Zoophytes appear to feed principallyon Infusoria, they required only the existence of that class to prepare the sea for their creation, and their re mains form the oldest fossil animals met with in the strata of the earth. They are used in medicine, in domestic economy, and in the arts. Corals are formed into various ornamental articles. The sponge is a valuable article of commerce, and ex tensively used in the arts. Nadrepores are used as building materials in countries where limestone is scarce, and many calcareous zoophytes are used as manure. Rocks, bays, and fertile islands owe their existence to these animals in tropical seas. They organise matter for the digestive organs of higher animals, particularly for the mollusca and the minutest crustacea. They precipitate, in form of a carbonate, an immense quantity of lime con tinually pouring by rivers, in a soluble form, into the bed of the ocean, and thus prepare the abyss for the maintenance of vertebrate animals.
The interesting researches of I mperati, 1\Iarsigli, Donati, Peysonnel, Cavolini, Olivi, and Schweig ger, on the species of the Mediterranean, those of Trembley on the Hydra, those of Reaumur, Jussieu, and Lamou roux on the species of the coast of France, those of Peron and Lesueur on the Zoophytes of the southern hemisphere, and, above all, those of our countryman Ellis, on the species of the British coasts, have greatly extended our acquaintance with the structure and economy of this class of animals. The useful labours of Bruguiere and Esper, the accurate and detailed descriptions of Pallas, the elaborate and interesting details of Lamouroux, and the acute discriminations and beautiful views of Lamarck, have eminently contributed to deter mine the true relations of these animals to each other, and advance the natural history of zoophy tes. The following orders are founded on the di visions pointed out by Lamarck, and for the most part retain the names and the order of succession that distinguished naturalist has assigned them.
The zoophytes of this order have been erro neously conceived to possess the power of swimming to and fro in the sea by the sudden elevation and depression of their lateral pinnx, or by the suc cessive strokes of the arms of the polypi, and they were thence termed polypi natantes by Lamarck. They are all marine animals, of a lengthened form, and possessing an internal calcareous axis. Their polypi have eight tentacula disposed in a single row around the mouth, and their cilia are long and not vibratory. They are not attached by their base, but either lie loose at the bottom of the sea, or are carried to and fro by the waves. The united bodies of the polypi form the principal fleshy part of the zoophyte, and the reproductive gemmules which make their appearance first at the bases of the polypi, pass out through the mouths of these organs, as we have observed in the Pennatula phos phorea and mirabilis. These gemmules
in several of the species are ciliated on the surface, and possessed of spontaneous motion. They are named Calamoida from their resemblance, in form, to a quill or feather. To this order belong the genera.
1. Pennatula. 4. UnV)ellularia, 2. Virgularia. 5. Bettina.
3. Veretillum. 6. Funiculina.
This term is applied by Lamarck to a small group of zoophytes, the polypi of which are en veloped by distinct tubes which open on the sur face of the body. They are fixed zoophytes, with a fleshy contractile body, and without a calcareous axis. The polypi in this group have, like those of the preceding order, eight tentacula around the mouth, and the cilia of these tentacula are not vi bratory organs, but appear to be only supple mentary to the tentacula. The ova or gemmules of the Lobularia are ciliated on the surface, and pass out through the bodies of the polypi as in the preceding order. The genera of this order are, The body is composed of a soft gelatinous sub stance, supported by a fibrous axis of a cartilagi nous, horny, calcareous or silicious nature. Some, as the Alcyonium, have distinct polypi with nu merous tentacula furnished with vibratory cilia; others, as the Halina and Leucalea have no polypi, and appear to have the cilia disposed on the sides of internal canals passing through every part of the body. In this order alone we meet with a silicious axis, and a soft gelatinous body almost destitute of irritability. The ova or gemmules in the most inert genera of this order, are ciliated on the sur face, and swim by the vibration of these cilia, as in the other orders. The genera of this order arc, 1. Alcyonium. 4. Cliona. 7. Hanna.
2. Geodia. 5. Spongia. 8. Flabellaria.
3. Tethya. 6. Leucalia. 9. Penicillus.
In the zoophytes of this order there is an internal axis of a calcareous or horny nature, sometimes regularly jointed. The axis is covered with a soft irritable fleshy substance, in which the polypi have their cells, there are consequently no cells observed on the internal axis. From the experiments so often and carefully repeated by Cavolini on the living Gorgonia verrucosa, in the bay of Naples, it is obvious that the fleshy crust of these zoophytes is the most essential and important part—the part which secretes the successive layers of the axis, and forms the polypi. The polypi have eight ten tacula, and the reproductive gemmules pass out through the bodies of the polypi. The gemmules of the Gorgonia move by means of their cilia. The red coral of commerce belongs to this group of zoophytes. The Corallina, generally placed in this order, appears, from the experiments of Pro fessor Schweigger of Konigsberg to be only a cal cified plant. The genera of this order are, 1. Gorgonia. 3. Isis. 5. Corralium.