Figure 16

Transverse section through the distal part of the genital operculum of a first instar. Limulus polyphemus, prone. TEM. The external cuticle (Cu) is multi-layered, with the more protected dorsal cuticle (top) much thinner than that of the outer ventral surface (bottom). Some hypodermal cells (C) are present just inside the cuticle, and the lumen (L) has what appear to be clusters of cell debris (CD) from deteriorating cells, leaving space for the passage of hemolymph. In the developmental stages examined herein, the external cuticle of the genital operculum has gradually become thicker with regularly spaced channels (Ch) filled with an electron-opaque material. The fine particulate material just inside and outside these channels suggests some of the channel contents are released during prepartion of the tissues for microscopy. Scale, 5 μm.