Homonomies within the ventral muscle system and the associated motoneurons in the locust,Schistocerca gregaria (Insecta,Caelifera)

To understand the segmental reiteration of an insect, the serially arranged neuromuscular system of the locust, Schistocerca gregaria, is studied. The ventral muscle system is chosen and its motoneuronal supply is described in the thoracic and pregenital segments. In general, repetitively arranged, similar sets of motoneurons (MNs) supply the ventral muscles of these segments. Common criteria of both topology of muscles and neural features (nerve branches and motoneuronal supply) suggest possible homonomies of the ventral longitudinal muscles and ventral diaphragm of the thoracic and abdominal system. Based on a segment-by-segment analysis, muscle topology and motor supply match, in most instances. There are, however, cases where such a parallelism is missing. In a particular cases the supply of apparently homonomous muscles shifts from one set of MNs to another. In another case, putatively equivalent MNs of different ganglia supply morphologically different muscle structures in the adult animal. Therefore, it becomes apparent that muscles and their supplying MNs are, in principle, independent elements which might be subjected autonomously to ontogenetic processes. As a consequence, in the search for the basic segmental Bauplan depending on homonomous structures, muscles and MNs have to be regarded as separate entities.Abbreviations A1–6 abdominal ganglion (or neuromere A1–3) - AS1–6 abdominal segment 1–6 - DUM doisal unpaired median - M muscle (number) - MN motoneuron - N nerve (number) - PMN paramedian nerve - T1–3 pro-, meso-, metathoracic ganglion - TS1–3 pro-, meso-, metathoracic segment - VD ventral diaphragm - VM ventral muscle