The porifera and coelentera . ys Zoological liesult). The four specimens obtained of this sponge were cylindrical in form, ADDENDUM TO SPONGES 167 about 10 mm. in height by 5 mm. in brcatlth. The openin<;8 of thecanal system are confined to the upper surface (Fig. 97, A; cf. Ttntwiwin^Fig. 31). Tlie skeleton of A.^trosclera is composed, not of spicules, wliich areentirely wanting, but of calcareous spherules, which arise in cells of tliedermal layer near the upper surface. Each spherule is deposited witliina single cell, and is from tlie first composed of radially arranged crystallinefibres
The porifera and coelentera . ys Zoological liesult). The four specimens obtained of this sponge were cylindrical in form, ADDENDUM TO SPONGES 167 about 10 mm. in height by 5 mm. in brcatlth. The openin<;8 of thecanal system are confined to the upper surface (Fig. 97, A; cf. Ttntwiwin^Fig. 31). Tlie skeleton of A.^trosclera is composed, not of spicules, wliich areentirely wanting, but of calcareous spherules, which arise in cells of tliedermal layer near the upper surface. Each spherule is deposited witliina single cell, and is from tlie first composed of radially arranged crystallinefibres. Its form is at first spherical, but by further increase in sizeadjacent spherules come into contact, and the interspaces between thembecome comjiletely filled in by continued deposition of the calcareous /^--/i^xJm. Via. it. Astrosilr<i WiUiijium, Lister. A, tlie sponge magiiilied about three diameters; , uppersurface earrjing tlie openings of the canal system ; h, base of attachment. B, section of tlieskeleton ; s/A., spherules ; c, canals. (,s by Mr. J. J. Lister.) substance, to the exclusion finally of the soft parts. The .spherules thusacquire a polyhedral form (Fig. U7, B, sph.), and by their union build upa solid calcareous skeleton without any admixture of soft parts, buttraversed by canals in which are lodged the soft tissues and the canalsystem of the sponge (Fig. 97, B, c). In the basal (older) jiart of thesponge the canals became obliterated, apparently by extension inwards ofthe spherules forming their wall ; just as in pedunculate sponges thecanal system is wanting in the stalk. The spherules are composed of aragonite, and contain an organicbasis which has the staining reactions as that of the spicules ofCalcarea. The canal system is of a leuconoid type with smal
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
