Scanning electron micrograph (SEM) of the fibre- like cells that form the lens of the human eye. The remarkable transparency of the 4-millimetre thick lens of the eye is due to the absence of nuclei in its cells, & to the crystalline precision with which they are arranged. The zipper-like rows of ball-&-socket joints that lock long lines of these cells together may also play a part. In cross-section lens cells are flattened hexagons, arranged in regular stacks. But the length of a line of lens cells, 10 millimetres, is some 2000 times their thickness of 5 micrometres - which why they are usually described as fibres. Magnification: x2,000 at 35mm size.