HYDRA (hi'drA), in classical mythol ogy, a .monster which infested the Lake Lerna Peloponnesus. It was the off spring of Ichidna's union with Typhon, It had 100 heads, and as soon as one was cut off, two grew up if the wound yk,as not stopped by fire. It was one of the labors of Hercules to destroy this mon ster; this he effected with the assistance of Iolaus, who applied a red-hot iron to the wound as soon as one head was cut off. The conqueror dipped his arrows in the gall of the hydra, and all the wounds which he gave proved incurable.
In astronomy, the hydra or water snake, one of the 15 ancient southern constellations. It is so long that it has been divided into four parts: (1) Hydra—i. e., Hydra proper; (2) Hydra et Crater; (3) Hydra et Corvus; and (4) Hydrx continuatio. Hydra proper is a little S. of the bright star, Regulus, which is in Leo.
In zoology the typical genus of the family Hydridx. The animal is locomo
tive, single, naked, gelatinous, sub-cyl indrical, but very contractile and vari able in form; the mouth surrounded by a single row of filiform tentacles. Prop agation by the formation of gemmw and ova upon or within the substance of the animal's body. If cut into pieces each will b"^ome a new hydra. If turned inside out the exterior surface will digest good and the interior one re spire. Hydra was first described by Trembley in 1774. The genus contains the fresh water polypes. Hydra viridis has 6 to 10 tentacles, shorter than the body; it is leaf-green, and is found in ponds and still waters adhering to the roots of duckweed. H. vulgaris has 7 to 12 tentacles, at least as long as the body; it is orange, brown, yellow, or red. H. attenuata and H. fusca are rare.