Light micrograph of cells from a corpus luteum cyst. The corpus luteum is a normal structure which forms in an ovary after ovulation. it secretes hormones which make the uterus ready for a possible pregnancy. The corpus luteum can sometimes become abnormally dilated and large, forming a cyst. The cells of the cyst resemble normal corpus luteum cells and have small oval-round nuclei (dark blue circles) and abundant bubbly cytoplasm (the light white-blue areas around the nuclei). Haematoxylin and eosin stained tissue section. Magnification: x400 when printed at 10cm wide.