The name alcyouium wtis formerly also given to many"zoophytes now found to be of very different structure, some of which now bear the name a/gonidiurn, others that of alcyonella. The genus ale,gonidium belongs to the class of zoophytes called polyzoa, order infundibulata. See ZOOPHYTES. The most common British species is aleyonidium gelatinosum. It resembles a sponge in appearance, but is more pellucid and gelatinous, and is full of polypes, each having 15 or 16 long slender tentacula. It is attached to old shells and stones, and is sometimes much lobed, as in the preceding figure, sometimes almost simple. The color varies from a very pale brown to clear yellow; the surface Is speckled with minute dots, from which, when it is placed iu sea-water, the polypes protrude. The polype differs widely from that of alcyonium in having an intestine, which, proceeding from the stomach to the aperture of the cell, opens there by an orifice distinct from the mouth, a difference characteristic of the classes to which they respect ively belong. The ova are clothed with cilia, and their motions either are or most strik ingly resemble voluntary motions.—aleyondla belongs to the class polyzoa, order hypo crepia. See ZoorurrEs. There is one British species, aleyonella stagnorum, found in stagnant waters, especially in autumn, in shapeless, jelly-like masses, of a blackish-green color, usually adhering to the leaves of aquatic plants. The jelly-like mass is traversed from base to surface by multitudes of tubes, which open by a roundish or 5-angled aperture ; the heads of the polypes project a little way from the aperture, and expand into a circle of about fifty tentacula. About 1600 polypes are situated on a square inch
of the surface of the mass. The number of tentacula on a specimen of moderate size has been computed at more than 5,000,000. The tentacula are covered with minute cilia, only to be observed with a high magnifying power, by means of which a constant whirl pool is maintained, centering in the mouth of the polype, and essential, probably, for breathing as well as for the supply of food. Each polvpe is oroanically connected with ° the mass, its tunic continuous with the tube. The alimentary canal has two open ings. The ova are to be found in vast numbers in the tubes which traverse the mass. They are dark brown, whilst the tubes are colorless or tinted with green, of a lens-like form and destitute of cilia. They are produced from all parts of the inner side of the gelatinous tubes ; and as there seems to be no aperture for their escape, it is supposed that they are liberated from the parent mass only on its death and decomposition. The aleyonel& is an interesting object in a fresh-water aquarium, but is rather difficult to pre serve. It is not, however, always to be found even in ponds where it might be expected, and is abundant in particular seasons and rare in others. The ova are probably capable of remaining long dormant, until some concurrence of circumstances favors the develop ment of the germ of life which they contain. See Johnson's History of British Zoophytes, 2 vols., Loud. 1847—a most interesting and valuable work.