OCR Text |
Show 1867.] DR. J. E. GRAY ON HYALONEMA LUSITANICUM. 121 among the sclerobasic alcyonoid, and of Antipathes among the scle-robasic zoanthoid polypes. The siliceous spicules of sponges (as for example, the very elongated filiform spicules of the genus Euplectella, which are most like those of Hyalonema) are formed of numerous very thin concentric coats formed of silica and horny matter ; but this is exactly the structure of the axis of Goryonia (of the alcyonoid polypes) and of Antipathes of the zoanthoid polypes. In Hyalonema the coats are siliceous, mixed with horny matter; in Gorgonia the coats are either almost entirely horny or of horny matter mixed with a greater or less quantity of calcareous and siliceous matters. Though the axes of the Gorgonia and Antipathes are generally found with an expanded base, by which they are fixed to marine bodies, the Pennatulee, which are free, have a fusiform axis, like the separate spicules that form the coil of Hyalonema. I can only consider that the spicula of Hyalonema are the fusiform axes of a coral which, instead of having one axis to the community of polypes, has several coiled together like a rope, but separated from each other by a layer of corium. The coil of the spicula in Hyalonema occupies the same position and answers the same purpose (that is of supporting the canal) as the axis of the sclerobasic alcyonoid and zoanthoid polypes-that is to say, the axis of Gorgonia, Antipathes, and Pennatula. III. The spicules of sponges are only covered with sarcode; while the spicules of the Hyalonema are each surrounded by a layer of corium exactly like the inner surface of the bark or corium of the polypes. The zoologist who regards the coil of spicules as part of the sponge considers the polypes on its surface a parasitic incrustation. Lf this were the case, the parasites would only form a layer on the surface of the coil without interfering with the coil of spicules on which it is placed; and the spicules of the coil, being part of the sponge, would only be covered with the sarcode of the sponge, which, in the sponge at the base of the Hyalonema, of which the coil is said to be a part, is very small in quantity, scarcely enough to unite the spicules of the sponge together, and scarcely visible on their surface. In Hyalonema, on the contrary, the bark that covers the coil consists of a thick hard fibrous corium covered with a thick external coriaceous coat, strengthened, as in Palythoa, with grains of sand or small spicules. The inner layer of corium near the spicules or coil is pierced by scattered small spicules; and the corium extends within the coil, surrounding each of the spicules with a thin fibrous coat, uniting them all into one mass of a much more solid and highly organized texture than the sarcode of any sponge I have examined. The zoanthoid polypes that form the bark on the coil of spicula differ from those of the genus Palythoa and all other allied genera in having the inner coat of their polype-cells and the base from which thev spring pervaded with siliceous spicules, similar in shape, but smaller and much shorter than the spicules of which the coil is formed. |