The formation of supernumerary structures after grafting anterior quail wing bud mesoderm of various ages into chick wing buds

Wedges of anterior quail mesoderm grafted into posterior slits in the wing buds of chick embryo hosts result in the formation of rods and nodules of supernumerary cartilage in a high percentage of cases. Identifiable digits do not form unless the ectoderm is allowed to remain on the grafts. Control experiments have shown that wedges of anterior or posterior wing mesoderm placed into homologous locations of host wing buds produce few or no supernumerary skeletal structures. Anterior-to-posterior grafts of stage 17 mesoderm evoke a 71.4% incidence of supernumerary cartilage. This percentage increases to 100% with stage 22 donor mesoderm. The percentage of supernumerary structures formed declines markedly with donor mesoderm of stages 24-30. By stages 35-36, only 10% of the grafts result in the formation of supernumerary structures. The period of decline coincides with the onset of overt cytodifferentiation within the donor mesoderm.