Figure 4.

Stereotyped CIS arrangement in walking leg neuromere 1 of Pseudopallene sp. (ES 4). (A,A’; B,B’; C,C’; D) Apical horizontal sections (2D projections of curved composite sections) of four different tubulin- and PH3-labelled embryos, in part shown with nuclear counterstain. Images lacking nuclear counterstain (A–C) correspond to the ones shown to their respective right (A’–C’). Dashed outlines indicate the extensions of the hemi-neuromeres. Solid arrowheads mark the six CISs that could be reliably identified in the great majority of specimens. Open arrowheads indicate less consistently encountered CISs in the postero-medial portion of the hemi-neuromeres. Ellipses highlight the region in which the central invagination begins to form. Arrows mark pycnotic bodies along the VMR. Note apical and in part clearly tangentially oriented divisions. The question mark in (D) indicates a region in which a typical antero-lateral CIS could not be securely identified, presumably due to transient rearrangements resulting from the nearby apical mitoses. (E) Scheme of apical horizontal view of walking leg neuromere 1 in ES 4. Black spots indicate reliably identified CISs, grey spots the more inconsistently identified CISs in the postero-medial region in which the central invagination (greyish area in the background) begins to form. Ectodermal cells with epidermal fate surrounding the hemi-neuromeres are depicted in grey; the cells in the VMR are shown slightly smaller. Small dark grey dots in the latter represent pycnotic bodies.