Studies carried out upon the larval, transitional, and adult stages of development show that: 1. But one pair of muscles breaks down (the abductors of the lateral lobes) during transformation. The remainder are reduced in size and changed in their attachments only in so far as the new functional conditions necessitate. 2. Changes in the function of certain pairs is clear, as in the secondary flexors which take on the duty of abduction in the imago. 3. Two pairs of muscles are here described for the first time: the secondary extensor, and the secondary flexor muscles. New details regarding the mechanism of extension and flexion are also described.