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Cnidus ► coati I 423
thread used for stinging, paralyzing, and capturing prey. Cnidarians have no well-defined separate respiratory, circulatory, or excretory organs; their tissues, composed of two cell layers, surround a cavity known as a coe- lenteron (gastrovascular cavity), which is the basic internal organ. Ten¬ tacles surrounding the mouth are used to capture and ingest food. Cnidarians are carnivorous, feeding mostly on zooplankton but also on small crustaceans, fish eggs, worms, smaller cnidarians, and even small fish. Cnidarians range in size from nearly microscopic to more than 100 ft (30 m) long and more than a ton (910 kg) in weight. There are two basic body forms: the polyp (e.g., coral) and the medusa (e.g., jellyfish). See also hydra; Portuguese man-of-war; sea anemone.
Cnidus Vnl-dosN Ancient Greek coastal city, southwestern Anatolia. An important commercial centre and the home of a renowned medical school, Cnidus was one of six cities in the Dorian Hexapolis. It came under the control of the Persian Achaemenian dynasty after 546 bc. A democracy in the 4th century bc, it fell under Ptolemaic control in the 3rd century bc. A free city within the Roman province of Asia, it lasted until the 7th century ad, when it was abandoned. Excavation has revealed numerous public buildings, including the Temple of Aphrodite, where fragments of the celebrated statue of Aphrodite by Praxiteles were discovered.
CNN or Cable News Network Subsidiary company of Turner Broadcasting Systems. It was created by Ted Turner in 1980 to present 24-hour live news broadcasts, using satellites to transmit reports from news bureaus around the world. CNN became prominent in 1991 with its coverage of the Persian Gulf War. The company also operates the news channels Headline News and CNN International. See also cable television.
coach Four-wheeled, horse-drawn carriage with an enclosed body and an elevated seat in front for the driver. The coach originated in the 15th cen¬ tury in Hungary (where kocsi originally meant “wagon from the town of Kocs”). It was introduced in England in the mid-16th century. Coaches were used as public conveyances with inside seats for passengers (as in the stagecoach) and for mail delivery. They were used mainly in European cit¬ ies into the 18th century, when the private carriage became more common.
Coachella \kd-'chel-3\ Valley Valley, southern California, U.S. Part of the Colorado Desert, the 15-mi- (24-km-) wide valley stretches 45 mi (72 km) between the Little San Bernardino Mountains and the San Jacinto and Santa Rosa mountains. A productive agricultural region, it also has popular desert resorts, including Palm Springs.
coagulation Process of forming a blood clot to prevent blood loss from a ruptured vessel. A damaged blood vessel stimulates activation of clot¬ ting factors, eventually leading to the formation of long, sticky threads of fibrin. These make a mesh that traps platelets, blood cells, and plasma. This meshwork soon contracts into a resilient clot that can withstand the friction of blood flow. Under abnormal circumstances, clots can form in an intact vessel and may block it. See also anticoagulant.
Coahuila V.ko-a-'we-laX State (pop., 2000: 2,298,070), northeastern Mexico. It covers 57,908 sq mi (149,982 sq km), and its capital is Saltillo. Coahuila occupies a roughly broken plateau intersected by several moun¬ tain ranges. The first Spanish settlement in the region was at Saltillo in 1575. Coahuila and Texas formed a single state (1824-36) until Texas declared its independence. In 1857 Coahuila was combined with Nuevo Leon, and in 1868 it became a separate state. Its economy is based on livestock raising, agriculture, and mining; southern Coahuila has long been known for the wine and brandy it produces.
coal Solid, usually black but sometimes brown, carbon-rich material that occurs in stratified sedimentary deposits. One of the most important fos¬ sil fuels, it is found in many parts of the world. Coal is formed by heat and pressure over millions of years on vegetation deposited in ancient shallow swamps (see peat). It varies in density, porosity, hardness, and reflectivity. The major types are lignite, subbituminous, bituminous, and anthracite. Coal has long been used as fuel, for power generation, for the production of COKE, and as a source of various compounds used in syn¬ thesizing dyes, solvents, and drugs. The search for alternative energy sources has periodically revived interest in the conversion of coal into liquid fuels; technologies for coal liquefaction have been known since early in the 20th century.
Coal Measures Major division of Upper Carboniferous (323-290 mil¬ lion years ago) rocks and time in Great Britain. The Coal Measures account for much of England’s coal production. The deposits consist largely of bituminous coal, though anthracite coals occur in southern Wales.
Though local variation in the coal seams occurs, great uniformity is evi¬ dent on a regional scale, and some coal beds can be identified through¬ out Great Britain and even on the European continent.
coal mining Extraction of coal deposits from the Earth’s surface and from underground. Because coal was the basic energy source that fueled the Industrial Revolution, the resulting industrial growth supported the large-scale exploitation of coal deposits. In the late 20th century, open pit mines replaced underground mines as the principal source of coal in the industrial nations. The MINING of coal from surface and underground deposits today is a highly productive, mechanized operation.
Coalsack Dark nebula in the Crux constellation (Southern Cross). It reduces the brightness of stars beyond it by 1—1.5 magnitudes. Easily vis¬ ible against a starry background, it is probably about 550-600 light-years from Earth and 20-30 light-years in diameter. It figures in legends of peoples of the Southern Hemisphere and has been known to Europeans since c. 1500. The Northern Coalsack, in the constellation Cygnus, is similar in nature and appearance but somewhat less obvious.
coarctation of the aorta See coarctation of the aorta
Coase \'koz\, Ronald (Harry) (b. Dec. 29, 1910, Willesden, Mid¬ dlesex, Eng.) British-U.S. economist. He received his doctorate from the London School of Economics and taught principally there and the Uni¬ versity of Chicago. In his best-known paper, “The Problem of Social Cost” (1960), he challenged the classical logic of prohibiting behaviour that damages others. He argued that legal scholars should focus on the importance of an efficient marketplace and on negotiation rather than liti¬ gation. He was awarded the Nobel Prize in 1991.
coast or shore Broad area of land that borders the sea. The coastlines of the world’s continents measure about 193,000 mi (312,000 km). They have undergone shifts in position and changes in shape over geologic time because of substantial changes in the relative levels of land and sea. Other factors that alter coasts are erosion processes such as wave action and weathering, deposition of rock debris by currents, and tectonic activity. Coastal features result largely from the interaction and relative intensity of these processes, though the type and structure of the underlying rocks also play a part.
coast guard Naval force that polices compliance with a nation’s mari¬ time laws and assists vessels wrecked or in distress on or near its coasts. First established in the early 19th century to discourage smuggling, coast guards may maintain lighthouses, buoys, and other navigational aids and provide emergency aid to merchant sailors and to victims of natural disas¬ ters. Duties may include icebreaking in inland waterways and the collec¬ tion and broadcasting of meteorological data concerning floods and storms. In several European countries, volunteer lifeboat associations handle coast-guard duties.