Light micrograph of cells of the corpus luteum, the structure which forms in an ovary after ovulation. The corpus luteum secretes hormones that make the uterus ready for a possible pregnancy. The cells have small oval-round nuclei (small dark blue dots) and abundant bubbly cytoplasm (the white-grey areas around the nuclei). Haematoxylin and eosin stained tissue section. Magnification: x400 when printed at 10cm wide.