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SEA-ANEMONE

1713

SEA-URCHIN

north and south. A similar circulation takes place in the north; the cold water which occupies the deeper parts of the Arctic basin is largely made up of the dense Gulf-Stream water which sinks to the bottom on being cooled in the Norwegian sea. The water evaporated from the sea is borne to the land, and condensed on the mountain slopes. Over 6,500 cubic miles of this water are yearly sent back to the sea by rivers, carrying with it salts and earthy matters ; in this way the ocean has in all probability become salt in the course of ages. The saltest waters are found where evaporation is the greatest, for example in the Red Sea, the Mediterranean and the trade-wind regions of the ocean-basins. Owing to the constant circulation in the ocean, oxygen and other gases of the air are carried down to the greatest depths; thus animals and plants may flourish throughout the whole extent of the ocean. Water is but slightly compressible, and almost any substance which will fall to the bottom of a tumbler of water will in time fall to the bottom of the ocean. Still, the pressure amounts to four or five tons per square inch; hence in an ocean with a depth of five miles, were the action of gravity suddenly to stop, the ocean-waters would rise 500 feet above their present level by expansion.

Pure sea-water is a light shade of blue; but it sometimes is a shade of green or brown, owing to foreign matter or plants and animals floating in it. Some form of life is scattered throughout the whole ocean. A trawl at a depth of over two miles brought up 300 specimens of living animals; a trawl in about three miles' depth yielded 50 specimens; and fishes and animals have been found at over four miles depth. The term benthos is now usM for all animals and plants which live attached to, or creep over the bottom of the ocean, plankton being the term for all plants and animals which live in and are carried along by the currents of the ocean. Life is most abundant in the surface waters down to about ipo fathoms, is less abundant in the intermediate regions, and becomes more plentiful within a few hundred fathoms of the bottom. The shells and skeletons of animals and fishes fall to the bottom after death and make a large part of the sea-deposits in many regions, especially in the deeper parts of the ocean. Besides these pelagic deposits, there are others, mainly made up of the debris from the solid land of the globe, laid down in greater or lesser nearness to the shores of continents and islands, which are called terriginous.

Sea-Anem'one. A kind of polyp which does not secrete a coral-stock. They resemble flowers in shape and coloration, and are among the most interesting organisms to be met with on the sea-beach. They prove a great attraction in aquaria. Their essential

SEA-ANEMONE

structure is that of a fleshy cylinder attached by its base to a rock and presenting at its free extremity the mouth

surrounded by a fringe of tentacles, some times as many as 200, by which the little animal seizes its food,— small crustaceae and mol-lusks. They '& a r e practically stationary, but can move very slowly over the surface to which they attach themselves. They grow to three inches in diameter. They multiply by budding and by eggs. They are very long-lived. One taken by Sir John Dalyell in 1828 lived until 1887. They are used as food in Italy, Greece, Provence and various other coasts.

Sea=Cu'cumber is a name applied colloquially to the holothurian, which is a soft and worm-like sea-polyp. All these species have a very simple bodily structure, with great power of reproducing parts that are injured or lost. They possess sensitive tentacles at the mouth. The large sea-cucumbers or sea-slugs, known as beche-de-mer or ire pang, are highly prized by the Chinese for food. Trepang properly is the dried body of this sea-cucumber. It is gelatinous, and used in soup. Sea-cucumbers are most numerous in the warmer reigons of the Pacific.

Sea=Hare. A small mollusk, slug-like in appearance, deriving its popular name from the prominent character of its front pail of tentacles, which somewhat resemble the ears of a hare. They are widely distributed and generally inhabit muddy or sandy tracts. They feed on sea-weeds and small crustaceans. Sea-hares were notorious among the ancients for their supposed venomous properties, and were used as ingredients of poisonous potions. A chief proof of the magic-practice of Apuleius was the fact that he obtained sea-hares from fishermen. They are harmless, but some species exude an acrid liquid irritating to the human skin. They also emit a rich, purple fluid which, like the ink of the cuttlefishes, has the property of diffusing itself quickly throughout the surrounding water. Sea=Lion. See SEAL. Sea-Ur'chin, a very common sea-animal grouped with the Echinoderms. The common sea-urchin has a globular shell or test composed of carbonate of lime, and made of