[Experimental data on the development of the primordia of the long bones of chick embryo extremities]

By means of various kinds of recombination of the two halves of the chick limb buds transected at the presumptive zeugopod mid-length a continuity was established between the opposite portions of the mesenchymal precursors of heterologous shaft bones of the zeugopod. In later development, both proximal and distal components of the recombined skeletal pieces consistently showed variously marked differences in size and shape in comparison with the corresponding parts of the control bones. Reciprocally, from the opposite portions of the presumptive territory of each zeugopodal bone separated the one from the other so that they could not contact and fuse, hypoplasic pieces developed which failed to attain the size and shape typical of the control segments. Those observations seem to show that morphogenetic interactions reciprocally exerted between the various parts of the presumptive territory of each shaft bone are mandatory to ensure the normal development of these skeletal pieces.