ABSTRACT
The kinetics of cell proliferation on during early ontogenesis of the brain and formation of the eye was studied in the chick embryo. Kinetic parameters--the mitotic index (MI), proliferative activity (P), the duration of mitosis (tm) and the generation time (T)--were measured in various regions of the brain and eye cup, using colchicine as a stathmokinetic agent. It was found that MI could be taken as an indicator of P during early development. In stage 11 it is also clear that the shortest T occurs in areas of rapid proliferation. By stage 12, although the generation time in the various regions studied differs, P and MI are approximately the same. A short tm is not always restricted to areas with a high P. P is affected by variation of T rather than by tm or time of any other parameter of the cycle. With increasing age, tm values decrease and T increase, probably owing to the progress of differentiation during embryonic development.
