バフンウニ幼生の光に対する行動
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概要
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When larvae of Hemicentrotus pulcherrimus were kept in a glass cylinder (3×50cm) tapered at the bottom, they tended to fall during the first 10 minutes. After this period, no increase in the percentage of larvae found at the bottom (about 60%) was detected. On the other hand, continuous increase in the number of larvae was observed in a small cylinder (Fig. 1, A a) placed on top of the large cylinder (Fig. 2). If the cylinder (0.8×25cm) was not tapered, however, 80% of larvae were found in the upper half of the cylinder after a period of 30-minute darkness (Fig. 3). This is contrary to the notion of geotaxis which has been proposed by Yasumasu (1963). The distribution pattern observed in the non-tapered cylinder at the end of a sufficient period of darkness (60min.) was disturbed by illumination of the upper part of the cylinder. Illumination of the lower part of similarly treated cylinders showed no effect (Fig. 3). The speed of downword movement was always higer than that of the upward movement. The former was affected by light to only a small extent, but the latter became significantly alower under brighter conditions (Fig. 6). If a vertical parallel light was illuminated from below or from above, larvae contained in a square trough (5×10×5cm) aggregated near the beam (Fig. 5, C). If the light intensity was gradually reduced, the mass of larvae shifted more and more into the beam. Such a concentrated mass began to disperse again when the beam was switched off. A horizontal parallel beam from the side and below the water surface was not effective. With a light beam diverged by 5-20 degrees, larvae were found near the water surface close to the beam. From these results, it is assumed that in darkness, larvae swim upwards by their active ciliary movements. At the water surface, they move about randomly. Illumination inhibits their upward movements, hence, probably their ciliary activity. Since the specific gravity of larvae is higher than that of the sea water (Yasumasu, 1693), a massive falling will result when they eventully enter a brighter condition. On reaching the bottom, larvac start upward movements again, provided the shape of the bottom is not tapered. Here, however, they take a path not in the beam but outside of it. On repeating such movements, the apparent aggregation will occur somewhere outside the beam where the photic condition is such that the speed of upward movement and that of downward falling are not much different.
- 社団法人日本動物学会の論文
- 1965-01-15