time post-surgery resulted in total recovery of normal flight muscle control. Further, in an interesting side experiment performed by Pringle (1938), when a thread was attached to the abdomen of haltereless flies, relatively stable flight was again achieved. The thread in these experiments presumably aided in keeping the fly from rotating (similar to the way a heavy basket below a hot air balloon prevents the balloon from tipping), which supported the hypothesis that halteres are responsible for sensing body rotations. The original balancer theory, which was postulated by Pringle (1948), only accounted for forces produced in two directions. Pringle claimed that yaw was the only direction of rotation that flies used their halteres to detect. Using high speed video analysis, Faust (1952) demonstrated that this was not the case and that halteres are capable of detecting all three directions of rotation. In response to this new discovery, Pringle reexamined his previous assumption and came to the conclusion that flies were capable of detecting all three directions of rotation simply by comparing inputs from the left and right sides of the body. Of course, this is not the actual mechanism by which flies detect rotation. Different fields of sensory organs located in different regions at the base of each haltere detect the different directions of rotation, which also explains why flies with one haltere are still able to fly without issue. Evolution It is generally accepted that the halteres evolved from the non-flight wings of insects – the hind-wings of Diptera and the fore wings of Strepsiptera respectively. Their movement, structure, function and development all support this hypothesis. Characterizations of the arrangement of sensory organs known as campaniform sensilla, found at the base of the haltere, show many similarities to those found at the base of the hindwings in other insects. The sensilla are arranged in a way so similar to that of hindwings, that were the halteres to be replaced with wings, the forces produced would still be sufficient to activate the same sensory organs. Genetic studies have also brought to light many similarities between halteres and hindwings. In fact, haltere development has been traced back to a single gene (Ubx), which when deactivated results in the formation of a hindwing instead. Because just a single gene is responsible for this change, it is easy to imagine a small mutation here leading to the formation of the first halteres. Convergent