Metamorphosis of midgut epithelial cells in the silkworm (Bombyx Mori L.) with special regard to the calcium salt deposits in the cytoplasm. I. light microscopy.

The morphological changes of the metamorphosing midgut cell in the silkworm were traced light-microscopically. The regenerative cells of the larval midgut proliferate rapidly during larval-pupal molt and finally replace the larval midgut, establishing new pupal midgut tissue composed of only one cell type. Pupal midgut cells contain numerous basophilic granules which are believed on histological grounds to be the deposits of calcium salts. Calcium seems to be transported from hemolymph to the pupal midgut cells and stored there temporarily as insoluble salts such as phosphate or carbonate, and then finally discharged into the lumen in a merocrine fashion. The midgut cells of the adult no longer contain calcium deposits.