Fig. 2. Myogenic cells provide the basis of hyperplastic growth. All images are from cross sections. (A) Low magnification electron micrograph of a 40-somite embryo (stage 1, warm regime). Undifferentiated cells assumed to be myogenic are clustered within the mesenchyme (mes) next to the dorsal apex of the myotome and attach to the myotome's surface (arrows). Scale bar, 10 µm. (B) Electron micrograph of two myosatellite cells (SC) inserting between white fibres (WF) of a larva at first feeding (stage 4, warm regime). Scale bar, 2 µm. (C,D) Presumptive myosatellite cells and activated myosatellite cells within epaxial muscle of stage-5 larvae (warm regime), as labelled by anti m-met (C) and anti MyoD (D), respectively (arrows). Scale bars, 50 µm. spc, spinal cord; nc, notochord; ne, nerve; ep, epidermis; WF, white fibres; RF, red fibres.