develops from develops into ommatidial precursor cluster immature eight-cell ommatidial precursor cluster mature eight-cell ommatidial precursor cluster Ommatidial precursor cluster composed of eight future photoreceptors. The nuclei of R8, R2 and R5 are displaced basally compared to the immature eight cell precursor clusters, whereas R7's nucleus is still ascending. The bilateral symmetry of the ommatidium is prominent at this stage. The apical processes of the cells that will become the anterior and posterior cone cells occupy their definitive niches, contacting R2 and R5, respectively (Cohen, 1993). symmetrical eight-cell ommatidial precursor cluster FBbt:00001773 fly_anatomy.ontology two cone-cell ommatidial precursor cluster