Peculiar pattern of interkinetic nuclear migration in the newt Notophtalmus viridescens

The distribution of mitotic figures was studied in the neuroepithelium of Notophtalmus viridescens embryos of stages 14, 16 and 18. On the average, 34% of the mitotic figures were counted near the neurocoele (here in described as zone 1), 10% were recorded in the outer portion of the epithelium (zone 3) and 56% were found between these two regions (zone 2). It is concluded that this neuroepithelium is the site of interkinetic nuclear migration although its pattern is peculiar when compared to what occurs in the chick embryo. Also, the analysis of one micron-thick serial sections showed that the neuroepithelium in Notophtalmus viridescens is pseudo-stratified throughout neurulation.