... these strategies. In some descendants, the fluorescent dextran fills the cells’ processes, and specific types of cells can be recognized by their characteristic morphology ( Dowling, 1976 ; Ramon y Cajal, 1972 ). For both optic vesicle cells and optic cup cells, all major cell types were present in clones...

... 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...