CELLULAR BASIS OF EPIBOLY OF THE ENVELOPING LAYER IN THE EMBRYO OF MEDAKA, ORYZIAS LATIPES. I. CELL ARCHITECTURE REVEALED BY SILVER STAINING METHOD

Abstract

A modification of silver nitrate staining, when applied to embryos of Oryzias latipes, was found to make clear not only the boundary of enveloping layer during epiboly, but also the outline of individual cells of the layer. The linear speed of advance of the enveloping layer was constant at fixed temperatures (20°, 25° or 30°C), except for the start and the end of the epibloy. Observation of the shape and arrangement of cells in the layer stained at successive stages of epiboly revealed that the enveloping layer expands uniformly over the yolk until late gastrula (3/4 epiboly). No cytokinetic figure was observed during epiboly until the blastopore was going to close. Total cell number of the layer remained constant during epiboly. Thus the expansion of the enveloping layer is accomplished without an accompanying increase in the number of constituent cells. In the last phase of epiboly, the surface area occupied by individual cells reduced locally at the region above the embryonic body, which suggests the occurrence in teleost of the convergence of cell sheets commonly observed in amphibian embryos.