The Function of the Calciferous Glands of Earthworms

1. In the Lumbricidae the secretion of the calciferous glands consists mainly of calcium carbonate, the percentage of carbonate in the calcite concretions being 95-97 per cent. 2. Feeding experiments indicate that the calcium of the secretion can be derived from the common inorganic salts such as the carbonate, sulphate, phosphate, oxalate, chloride, and nitrate, and also from pear leaves. 3. Measurements of the hydrogen-ion concentration of the gut, soil, and castings of specimens of Lumbricus terrestris show that the tendency of the cast to be more neutral than the soil is due to the secretions of the gut as a whole, and not to the secretion of the calciferous glands. 4. The optimum pH's of two of the main intestinal enzymes have been measured. Amylase has an optimum at pH 6·8-7·0, and lipase at pH 6·4-6·6 and 7·3-7·7 depending on the substrate. 5. The amount of carbon dioxide bound as carbonate by the glands was measured in a series of experiments with earthworms kept in different calcium salts. The percentage of carbon dioxide excreted as carbonate never exceeded 10 per cent, of the total metabolic carbon dioxide. 6. Absorption of iron saccharate injected into worms took place occasionally, in groups of adjacent cells in the intestine and in isolated cells in the calciferous glands. 7. The true function of the calciferous glands is excretion, calcium carbonate being passed into the gut as crystals of calcite which are chemically inactive in the gut.