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Uterus lining. Coloured scanning electron micro- graph (SEM) of the surface mucosa (endometrium) of the uterus of a 35 year old woman. This is during the early secretory phase of the menstrual cycle. Mucus secreting cells (blue) and ciliated cells (yellow) are both seen here. The pink blobs are some of the lining's secretions. The lining builds up (early to late proliferation) in the first 14 days of the cycle to prepare for pregnancy, an egg is released, and then the lining becomes secretory to nourish the embryo. If no pregnancy occurs, it breaks down at menstruation after 28 days. Magnification: x1550 at 6x7cm size. (KEYSTONE/SCIENCE PHOTO LIBRARY/PROFESSORS P.M. MOTTA & S. MAKABE)