Developmental interactions between the adjacent parts of combined heterologous skeletogenous territories

The right limb buds of chick embryos (H.-H.stages 22 to 26) were transversely divided at approximately the presumptive zeugopod mid-length, and (1) the distal parts exchanged between wing and hind-limb bud in apdv-reversed orientation (operation A), or (2) the severed distal part of the leg bud was reoriented in situ (operation B). Both the proximal and distal segments of the zeugopodal bones developing from the recombined portions of presumptive heterologous territories showed characteristic differences of size and shape in comparison to the corresponding parts of the skeletal pieces of the zeugopod of the intact, control limbs. These developmental changes are interpreted as being the consequence of reciprocal influences exerted by the adjacent parts of mesenchymal territories (or blastemata) that, under normal developmental conditions, are destined to give rise to different bones. Such influences may enhance or depress the growth potential of the skeletogenous populations affected, and, within each cell population, modify the geometry of the growth processes by which the various parts of each skeletal piece attain their typical shape.