Polarised light micrograph of crystals of progesterone, a female sex hormone which is secreted monthly in the ovary and which stimulates development of the uterus to receive a fertilised egg and to nourish the embryo. In pregnancy, progesterone prevents menstruation and the release of more eggs; this characteristic of progesterone is the basis of the contraceptive pill. Magnific- ation: X 40 at 35mm size, X 80 at 6x7cm size.