Electron micrograph of a proximal convoluted tubule cell from a rat. A peroxisome is visible near the cell base containing both crystals and a few circular profiles of cylinders in cross section. Despite their unusual appearance, these organelles can be identified as peroxisomes by positive staining for catalase and a negative reaction for acid phosphatase. Micrograph courtesy of Michael Barrett and Paul Heidger. THE CELL 2nd edition.