. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MNEMIOPSIS GIANT SMOOTH MUSCLE RBERS 211 other fragile planktonic species they cannot be kept in good condition for more than one or two weeks in the laboratory. We thus tried to identify another species which could (1) yield giant smooth muscle fibers, (2) be available over long periods at low cost, and (3) be kept in a marine laboratory without excessive care. We found that the lobate species Mnemiopsis leydii (Fig. 1) meets all these re- quirements: it is possible to isolate functional giant smooth muscle fibers from the
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MNEMIOPSIS GIANT SMOOTH MUSCLE RBERS 211 other fragile planktonic species they cannot be kept in good condition for more than one or two weeks in the laboratory. We thus tried to identify another species which could (1) yield giant smooth muscle fibers, (2) be available over long periods at low cost, and (3) be kept in a marine laboratory without excessive care. We found that the lobate species Mnemiopsis leydii (Fig. 1) meets all these re- quirements: it is possible to isolate functional giant smooth muscle fibers from the two sagittal muscle bundles; it is an ubiquitous neritic species of the southern shores of North America and is, for example, common throughout the summer in Woods Hole, Massachusetts; and the animals can be kept several days in still sea water, renewed every day. The possibility of rearing closely related species through long periods has been demonstrated (Baker and Reeve, 1974; Ward, 1974). The present report describes the method used to obtain functional single muscle cells and gives a detailed electron microscopic description of the in situ and isolated cell together with a stereological analysis of the sarcoplasmic reticulum (SR). The ultrastructural features oi Mnemiopsis giant smooth muscle cells are compared with those of Beroe. A preliminary electro-physiological investigation has been conducted prior to this morphological study to ascertain the physiological integrity of freshly isolated cells. Figure 1. Photograph of a living Mnemiopsis leydii. viewed from the tentacular side. The animal is swimming downward with mouth (m) and oral lobes (lo) below and aboral organ (arrow) uppermost. The pharynx (p) is visible through the transparent mesoglea. 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
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