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Show 904 DR. BOWERBANK ON HYALONEMA LUSITANICUM. [Nov. 28, to reiterate his belief that " Hyalonema is a type of a peculiar family of Corals, formed by zoanthoid polypes, characterized by forming for their support a siliceous axis formed of many thread-like spicules coiled together into a rope-like form, each formed of numerous concentric laminae, and surrounded and separated from one another by the corium of the community of polypes." I should not have noticed this reassertion of his opinions if he had not endeavoured to establish certain laws which are in themselves essentially false, and on which he bases his reasonings in favour of his own theory. In the first of these Dr. Gray asserts, " Silica is not exclusively secreted by sponges, as the advocates of the sponge-theory seem to believe, but is found mixed with corneous matter (as it is mixed in Hyalonema and Euplectella) in Gorgonia and Antipathes, and with calcareous matter in Madrepores." In the first place, no one, to m y knowledge, has ever asserted that silica is exclusively secreted by sponges; nor is the silica to be obtained from Corals and Gorgonias in the same state as it is in Hyalonema and Euplectella. In the former two it has never been discovered in an organized condition, while in the latter two it is always in that state. Dr. Gray quotes the analysis by Mr. Children of Gorgonia flabellum, in which he found silica enough to form " a globule before the blowpipe;" and the Doctor says, " This proves that silica is found in the coral of Alcyonaria or polypes with pinnate tentacles." But the results of this analysis by Mr. Children do not bear effectively on the point in dispute, which is whether polype-bearing animals secrete silex as well as carbonate of lime in an organized form as portions of their bony skeletons. There is no doubt that corals, Gorgonias, and zoophytes living in waters continually charged with minute grains of sand and with silex in solution would receive and retain within their fine pores numerous grains of that substance which would only be liberated and recognized by the chemical dissolution of those bodies. But this adventitious acquisition of silex by creatures whose organic structures are essentially calcareous is no proof of their power to secrete and organize silex as well as carbonate of lime ; and Dr. Gray does not produce a single example of any polypiferous animal, either among the bony corals, the Gorgoniadae, or zoophytes, secreting and organizing silex as part of their skeleton-structure. The difficulty of the purely siliceous structure of all parts of the skeleton and internal siliceous organs of Hyalonema, considered by Dr. Gray a coral, still remains to be solved by him ; and among all the beautiful siliceous organized forms so familiar to microscopists of the present day there is not one that can be assigned to any polype-bearing animal, described or undescribed ; and I believe that the animal power of organizing siliceous matter to form either an internal or an external skeleton will be found to be strictly confined to the great subkingdom of the Protozoa. The second law that Dr. Gray enunciates is, " The structure of the siliceous spicules of sponges is very similar to, almost identical with, the structure of the axis of Gorgonia among the sclerobasic |