Ultrastructural effects of dark‐adaptation on eyes of a snail. Helix aspersa

Abstract
Pulmonate snails (Helix aspersa) were raised from embryos to adulthood in total darkness. Unique ultrastructural features found in their photosensory cells were: 1. Break up of large aggregations of 800 A photic vesicles into smaller clusters by thick layers of membranes. 2. Increase in lipid droplets and in number and size of lysosomes. 3. Decrease in formation of photic vesicles by Golgi centers. 4. Flattening and bending of the tips of the microvilli. Tentative conclusions: the reduction in number of photic vesicles in dark‐adapted snails, by break down and decreased production, supports the hypothesis that the vesicles transport materials (photopigment ?) essential for light‐sensitivity of the microvilli.

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