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Studies on eye regeneration in a snail, Helix aspersa.

Part I is a study of the fine structure of the regenerating optic tentacle of a pulmonate snail, Helix aspersa. Electron microscopy demonstrates marked similarity between regeneration and embryonic development of the eye and its photoreceptoral microvilli, lens-forming secretory droplets, clear photic vesicles, neurites, pigment granules, and bundles of tonofilaments. A cell type, heretofore undescribed, prominent in the regeneration of the tentacle, is a pigmented interstitial cell. This cell is characterized, and its presumed role in the tentacle is discussed. Part II is an attempt to test the importance of nerve fibers in the induction of a regenerating eye in the newly formed epithelium of the outer tentacular sheath. Ligatures were placed around the inner tentacular sheath above the stumps of severed optic and tentacular nerves. No eye regenerated in snails with the ties in place, some as late as 90 days postoperative. The results suggest that nerve fibers exert an influence on the regeneration of the eye in Helix aspersa.