. The Cambridge natural history. Zoology; Zoologia Geral. 194 PORIFERA CHAP. fusion of apposed terminal flat expansions of the rays, and in some, possibly all, genera a continuous deposit of calcium carbonate ensheaths the spicular reticulum. Thus they recall the forma- tion of the skeleton on the one hand of the Lithistida and on the other of the Dictyonine Hexactinellida (see pp. 202, 211). " Tuning-forks " may occur in the dermal membrane. The Astroscleridae, as known at present, contain a single genus and species, apparently the most isolated in the FIG. 88.—Astrosclera
. The Cambridge natural history. Zoology; Zoologia Geral. 194 PORIFERA CHAP. fusion of apposed terminal flat expansions of the rays, and in some, possibly all, genera a continuous deposit of calcium carbonate ensheaths the spicular reticulum. Thus they recall the forma- tion of the skeleton on the one hand of the Lithistida and on the other of the Dictyonine Hexactinellida (see pp. 202, 211). " Tuning-forks " may occur in the dermal membrane. The Astroscleridae, as known at present, contain a single genus and species, apparently the most isolated in the FIG. 88.—Astrosclera wil- h'l/ana, Lister. A, the Sponge, x about 3. p, The ostia on its distal surface. B, a portion of the skeleton show- ing four polyhedra with radiating crystal- line fibres. C, an ostium ; the surround- ing tissue contains young stages of poly- hedra. (After Lister.) Astrosclera willeyana^ was brought back from the Loyalty Islands, and from Funafuti of the Ellice group. Its skeleton is bntli chemically and structurally aberrant. In other Calcarea the calcium carbonate of the skeleton is present as calcite, in Astrosclcru as aragonite, and the elements are solid polyhedra. 1 J. J. Lister in Willey's Zwlo'jical Results, pt. iv. 1900, p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harmer, S. F. (Sidney Frederic), Sir, 1862-; Shipley, A. E. (Arthur Everett), Sir, 1861-1927. [London, Macmillan and co. , limited; New York, The Macmillan company
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