Scanning electron micrograph of larvae of the vinegar fly, Drosophila melanogaster in laboratory culture. The picture shows the surface of the medium - agar, dried yeast and sugar - with 3 larvae (maggots ) of D. melanogaster. The central larva is on the surface; to its left and above, two others are partially covered by the medium. The central larva, 2mm long, shows a segmented body (ochre), its head (brown) to foreground, with two rudimentary eyes. To its rear are short spiracles through which it breathes. The larvae pass through three moults (instars); each lasting about one day. During this time, imaginal discs develop within the body, in preparation for the next stage in the life cycle, pupation. In the pupa, larval tissues are broken down and the imaginal discs develop into the tissues that will form the adult fly. D melanogaster is a model organism for genetic research