The polypidom is a simple obtuse process, the outer skin of which is tough and coriaceous, studded all over with star-like figures, which on examination are found to be divided into eight rays, indicating the number of the polyps enclosed in its transparent vesicular membrane. It is dotted with minute calcareous grains, and marked with eight longitudinal lines or septa, stretching between the membrane and the central stomach, which divide the intermediate space into an equal number of compartments. These lines not only extend to the base of the tentacula, but run across the anal disk, and terminate in a central mouth. The tentacula are short, obtuse, ciliate on the margins, and strengthened at their roots by numerous crystalline spiculæ. The polyp cells are oval, placed just under the skin, and are the terminating points of certain long canals which traverse the whole polypidom. The polyps, which are distributed over the whole surface, can withdraw into the cavities; they are, besides, of an extremely vital sensibility: the least shock impresses itself on the tentacula, the impulse of a wave even producing contraction; in response, the animal, which is well developed, sallies out perceptibly, but immediately retires again to hide itself in the cell. We find on the coast, in the Channel, and in the North Sea, _Alcyonium digitatum_, the mass of which is of a reddish white, ferruginous, or orange; _A. stellatum_, found on the shores of the Mediterranean, is expanded in its upper part, narrow towards its base, very rough on the surface, and rose-coloured; _A. palmatum_, is cylindrical, branching at the summit, of a deep red, except at the base, where it is yellow: this is met with in the Mediterranean. We may note as a type, altogether different from any yet touched upon, the _Nephtys_, in which the polypidom is a coriaceous tissue bristling with spiculæ over its whole surface. In _N. Chabroli_, the polypidom is squat, with thick spreading arms covered with lobiliform branches, the tubercular polypidom of which are columnar and obtuse, the sicula green, and the tentacula of the polyps yellow.