Fig. 1. Imaging and grid to locate position of DiI injections at ‘0’ hours. All images are ventral views of the embryo. DiI labeled cells are seen in red. (A) Fluorescence image of embryo 127 (stage 4+). (B) Bright field image of the same embryo; (C) superimposed images of the embryo shown in A,B with an overlay of the same grid used on the template at stage 4 (Fig. 2A). (D-F) Imaging of the same embryo 20 hours later: (D) fluorescence image; (E) bright field image; (F) superimposed images in D,E showing the location of DiI in the ventricle 20 hours post-injection. HN, Hensen’s node; Ht, heart; arrows indicate superimposed images of A and B in C, and D and E in F.