Studies of the Cleavage in the Frog Egg

The time scale of nuclear division with reference to cleavage time was prepared for the normal egg of Rana nigromaculata. Two experimental procedures, (a) removal and (b) screening of the mitotic apparatus, were performed in the eggs at various times before the beginning of the first cleavage, in order to determine when the furrowing activity of the cortex became independent of the mitotic apparatus. The two experiments concordantly indicated that an autonomous capacity for furrowing was established in the cortex between the metaphase and the late anaphase. Notwithstanding its extremely large size, this critical stage for the frog egg is practically the same as those which have been reported in other smaller cells.