[An electron microscopic study of the structure of the indirect flight musculature at the pupal stage in the muscle mutant of Drosophila melanogaster].

Ultrastructure of indirect flight muscles was analyzed in Drosophila pupae heterozygous for the mutation l(2)MhcM66, which is an allele of the locus Mhc (Myosin heavy chain). It is demonstrated that the initial stages of muscle fiber differentiation in mutants proceed normally. First visible changes (elimination of individual thick protofibrils) are observed when myofibrils attain a certain size. Disintegration of the contractile apparatus progresses with growth of myofibrils. Mechanisms responsible for onset and development of these destructive processes during ontogeny are discussed.