The central projections of mesothoracic sensory neurons in wild-type Drosophila and bithorax mutants

Sensory axons entering the CNS from large campaniform sensilla on the normal, mesothoracic wings of four-winged flies of the genotype $\text{bx}{}^3\text{pbx}\text{Ubx}{}^{130}$ follow the same two tracts as do the corresponding axons in wild-type flies. However, they produce more branches along the ventromedial tract (including some in the mesothoracic neuromere), more fibers crossing the midline in the metathorax, and several other modifications of the wild-type pattern. No morphological differences between the receptors in normal and mutant flies could be detected, even with the SEM. The extra branching and other altered characteristics are present in bithorax flies which are also genetically wingless and do not form the homeotic appendages, so they appear to be due to the $\text{bx}{}^3\text{pbx}\text{Ubx}{}^{130}$ or $\text{bx}{}^3\text{Ubx}{}^{130}$ genotype and not to some effect of the axons from the homeotic wings.