who paid much more attention to the butterflies of the tropical seas than to those of the nearer Mediterranean, pronounced them nocturnal high-sea animals. They had never been seen near the coast, nor before sunset. They were not found at a less distance than about ten marine miles from the coast, and disappeared in the deep at daybreak. That may be correct for the tropical regions, where a dazzling sunlight is poured upon the highly heated surface of the sea; but it must not be forgotten that the sea-butterflies have no eyes, and their keeping away from the coast, where the water is highly warmed to a considerable depth, may indicate that temperature is more a determining factor in this behavior than light. The sea-butterflies behave differently in the Mediterranean. They are not wanting on sunny days, but are more numerous when the sky is clouded and in the night. In midsummer they are, like many other pelagic animals, extremely rare, and keep themselves in the great deeps. Prof, Chun, of Königsberg, who investigated this matter in the summer of 1886, fished larvae of Cymbulia and Tiedemannia from as great depths as a thousand metres. Temperature may also be the decisive moment in this case; why should the animals not spend their summer vacation there? The sea-butterflies of the Mediterranean are not at all afraid of the coast. The Bay of Villafranca is hardly two kilometres wide, and they swim in the straits and harbor of Messina, I have caught multitudes of needle-butterflies in the daytime in that stream, close by the shore.
The case is somewhat different in the polar seas. We hunt the whale during the polar summer, when the sun does not set for months, and not in the polar nights, which are also months long, and when the ships would be frozen in the ice. If the Cliones and Limacinas were night animals they would not come to the surface during the whaling season, and would also not be known to sailors and hunters. They might, in fact, seek the deep in winter for the same reasons that they resort to it in summer in the Mediterranean—to escape extremes of temperature. Everything that lives depends on external conditions, and, as these are not everywhere the same, the behavior of the organisms subject to them must adapt itself to the local relations.—Translated for the Popular Science Monthly from Land und Meer.