Figure 12

Formation of space holders (asterisks) and longer lengths of air sacs as a result of fusion and cuticularization of former cell fragments, now cuticle-enclosed components (CuC) of the air sac. First instar, Centruroides gracilis. TEM. Compared with earlier stages (Figs. 8, 9, 10, 11), the outer wall of these components is now relatively thick (~0.1-0.2 μm) and dense. The walls of these components appear to fuse (asterisk) and form a bridging trabecula (space holder) that helps hold the developing cuticular walls in place (Figs. 13, 15, 16, 17). Many of the aligned precursor cells like this one (N, nucleus) release their contents and deteriorate (holocrine secretion) between the developing air sacs, thereby resulting in hemolymph channels (H) with increasing width and space for passage of fluid. Granules (G) and vesicles (V) from these cells appear to increase the thickness of the cuticular walls (Cu, Fig. 13) of the developing air sacs. Scale, 2 μm.