Morphology of the longitudinal visceral muscles in third-instar larvae. This P[GAL4] insertion line exhibits a strong GAL4-expression in the longitudinal muscles, as highlighted with cytoplasmically expressed GFP reporter. The overview of the posterior part of the midgut (left) reveals the assembling of the longitudinal muscles into rows. The higher magnification (right) reveals the numerous cytoplasmic projections, which sometimes extend from one fibre to the neighbouring one.