larva Active, feeding stage in the development of many animals, occur¬ ring after birth or hatching and before the adult form is reached. Larvae are structurally different from adults and often are adapted to a different environment. Some species have free-living larvae but sessile (affixed) adults, the moving larvae thus helping to spread the species; others have aquatic larvae but terrestrial adults. Most larvae are tiny; many are dis¬ persed by entering a host’s body, where the adult form of the parasite emerges. Many invertebrates (e.g., cnidarians) have simple larvae. Flukes have several larval stages, and annelids, mollusks, and crustaceans have various larval forms. Insect larvae are called caterpillars, grubs, maggots, or worms; the larval stage of many insects may last much longer than the adult stage (e.g., some cicadas live 17 years as larvae and a week as adults). Echinoderms also have larval forms. The larvae of frogs and toads are called tadpoles. See also metamorphosis, pupa.
laryngeal Ms-'rin-joL cancer Malignant tumour of the larynx. The larynx is affected by both benign and malignant tumours. Squamous-cell carcinoma, the most common laryngeal malignancy, is associated with smoking and alcohol consumption; it is more common in men. Prolonged hoarseness without pain is the major symptom and should always be investigated. Radiation therapy or surgery may be used to treat tumours.
laryngitis \,lar-9n-'jl-t9s\ Inflammation of the larynx, causing hoarse¬ ness. Simple laryngitis usually occurs with infections such as the com¬ mon cold. Other causes include inhalation of irritants. The larynx’s lining becomes swollen and secretes mucus. In chronic laryngitis, caused by excessive smoking, drinking, or vocal-cord use, the larynx is dry and has polyps. Other types are caused by diphtheria spreading from the upper throat, tuberculosis bacteria spreading from the lungs, and advanced syphi¬ lis. The last can produce severe scarring and permanent hoarseness.
larynx \'lar-inks\ or voice box Hollow, tubular structure connecting the pharynx with the trachea, through which air passes on the way to the lungs. The larynx consists of a framework of cartilage plates, with a ridge in front (Adam’s apple); the epiglottis, a flaplike projection up into the throat that covers the airway during swallowing to keep food and liquid from entering; and the vocal cords, whose vibration produces the sound of the voice (see speech). See illustration on following page.
Las Casas, Bartolome de (b. August 1474, Sevilla?—d. July 17, 1566, Madrid) Spanish historian and missionary, called the Apostle of the Indies. He sailed on Christopher Columbus’s third voyage (1498) and later became a planter on Hispaniola (1502). In 1510 he became the first priest ordained in the Americas. He devoted his life to protesting the mistreat¬ ment of the Indians, with whom he worked in Guatemala, Peru, Cuba, Nicaragua, and Mexico. His call for an end to the encomienda system aroused implacable opposition. His proposed and quickly regretted solu¬ tion, the importation of slaves from Africa, was adopted, but the servi¬ tude of the Indians had already been irreversibly established. His Brief
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1078 I Las Navas de Tolosa ► Lassalle
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epiglottis hyoid bone
thyroid cartilage cricoid cartilage trachea
(A) Frontal view and (B) cutaway side view of the human larynx. The larynx is com¬ posed of cartilage plates that are joined together by muscles and ligaments. The thyroid cartilage, the largest, forms a prominence in front called the Adam's apple. The leaf-shaped epiglottis, attached to the upper part of the thyroid cartilage, closes during swallowing. The vocal cords in the cavity of the larynx are large folds in the mucous membrane lining the larynx. They stretch between the thyroid cartilage in front and the arytenoid cartilages in the back. As air passes between them, they vibrate to emit sound.
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Report on the Destruction of the Indians (1552) and his unfinished His¬ tory of the Indians inspired Simon Bolivar and other revolutionary heroes. See also black legend.
Las Navas de Tolosa Uas-'na-vas-tha-to-'lo-saV, Battle of or
Battle of Al-'Uqab \,al-u-'kab\ (July 16, 1212) Major battle of the Christian reconquest of Spain. It occurred during a Christian Crusade against the Muslim Almohad dynasty. Led by King Alfonso VIII, the com¬ bined armies of Leon, Castile, Aragon, Navarra, and Portugal found a secret route through a mountain pass in Andalusia (southern Spain) and surprised and defeated the Almohads at a site about 40 mi (65 km) north of Jaen.
Las Palmas or Las Palmas de Gran Canaria Seaport city (pop., 2001: 354,863), northeastern Grand Canary Island, Spain. The largest city and chief port of the Canary Islands, it was founded in 1478 and served as a base for the Spanish conquest of Tenerife and La Palma islands. It grew after the port was constructed in 1883. It is a year-round resort; his¬ toric sites include a 15th-century cathedral and the house of Christopher Columbus.
Las Vegas City (pop., 2000: 478,434), southeastern Nevada, U.S. It is famous for its luxury hotels, casinos, and nightclubs, located in the area known as “the Strip.” Mormons from Utah settled the site in 1855 and abandoned it in 1857. It became a railroad town in 1905 and was incor¬ porated in 1911. Gambling was legalized in 1931, and Las Vegas expanded rapidly after 1940. Its connections to crime syndicates began in 1946, when Bugsy Siegel opened the Flamingo Hotel. By the early 21st century it was one of the country’s fastest-growing metropolitan areas, attracting a year-round population as well as tourists.
Lascaux \la-'sko\ Grotto Cave near Montignac, Fr., that contains per¬ haps the most outstanding known display of prehistoric art. Discovered in 1940, it consists of a main cavern and several steep galleries, all mag¬ nificently decorated with engraved, drawn, and painted animals, some of them portrayed in a “twisted perspective.” Among the most notable images are four great aurochs bulls, a curious unicorn-type animal that may represent a mythical creature, and a rare narrative composition involving a bird-man figure and a speared bison. About 1,500 bone
engravings have also been found at the site, which has been dated to the late Aurignacian period (c. 15,000 bc). Because of heavy tourist traffic, the cave was closed to the public in 1963, but a full-scale facsimile, Las¬ caux II, was opened in 1983. See also rock art.
laser Device that produces an intense beam of coherent light (light com¬ posed of waves having a constant difference in phase). Its name, an acro¬ nym derived from “light amplification by stimulated emission of radiation,” describes how its beam is produced. The first laser, constructed in 1960 by Theodore Maiman (born 1927) based on earlier work by Charles H. Townes, used a rod of ruby. Light of a suitable wavelength from a flashlight excited (see excitation) the ruby atoms to higher energy lev¬ els. The excited atoms decayed swiftly to slightly lower energies (through phonon reactions) and then fell more slowly to the ground state, emitting light at a specific wavelength. The light tended to bounce back and forth between the polished ends of the rod, stimulating further emission. The laser has found valuable applications in microsurgery, compact-disc play¬ ers, communications, and holography, as well as for drilling holes in hard materials, alignment in tunnel drilling, long-distance measurement, and mapping fine details.