Fig. 1. (A-C) Sequential formation of invagination sites in the ventral neuroectoderm of Cupiennius salei embryos stained with phalloidin-rhodamine. (A) Confocal micrograph of a flat preparation of an embryo 130 hours after egg laying. Limb buds have developed in the prosoma (ch, ped, l1 to l4). The first five to eight invagination sites (arrow) are visible in the prosomal hemisegments and the first opisthosomal hemisegment. No invagination can be seen in the remaining opisthosomal hemisegments. (B) Three additional segments have been generated by the posterior growth zone 175 hours after egg laying. Abdominal buds are visible on the second to fifth opisthosomal hemisegments (o2 to o5). New invagination sites are not only added posteriorly but also anteriorly (arrows). (C) Left half of the germ band of a 200 hour embryo. At this stage 9 opisthosomal segments are visible. 30 to 32 invagination sites can be detected in each hemisegment of the prosoma and the opisthosoma. Ch, cheliceral segment; ped, pedipalpal segment; l1 to l4 walking legs 1 to 4, corresponding to prosomal segments 3 to 6; o1 to o6 opisthosomal segments 1 to 6. Scale bars: 200 µm.