抄録
The musculature of the larval midgut of the silkworm, Bombyx mori, is composed of outer set of longitudinal muscle fibers and inner set of circular muscle fibers. The circular muscle fibers are closely approximated and their plasma membranes are occasionally seen to be in close apposition. The muscle fibers are elongate uninucleate cells with a single myofibril in their sarcoplasm. The sarcomeres are divisible into A-, I-, H- and Z-bands. In the A-band region 12 thin myofilaments surround each thick myofilament. In fully contracted muscle fibers, the Z-band material is completely broken up into separate masses with spaces between them and there is an interdigitation of thick myofilaments from adjacent sarcomeres across these spaces. the sarcoplasmic reticulum frequently constitutes surface dyads with the plasma membrane but rarely associates with the transverse tubular system in the dyad configuration. The tracheal tissue appears to be the only cellular element that occurs in the interior of the musculature. Basal-granulated cells occur in the midgut epithelial layer.
