Fig. 2. (A-D) Morphology of the invagination sites. (A) Confocal micrograph of an apical optical section of the ventral neuroectoderm between leg 2 and leg 3 of an 175 hour embryo stained with phalloidin-rhodamine. The arrows point to dots of high phalloidin staining. (B) Basal optical section of the same region of the ventral neuroectoderm shown in A. The arrows point to groups of basally enlarged cells that are located underneath the dots of high phalloidin staining. (C) Confocal micrograph of a transverse optical section through two invagination sites (arrows). The cell processes of the basally enlarged cells extend to the apical surface. (D) Light micrograph of a transverse section through an invagination site. This invagination site consists of approximately nine cells (asterisks). The cell processes extend to the apical surface (arrow). Scale bars: 40 µm in A,B; 20 µm in C,D.