Normal development of the chick wing following removal of the polarizing zone.

The negative results of assays for polarizing activity along the posterior border of the chick wing 24 and 48 hours after removal of the polarizing zone demonstrate that this zone is not regenerated following removal. These results, and the fact that normal wing development can occur after polarizing zone removal from stages 15 through 24 wing buds, indicate that during these stages the polarizing zone has no direct role in normal development of the limb bud. It is speculated that the polarizing zone is effective only during limb induction and that after this time it exists in latent or residual form.