NAUTILUS (Lat.. from (:k. vaetraor, mu/ W(4s, sailor, from vats, na us, ship) . The pearly nautilus I ;ZeIllIS .Nautilus) is the only living representative of an immense assemblage of shelled cephalopods of the sulaolass Tetrabran ehiata, whielo flourished during past geological ages. The shell is coiled in ono 11/ 1111e. divided hal) that by partitions or septa. the outer most being footled the 'living chamber.' as it con tains the animal: the septa are perforated by the siplouncle, which is central or nearly so. and the aperture is wide m141 spacious. The shell eon sists tf two layers, the miter being poreellanons, the inner pearly. or nacreous. whence the name 'pearly' nautilus. The initial ehamber consists of an obtuse incurred cone, marked on the miter surface of its posterior wall by a small sear called the rricgInl r, It is supposed that a perish able embryonic shell fprotoconclit fOrified, the presence of which is indicated by the cicatrix.
The body is short and thick, divided into a large obtusely conical head bearing eyes, ten tacles, ears (otocysts), and a rounded sac-like trunk. The mouth is surrounded by about 90 ex ternal filifo•m tentacles. The pair of tentacles on the inner or dorsal side are fused so as to form a hood-like. lobe by which the aperture of the shell is closed when the animal is withdrawn into the living chamber. Beneath is the funnel ( hypo nome ), not forming a completely closed tube as in the squids, but a locomotive organ, through which, as in other eeldialopods, the water is ejected with sufficient force to throw the ani mal backward. In swimming forward. says Kent. the tentacles are extended radially from the head.
The mouth is in the centre of the lobes and groups of tentacles, armed with a tongue (ra dula ) and a pair of remarkably powerful horny jaws tipped with carbonate of lime. Olfactory organs and osphradia are present. The animal is attached within the living chamber by two oval muscles. The compartments of the shell are usually said to he filled with air or gas, hut according to Verrill they are filled with sea water, which may Iso taken in o• expelled so as to equalize pressure at varying depths.
Until recently the living nautilus was exceed ingly rare, though the empty shells are cast ashore in great quantities in the Pacific and Indian oceans. Vet they have been for a long time trapped in baskets like lobster-traps by the na tives of some of the Melanesian and Fiji islands and used as food. Willey at Ralum. in New Britain, succeeded in trapping the nautilus in 70 fathoms of water. He also succeeded at Li fu, one of the Loyalty Islands. in capturing speci mens at a depth of only three fathoms. These he kept in a large submerged cage. feeding them daily until his efforts were rewarded early in December, 1894, by finding that they had spawned in the cage, yielding an abundance of eggs. These are not laid in bundles, as is the case with those of the squid. but are deposited separately by the female. Each egg is as large as a grape. There are said to be three species now divine in the Pacific Ocean, while the number has been carried up to even four. The two better known species are Nauti/US ponipilius and Nauti/us