POSSIBLE SIGNIFICANCE OF NUCLEAR VOLUME CHANGE DURING EARLY DEVELOPMENT OF NEWT EMBRYOS

The nuclear volumes at several stages of development were measured on Triturus pyrrhogaster embryos and changes in the fine structure and reactivity towards alkaline fast green of the nuclei were also examined. It was shown that the blastula nuclei were reduced about 80% to reach a constant volume of about 1,400 μm3 by the tail bud stage in ectomesodermal parts of the embryos. In the endoderm, the decrease in the nuclear volume was slightly delayed. Application of the decreasing rate of nuclear volume, from blastula to gastrula, to a simple model suggested that an amount of material, equivalent to that of a full-sized germinal vesicle, is stored in the egg to support the rapid nuclear divisions during the early phase of development.