Fig. 1. Comparison of eye anatomy of Drosophila melanogaster (A) and Xenos peckii (B). The retina of D. melanogaster is composed of hundreds of long, narrow ommatidia, each containing eight receptor cells. In X. peckii an extended, cup-shaped retina lies beneath each of the large lenses. (C) Two principal sample bases () are hypothesized: a smaller based on comparisons within eyelets (right), and a larger based on comparisons between photoreceptors in neighboring eyelets (left). Scale bars, 50 µm.