Figure 7

A region of a gill lamella after the fourth embryonic molt (stage 21). Limulus polyphemus, prone. TEM. This lamella is at a more advanced stage than those in Figures 5 and 6, and it has a clear central lumen (L), an outer hypodermal layer (H) and a thin cuticle (Cu). At this site, two cells protrude outward as commonly occurs among the appendages and lamellae at this early stage (Figures 2A, B and 3, 4, 5, 6). One hypodermal cell (C) is extending a process (Pr) toward a developing pillar-type trabecula (T; Figures 2A, B). The fine particulate material in the lumen is probably hemocyanin [30, 31]. Scale, 2 μm.