ALCYONIDIE. - The races of polypiferous .zoophytes which next offer themselves for our examination may be described as consisting of a common body or central mass, over the surface of which are disseminated numerous polypes, ali of which contribute to the nutri tion of the community to which they belong. In the first family, Aleyonium, examples of which are abundant on our own shores, the substance of the polypary or general body, which may frequently be picked up upon the beach, appears to be a shapeless lump of a tough gelatinous substance, upon which, to an ordi nary observer, no indications of its wonderful organization are apparent ; so that we cannot wonder at its being so frequently passed by as an object devoid of interest. On putting one of these amorphous masses into a glass of sea water, however, and allowing it to remain for a little time undisturbed, its real nature be comes apparent and a series of most interest ing phenomena present themselves. The MaSS, which was at first opaque and of a dense tex ture, slowly swells and becomes more diapha nous, apparently by the absorption of the surrounding water into its substance, until, having attained its full dimensions, numerous dimples appear, studding its entire surface, each of which, as it gradually expands, reveals itself to be a cell, the residence of a polype, which, emerging from its abode, displays eight pinnated arms, and the entire Alcyon, thus studded with living flowers, presents a spec tacle of extraordinary beauty, but if disturbed speedily withdraws from observation and again shrinks into its former shapeless condition.
M. Milne Edwards* has thrown considerable light upon the organization of these beautiful structures by his indefatigable researches, the results of which we shall lay before the reader at sorne length, as they are of great importance in illustrating the economy of the poly piferous zoophytes.
The genus Alcyonide (fig. 30) has the poly pes grouped together in great numbers upon the surface of a soft cylindrical polypary or common body, which consists of two portions. The lower portion (6), which is attached by its base to fuci or other submarine substance, is of a brown colour and firm texture, whilst the upper part is white, membranous, and ex tremely delicate, divided into branches the summits of which are crowned with elegant polypes (d) of almost microscopic dimensions.
Each of these polypes has eight pinnated ten tacles, in the centre of which is the opening of the mouth.
On observing these zoophytes in the living state, each polype is seen to be capable of executing individual movements! sometimes they expand their tentacles, or bend them in wards towards their mouth, or retract them into the interior of their bodies, or retreat en tirely into the substance of the common poly pary, as into a cell, without the neighbouring polypes at all changing their position. In this respect each polype is independent of the sur rounding ones. Under other circumstances, however, this is not the case, for sometimes the common body of the creature evinces movements that influence all the polypes, and cause their simultaneous contraction ; and this contraction is occasionally continued to such a degree that all the soft upper portion shrinks into the coriaceous stem, so as to become im perceptible, as represented in the figure ( fzg. 30, e). On separating one of the polypes from the common mass, and opening it under a microscope in a longitudinal direction, it is found that its central portion is occupied by a cylindrical stomach (fig. 31, c) which is open at both extremities, and presents in ternally eight longitudinal bands and a multi tude of transverse folds : inferiorly it is con tracted, and looks as if its termination was surrounded by a sphincter, although no mus cular fibres are perceptible. At length the inferior contracted orifice of the stomach opens into a wide cavity (d), which occupies the en tire diameter of the polype, and is prolonged inferiorly into the substance of the polypary. The calibre of the stomach itself is much smaller than that of the body of the animal, in the centre of which it is suspended by means of eight membranous and extremely delicate septa (f), which pass between the outer sur face of the stomach and the parietes of the polype, forming so many vertical partitions. By their upper extremity these septa are blended with the periphery of the mouth, and thus circumscribe between them eight longi tudinal canals (g), which are continuous with the corresponding tentacles. These latter ap pendages are in fact entirely hollow, and pre sent on each side of the cavity which they enclose a series of ten or a dozen little aper tures opening into the pinnules along their borders.