Stage 11, Opisthosomal limb buds. All scale bars 100 μm. Sytox staining, a-a''; SEMs, b-e. a: Lateral view. The single precheliceral area (Pc, Figure 6) is now divided into bilateral precheliceral lobes (PcL). a': Frontal view. Laterally adjacent to the ventral sulcus, segmentally iterated point-like depressions are evident (black arrow heads). This is presumably neural precursor tissue. a'': Posterior view. The ventral sulcus (VS) is prominent between the developing limb buds in the prosoma and opisthosoma. b: Frontal view clearly showing that the single precheliceral area in earlier figures is now divided into bilateral precheliceral lobes (PcL). Each of these lobes has evenly distributed point-like depressions (some indicated by black arrow heads). The white arrow shows the postero-medial furrow of the forming stomodeum. Laterally adjacent to it are two conspicuous point-like neural depressions (white arrow heads). At the pedipalps (P), the anlage of an endite (en) is evident as a proximo-medial swelling. c: Detail of left prosomal region. Prosomal limb buds (L3-4) appear three-segmented, and in between the limb buds is a larger invaginating region (black arrows) of presumptive neural precursor cells. Barely visible are the remnants of limb buds (white arrow head) on opisthosomal segment one (O1). d: Opisthosomal region. Seven clearly separated opisthosomal segments (O1-O7) are visible while an additional segment (vertical dotted line) is still connected with the growth zone (GZ). The ventral sulcus (VS, horizontal white dotted lines) extends posteriorly (black arrow) as the limb buds become differentiated e: At the medio-posterior base of the limb buds of opisthosomal segments two and three (O2, O3) are conspicuous depressions (white arrows) made up of primordial tissue for the respiratory system. The white dotted line indicates the right boundary of the ventral sulcus (VS). Ch: chelicere, P: pedipalp.