Abstract
1. Electron microscopy reveals the lens in the eye of nereid annelids (Nereis vexillosa, N. limnicola, Neanthes succinea) to be composed of highly folded, interdigitating processes of the pigment cells of the retina. The processes are filled with osmophilic vesicles. The lens in the eye of the snail, Helix aspersa, is a secreted sphere of fine granular material. Lenses are lacking in the ocelli of sea stars (Patiria miniata, Leptasterias pusilla, and Henricia leviuscula) and of a hydromedusan (Polyorchis penicillatus), the cavity of an eyecup being filled with ciliary-type photoreceptoral processes. 2. The cornea of the nereid eye consists of two layers: 1) a thick cuticle surfaced with fine projections and composed of a dense matrix containing granules, fibrils, and vertically arranged rows of lacunae, and 2) a layer of large epithelial cells. The cornea of Helix has three layers: 1) a one-cell thick stratum of epithelial cells, the external surfaces of which are studded with microvilli embedded in a coat of jelly, 2) a narrow stratum of horizontally oriented fibers (collagen ?) into which processes of the outer epithelial cells extend, and 3) an inner layer of columnar cells packed with granules and possessing microvilli on their under surfaces. 3. The young photoreceptoral cell in a developing adult eye of a 3-segment nereid larva was found to possess a cilium (flagellum) at its distal end. The cilium does not appear to be involved in the formation of the microvilli which arise from the sides of the sensory cell and below the cilium. Thus, the nereid photoreceptor is basically rhabdomeric rather than ciliary in type. 4. The larval eye in the nereid trochophore is a 2-cell organ resembling that of flatworms and composed of a slightly concave pigment cell and a sensory cell. The latter bears at its distal end an array of microvilli which project into the concavity of the pigment cell and lies next to a nerve cell that sends an axon to the ciliated prototroch.
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Schedule a callMore From: Zeitschrift fur Zellforschung und mikroskopische Anatomie (Vienna, Austria : 1948)
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