The interval of the cytoplasmic cycle observed in non-nucleate egg fragments is longer than that of the cleavage cycle in normal eggs of Xenopus laevis.

Non-nucleate fragments of animal eggs are known to show a cyclic change in rigidity similar to the change observed in the cleavage of normal eggs. The interval of cyclic change was compared with that of the cleavage cycle in Xenopus eggs. Procedures employed by both Hara and co-workers and Sakai & Kubota to obtain non-nucleate fragments were carefully repeated. Non-nucleate fragments produced by either of those procedures had a longer duration of cycle than the normal cleavage cycle (about 30%). By injection of colchicine or vinblastine the cycle of the nucleate fragment was lengthened to coincide with that of the non-nucleate partner. It is suggested that the basic cycle length intrinsic to egg cytoplasm is modulated by assembly-disassembly of the mitotic apparatus, as demonstrated by Sluder in the chromosome cycle of sea urchin eggs.