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Show 1869.] DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. 67 zoophytes rather than sponges." In his " Notes on the Arrangement of Sponges (Proc. Zool. Soc. 1867, p. 492) he arranges them as sponges ; but in his description of his genus MacAndrewia he commences thus : - " The coral expanded, cyathiform," &c. This confusion of ideas can only be accounted for on the supposition that Dr. Gray has really never taken the trouble to ascertain the structural characters of the specimens that have been so many years in his possession. Although differing to a considerable extent from the general mass of the Spongiadce, the primary design of sponge-life in the siliceo-fibrous species is in perfect accordance with the great mass of the sponges. The external and internal defensive systems are as those of other sponges, and their minute organs, as in other species, are exceedingly various in form and strikingly demonstrative of their specific characters; in truth they possess in perfection every essential organ of the Spongiadce. Dr. Gray, in his " Notes on the Arrangement of Sponges" (Proc. Zool. Soc. 1867, p. 505), has formed an order to receive the siliceo-fibrous sponges, which he has designated Coralliospongia, and he thus defines the members of his order:-" Sponge hard, coral-like. Skeleton entirely formed of siliceous spicules, anchylosed together by siliceous matter, forming a netted mass covered with sarcode." Prof. Wyville Thomson, in the 'Ann. & Mag. Nat. Hist.' for February 1868, p. 120, in describing the siliceo-fibrous sponges, under the head of the " siliceous skeleton," says : - " In Habrodictyon [Alcyoncellum speciosum, Quoy et Gaimard j and Hyalonema the skeleton is composed entirely of separate siliceous spicules of various forms, interwoven in fascicles and connected by the thin sarcode layer, or scattered irregularly among the fascicles of spicules. In Euplectella, Aphrocallistes, Dactylocalyx, and Farrea, certain kinds of these spicules are more or less completely fused together, forming a continuous anastomosing network." In m y observations on Dr. Gray's "Notes on the Arrangement of Sponges" (Proc. Zool. Soc. 1868, p. 118), I have already pointed out the error the author has fallen into in describing Dactylocalyx as " entirely composed of siliceous spicules anchylosed together by siliceous matter into a network ;" and I have there stated, and have not since seen reason to alter m y conviction, that the description of Dr. Gray is eminently incorrect, as no one, " I believe, ever saw the terminations of spicula united into a network through the morbid action of anchylosis by means of siliceous matter ;" and I may add that I have never yet seen a case of the anastomosis of spicula. Ihe normal condition of these organs is never to anastomose, however closely they may be packed together, while that of siliceo-fibrous structure is always to anastomose when they touch each other; and this law is abundantly illustrated in the fibrous structure of the skeleton of Euplectellaaspergillum, Owen, now so common a specimen in the cabinets of collectors. This error of Dr. Gray, regarding the spicular structure of Dactylocalyx and other siliceo-fibrous sponges, seems to have been unhesitatinglf adopted by Prof. Wyville Thomson, and without any |