. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. Potash on the Siliceous Skeletons of Sjjonges. 289 The siliceous cement which, with the included spicules, forms the skeletal fibre does not scale off under the action of potash in concentric layers, as happens in the case of true spi- cules, but dissolves away amorphously both in the interior and on the exterior of the fibre, without in the latter case producing those hemispherical pit-like markings which cover the exterior of many deciduous recent and fossil spicules, and wh
. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. Potash on the Siliceous Skeletons of Sjjonges. 289 The siliceous cement which, with the included spicules, forms the skeletal fibre does not scale off under the action of potash in concentric layers, as happens in the case of true spi- cules, but dissolves away amorphously both in the interior and on the exterior of the fibre, without in the latter case producing those hemispherical pit-like markings which cover the exterior of many deciduous recent and fossil spicules, and which in some cases have been shown by Mr. Carter to result from the depredations of some algoid parasite. Fine longitudinal striations, however, are generally obser- vable along the fibre, and may perhaps indicate a lamellar structure; in one or two instances I have seen indications of more rapid solution at a point (p) midway between the spicular canal and the periphery of the fibre, thus (fig. 2), as though along the line where the siliceous cement first covered over the contained spicule. Fig. 2, Fig. 3. ^. The appearance shown in fig. 3 seems to result from a change in the refractive index of the spicular component of the fibre ^ for the included spicule (s) is quite distinctly defined from the surrounding fibre and is yet composed of solid silica, which opposes the expansion of a well-defined thread of air (a) contained in its relatively narrow axial canal. Long before the spicular canals in the interior of the fibre have become fully developed by the action of the potash, the minute "rosettes" of the sarcode have completely disappeared in solution, so that before stage 2 is passed a careful search with high powers fails to reveal even the slightest trace of them. The free sexradiates follow shortly after; but the spines of the fibre remain for some time longer, and do not disappear. Please note that these images are extracted from scanned page images that may hav
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