The _Sertularias_ have a horny stem, sometimes simple, sometimes branching, and may easily be mistaken for small plants. Their name is derived from the Latin _sertum_, a bouquet; and, indeed, they can only be described as trees in miniature, with branches yellow and semi-transparent, each tree having seven, eight, twelve, or twenty small panicles, each of which will contain about five hundred animals, the tree itself containing probably an association of ten thousand. Occasionally _Sertularia argentea_ is said to afford shelter and employment for a hundred thousand of these creatures. _S. falcata_, having all the grace and elegance of the delicate and slender Mimosa, is now placed among the Bryozoares. The minute cells in which the polyps are lodged are not always arranged in the same manner. Sometimes the cells occupy one side only; in other instances they occupy both; sometimes they are grouped like the pipes of an organ, at others they are ranged spirally round the stem, or arranged at intervals, forming horizontal rings round it. The _Alcyonaria_ are very common on some parts of our coast, where scarcely a stone or shell is dredged up that does not support one or more specimens known to the fishermen as "cow's paps," "dead men's fingers," and other popular names. This round and lobed fleshy mass is quite a colony in itself; placed in pure sea water, it very soon presents certain yellow or grass-like points, which gradually expand and display themselves in their native transparent and animated coralline. Each of these polyps have eight dentate petals, in the centre of which is the mouth; the body of the polyp is tubular, varying externally in length, traversed internally throughout its entire mass by a tissue studded with reddish spiculæ, and furrowed with small reed-like ribbons, common to all the individuals of the association. Among the _Tubiporidæ_ may be noted _Tubipora musica_ (Linnæus), from the Indian Ocean, characterised by its stony tubes, simple, numerous, straight or flexible, parallel, and slightly radiating, of a fine purple, and united together at intervals by transverse bands, so as to resemble the pipes of an organ. The polyp is a brilliant grass green, according to Péron; the tentacula furnished on each side with two or three rows of granulous fleshy papillæ, to the number of sixty to eighty (Lesson). The _Gorgonia_ is studded with calcareous or siliceous spiculæ which form a crust in drying. This crust is friable, and frequently preserves the colours more or less brilliant which characterise it. Their cells are sometimes hollowed out of the plain surface; sometimes they occur in the projecting mammals; these are smooth, rough, or scaly--sometimes pendent the one from the other.