[Disordered mitoses and extranuclear chromatin in the cells of normally developing embryos of Brachydanio rerio]

In the cells of normal embryos of zebrafish, Brachydanio rerio, the Feulgen-positive particles were found in the cytoplasm, in addition to the following abnormalities of mitoses: retardation and loss of chromosomes, disorganization of mitotic figures similar to those seen with C-mitosis, condensation and pycnotic transformation of chromatin preceding the cellular death. The dynamics of these phenomena was traced in the course of development starting from the 8 cell stage to the late blastula stage. The high frequency of the above findings, as well as a certain extent of the topological correspondence of abnormal mitoses enable the author to propose that the normal development of bony fishes is accompanied by degradation of the hereditary material in some cells of the embryo. This may constitute a step of differentiation for at least provisional structures of the embryos.