The quail-chick-marker technique has been employed to elucidate the determination of embryonic tissues in the avian wing bud. It was found that myogenic cells of somitic origin are determinated to give rise only to muscular tissue from HH-stage 19 on. Mesenchyme in the cartilage forming regions is determinated to form cartilage from HH-stage 20 on. Tissue from non-cartilage forming regions retains the option to form cartilage at least up to HH-stage 26. Whereas cells of somatopleural lineage do not migrate within the limb bud, cells of somitic origin do so up to at least HH-stage 28.