DEVELOPMENTAL INFLUENCES EXERTED BY THE PRE-AXIAL UPON THE DISTAL TERRITORIES OF THE CHICK EMBRYO LIMB BUD

Abstract

Isolates from the free edge of chick embryo hind-limb buds, containing the whole apical ridge of the ectoderm (or only a segment of It) and a variously thick layer of the underlying mesoderm, were implanted to the pre-axial or to the intermediary region of the wing bud in pd orientation, or to the trunk. Autotmplantations in embryos of various stages (from 18 to 26), and homoimplantations from donors to hosts of different stages were carried out. The apical material of the limb bud, isolated in early stages (18 to 22), is not yet capable of full self-development. Its organogenesls appears to depend, to a large extent, on influences transmitted from the mesoderm of the implantation site. The mesoderm of the trunk does not exert any detectable influences on the apical material of the limb bud implanted there. The whole mesoderm of the limb bud is capable, instead, of influencing growth and organo genesis of the implant. These organogenetic influences appear to vary qualitatively and quantitatively along the ap and the pd axes of the host limb bud.