Abstract
Transient stimulation of cell division within chick wingbud mesenchyme is associated with the reorganization of limb pattern that follows insertion of a small graft from the posterior zone of limb polarizing activity into the anterior border of a host bud. This increase is initiated as an enhanced rate of entry to S phase, correlated with a decrease in packing density among mesenchyme cells, through much of the limb rudiment a few hours after the operations.