Neuromuscular systems in the fifth instar larva of silkworm Bombyx mori (Lepidoptera: Bombycidae): II- Abdominal musculature and its innervation

Abstract

The gross organisation of abdominal musculature and its innervation by segmental ganglionic nerves were studied in the fifth instar larva of Bombyx mori. The musculature comprises dorsal, ventral and lateral groups of muscles, represented as external and internal layers. The dorsal group includes musculi dorsales interni mediales (DIM), musculi dorsales externi mediales (DEM), musculi dorsales interni laterals (DIL) and musculi dorsales externi laterales (DEL). The ventral group includes musculi ventrales interni mediales (VIM), musculi ventralesexterni mediales (VEM), musculi ventrales interni laterales (VIL) and musculi ventrales externi laterales (VEL). The lateral group is represented by musculi laterales interni (LI) and musculi laterales externi (LE). The abdominal muscles are innervated by the dorsal (DN) and ventral (VN) nerves of abdominal ganglia. The DN innervates ventral internal, lateral internal and both dorsal external and internal muscles, while the VN innervates ventral external and lateral muscles. The sensory branches of DN and VN innervate the bodywall in the dorsal and ventral regions respectively with a sort of overlapping in the lateral region. The neuromuscular integration and intersegmental coordination in the abdominal region is discussed with reference to locomotion in the silkworm larva.