MICROSCOPIC EVALUATION OF THE CRYSTALLINE LENS OF THE SQUID (LOLIGO-OPALESCENS) DURING EMBRYONIC-DEVELOPMENT

The similarity between the cephalopod lens and the teleost (vertebrate ) lens can be considered an optical example of convergent evolution. H owever, the embryology and ultrastructure of the cephalopod lens appea r to be different from that of vertebrates, and perhaps unique to the animal kingdom. Using light and scanning electron microscopy, the morp hogenesis of the squid (Loligo opalescens) lens is characterized. Resu lts indicate that the posterior lens primordium appears first during d evelopment and is derived from cellular processes which extend from a middle group, group 2, of lentigenic (ectodermal) cells. The processes extend from the basal aspect of the lentigenic cells, project down in to the optic vesicle during early stages of development, and fuse to f orm the posterior lens primordium. During later stages, the processes extend from surrounding lentigenic cells and are applied to the stalk of the lens, where they form bud-shaped protrusions. Once applied to t he lens, the processes form lens elements that later fuse into plate-l ike elements evident in later-staged embryo and adult lenses. The ante rior lens primordium is derived from an anterior group, group 1, of le ntigenic cells, during later stages of development. Lentigenic process es extend from these lentigenic cells and are laid down in a circumfer ential fashion to form the anterior lens cap. As in the posterior lens , evidence indicates that the anterior lens elements fuse to form plat e-like elements. The ultrastructure and morphogenesis of the cephalopo d lens is discussed and contrasted with other strategies of lens devel opment.