Hydra
Hydra names 3 different subjects across the 6 encyclopedias on this shelf. Each is set out below. 1 of them is described by more than one encyclopedia.
Hydra in classical mythology
Described by 2 of the 6 encyclopedias.
Collier's New Encyclopedia (1921)
in classical mythology, a monster which infested the Lake Lerna in Peloponnesus. It was the offspring of Ichidna's union with Typhon. It had 100 heads, and as soon as one was cut off, two grew up if the wound was not stopped by fire. It was one of the labors of Hercules to destroy this monster; this he effected with the assistance of Iolaus, who applied a red-hot iron te 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 watersnake, 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) Hydræ continuatio. Hydra proper is a little S. of the bright star, Regulus, which is in Leo. In zoölogy the typical genus of the family Hydride. The animal is locomotive, single, naked, gelatinous, sub-cylindrical, but very contractile and variable in form; the mouth surrounded by a single row of filiform tentacles. Propagation by the formation of gemmæ and ova upon or within the substance of the animal's body. If cut into pieces each will become a new hydra. If turned inside out the exterior surface will digest good and the interior one respire. 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.
Aiton's Encyclopedia (1910)
a fabulous serpent infesting the Grecian lake of Lerna in Argolis. It had nine heads. If any one of these was cut off, two grew in its place. The destruction of this monster was one of the twelve labors of Hercules. The term hydra-headed is often applied to an evil which it is difficult to suppress. In zoology, the hydra is a small cylindrical animal of low organism found in cold and fresh waters. One end of the cylinder is attached to a suitable base, the other is surrounded by a whorl of tentacles which waft water containing food into the central cavity.
Hydra A celebrated monster which infested the neighborhood of Lake
1000 Classical Characters (1900)
A celebrated monster which infested the neighborhood of Lake Lerna in Peloponnesus . It was one of the labors of Hercules to destroy the monster, which he effected with the aid of Iolas.
Hydra or IDRA, an island of the Grecian archipelago
Collier's New Encyclopedia (1921)
or IDRA, an island of the Grecian archipelago, on the E. coast of the Morea, between the gulfs of Nauplia and Ægina; arca, 20 square miles. Pop. about 6,500.
What Has Changed in the Last Century
The myth is unchanged — the Lernaean monster still loses two heads for one, though the accounts here can't agree whether it had nine (Aiton's, 1910) or a hundred (Collier's, 1921), a disagreement that goes back to the ancient sources themselves. The freshwater polyp has fared very differently: Collier's noting that "if cut into pieces each will become a new hydra" is now the basis of a major research field, since Hydra's body is continuously renewed from stem cells and laboratory animals show no measurable increase in death rate with age, making it a standard model for the biology of ageing; its genome was sequenced in 2010. Collier's dates Trembley's discovery to 1774, but his famous experiments were made around 1740 and published in 1744. Two smaller corrections: the constellation Hydra, no longer split into the four parts Collier's lists, was fixed by the International Astronomical Union in the 1920s as the largest of the 88 modern constellations; and the island of Hydra, with 6,500 people in 1921, now has fewer than 2,000 permanent residents and lives on tourism, with wheeled motor vehicles banned so that goods still move by donkey.
Written for this edition, 2026.