Polarised light microscopy of the tongue, or radula, of the common limpet (Patella vulgata). The tongue is used to scrape algae of the surface of rocks. In life the radula is looped within the body and as each exposed section is worn down it is replaced by a new section. The teeth are formed from a histidine rich protein and are one of the hardest natural substances known. The tongue has been coiled for visual impact. Magnification: x38 at 10cm wide.