Fig. 1. Transmission electron microscopy of an ommatidium of the eye of the yellow tip Anthocharis scolymus. (A) Transverse section of the proximal part of the ommatidium, where only the proximal photoreceptors, R5–R8, contribute rhabdomeres to the fused rhabdom (Rh) (and not the distal photoreceptors, R1–R4, and the basal receptor, R9). Tracheoles (T) with their characteristic rippled walls are well recognizable. (B) Transverse section of the basal part of the ommatidium, where the R9 cell body fully occupies the space proximal to the rhabdom. (C) Longitudinal section of an ommatidium near the basal membrane (BM) that limits the retina at the proximal side. The trachea is clearly not elaborated into a tracheolar tapetum apposed to the fused rhabdom, as is the case in other pierid butterflies (cf. Ribi, 1980; Qiu et al., 2002). The levels of the sections of A and B are indicated by the horizontal dotted lines and the arrowheads. Bar, 5 µm.