Figure 6.

Mitotic activity in the VNE and early hemi-ganglion anlagen of Pseudopallene sp. (ES 2 – ES 6). Optical sections of tubulin- and PH3-labelled embryos with nuclear counterstain. Apical horizontal sections (A,E,G) represent 2D projections of curved composite sections. Dashed vertical lines indicate the ventral midline region. Dashed horizontal lines mark presumptive segment borders. Stars (F,H) mark embryonic entodermal cells. (A–D) Late ES 2. Rectangles in A highlight the magnified regions shown in B–D. Mitoses are exclusively found apically in the VNE. Note the tangential orientation of cell divisions, clearly recognizable during meta-, ana- and telophase of mitosis. Small white lines in A connect the forming nuclei of two sister cells during telophase. There is no preferred orientation of the divisions within the horizontal plane, all divisions being symmetrical (delicate stippled lines in B–D indicate the plane of cytokinesis). (E,F) ES 4. Mitoses are still encountered in the apical cell layer of the neuromeres. The formation of the central invagination of the postero-medial portion of walking leg neuromere 1 is already advanced. White solid arrowhead marks one of the CISs in the anterior portion of this neuromere. White spots in the corresponding transverse section (F) highlight the nuclei of flask-shaped cells in this CIS. In its contra-lateral counterpart, an exceptional division of a cell with slightly basally displaced nucleus is found (open arrowhead). (G,H) ES 6. Mitoses occur in the centre and at the margins of the paired invaginations of walking leg neuromeres 1 and 2. Note the tangential orientation of the mitoses in meta-, ana- and telophase. The cross (G) marks a damaged region. In the sagittal section (H), two of the scattered basal NPs in mitosis are indicated (open arrowheads). Asterisks mark detached basal GCs.