Light micrograph of a section through a healthy endometrium (uterine lining) during the proliferative stage of the menstrual cycle. The endometrium is a membrane that is rich in blood vessels and glands. During the menstrual cycle it increases in thickness in preparation for the implantation of a fertilised egg. If at the end of the cycle an egg has not implanted the endometrium is shed during menstruation (period). Tubular glands (darker purple) in the endometrium secrete mucus during this stage to moisten the uterus. Magnification: x40 when printed at 15cm wide.