Histochemical changes correlated with reproductive activity and nutrition in the chiton, Katharina tunicata

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Abstract
The chief sites of nutrient reserves observable histochemically are the germinal epithelial cells of the gonads and storage cells of the foot and mantle ridge. The germinal epithelial cells store neutral lipid and a glycogen-like material, both of which diminish in quantity during gametogenesis. In the female the disappearance of lipid from the germinal epithelium coincides with the accumulation of lipid in the oocytes. Special storage cells of the foot and mantle contain neutral lipid globules and minute granules (1 to 2 μ) which stain with phospholipid and protein procedures and the PAS reaction. The globules and granules are embedded in a matrix of glycogen-like material. The granules disappear from the cells two months before spawning and reappear after spawning. There is no histochemical evidence for marked utilization of lipid from the storage cells of the foot and mantle during normal gametogenesis, but these lipid depots are depleted when a period of starvation is coextensive with the 5 months of active gametogenesis. A starving animal produces fewer gametes than a normal one, but the gametes are normal in so far as can be determined histochemically. Muscles are surrounded by a sheath of glycogen-like material which is still present after 5 months of starvation. The connective tissue ground substance throughout the animal, the secretory cells of the glandular oviduct, the mucous cells of the intestinal valve, and the mucous cells of most of the epithelium of the foot and palliai groove have similar staining affinities. They appear to contain either neutral and unsulphated acid mucopolysaccharide or a hyaluronate-like polymer with some simple sugar residues. Certain epithelial cells of the mantle ridge and of the lateral surface of the foot secrete a sulphated acid mucopolysaccharide. The anterior gut secretes a neutral mucopolysaccharide. Lipid droplets are found in the epithelium of the stomach and intestines, and in the ‘enzyme cells’ of the digestive gland.