EM of a tertiary lysosome. Also called a residual body (RB), it is much more variable in shape and appearance than primary and secondary lysosomes. Note both electron-dense and electron-lucent areas in its lumen. Lysosomes arise from the trans –face of the Golgi complex, so they are often seen nearby. Several mitochondria (Mi) are in the cytoplasm; the cell?s plasma membrane (PM) is indicated. 40,000×.