Falsecolour scanning electron micrograph of human sperm migrating up the uterus. They are travelling across a background of uterine mucosa cells (purple, yellow) interspersed with tufts of cilia (one at right). The hairlike surface of the mucosa gives sperm a chemical protection if they are to reach and fertilize the female egg. The head of each sperm contains the human genetic material, and its whiplash tail is responsible for movement. 200300 million sperm start the journey through the uterus and fallopian tubes, lasting 12 to 24 hours, but only a few hundred may reach the egg. Magnification: x2600 at 6x7cm size.