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Show 120 DR. J. E. GRAY ON HYALONEMA LUSITANICUM. [Jan. 24, the polypes with which it is covered as a species of Palythoa; and Professor Max Schultze has supported this theory by a microscopic examination of the spicules of the sponge, of the axis, and the bark or corium*. Some of the arguments in favour of this view of the question may be thus condensed -- I. Silica is not. exclusively secreted by sponges, as the advocates the sponge-theory seem to believe, but is found mixed with corneous matter (as it is mixed in Hyalonema and Euplectella) in Gorgonia und Antipathes, and with calcareous matter in Madrepores. Mr. Children, in my paper " O n the Chemical Structure of Sponges" (see Annals of Philosophy, 1825, ix. p. 431), in which I first showed that the spicules of some sponges are composed of silica, states that he found sufficient silica in the carefully prepared ashes of the axis of Gorgonia flabellum to form a globule before the blowpipe. This proves that silica is found in the coral of the Alcyonaria or polypes with pinnate tentacles. Professor R. Silliman, in the " Appendix to Dana, on the Structure and Classification of Zoophytes," states that in three genera of Madrepores (Madreporaria) which he examined he found that one contained nearly 9, another 12, and a third 23 per cent, of silica; he further states that " the silica exists in the coral in its soluble modification, and probably united to the lime." If nearly one-quarter of the solid parts of a calcareous coral of a zoanthoid polype consists of silica, there can be no reason that a zoanthoid polype might not produce a coral of pure silica without any calcareous material. M. Milne-Edwards calls one genus of Antipathidae Hyalopathes, because the axis is smooth and has a vitreous appearance; further, he believes that the axis differs in chemical composition from that of the other genera of Antipathidae (see Coralliaires, vol. i. p. 323). I have not seen this genus; but it is to be observed that he forms for the Antipathes a group which he calls Zoanthaires sclerobasiques, and it is to this group that the Hyalonemidae must be referred; indeed, from the manner in which M . Milne-Edwards refers to the genus, this is where he would have placed it if he had not been informed by M . Valenciennes that he considered it a sponge with a parasitic Zoanthus. II. The structure of the siliceous spicules of sponges is very similar to, almost identical with, the structure of the axis of Gorgonia * The truth of Dr. Bowerbank's assertion (also supported by Dr. William Carpenter), that the zoanthoid polype of this coral, described by Brandt, Schultze, Bocage, and myself, is only the oscule of the sponge, can be at once disproved by the examination of a specimen, or the study of the works of the authors cited, and can scarcely be considered an object of discussion. It is true Dr. Bowerbank has written a long and diffuse paper to attempt to prove his position, when a cut in the polype-cell could have settled the question. It is a pity he did not recollect King Charles's question about the fish and the water. I have made some observations on M. Valenciennes's and Dr. Bowerbank's theories in the 'Annals and Magazine of Natural History' for 1866, vol. xviii. |
