Fig. 2. ey and pb collaborate in maxillary palp development. (A-C) Interaction of HSPB^sy and ey^JD in head development. (A) This frontal view of the head of an ey^JD heterozygote shows no marked defects [as for a female harboring two copies of HSPB^sy (see Fig. 1B)], whereas the combination 2xHSPB^sy; ey^JD/+ often leads to complete eye loss resembling the head in Fig. 1C. (B) Frontal view, head of a HSPB^sy/HSPB^sy; ey^JD/ey^JD female showing complete eye loss and the fusion of an antenna and maxillary palp (boxed). (C) Detail of B. This female lacks a normally placed maxillary palp associated with the labial palps (lb) (arrow); the maxillary appendage (with sensilla trichodea, arrowheads) is fused to the antenna. (D-F) Profile view of the head of an ey^JD heterozygote. (D) This head possesses normal antennae (ant), maxillary palps (mx) and labial palps (lb). (E) Enlargement of the maxillary palps. Arrowheads indicate the two maxillary sensilla trichodea. (F) Enlargement of the antennal segment A3 (ant) and arista (ar). (G-I) Profile view of the head of an ey^JD homozygote. (G) Overall reduction in head size, full eye loss, altered antennae (ant) and maxillary palps (mx), but normal labial palps (lb). (H) Higher magnification of the maxillary palps. Arrowheads indicate the two maxillary-specific sensilla trichodea signaling maxillary identity, but the appendage is strongly reduced (compared with E, same magnification). (I) The antennal segment A3 (ant) is malformed, slightly enlarged and extended from the head. The arista (ar) is shortened, curved and thickened at the base, malformed and extended from the head. This image is from a different individual from that shown in G, but the phenotype is equivalent.