Figure 4.

Sequence of still photos from time-lapse video records of cleavage at the vegetal pole. (a) Late 16-cell stage. Micromere nuclei are intact whereas macromeres are beginning to furrow (arrowhead) (b) At the 5^th cleavage, the micromeres have a slower cleavage schedule than the macromeres (c) The 32-cell stage, showing 4 small micromeres (SMi) atop 4 large micromeres (LMi); the 8 macromeres surround them. (d) The 4 LMi retain their nuclei while the macromeres undergo 6^th cleavage. The SMi are above the plane or focus. (e) The 6^th cleavage of the LMi. (f) The 60-cell stage showing 4 small and 8 LMi surrounded by the macromeres. (g) The 7^th cleavage of the macromeres. Both small (arrowheads) and large (arrow) micromeres retain intact nuclei. Most micromere nuclei are not in focus in this photo, but all are intact. (h) The 6^th cleavage of the SMi. LMi nuclei have broken down for the 7^th cleavage. (i) The 8^th cleavage of the macromeres. Note intact nuclei of the 24 micromeres. The numbers in the upper right of each frame are minutes elapsed from the first frames in the sequence at 17 °C.