Mutants show a tendency to transform labial into maxillary structures. The mutated labial segment appears to be transformed into something closely resembling the more anterior segment, resulting in duplication of maxillary structures. This simplistic, rather linear view of gene action is belied by more than five years research into the regulation of Sex combs reduced .
Complex regulation implies a complex function.
The biological tools currently employed are as yet too crude to elucidate what must be a high level of interactive complexity. Current understanding is partial and at times contradictory, like the divergent views of the fabled elephant examined by blind men. From the vertebrate perspective, the labial segment produces what is perhaps the most ornate and alien of the fly's structures, the proboscus. The proboscus protrudes out and downward from the head, a flexible dipstick adapted to gather liquid nourishment. At its working end hang the labella, or labial palps.