Pulsation in Animals 1

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JELLY-FISHES have been the subjects of frequent J experimentation-?we need only refer to the admirable researches of Romanes?and Mr. Alfred G. Mayer, director of the Department of Marine Biology of the Carnegie Institution of Washington, has been able to draw some new and exceedingly interesting general conclusions from a study of their pulsations. When the marginal sense-organs of the jelly-fish Cassiopea are cut off, the disc is paralysed and does not pulsate in sea-water. If a ring-like cut, or a series of concentric broken-ring-like cuts, be made through the muscular tissue of the subumbrella, the mutilated disc (without marginal sense-organs) responds to a momentary stimulus, e.g. a mechanical or electrical shock, or a single touch with a crystal of potassium sulphate, and suddenly springs into unusually rapid rhythmical pulsation. This is regular and sustained like clockwork, and continues indefinitely in normal sea-water without further external stimulation. The waves of pulsation all arise from the stimulated point, and the labyrinth of sub-umbrellar tissue around this centre must form a closed circuit—the stimulus being transmitted by the diffuse nervous or epithelial elements of the subumbrella. Any cut that breaks the circuit stops the waves of pulsation, and continuous movement cannot again be started. When each wave in a complete circuit returns to the centre it is reinforced and again sent out through the circuit. The centre once established remains a fixed point, while the disc continues to pulsate. The pulsation is fully twice as rapid as that of a normal Medusa, its rate varying with the length of the circuit, and it is self-sustaining (i.e. sustained by internal stimuli) once it be started by an external momentary stimulus.

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