Convergent thickening describes the morphogenic movement seen in the marginal zone of sandwich explants, in which cells converge along the mediolateral axis while thickening in the radial axis of the embryo.  In explants of ventral marginal zone, this process operates beginning in early gastrula stages and continuing into early neurula stages.  In explants that include the dorsal marginal zone (the organizer), convergent thickening begins as in

Several approaches to understanding biomechanics in embryonic tissues.
	assays of affinity between deep tissue and marginal zone epithelium.
	Confocal timelapse sequences
	Low-light digital microscopy