Figure 6

Atrial lumen (At) with early indications of air sacs (AS) that are separated by double rows of aligned cells. First instar, Centruroides gracilis. TEM. In some places closer to the atrium, the cells are releasing elongate fragments of cytoplasm as an early step in the development of the air sacs while farther inward there are only dense secretions (asterisks) that show the initial site of air sac formation (Fig. 5). No widening of the air sac entrance is evident at the sites where these early air sacs are forming. In these early stages, it is often difficult to identify where the air sac and hemolymph channels will be formed among the cells. N, nucleus; H, primordial hemolymph channel. Scale, 5 μm.