Abstract
The tubular heart of the moth, Hyalophora cecropia, is composed of a single layer of striated muscle cells linked together by intercalated disks. The intercalated disk can be resolved into two components: interfibrillar junction and septate desmosome. The width of the cells varies from 10 to 30 μ and the cell length is 60 to 100 μ. The A Bands of the heart muscle are 1·8 μ long. The diameter of the thick filaments is 200 Å and that of the thin filaments 60 Å. Each thick filament in the overlap region in the A Band is surrounded by an orbit of ten to twelve thin filaments. Transverse tubules and sarcoplasmic reticulum vesicles are irregularly spaced throughout the cells. Sections of the heart from different abdominal segments were studied, and no significant differences were observed in cell size, sarcomere structure, distribution of mitochondria, transverse tubules and sarcoplasmic reticulum, or in the components of the intercalated disk in any of the cells. The physiological significance of these observations is discussed.
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