Distribution of the Two Kinds of Myofilaments in Insect Muscles

Abstract

Different insect muscles have been studied with the electron microscope and the distribution of the two kinds of myofilaments compared. In muscles other than those of flight, each thick filament is surrounded by 9–12 thin filaments, whereas, in the flight muscles, the contraction frequency of which is much higher, there are only 6 thin filaments surrounding each thick one; nevertheless, in the flight muscles of some butterflies, the wing stroke frequency of which is particularly low, there are 7–9 thin filaments. It seems then that there may be a relation between the ratio of the two kinds of myofilaments and the frequency of muscular contraction. In the muscles which have more than 6 thin filaments surrounding each thick one, the structure of the 7, line appears to be different from that which was described in dipteran flight muscles. A peculiar aspect of the M line is observed in lepidopteran flight muscles.