Fig. 3. Electron miscroscopic immunohistochemistry using anti-Papilio RBP secondary antibody conjugated to 15 nm colloidal gold. The areas marked by broken squares in A, C, E, G and I are magnified in B, D, F, H and J, respectively. (A,B) Primary pigment cells (PPC) surround the crystalline cone (CC). Both the cytoplasm and the nucleus (N) were densely labeled. (C,D) Photoreceptor cells (Pr). No labeling was found in the cell body of the photoreceptor or in the rhabdom (Rh). (E,F) Secondary pigment cells (SPC) fill the space between photoreceptors (Pr). The cytoplasm of the secondary pigment cell was strongly labeled. (G,H) The nucleus (N) of the secondary pigment cell was also strongly labeled. (I,J) Tracheal cells. Labeling was found both in the cytoplasm surrounding the tracheole (T) and in the nucleus (N). Photoreceptor axons (Ax) were not labeled. Scale bars, 2 µm (A,I); 1 µm (B,C,E,G,J); 500 nm (D,F,H).