HYDRA

in Greek legend, the offspring of Typhon and Echidna, a gigantic monster with nine heads (the number varies), the centre one immortal. The monster's haunt was the marshes of Lerna near Argos. The destruction of Hydra was one of the 12 Labours of Heracles, which he accomplished with the assistance of Iolaus. As one head was cut off, two grew in its place; therefore, they finally burned out the roots with firebrands and at last severed the immortal head from the body. The arrows dipped by Heracles in the poisonous blood or gall inflicted fatal wounds. genus of invertebrate freshwater animals of the class Hydrozoa (phylum Cnidaria). The body of such an organism consists of a thin, usually translucent tube that measures up to about 30 millimetres (1.2 inches) long but is capable of great contraction. The body wall is comprised of two layers of cells separated by a thin, structureless layer of connective tissue called the mesoglea and the enteron, a cavity containing intestinal organs. The lower end of the body is closed, and an opening at the upper end both ingests food and ejects residue. Around this opening is a circlet of 4 to about 25 tentacles. Eggs and sperm appear in separate swellings (gonads) in the outer body layer, and individuals are usually hermaphroditic, (i.e., functional reproductive organs of both sexes occur in the same individual). Gametes are released from the body, and fertilization takes place in the water. Vegetative reproduction by budding is also common. Finger-shaped outpushings of the wall develop mouth and tentacles and finally nip off at the base, forming separate new individuals. Locomotion is by creeping on the adhesive base, or by looping; i.e., tentacles attach to the substrate, the base releases, and the whole body somersaults, enabling the base to attach in a new position. The genus is represented by 20 to 30 species, which differ chiefly in colour, tentacle length and number, and gonad position and size. All Hydra species feed on other small invertebrate animals such as crustaceans. Modern Greek dhra, island of the Saronic group in the Aegean Sea, noms (department) of Attica, Greece, just off the eastern tip of the Argols peninsula of the Peloponnese. Its maximum length, northeastsouthwest, is 13 mi (21 km), and it has an area of only 19.2 sq mi (49.6 sq km). The highest point, Mt. Ere, is 1,936 ft (590 m). Once quite wooded and well watered, as its Turkish name, amliza (place of pines), shows, it is now denuded and dry, with almost no arable land. Water is collected from rain in cisterns and is also shipped from the mainland. First prominent in the late 15th century under Turkish rule, it became a seafaring centre. In the 17th century the island received an influx of Albanian refugees from the Peloponnese; maritime trade then thrived. After an abortive insurrection against the Turks in 1770, Hydra received Greek refugees, who also concentrated their energies on commercial shipping. In 1821, at the outbreak of the War of Greek Independence, the island's population had risen to 30,000. With neighbouring Sptsai and Psar islands, the Greeks and Albanians of Hydra placed their considerable merchant fleets and fortunes at the disposal of the insurgents, and Hydriote sea captains commanded Greek ships in several successful encounters with the Turkish fleet. With the advent of steamships, however, the maritime activities of the island declined. Industries now include sponge fishing, cotton weaving, shipbuilding, and international tourism. dhra, the chief town, on the north coast, is an artists' and writers' colony and the residence of a metropolitan bishop. Its narrow, rock-cut streets surround a sheltered harbour. Three other small ports on the north coast are Mandrkion, Mlos, and Panaya. Pop. (1971) 2,531.