develops from ommatidial precursor cluster two cone-cell ommatidial precursor cluster four cone-cell ommatidial precursor cluster FBbt:00001775 Ommatidial precursor cluster composed of eight future photoreceptors and four cone cell precursors. The four cone-cell ommatidial precursor cluster is achieved with the apical arrival of the nuclei of the polar and equatorial cone cells that have risen over future photoreceptors R3 and R4 on the polar side and R7 on the equatorial side. At this stage all nuclei are displaced basally. R8 begins to move anteriorly squeezing between R1 and R2, where it will remain through adult life (Cohen, 1993). fly_anatomy.ontology four cone-cell stage ommatidial cluster