Studies on the gastrulation of amphibian embryos: Cell movement during gastrulation inXenopus laevis embryos

In order to investigate the movement of cells during gastrulation inXenopus laevis embryos, mid-sagittal 1 μm Epon sections were made from the embryos, the stages of which were characterised numerically. Montage photographs were prepared from these sections. Cells in the section were classified into four groups according to sizes of the yolk platelets contained, and the distribution of cells belonging to each group was indicated in the montage photographs. Using such photographs, mean velocities were calculated for the movement of each cell group and the elongation of the archenteron. During the initial period of gastrulation, the groove of the archenteron deepened slowly (ca. 1 μm/min). When the blastopore became semi-circular, cells of the presumptive foregut endoderm, prechordal plate and mesoderm began to move toward the animal pole along the inner surface of the blastocoelic wall at the rate of about 6 μm/min. The archenteron elongated parallel to the inner surface of the blastocoelic wall at the rate of 9 μm/min. In the ventral part, the elongation of the archenteron and movement of the cell groups were slower than in the dorsal part. Cells taking part in the movement were loosely packed and were seen to form pseudopodia.