Fig. 3. Ultrastructural analysis of rols mutants show that Rols is required for alignment of muscle precursor cells with FCMs. Electron micrograph of an early stage 13 rols^AD328 mutant embryo (A) reveals closely associated cells (arrow) but in contrast to the wild type, no fusion complexes are evident. At stage 14 (B) myoblasts in rols mutant embryos have lost contact with muscle precursor cells compared with wild-type where prefusion complexes (Doberstein et al., 1997) are evident. Arrowheads indicate myoblasts, whereas the double arrowhead shows a trinucleated precursor cell. Regions of the endoderm (en) and the visceral mesoderm (vm) are marked with arrows.