Fine structure of the dioptric apparatus in the stalk eye of Onchidium verruculatum (Gastropoda, Stylommatophora): a distinct lamellar substructure of the lens |
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Authors: | N Katagiri Yasuo Katagiri |
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Institution: | (1) Medical Research Institute, Tokyo Women’s Medical University School of Medicine, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162-8666, Japan e-mail: nokokata@lab.twmc.ac.jp, Fax: 81-3-5269-7364, JP;(2) Department of Physiology, Tokyo Women’s Medical University School of Medicine, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162-8666, Japan, JP |
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Abstract: | The dioptric apparatus of the stalk eye in Onchidium verruculatum, including a tentacular epidermis, a cornea, and a lens, was examined using transmission electron microscopy. The tentacular
epidermis was formed by columnar epidermal cells, sensory dendrites, and glandular cells. The cornea was an anterior part
of the eye vesicle and consisted of corneal cells which contained abundant glycogen particles but no dark pigment granules
in their cytoplasm. An acellular, transparent, ellipsoidal lens was located in the center of the eye vesicle. The lens showed
a marginal zone, an outer zone, a transitional zone, an inner zone, and a central region arranged concentrically. The outer
zone was the most intense electron-dense region and was finely granular in structure. The marginal zone was also finely granular
and surrounded the outer zone with many hair-like slender strands on the retinal side. Toward the center of the lens this
homogeneous fine granularity gradually changed into globular or rod-like substructures, about 30 nm in diameter, and then
abruptly transformed into a lamellar substructure of about 30 nm in thickness. The inner zone contained a mosaic of lamellar
substructures which were arranged in a fingerprint pattern that was particularly enhanced with periodic acid methenamine silver
proteinate staining. The center itself consisted of deformed lamellar substructures. The concentric arrangement of substructures
inside the lens of the O. ver-ruculatum stalk eye is probably responsible for the concentration and/or refraction of light.
Accepted: 5 December 1997 |
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