The 2nd and 3rd division from the 2- to 8-nuclei stage. A 3D reconstruction using semi-thin sections of the 2nd division (metaphase). Black lines: spindle orientations; A - yellow, B - red, C - green, D – blue: the four quadrants; the gray sphere: ncr. B Semi-thin section of the same egg. Dense granules (white arrow head) surround the ncr (arrow) in quadrant D. Dense yolk (y) dominates the animal region. C The vegetal pole at the 4-nuclei stage. The short cross furrow between B and D (arrow heads) is still covered by the cavity-like structure. D The animal pole at the 4-nuclei stage with a cross furrow between A and C (arrow heads). E Quadrant D at the 4-nuclei stage, animal pole is facing up. The ncr in D is shifted towards C. F Confocal section of the same egg as in E. The yolk (y) is condensed at the animal half. The white arrow marks the ds and the black arrow head the cavity-like structure. G The vegetal part of B forming a short cross furrow (arrow heads) with D; white arrow: ncr. H The vegetal B-D contact, slightly later as in G; white arrow: ncr. I The transient delay of the D division. J The vegetal pole with the quadrants in late anaphase. K Vegetal pole after 3rd division; arrow heads: cross furrow between B and D derivatives. L, M Semi-thin section of the same embryo. The membranes do not completely penetrate the yolk (L). The white arrow points to the cavity-like structure between D and B. The ncr lies in dI (M). N The animal pole of an 8-nuclei stage showing the cross furrow between macromeres aII and cII (arrow heads). O Animal-vegetal section of an 8-nuclei stage. The ds (black bordered arrow) has reached the center of the egg. Towards the vegetal pole, the cavity-like structure is visible (white arrow head) between B and D micromeres. Scale bars - 20 μm.