Fig. 5. Growing spicules in sclerocytes obtained from primmorphs cultured in the presence of 60 µmol l^-1 silicic acid; sequence of TEM images. (A) Two sclerocytes (scl) in the primmorph start to synthesize spicules (sp). The blunt end of one newly growing spicule (B) is associated with collagen-related fibrils (col), but not the second spicule (shown enlarged in C). The sharp end of the spicule shows inhomogeneous structure (D), suggesting less dense packing of silica in the spicule. Collagen fibers (col) surround the two spicules.