(b) THE PRODUCTION OF POSITIVE HELIOTROPISM BY ACIDS AND OTHER MEANS AND THE PERIODIC DEPTH-MIGRATIONS OF PELAGIC ANIMALS.英文原著 · 《Darwin and Modern Science》
The faint light from the sky is sufficient to cause animals which are in a high degree positively heliotropic to move vertically upwards towards the light, as experiments with such pelagic animals, e.g. copepods, have shown. When, in the morning, the absorption of carbon-dioxide by the green algae begins again and the temperature of the water rises, the animals lose their positive heliotropism, and slowly sink down or become negatively heliotropic and migrate actively downwards.英文原著 · 《Darwin and Modern Science》