Figure 1

Variation in the rate of third cleavage revealed by nuclear staining. (A - F) Propidium iodide staining of early H. asinina embryos allowed the number of discrete nuclei to be accurately determined. All views are lateral except the inset in (B) which is from the animal pole. (A) A four-cell embryo with two distinct nuclei in the focal plane (four nuclei in total). (B) A morphologically similar embryo to that shown in (A) with four nuclei in the focal plane. When the same embryo is viewed from the animal pole (inset) eight nuclei are visible. Embryos shown in (A) and (B) are of the same chronological age. (C) Following cytokinesis, eight distinct cells can be seen with four of the eight nuclei visible in this focal plane. (D-F) Bright field views of the corresponding embryos as in (A-C). (G) Embryos from three unique fertilizations were monitored at five-minute intervals for the time taken to progress from four discrete nuclei to eight discrete nuclei. Each point represents a minimum of 20 observations