Image of the wing and haltere discs in flies expressing UAS CD8-GFP under the control of en. GAL. 4.This shows the respective engrailed expression patterns. The lighter areas indicate the imaginal disc outlines. In the wing disc (lower left, located above the tracheal branch), the engrailed expression pattern, showing the posterior compartment, is oriented as expected in respect to the larva. In the haltere disc (upper right, located below the tracheal branch) the engrailed expressing cells are oriented quite differently in this stage, although they show the same orientation as the wing disc in later larval stages. This change in orientation over time may be induced by the muscle fiber between the wing, leg and haltere discs.