same group of muscles (see dynamics section). In addition to the indirect flight muscles which are responsible for the flapping motion, there are also steering muscle which control the rotation/angle of the wings. Because halteres evolved from hindwings, the same complement of steering muscles exists for the other directions of movement as well. Chan et al. (1998) identified 10 direct control muscles in the haltere similar to those found in the forewing. In 1998, Chan and Dickinson proposed that the planned haltere movements (without external forces acting on them) were what initiated planned turns. To explain this, imagine a fly that wishes to turn to the right. Unfortunately, as soon as it does, the halteres sense a body rotation and reflexively correct the turn, preventing the fly from changing direction. Chan and Dickinson (1998) suggested that what the fly does to prevent this from occurring is to first move its halteres as if it were being pushed in the opposite direction that it wants to go. The fly has not moved, but the halteres have sensed a perturbation. This would allow the haltere-initiated reflex to occur, correcting the imagined perturbation. The fly would then be able to execute its turn in the desired direction. This is not how flies actually turn. Mureli and Fox (2015) showed that flies are still capable of performing planned turns even when their halteres have been removed entirely. Campaniform sensilla The way in which rotation sensation is accomplished is that there are five distinct sensory fields located at the base of the haltere. These fields, which actually contain the majority of campaniform sensilla found on the exoskeleton of blowflies (more than 400 campaniform sensilla per haltere), are activated in response to strain created by movements at the haltere base in different directions (due to Coriolis forces acting on the end knobs). Campaniform sensilla are cap-shaped protrusions located on the surface of the exoskeleton (cuticle) of insects. Attached inside the cap is the tip of a dendritic projection (or sensory nerve fiber). The outer segment of the dendritic projection is attached to the inside surface of the cap. When the haltere is pushed to one side, the cuticle of the insect bends and the surface of the cap is distorted. The inner dendrite is able to detect this distortion and convert it to an electrical signal which is sent to the central nervous system to be