Fig. 4

Cell tracking during the formation of the germ-disc. Stills from Additional file 7 and Additional file 8: Movies 7 and 8. a-d Two cells that will contribute to the germ-disc (yellow and blue) and two cells that will contribute to the extra-embryonic region (orange and magenta) have been analysed for their division rate. During the course of germ-disc formation from late stage 2 to stage 3 the cells divide either two times (resulting in 4 cells; yellow and orange) or three times (resulting in 8 cells; blue and magenta). e-h Only the cells that will contribute to the extra-embryonic region of the spider embryo have been tracked from late stage 2 to late stage 3. Please note that the majority of the cells of the early blastoderm (e) will contribute to the germ-disc during later stages of development. Time is in hours (h). Only the nuclei with its attached perinuclear cytoplasm have been tracked, as cell outlines are not visible under bright field light conditions