Figure 4

Embryos of B. longimanus during the 4th and 5th division cycle towards the 32-cell stage. A View of the vegetal pole with the division delayed gc. Micromeres aII, bI, and cII have divided in equatorial direction, while gc divides in animal-vegetal direction (small stars: cellular relicts as artifacts). B Embryo at a similar stage as in A with view of the D derivatives. The delayed division of gc is at the top (long white line). C View of the vegetal pole of a 16-cell stage with all cells at metaphase apart from gc and en. gc is in contact to all micromeres at the vegetal pole: aII1, aII2, bI1, bI2, cII1, cII2, and en. D Single image of a confocal scan near the center of the embryo where the macromeres appear in a clover leaf-like arrangement. The ds lies in the center. E The animal pole at the 16-cell stage. BII1 and BII2 have not contact to DII1 and DII2. F Confocal section of the area with the small cavity-like structure in the center (surrounded by a white line). G View of the vegetal pole. The division of gc is delayed compared to en, resulting in a 31-cell stage. H View of the D derivatives of a similar stage as in G. The direction of the division of en and gc is perpendicular to that of DII1 and DII2 (short lines represent the sister cell relationships of all visible cells; in gc the direction of division is marked by arrows). I-K View of the animal pole with different positions of macomeres in which BII and DII derivatives do not contact each other. L Confocal section with two ds (white arrow heads) adjacent to the cavity-like structure (surrounded by a white line) in the center of the embryo. Scale bars - 20 μm.