Development of muscle fibre nuclei in holometabolous insect larvae.

The growth and development of the nuclear population from intersegmental dorsal longitudinal muscles (IDLM) of Bombyx mori and Pieris brassicae during larval development were studied. Using whole muscle mounts, examined with an image analysis system, we observed increases in muscle size but a constant number of fibres and concomitant increases in the number and size of fibre nuclei. The gradual growth of the nuclei throughout larval life, corresponding very probably to an increase in their DNA content, is unequal and results in heterogeneity of the nuclear population.

[Mode of formation of the flight muscles in a nematocerous Diptera].

An electron microscope study was conducted on the origin of the dorsal longitudinal muscles of a Nematocerous Diptera (Chironomus). These imaginal muscles arise from three pairs of slender larval muscles that are characterized by the presence of myoblasts located beneath the basal lamina and adhering to the sarcoplasmic membrane. During the last larval instar the myoblasts increase in number, each of the associated muscle fibers loses its contractile material and splits longitudinally into two to form six columns of sarcoplasm.