Cyclic changes in the cortical layer of non-nucleated fragments of the newt's egg.

Various changes in the cortical layer of the amphibian egg have been observed during cleavage; for example, rounding up in the animal hemisphere, increase in stiffness of the surface and reactivity of the cortex to furrow-inducing cytoplasmic components. The three kinds of change occur synchronously with the cleavage cycle. The present experiments were aimed at determining whether the above changes in the cortical layer are caused exclusively by the nucleus or autonomously by the cytoplasm. Uncleaved fertilized eggs of the newt, Cynops pyrrhogaster, were divided into two parts, one nucleated and one non-nucleated, by cutting with a fine glass needle. Special attention was paid to the behaviour of the non-nucleated fragments, where the above-mentioned changes were also observed. The cycle of these changes did not necessarily start synchronously with the cleavage cycle of the nucleated partner, but, once started, the rhythm of both cycles had almost the same timing. These results suggest that some change in the cortex necessary for cleavage furrow formation in the amphibian egg is brought about by cyclic change in the cytoplasm, independently of the nucleus.