Fine structure of the alary muscles of the American cockroach

The alary muscles of the cockroach, Periplaneta americana, are striated with an A-band of 3·0 to 3·5 μm long. Each muscle fibre was 10 to 12 μm in diameter and Z-lines appeared as small discrete units staggered throughout the sarcoplasm. Mitochondria were conspicuously located near the Z-line areas and were absent from the middle portion of the sarcomere. A transverse membrane system was present which formed dyad structures with a relatively sparse sarcoplasmic reticulum. Cockroach alary muscles were innervated by axons containing electron-dense granules of near 100 nm in diameter. These are thought to be typical of ‘neurosecretory’ axons based on their ultrastructural appearance.