. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 366 C. D. DREWES AND C. R. FOURTNER \ - 50uV 100ms Figure 3. LGF response to an abrupt decrease in light intensity. In the upper trace, two LGF spikes (at least) preceded a burst of presumed muscle activity. The short bar below the trace designates when behav- ioral shortening occurred, as determined from videotape recordings. The lower trace shows the decreased output from the photocell, corre- sponding to onset of the stimulus. potentials usually made it difficult to resolve any later LGF spiking in the response. An exampl
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 366 C. D. DREWES AND C. R. FOURTNER \ - 50uV 100ms Figure 3. LGF response to an abrupt decrease in light intensity. In the upper trace, two LGF spikes (at least) preceded a burst of presumed muscle activity. The short bar below the trace designates when behav- ioral shortening occurred, as determined from videotape recordings. The lower trace shows the decreased output from the photocell, corre- sponding to onset of the stimulus. potentials usually made it difficult to resolve any later LGF spiking in the response. An example of LGF spiking in response to an abrupt decrease in light intensity is shown in Figure 3. Such re- sponses were always accompanied by rapid escape short- ening. The mean latency from stimulus onset to the first LGF spike was 314 ms ± 48 SD (n = 24 measurements; 11 worms). An example of a videotape sequence of rapid escape withdrawal in response to an abrupt decrease in light in- tensity is shown in Figure 4. Here, marked tail with- drawal occurred between the ninth to eleventh frames after the stimulus onset. The mean latency from stimulus onset to detectable tail withdrawal was 389 ms ± 99 SD (58 measurements; 15 animals). Animals were also tested for responsiveness to moving shadows or decreased light intensity at times when their tails were protruded vertically above the sediments, but not lying horizontally at the air-water interface. Care was taken to ensure that sufficient time had elapsed (>30 min) for recovery from previous test stimuli. Neverthe- less, no escape withdrawal was observed in response to such stimuli, suggesting that the worm's responsiveness to moving shadow or abruptly decreased light intensity is dependent on its behavioral state. Escape responses in body fragments Isolated body fragments were screened for behavioral responsiveness to a moving shadow. The results (Fig. 5) showed that nearly half of the tail fragments, but no ante- rior or middle
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
