[Genesis of malformations of the distal parts of chick embryo extremities (adactylia, hemimelia)].

Two series of experiments were carried out on chick embryos, stages 24 to 28 pairs of somites. (1) Denuded mesenchyme obtained from leg presumptive area previously treated with nitrogen mustard, was grafted into the right flank of embryos, stages 15 to 24 pairs of somites. (2) Conversely, denuded mesenchyme was implanted into the flank of nitrogen mustard-treated embryos. In most of the embryos, a supernumerary abnormal limb appeared; 58% of the legs produced in the first set of experiments had distal parts, whereas only 15% of the legs in the second set of experiments showed toes. Most of these legs had a hemimelic aspect or were reduced to stumps. This study demonstrates that deficiencies localised in the ectodermal apical part of the bud may be responsible for the stumpy limb defect.