... of a chick host. Apposition of rhombomere 4 (r4) with r3 was concomitant with negligible cell mixing across the interface. By contrast, combinations of r3 with r5 or with r3 tissue led to cell mixing that was more extensive in combinations of identical rhombomeres (r3 with r3) than between two alternate ones...

... these alternative hypotheses. If blastomeres are predetermined, then random intermixing of the descendants with neighbouring cells could not alter their fate. To follow cell mixing during Xenopus development, fluorescent dextran lineage tracers were microinjected into identified blastomeres at the 16-cell stage...