The mesenteries bear upon their free edges the mesenteric filaments. These organs are usually more complicated in structure than the corresponding organs of the Alcyonaria, and the dorsal pair of filaments is not specialised for respiratory purposes as it is in that group. In many genera the mesenteric filaments bear long, thread-like processes—the "acontia"—armed with gland cells and nematocysts which can be protruded from the mouth or pushed through special holes (the "cinclides") in the body-wall. The gonads in the Zoantharia are borne upon the sides of the mesenteries and are usually in the form of long lobed ridges instead of being spherical in form, and situated at the edges of the mesenteries as they are in the Alcyonaria. {370}Nearly all the zooids and even the colonies of the Zoantharia are unisexual, but some species, such as _Manicina areolata_ (Wilson), _Meandrina labyrinthica_ (Duerden), _Cerianthus membranaceus_, and others, are hermaphrodite. Mr. J. S. Gardiner has recently given reasons for believing that the genus _Flabellum_ is protandrous. SKELETON.—The soft tissues of the Zoantharian zooids may be supported or protected by hard skeletal structures of various kinds. In the Zoanthidea and the Actiniaria there are many species that have no skeletal support at all, and are quite naked. These seem to be sufficiently well protected from the attacks of carnivorous animals by the numerous nematocysts of the ectoderm, and perhaps in addition by a disagreeable flavour in their tissues. Anemones do not seem to be eaten habitually by any fish, but cases have been described of _Peachia hastata_ being found in the stomach of the Cod, and of _Edwardsia_ in the stomach of the Flounder.[395] On the Scottish coasts Anemones are occasionally used with success as a bait for cod.[396] The body-wall of _Edwardsia_, however, is protected to a certain extent by the secretion of a mucous coat in which grains of sand and mud are embedded. Some Anemones, such as _Urticina_, _Peachia_, and others, lie half-buried in the sand, and others form a cuticle, like that of _Edwardsia_, to which foreign bodies are attached. _Cerianthus_ is remarkable for constructing a long tube composed of a felt-work of discharged nematocysts mixed with mud and mucus, into which it retires for protection. In the Zoanthidea the body-wall is frequently strengthened by numerous and relatively large grains of sand, which are passed through the ectoderm to lie in the thick mesogloea.