These Alcyons, when expanded, are about an inch-and-a-half high and two-thirds of an inch thick, but individuals are met with two or three times as large, and much divided into blunt finger-like lobes. The sarcode mass of these compound animals is channelled like a sponge, by branching canals, the orifices of which open into the stomachs of the polypes; and, by bringing them into communication with each other, unite the whole into one compound animal, which is maintained by the food caught and digested by each individual polype. Currents of sea-water mixed with the nutritious juices are made to circulate through the branching canals by the vibrations of cilia with which they are lined; they flow round the stomachs of the polypes, supply their juices with oxygen, and carry off the carbonic acid gas and refuse of the food. In this case, as in many others, the cilia may be regarded as respiratory organs. The unarmed Alcyons are generally thick, short, and rough; some form a crust on rocks from whence lobes rise. With the exception of the Xenia, a tropical species, the polypes of the unarmed Alcyons can retreat within their polypary, so as to be entirely or partially out of sight. The polypary, or mass, of the armed Alcyons is either membranous or leathery, and is entirely bristled with large spicules similar to the very small ones in the tentacles of its polypes. It forms branching masses terminated by prominent tubercules thickly beset by spicules. The polypes retreat into the mass when they are in a state of contraction. The Gorgons, which form the second family of Alcyonian zoophytes, are compound animals, consisting of a solid stem or axis either simple or branched, adhering by its base to a rock or some submarine body, and coated by a layer of a softer fleshy or horny substance exactly in the same manner as the bark covers the stem and branches of a tree. This bark or fleshy substance is filled with polypes similar to those described; however, they are shorter, their base is a little enlarged, and is turned towards the axis of the stem and branches of the Gorgon. The softer substance or bark is much developed between the polypes, and is full of spicules, of forms varying with the genera. A system of almost capillary canals traverses the soft coating and opens into the lower part of the cavity containing the viscera of the different individuals, thus affording a passage for the circulation of the nutritive juices.