Repeated regeneration of the German cockroach legs.

Two series of repeated-regeneration experiments were carried out on each fore-, mid- and hindleg of both sexes during the entire postembryonic development period. One was autotomy at trochanterofemoral articulation; the other was amputation from basal coxa. In both experiments, one of the six legs was operated on before the regeneration critical period in the 1st instar. If a regenerate appeared in the following instar, it was repeatedly operated on; if not, operation was postponed until a regenerate appeared. The number of instars required to reach the adult stage increased in both autotomy and amputation experiments. Total larval duration was also prolonged in both experiments. In autotomy regenerates repeatedly appeared almost every instar until the adult stage, while in amputation no regenerates were present just after postoperative molts. Regenerated femur and tibia developed well after autotomy, whereas those after amputation were considerably smaller. All the regenerated legs had tetramerous tarsi. Regenerated legs from autotomized stumps showed incomplete homoeotic regeneration as to the kind of legs. Regenerates from foreleg stumps showed intermediate tibia/femur ratios between normal foreleg and midleg, and those from the hindlegs, intermediate between normal hindleg and midleg. After amputation, the tibia/femur ratios of regenerates were variable. Possible modifiers were suggested for the homeotic and tetramerous regeneration.