[Proliferative activity and the kinetics of the cell populations of chick embryo blastoderm in the period of gastrulation and early organogenesis. I. The proliferative activity and nature of the transition by mitotic cycle cells].

The intensity of entry of cells of different rudiments of the chick embryo in mitosis and S-phase at the stages of gastrulation and early organogenesis was studied by means of statmokinetic method and thymidine autoradiography. Regular changes in the percentage of cells entering mitosis and S-phase during development were found. The fluctuations of one index do not coincide often with those of another. The values of these indices within the limits of one rudiment may be interrelated in different ways. These interrelations change in their turn from one stage to another. A suggestion is put forward to the effect that the regular changes found represent a form of expression of parasynchronous proliferation pattern, related to the regular changes of the composition of cell polations due to unequal pasage of cells through the mitotic cycle.