Polyingression, an Important Morphogenetic Movement in Chick Gastrulation

Abstract

Three lines of evidence are presented to support the concept that polyingression represents a major morphogenetic movement in the genesis of the primary hypoblast, definitive endoderm and the mesoderm layers in chick gastrulation. Colchicine treated embryos produce a primary hypoblast layer thereby indicating that cell proliferation in the posterior marginal zone and elsewhere in the early embryo does not make a necessary contribution to hypoblast formation. Scanning electron microscopy provides morphologic complementary evidence that polyingression from the epiblast is a principal source of cells for the hypoblast. Finally, the morphology of cells with acetylcholinesterase activity suggests that this enzyme is related to release of cells from the epiblast so that ingression can occur.