Sperm tails. Coloured transmission electron micrograph (TEM) of cross sections through sperm tails. A sperm's tail's ability to move is partly due to the arrangement of microtubules (part of the cell's cytoskeleton, dark rings) within the tail. The microtubules are arranged in a central axoneme with two central single microtubules and nine peripheral double microtubules. Surrounding the axoneme is a layer of mitochondria, which provide the energy for movement. Finally the tail is wrapped in a protective outer sheath. Magnification: x8000 when printed 10 centimetres wide.