Regulation capacities of the wing- and halterediscs of wild type and bithoraxDrosophila.

1. On removal of one dorsal mesothoracic disc from third-instar larvae ofDrosophila melanogaster (wild stock), regulation took place in one fourth of the cases, by the activity of the corresponding disc of the intact side. 2. In larvae of abithorax stock, regulation took place in the majority of cases, but it was due to the activity of thebx dorsal metathoracic disc of the operated side. 3. The sternopleura is present after extirpation of the wing disc but absent after extirpation of the ventral mesothoracic disc. 4. The findings under 1 and 2 are discussed in connection with previous work on regulation in larval discs.