Myoblast fusion in Drosophila is not mediated by a series of fusion pores along the muscle cell contact zone. Electron micrographs of stage 14 wild-type (A and E, wt), scar^mat/zyg (B), and sltr (C, D, and F) embryos. Samples were prepared by conventional chemical fixation in A–D and by HPF/FS in E and F. (A–D) Multiple membrane discontinuities (MMDs, arrows) are visible along the contact zone of adherent muscle cells in wild-type (A, wt), scar^mat/zyg (B), and sltr (C) embryos. Note that MMDs are also observed between nonfusing cells in the ventral nerve cord (D, VNC). (E and F) Plasma membranes in wt (E) and sltr (F) embryos prepared by HPF/FS do not contain discrete MMDs. Asterisks mark “fuzzy” membrane segments that resulted from imperfect fixation. Bar, 200 nm.