Fig. 1. (A,B) Nomarski Differential Interference Contrast (DIC) images of larval zebrafish outer, red (A) and inner, white (B) muscle fibres. The outer, red fibres constitute a single, superficial cell layer and run parallel to the notochord, while the inner, white fibres are several cell layers thick and run obliquely to the notochord and midline. (C,D) Individual red (C) and white (D) muscle fibres from 5 d.p.f. larvae filled with Lucifer Yellow (0.1%) in the presence of 1-heptanol (2 mmol l^–1). Arrows point to the edges of the muscle fibres. Scale bars, 50 µm.