Electron microscopic study of the mantle of normal and regenerating Helix

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Abstract
Histology of the mantle of normal Helix pomatia has been studied both by light and electron microscopes, and changes that occur in the general outer mantle epithelium during shell regeneration have been recorded. Mantle edge can be subdivided into three zones, (a) glandular epithelium (b) periostracal gland, (c) general outer epithelium. Ephithelial cells lining each of these three zones have a characteristic structure. Cells of the glandular zone have two types of inclusions: (1) near the secretory surface, which are nearly empty looking and oval; (2) mostly round and present in the basal region of the cells showing characteristic patterns. Underneath the glandular epithelium are five types of gland cells. Cells of the periostracal gland contain secretory droplets, most of which are homogenous, while others contain closely apposed membranes. It is suggested that these glands be called "shell glands" instead of "periostracal glands" because of the absence of direct evidence that they elaborate periostracum. Outer epithelial cells have lamellar organelles of 0,4 μ to 0.8 μ, in diameter, many glycogen granules, fibrous structures, and secretory droplets. These droplets are different from those in the periostracal glands in that they are not delimited by a membrane.Situated in the thickness of the mantle are the Leydig cells and cells containing droplets showing different patterns.During shell regeneration, several changes in the outer mantle epithelium can be noticed, including an initial increase of the lamellar organelles followed by a decrease and eventual loss of these organelles. Mitochondria increased in number. Lamellar organelles are either transformed mitochondria or formed from multivesicular bodies.

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