. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 240 ANDREW N. SPENCER. FIGURE 2. A swimming burst consisting of three contractions of the circular muscle. One electrode (a) was attached to a tentacle and recorded a single tentacle contraction; the other electrode (b) was attached to the margin on the subumbrella surface and recorded three swimming pulses (SP's), each preceded by a pre-swim pulse (PSP). The horizontal bar represents 200 msec and the vertical bar, 100 recording electrodes are positioned 90° apart. For this preparation a mean value of 25 cm/sec (14° C, N = 2
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 240 ANDREW N. SPENCER. FIGURE 2. A swimming burst consisting of three contractions of the circular muscle. One electrode (a) was attached to a tentacle and recorded a single tentacle contraction; the other electrode (b) was attached to the margin on the subumbrella surface and recorded three swimming pulses (SP's), each preceded by a pre-swim pulse (PSP). The horizontal bar represents 200 msec and the vertical bar, 100 recording electrodes are positioned 90° apart. For this preparation a mean value of 25 cm/sec (14° C, N = 27) was calculated if it is assumed that the conduction route is circular between recording electrodes. If three recording electrodes are positioned 120° apart at the same vertical height on the subumbrella then the syn- chrony of excitation of the circular muscle sheet can be observed, with excitation reaching all three sites within 20 msec, normally it is much less than this (4—6 msec at 14° C). When a mature jellyfish is placed in a solution containing one part of isotonic magnesium chloride and one part seawater spontaneous swimming stops after some L FIGURE 3. Reappearance of pre-swim pulses (PSP's) after Mg++ anaesthesia. The two traces form a continuous recording. The large potential on the upper trace is a marginal pulse. The horizontal bar represents 100 msec and the vertical bar, 50. 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 Marine Biological Laboratory (Woods Hole, Mass. ); Marine Biological Laboratory (Woods Hole, Mass. ). Annual report 1907/08-1952; Lillie, Frank Rattray, 1870-1947; Moore, Carl Richard, 1892-; Redfield, Alfred Clarence, 1890-1983. Woods Hole, Mass. : Marine Biological Laboratory
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