The development of the eye midline. A confocal image of a whole mount late third instar eye disc stained to show neural nuclei (red), actin (green) and beta-galactosidase (blue). The furrow is about half way across the eye field in this picture, and is moving from left to right. Anterior is to the right. The blue stain shows a genetic marker that is expressed in the midline and ahead of the furrow (Eq1, see Sun et al. (1995). Genetics 141, 1075-1086). The green actin stain shows the outlines of the cells (which are very small in this image) and the tips of each cluster can be seen as a green dot behind the furrow. The red clusters are the developing eye facets.