[Intercalary regeneration and segmental gradients in the extremities ofLeucophaea larvae (Blattaria) : III. The origin of the intercalary regenerate].

Under certain conditions transplantation and extirpation experiments with the legs ofLeucophaea maderae (Blattaria, Blaberidae) are followed by the development of intercalary regenerates. Such experiments have suggested the existence of segmental gradients. The experiments in this study were done to elucidate the origin of the intercalary regenerate by exchanging parts of the legs between the closely related speciesLeucophaea maderae andGromphadorhina portentosa. 1. Following the extirpation of middle pieces out of a leg segment,Gromphadorhina responds with the development of an intercalary regenerate in the same manner as doesLeucophaea. These results suggest that there are segmental gradients in the legs ofGromphadorhina, too. 2. If one combines the tissues of both species, they react in a coordinated manner. An intercalary regenerate develops only when, by transplantation, gradient discontinuities are established. The coordinated action of the tissues suggests that the gradient factors are the same or at least very similar in both species. 3. Both participants may share in building the intercalary regenerate to a varying extent. Including the results of earlier experiments one may state: The regenerate in most cases is built entirely or to a great extent by that participant which has the most distal amputation level. As a rule, the intercalary regenerate is built up by disto-proximal regeneration, i.e. the regeneration of a proximal segment area occurs from a distal level. 4. The tissues regenerating an intercalary regenerate preserve their characteristic, leg specific state of determination: no change of fore leg tissue to hind leg tissue (or the reverse) has ever been noticed. So, the origin of a regenerate is deducible from its structure.