Figure 2

During the first division structural changes are cell-morphologically visible. A Zygote with the polar body remnant characterized by relicts of the spindle apparatus (black arrow). The yolk (y) is evenly distributed and fine dense particles are scattered throughout the egg (arrow heads). A’ Detail of a section close to the surface of the same egg as in A. Only some small granules appear around the ‘nurse cell remnant body’(ncr) (black arrow). B Zygote with central nucleus (n). The dense granules now appear much clearer (white filled arrow heads). C Section of a zygote with ‘nuclear blister’ (black filled arrow head). Dense granules (white filled arrow heads) appear around the ncr (not visible). D The 1st mitotic division in metaphase. The ds (black filled arrow head) appears at the metaphase plane connected to the spindle apparatus. Dense granules around the ncr (not visible) are indicated by the white arrow head. D’ Detail of the ncr (black arrow head) of the same egg as in D. E The spatial relationship between the positions of two nuclei and the ncr (violet sphere) shifted towards the CD nucleus. F, F’ Metaphase of the first division. F The ds (white bordered arrow head) appears at the metaphase plate. F’ View of the xz axes of the same image stack of F. The region around the vegetal pole (asterisk) contains more condensed yolk. The direction of the first mitosis (double arrow) is perpendicular to the a/v-axis (white line) ap - animal pole and vp - vegetal pole. The ncr (arrow) is shifted towards the CD nucleus. A-D, A’, D’ Semi-thin sections stained with toluidin blue. E 3D reconstruction based on semi-thin sections (toluidine blue). F, F’ Sytox-stained confocal image stacks in ‘section mode’ view. Scale bars - 20 μm.