In the Drosophila melanogaster, developmental signals orchestrate cell differentiation in a sequential manner which lead to precise neural and cellular patterns. The previous work demonstrated that the rugose (rg) gene is required for proper differentiation of the cone and pigment cells in the Drosophila compound eye. In this study, the pigment cell number in several ommatidia in rugose mutant eyes was analyzed and showed multiplication of secondary pigment cells in the null mutation. In addition, rugose mutant-flies exhibit optic lobe defects. The lamina, medulla, lobula and lobula plate are affected by mutation. The results suggest that rugose gene encodes a secondary pigment cell specific function, and plays an essential role in determining the optic lobe's structure.