. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 130 RICHARD B. FORWARD in 60 50 40 30 20 10. .---A A A- 12 10 10-5 IQ-" ID'S Intensity (w/m 10-2 2 10 100 FIGURE 2. Per cent positive phototaxis (left ordinate) by dark-adapted larvae (open triangle-dashed line) upon stimulation with 500 nm light (10 nm full band pass) at different intensities (abscissa) (replotted from Forward, 1974a). The closed circles-solid line indicates per cent descent subsequent to termination of stimulation. The average sample size for each phototaxis and geotaxis point are 73 and 53, respe
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 130 RICHARD B. FORWARD in 60 50 40 30 20 10. .---A A A- 12 10 10-5 IQ-" ID'S Intensity (w/m 10-2 2 10 100 FIGURE 2. Per cent positive phototaxis (left ordinate) by dark-adapted larvae (open triangle-dashed line) upon stimulation with 500 nm light (10 nm full band pass) at different intensities (abscissa) (replotted from Forward, 1974a). The closed circles-solid line indicates per cent descent subsequent to termination of stimulation. The average sample size for each phototaxis and geotaxis point are 73 and 53, respectively. C-closed circle is the control level of descent (sample size is 73). The closed circles indicate the mean descent rates (right ordinate) at the different light intensities, and the vertical lines are the standard deviation. The average sample size is 19. ing the light on. To establish the relationship between light intensity and this response, light-adapted larvae were stimulated at different intensity levels for 2, 20 and 200 seconds and upon extinguishing the light, the percentages of larvae showing the descent were determined. The procedure was to place larvae within the test cuvette upon the microscope stage for one minute (filtered microscope illumination only) and then stimulate three times for two seconds at 15 second intervals or two times with 30 seconds between termination and onset of stimuli for the 20- and 200-second duration stimuli. Each stimulus exposure for each larval preparation was at a different intensity. As seen in Figure IB, the longer the stimulus duration, the greater the percentage of descending larvae at lower in- tensities. However, considering those intensities at which positive and negative phototaxis occur (Fig. 1A), it is apparent that the descent is only seen subsequent to stimulation at light intensities that initiate positive phototaxis. This finding is further established by measuring per cent descent subsequent to stimulating larva
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