Premetamorphic changes in the ultrastructure of Calliphora fat cells.

In the fat body of Calliphora a drastic reorganization of the cell structure, which is related to premetamorphic functional changes, can be observed during the 3rd larval stage of development. These changes include an accumulation of protein storage granules, a decrease in the relative volume of the mitochondria and the surface area of endoplasmic reticulum membrane, and the disappearance of vacuoles. "Absolute" values obtained for organelle areas and membrane perimeters confirm the assumption that large numbers of organelles are eliminated by autophagic activity prior to the pupation period. A temporary restoration of the endoplasmic reticulum is found immediately before pupariation. Large variations in organelle density were found between individual fat cells and between the nuclear, mid- and peripheral regions of the cytoplasm.