Studies of the cleavage in the frog egg. I. On the temporal relation between furrow determination and nuclear division.

The cleavage plane in normally dividing animal cells is closely related to the position and the direction of the mitotic apparatus (cf. Gray, 1931). A displacement of the mitotic apparatus induces a corresponding shift in the position of the furrow in seaurchin eggs (Harvey, 1935; Rappaport & Ebstein, 1965), in the grasshopper neuroblasts (Carlson, 1952; Kawamura, i960) and in amphibian eggs (Waddington, 1952; Dan & Kojima, 1963). Recently, Zotin (1964), compressing axolotl eggs between slides to displace the mitotic apparatus, concluded that the position of the furrow is determined by the mitotic apparatus at the ana-telophase. On the other hand, it has been shown in sea-urchin eggs that once a stage between the metaphase and mid-anaphase is reached, the cell can form the cleavage furrow even after the mitotic apparatus is destroyed (Cornman & Cornman, 1951); Swann and Mitchison, 1953; Hiramoto, 1965) or removed (Hiramoto, 1956). However, since it is still not certain whether or not the same situation exists in amphibian eggs, a test for this point is desirable. In this paper, the eggs of Rana nigromaculata were employed. Two experimental procedures, (a) removal and (b) screening of the mitotic apparatus of the first cleavage, were performed during the period between the nuclear division and the appearance of the furrow, and the critical stage was studied at which the furrow formation became independent of the mitotic apparatus.