[Stratification in the central nervous system]

Stratigenesis in the optic tectum of developing chick embryos was investigated between the 4th and the 11th day of incubation. Stratification is achieved by successive emigration of cell contigents from the proliferative layer. In the opinion of the authors the main factor which determines this very regular cell migration would be a gradient of oxygen and of metabolites. The gradient has to appear in the wall of tectum due to its typical vascular network. Experiences with induced hypoxia or with selective damage of the proliferative layer strengthen the hypotesis of an oxygen gradient playing the role of a generally active epigenetic factor in the stratigenesis of the central nervous system.