The radius of curvature of the corneal lens was larger at the outer surface than that at the inner surface (retinal side) (Figs. 4 and 5). Thus, the corneal lens looked like a combination of a larger upper hemisphere and a smaller lower hemisphere, a geometry that was distinct in SEM images (Fig. 5A). Subsequent morphometry of the corneal lens
was carried out in sections as shown in Fig. 4A, as well as in isolated specimens as shown in Figs. 5B and C. Since a pigmented envelope surrounded the lower part of the corneal lens, this seemed to function as an aperture (Figs. 4A and B). The corneal lens consisted of a thin external cortical layer and a spherical medullar region (Figs. 4A and B). The cortical layer, less than 10 lm in thickness, was continuous
with the surrounding cuticular integument. The medullar region was non-uniform in both structure and staining properties, in epoxy embedded sections being stained densely by toluidine blue in the central part (Figs. 4A and B). Moreover, the medullar region consisted of concentric lamellae, like an onion, which were clearly visible in sections viewed in air, without a coverslip (Fig. 6A). The center of the concentric layers was not positioned at the center of the lens, but displaced into the distal region Fig. 6B). The posterior margin of the corneal lens was separated from the underlying retina by an extracellular matrix. However, the boundary between the lens and the
extracellular matrix was less clear in some specimens, because concentric lamellae were spread toward the extracellular matrix, as shown in Figs. 6A and B.