Origin, structure, composition and age-dependence of mineralized dense bodies (concretions) in the midgut epithelium of the adult housefly, Musca domestica.

The epithelial cells of the midgut in 1-40 day old adult female houseflies were examined by electron microscopic X-ray microalnalytic and histochemical techniques in order to study the mode of genesis, chemical nature and age-associated distribution of dense bodies. Dense bodies contain high concentration of phosphorus sulphur, chlorine, calcium, iron and copper; they are therfore termed concretions. Concretionary material is initially deposited within Golgi vesicles, lamellar bodies and residual bodies. The average size of the concretion granules and the concentration of the sequestered material increases with age, while new concretions are continually formed throughout life. With advancing age, concretions accumulate in the epithelial cells and occupy a considerable proportion of the cytoplasm in old flies. It is postulated that the concretions sequester superfluous minerals and may play an important role in the excretory system of the adult housefly.