EVALUATION OF THE CHICK WING TERRITORY AS AN EQUIPOTENTIAL SELF-DIFFERENTIATING SYSTEM

Harrison (1918: J. Exp. Zool. 25: 413-461) described a developmental f ield as an ''equipotential self-differentiating system.'' The present study was undertaken to address the question: To what extent can the p re-limb territory of a chick embryo be considered a developmental fiel d? To what extent is the chick pre-limb territory an equipotential sel f-differentiating system? Two sets of experiments were undertaken to a ddress these questions: (1) Whole and half limb territories were expla nted to the celoma of host embryos, and (2) portions of the wing terri tories were extirpated. The wing exhibited the quality of self-differe ntiation after stage 12, in that the isolated wing territory, grafted to a host celom, could form limbs beginning at stage 12 (however, comp lete wings formed only from wing territories of stage 16 and older). O n the other hand, the chick wing territory did not appear to exhibit e quipotentiality. No posterior half limb graft formed normal limbs, and only in two exceptional cases did anterior half limb grafts form limb s. If part or all of the wing territory was removed from chick embryos , normal limbs formed in less than 15% of the cases after stage 15, in about 30% of the cases at stages 13 and 14, but in over half the case s at stages 10-12. Wound healing and reinitiation of limb potential ma y be responsible for the higher incidence of limb formation at the you nger ages. (C) 1993 Wiley-Liss, Inc.