Transmission electron microscopy (TEM) pictures of mouse (a,b) and zebra finch (c,d) erythrocytes. a) Standard preparation (PBS) showing mouse erythrocytes with empty cytoplasm. b) Saponin treated mouse erythrocytes with empty cytoplasm. Note here that saponin treatment does not seem to deplete completely every cell from haemoglobin content, but alter the cell shape. c) Standard preparation showing zebra finch erythrocytes with apparent nucleus and occasional mitochondria (arrow). d) Saponin treated zebra finch erythrocytes, with apparent nucleus and numerous apparent mitochondria (arrows). Black bars represent 2 μm.