Experimental Observations on the Development of Ectoderm-free Mesoderm of the Limb Bud in Chick Embryos

Abstract

A NORMAL extremity does not develop from the mesoderm of the early chick limb bud completely freed of its ectoderm by treatment with ethylenediamine tetraacetic acid (EDTA)^1–3, but epithelial residues accidentally left adhering to the surface of the denuded mesoderm seem to be sufficient for the regeneration of the entire ectodermal cover. Thus, limb development is ensured⁴, and the epithelial component of the limb bud appears to be necessary for normal limb development. It remains undecided whether failure of limb development after the removal of ectoderm depends merely on the exposure of the mesoderm to artificial and unfavourable environmental conditions^5,6 or on the absence of a structure, the apical ridge of ectoderm, which plays a morphogenetic role in the development of the bud mesoderm^1–4.