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Judging from these observations, Argonauta is a pelagic animal which lives and feeds near the surface of the ocean. Several species of Argonauta are known, distributed in the tropical parts of all the great oceans. The male is much smaller than the female, not exceeding an inch or so in length. It secretes no shell and its dorsal arms are not modified. The third arm on the left side, however, is modified in another way in connexion with reproduction.

The animal known as the Pearly Nautilus was unknown to the ancient Greeks, since its habitat is the seas of the far East, but in the middle ages, when its shell became known in Europe, it was called, from its superficial similarity to that of the original nautilus, by the same name. It was Linnaeus who, in order to distinguish the two animals, took the name “nautilus” from the animal to which it originally belonged and bestowed it upon the very different East Indian Mollusc, giving to the original nautilus the new name Argonauta. Zoological nomenclature dates from Linnaeus, and thus the nautilus is now the name of the only living genus of Tetrabranchiate Cephalopods. A detailed description of this animal is given in the article (q.v.); it is only necessary to add here a brief account of its mode of life and habits.

Four species are known from the Indian and Pacific oceans; they are gregarious and nocturnal animals living at some depth and apparently always on the bottom. The natural attitude of the animal as represented by Dr Willey is with the oral surface downwards, the tentacles spread out, and the shell vertical. The chambers of the shell have no communication with one another nor with the siphuncle. they are air-tight cavities and filled, not with water, but with a nitrogenous gas. This necessarily very much reduces the specific gravity of the animal, but it is still heavier than the water and does not seem capable of rising to the surface any more than an octopus. Nautilus is rather abundant at some localities in the East Indian Archipelago, for example at Amboyna in the Moluccas. In 1901–1902 Dr Arthur Willey of Cambridge University spent some time in that region for the purpose of investigating the reproduction and development of the animal. He stationed himself at New Britain, known to the Germans as Neu Pommern, an island of the Bismarck Archipelago off the coast of Papua. The natives of this island use the nautilus for food, capturing them by means of a large fish-trap similar in construction to the cylindrical lobster-traps used by British fishermen. Fish is used for bait. Dr Willey found the males much more numerous than the females; of fifteen specimens captured on one occasion only two were females. He kept specimens alive both in vessels on shore and in large baskets moored at the bottom of the sea. He found that when they were placed in a vessel of sea water numbers of a small parasitic crustacea issued from the mantle cavity. Some of the females laid eggs in captivity, but these were found not to be fertilized; they were about 3.5 centimetres long and attached singly by a broad base to the sides of the cage in which the animals were confined.

 NAUVOO, a city of Hancock county, Illinois, U.S.A., on the Mississippi river at the head of the lower rapids and about 50 m. above Quincy. Pop. (1900) 1321; (1910) 1020. On the opposite bank of the river is Montrose, Iowa (pop. in 1910, 708), served by the Chicago, Burlington & Quincy railway. Nauvoo is the seat of St Mary’s Academy and Spalding Institute (1907), two institutions of the Benedictine Sisters. “Commerce City” was laid out here in 1834 by Connecticut speculators; but the first settlement of importance was made by the (q.v.) in 1839–1840; they named it Nauvoo, in obedience to a “revelation” made to Joseph Smith, and secured a city charter in 1840. Four years later its population was about 15,000, and a large Mormon temple had been built, but internal dissensions arose, “gentile” hostility was aroused, the charter of Nauvoo was revoked in 1845, two of the leaders, Joseph Smith and his brother Hyrum, were killed at Carthage, the county-seat, by a mob, and in 1846 the sect was driven from the state. Traces of Mormonism, however, still remain in the ruins of the temple and the names of several of the streets. Three years after the expulsion of the Mormons Nauvoo was occupied by the remnant (some 250) of a colony of French communists, the Icarians, who had come out under the leadership of (q.v.). For a few years the colony prospered, and by 1855 its membership had doubled. It was governed under a constitution, drafted by Cabet, which vested the legislative authority in a general assembly composed of all the males twenty years of age or over and the administrative authority in a board of six directors, three of whom were elected every six months for a term of one year. Each family occupied its own home, but property was held in common, all ate at the common table, and the children were taught in the community school. In December 1855 Cabet proposed a revision of the constitution to give him greater authority. This resulted in rending the colony into two irreconcilable factions, and in October 1856 Cabet with the minority (172) withdrew to St Louis, Mo., where he died on the 8th of November. In May 1858 the surviving members of his faction together with a few fresh arrivals from France established a new