. The Biological bulletin. Biology; Zoology; Marine biology. 532 BORI L. OLLA AND WARREN W. MARCHIONI watt tungsten light bulb. To ensure complete penetration of the fixative, we slit the eyes at the sclerocorneal junction after they had been fixed for 24 hours in darkness. After an additional 24 hours of fixation, we enucleated the heads and removed corneas and lenses. We then dehydrated the eyes in an eth}-l alcohol series, cleared them in toluene and embedded them in paraffin (mp ° C). We sectioned the embedded eyes serially in a transverse plane at 8 /x and stained with Harris' hematox
. The Biological bulletin. Biology; Zoology; Marine biology. 532 BORI L. OLLA AND WARREN W. MARCHIONI watt tungsten light bulb. To ensure complete penetration of the fixative, we slit the eyes at the sclerocorneal junction after they had been fixed for 24 hours in darkness. After an additional 24 hours of fixation, we enucleated the heads and removed corneas and lenses. We then dehydrated the eyes in an eth}-l alcohol series, cleared them in toluene and embedded them in paraffin (mp ° C). We sectioned the embedded eyes serially in a transverse plane at 8 /x and stained with Harris' hematoxylin and eosin. To determine the presence of a retinomotor rhythm under continuous dark- ness, we held the fish for seven days under an artificial photoperiod of 13 hours light of constant intensity (50 ) beginning at 0630 and 11 hours dark be- ginning at 1930. We assumed that by then the fish had become acclimated to the light cycle. Then beginning at the time the light went off on the seventh 40 10 = S\A/IMMING SPEED = CONE MOVEMENTS. ~. u 1BOa S400 0600 1SOO 1800 TIME OF DAY CHOURS) Figure 2. Mean values of cone position from fish held in constant darkness compared with swimming activity under constant low illumination (9 ). day (1930) we held the fish in constant darkness for 49^ hours. At 0900 hours of the eighth day and every three hours thereafter for 36 hours, we sampled two fish from the aquaria and prepared the eyes for histological examination in the same way as described above. With a calibrated ocular micrometer we measured the position of 20 consecutive cone ellipsoids from one eye of each fish beginning 50 /x dorsad and 50 /x ventrad to the optic nerve insertion. We expressed measurements as percentages of the width of the combined pigment epithelial and visual cell layers to compensate for variations in retinal cell layer thickness. We did this by dividing the distance from the external limiting membrane to the proximal end of the cone ellipsoid by t
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