Evolutionary loss of a neural pathway from the nervous system of a fly (Glossina morsitans/Diptera)

Three pairs of specialized axons found in other muscoid flies are absent in the tsetse, Glossina morsitans, which also lacks the tergotrochanteral muscle. Neither light nor electron microscopy could demonstrate any evidence for the cervical giant fiber axon, the peripherally synapsing axon, or the tergotrochanteral motor axon. The specialized characteristics of these axons must have been altered during the evolution of Glossina. This divergence of individual neurons from the more typical muscoid pattern not only demonstrates the evolutionary modification of specific identified cells; it may also provide an opportunity to study the ontogenetic determination of unique neuronal features.