CLASS B. Aczncozo,k (Gr, actin, a ray). Ccelenterata, in which the imperfect stomach, or wide tube, which is so called, empties into the -body cavity, which latter is divided into a number of compartments by vertical partitions. the reproductive organs are internal. As in hydrozott. the tissues are chiefly divided into two layers, an ecto derm and an endoderm, but there is more tendency to the formation of special organs, and in some pf the members of the class muscular fibers arc well developed. No vas cular system has been found in any of the actinozoa, nor any traces of a nervous sys tem except in ctenophora. Most of the actinozoa are permanently fixed. Sea-anemones have sonic locomotive power, and one order, ctenophora, above mentioned. consists of active, free-swimming organisms. 3leny of the class secrete a horny or calcareous skele ton called a coral, or corallum. The z.ctinozoa are divided into four orders: Order I. Zoantharia (Gr. zmin, animal, and anthos, a flower). In this order the soft. parts are disposed in multiples of five or six, typically six, and they also have simple tentacles, usually numerous. The zoantharia are divided into three sub orders: Sub-order I. Zoantharia malacodermata. In these organisms there is either no coral lum or a psendocorallum in the form of adventitious spicules scattered through the soft parts. This sub-order comprises three families: itlimi"y 1. Actinide. These are commonly known as sea-anemones. They have no corallum or only a pseudocorallum, and arc seldom compound. They have locomotive power.
leamgy 2. Illyanthidce. No corallum; polyps single and free, with rounded tapering base. The genus ilyanthns is in most respects identical with the ordinary actince, but the base of its conical body is much attenuated, and by separating allows of a free existence.
3. Zoanthides. These organisms are in colonies, and exist in the form of a crust or of creeping roots, and have no power of locomotion.
Sub-order II. Z.santharia sclerobasica. These are the black corals, and are always composite, composed of a number of polypes united by a common, fleshy material, which is thin and internally supported by a simple or branched horny axis called a sclerobase. The polypes do not secrete a calcareous, but a horny corallum. and they generally have six simple tentacles. All the black corals form colonies, which are fixed to some foreign object.
Sub-order III Zoantharia, Sclerodermata, or .31adreporide. The animals comprising this sub-order include most of the coral-producing zoophytes of recent seas. See ZOAN THAR IA.
Order II. Alyconaria. The asteroid polyps. Tentacles fringed; soft parts arranged in multiples of four instead of five or six, as in zoantharia. All the members of this order are composite, the whole colony forming a branched mass, with the exception of one genus, haimeia. Divided into five families: 1. aleyonidm; 2. tubiporidre; 3. pen natulidx; 4. gorgonidm; and 5. heliophoridai; the fifth family being recently founded by Mr. Moseley. The alconyum, or " dead-men's toes," may he regarded as the type of the family alcyonidec. The tubiporldre contain the organ-pipe corals, the corallum being composed of bright scarlet cylinders united by plates. See CORAL, POLYPI, Goit