Fig. 7. (A-J) Mitotic divisions during neurogenesis. (A-D,F-H) Confocal micrographs of flat preparations of embryos stained with phalloidin-rhodamine and anti-PH3; anterior is towards the top. (A) At 130 hours, when the first five to eight invagination sites (arrow) are visible, only single cells are marked by anti-PH3. (B) The same pattern can be seen until 180 hours after egg laying. (C,D) Higher magnifications of A,B, respectively. The arrows point to single cells marked by anti-PH3. (E) Horizontal optical section of the apical region of the ventral neuroectoderm. Cell nuclei are stained with YOYO. The cells divide perpendicular to the surface. The arrow points to the separated chromosomes of a dividing cell. (F) At 190 hours, when most of the invagination sites have already formed, groups of labelled cells can be seen in the ventral neuroectoderm (arrow). (G) At 200 hours, when all invagination sites have formed, only single labelled cell can be detected (arrow). During decrease of the invagination sites at 220 to 240 hours, groups of labelled cells are visible again (arrow). (I) Transverse optical section of the ventral neuroectoderm of a 190 hour embryo. Cell division is restricted to the apical layer of the ventral neuroectoderm (arrow) with the exception of a few cells (arrowhead). (J) Transverse optical section of the ventral neuroectoderm of a 220 hour embryo. The invaginated cells do not divide (asterisks). Dividing cells can be seen only in the apical layer (arrowhead). The arrows point to invagination sites. 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 in A,B; 40 µm in C; 50 µm in D; 10 µm in E; 100 µm in F-H; 20 µm in I,J.