In contrast to the cone cell body, the wild-type rod soma is small and nearly round. It has a single, large clump of dense heterochromatin, a thin rim of moderately electron-dense euchromatin, and very scant juxtanuclear cytoplasm without organelles [26,27]. The second cell population in the ONL of the rd7 retina has some of the nuclear features of normal rods, such as a single, dense mass of heterochromatin and moderately electron-dense euchromatin (Figure 7H); yet these cells also show features of cones. First, the euchromatin is, on average, more abundant in these cells than in wild-type rods (compare Figure 7G and 7H). In addition, comparison of the diagrammatic representation of the wild-type and rd7 ONLs suggests that the average area of the S-opsin–negative cells in rd7 is greater than in the wild-type (Figure 7C and 7D). In order to confirm this impression, we quantitated the area of 50 wild-type and 50 mutant rod-like cell bodies (see Materials and Methods for details). This experiment confirmed that the average area of the rod-like somata in rd7 is approximately 30% larger than that of wild-type rod somata (mean area in rd7 was 9.75 ± 1.36 (standard deviation) μm2, compared to wild-type rods, with 7.53 ± 0.72 μm2 ; n = 50; p = 7.6 × 10–16, Student's t-test). It is also notable that the standard deviation of the somal area is nearly twice as great in rd7 than in wild-type, confirming the subjective impression of greater variability in somal size and shape in the mutant compared to the wild-type (compare Figure 7C and 7D).