Close up of the exoskeleton of the fruit fly (Drosophila melanogaster) in an area of the head close to the eye region, coloured scanning electron micrograph (SEM). The exoskeleton is an external protective structure that covers the outside of the body of the fruit fly. The fruit fly is considered a model organism as it is widely studied, able to reproduce rapidly, easy to maintain in a laboratory and has a genetic system that is well understood. The fruit fly has been used for over a century to study a range of biological processes including genetics, embryonic development, physiology and pathology. Many biological mechanisms and pathways that control development are conserved across evolution between humans and fruit flies with about 75% of human disease genes having a recognizable counterpart in the genome of the fruit fly. Magnification: x3000 when printed at 10cm wide