Fig. 1. mask was identified as a modifier of the csw^CS phenotype. (A-C,I-L) Scanning electron micrographs of adult eyes. (D-F) Tangential sections of adult eyes. (A,D) w. (B,E) w; sev-csw^CS/+. (C,F) w; sev-csw^CS/+; mask^10.22/+. (G,H) The number of inner and outer photoreceptors per ommatidium was tabulated in w; sev-csw^CS/+ (white bars) and w; sev-csw^CS/+; mask^10.22/+ (black bars) eyes. (I-L) mask genetically interacts with ras. (I) ras^V12/+ (J) ras^V12/ mask10.22 (K) w; ras^N17/+ (L) w; ras^N17/mask^10.22. All constructs are expressed under the control of the sev promoter. In all figures, anterior is to the left, posterior is to the right.