Sperm in uterus. Colored scanning electron micrograph (SEM) of human sperm on the inner surface or endometrium of the uterus (womb). The heads of the sperm appear to be brushing against the grass-like ciliated epithelium. Tiny projections or microvilli (white) cover the remaining secretory cells which provide a moist environment and nutrition to both sperm and the female egg. Sperm remain incapable of fertilizing an egg (ovum) until after undergoing capacitation, a process which occurs within the female tract. The close association of the sperm with the ciliated cells in this image may relate to this process.