Elementary text-book of zoology . elementarytextbo0101clau Year: 1884 POHIFEEA. 215 gelatinous Sponges or Myxospongia, is composed of horny fibres or silic-ious or calcareous The horny fibres form, without exception, anastomosing networks of varying degi-ees of thickness, and present a lamellated structure (fig. 158), which indicates that they are formed of a number of layers. They are formed by excretion as hardening portions of sarcode. The calcareous needles (fig. 159) are simple or three- and four- rayed spicules, and take their origin, as do the silicious structures, in the in
Elementary text-book of zoology . elementarytextbo0101clau Year: 1884 POHIFEEA. 215 gelatinous Sponges or Myxospongia, is composed of horny fibres or silic-ious or calcareous The horny fibres form, without exception, anastomosing networks of varying degi-ees of thickness, and present a lamellated structure (fig. 158), which indicates that they are formed of a number of layers. They are formed by excretion as hardening portions of sarcode. The calcareous needles (fig. 159) are simple or three- and four- rayed spicules, and take their origin, as do the silicious structures, in the interior of cells. The silicious spicules present, however, an extraordinary variety of form: some of them constitute a connected frame- work of silicious fibres, and others are free silicious bodies with simple or branched central canals (fig. 160). The latter are found in the form of needles, spindles, cylinders, hooks, anchors, wheels, and crosses, and arise in nucleated cells, pro- bably as deposits round a hardening of FIG. 158.—Piece of network of organic matter (central fibre). In order to understand the morphology of the Spongiaria we must begin by examining the structure of a young Sponge, which proceeds from the fixed larva. The young Sponge, after the formation of a ciliated gastric cavity and an ex- halent opening or osculum, has the form of a simple hollow tube, the walls of which are pierced by pores for the passage of small food particles suspended in the water (fig. 152). horny fibres from Etispongia equina.
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