Figure 5

The processes from the 6th division cycle on through the beginning of gastrulation. A View of the vegetal pole of the 32-cell stage during 6th division cycle. Apart from gc1, gc2, en1, and en2 the cells are in metaphase. B An embryo at a similar stage as that in A with view of the D derivatives. The orientation of their divisions is indicated by arrows. C Embryo at the 6th division cycle in which bI21 and bI11 (nuclei represented by red spheres) adjacent to gc1 and gc2 divide perpendicularly compared to the direction they reveal in A. D 3D reconstruction of the 60-cell stage after the completion of this cycle. The positions of the two cells gc1 and gc2 in this embryo are not symmetrical with respect to the other cells and appear slightly rotated clockwise. E 60-cell stage with the view of the B derivatives. F View of the animal pole of the same embryo as in E; the D derivatives are smaller compared to the other macromeres with DII122 being the largest D macromere. G Animal pole of a 60-cell stage, with the d macromeres at metaphase initiating the following division cycle. H View of the animal pole of an embryo consisting of 175 cells of which 17 are in mitosis at the vegetal pole. The nuclei of the macromeres are arranged in a circle. Each two AI and CI derivatives (transparent white overlay) are in contact and the BII and DII macromeres do not share a common border. I View of the vegetal pole of an embryo comprising 236 cells showing eight macromere derivatives arranged in a ring. J, J’ Embryo of 215 cells with 16 macromeres arranged star/cross-like and with 21 cells in mitosis at the animal pole (represented by red spheres in J’). Scale bars - 20 μm.