metamorphosis of the muscular system metamorphosis of the muscles of the thorax and abdomen IDOMAL:0002364 IDOMAL:0002364 The muscles of the thorax and abdomen are carried over to the adult but the main part of the adult thoracic musculature is new, including the muscles of the appendages, largely formed within the imaginal buds, and the indirect flight muscles. The larval abdominal muscles degenerate early in adult life, having been used for swimming by the pupa and pharate adult. Movements of the adult abdomen are due to small adult muscles which develop from myoblasts in the pupa. Histolysis of the musculature, as of other organs, takes place entirely by autolysis and without the intervention of phagocytes. idomal_namespace