White blood cell. Transmission electron micrograph (TEM) of a white blood cell (leucocyte) from mouse bone marrow. Cell organelles can be seen here. At centre is a dumbbell-shaped nucleus (dark). Light- er chromatin within the nucleus contains the DNA chromosomal material. The cell cytoplasm is grey. Around the perimeter of the cytoplasm are lighter coloured membrane channels: endoplasmic reticulum (ER). Dotted along this ER are ribosomes. Dark lysosomes of many shapes are found in the cyto- plasm: they store enzymes. White blood cells with this type of multilobed nucleus and granules (lysosomes) in their cytoplasm are called granulo- cytes. Magnification: x22,750 at 8x10 inch size.