Cell Movements during Gastrulation of Starfish Larvae.

Abstract

Archenteron formation was monitored by measurement of cellular volume, injection of tracer enzyme, and vital staining. The cellular volume of the whole embryo did not change significantly from the start of gastrulation to the beginning of the mesenchyme-migration stage; the archenteron increased from about 10-20% during these stages. Tracer injection revealed that the boundary between the progenies of the veg1 and veg2 blastomeres of 32-cell-stage embryos was in the outer layer at the early gastrula stage, and at the rear end of the stomach at the bipinnaria stage. These results demonstrate a migration of cells from the outer layer to the archenteron wall during starfish gastrulation. Vital staining marks around the blastopore showed that the presumptive esophagus, stomach, and intestine area were added to the archenteron at the start of gastrulation, during the early to late gastrula stage, and thereafter, respectively. Tracer injection also indicated that the presumptive zone of the cardiac sphincter was twisted about 180{deg} clockwise around the axis of the archenteron after the late gastrula stage, dragging the cells in the presumptive zone of the esophagus and stomach.