Credit: MRC NIMR

This picture of sperm developing in a testis is one of 23 winning images in the 2008 Wellcome Image Awards, which focus on the visual wonder of the microscopic world.

The cell nuclei are shown in blue and the mitochondria appear red in this striking image taken by Kate Sullivan, an electron microscopist at the Medical Research Council's National Institute for Medical Research in London. The tails of the sperm are pointing inwards.

Other images from the competition, including a fly standing on sugar crystals and an array of vitamin C crystals, can be found at http://www.wellcome.ac.uk/en/wia/gallery.html .