off at the base, which is somewhat broader (Fig. 2,1). From this primitive form it is easy to derive what Hertwig (9) FIG. 2.—o, Transverse section through Calls " intra-epithelial " UlUSCleS, ill the muscular layer of a septum -i • i ,1 • n i i HIT ofs«^apm-as^c«,perpendicu- which the spindle-shaped cell-bodies lar to the long axis of the basai are only interspersed between the epi- fibrils; 6, epithelial muscle-cell , .. , (isolated) of Actinia. (Hertwig.) thelial cells proper, and take no part in bounding the upper surface. The " sub- epithelial " muscles are directly connected with these forms; they consist of long fine bands (bundles of fibrils), which only retain a thin sheet of formative plasma on the side nearest to the epithelium. There can be no doubt that the nucleated mass of protoplasm here corresponds with the body of a genuine epithelial muscle-cell. There is merely a structural diff
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