. Carnegie Institution of Washington publication. Rhythmical Pulsation in Scyphomedusce. 119 in fig. 3, A-C, we see how a single broad ring may be finally divided by two annular cuts into three separate rings, all of which remain in sustained pul- sation. In this case ^ marks the stimulated point whence the contraction- wave started, yet the two inner circles which are finally isolated from the point ,? continue to transmit and maintain the wave. Similarly in fig. 3, D-I, we may completely isolate the stimulated point and prevent its sending out any stimuli, yet the narrow inner and outer annu
. Carnegie Institution of Washington publication. Rhythmical Pulsation in Scyphomedusce. 119 in fig. 3, A-C, we see how a single broad ring may be finally divided by two annular cuts into three separate rings, all of which remain in sustained pul- sation. In this case ^ marks the stimulated point whence the contraction- wave started, yet the two inner circles which are finally isolated from the point ,? continue to transmit and maintain the wave. Similarly in fig. 3, D-I, we may completely isolate the stimulated point and prevent its sending out any stimuli, yet the narrow inner and outer annuli, made from the original broad ring, still remain in pulsation. Fig. 3, J-L illustrate the same point by showing that by a series of cuts we may obtain two independent pulsating circuits in the place of the orig- inal simple ring-circuit. In this case it is evident that the original center of stimulation can be in but one of these circuits, yet both can remain in pulsation. It is remarkable that these isolated circuit-waves, moving constantly in one direction through a circuit, are not met tcvV/; in nature. Each pulsation of the heart, or of the medusa, is a thing separate and distinct from the con- traction which preceded or from that which is to follow it. Indeed, the. FIG. 4.—Showing that under normal conditions interference of contraction-waves coming in opposite directions prevents a rotary wave from being entrapped in the circuit. heart, or pulsating medusa, contains within itself the means to prevent any single pulsation-\vave from coursing constantly in one direction through the tissue. In the scyphomedusa, for example, the pulsation-stimuli originate in the marginal sense-organs, and the fastest-working sense-organ controls the rate of the pulsations. For example, the course of events in the case of each separate contraction is shown for Cassiopea in figure 4, where A is the sense-organ which has originated a contraction-wave. The wave of contraction spreads out on
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