Studies on the fine structure of the dorsal vessel of arthropods

Summary The heart of the lobster (Palinurus vulgaris L.) is a sleeve of muscle fibres, with the characteristics of the slow muscles of Crustacea: thin/thick filament ratio of about 6/1, sarcolemmal invaginations from which radial tubules arise, diads and triads formed by tubules and sarcoplasmic reticulum, large mitochondria, great amounts of glycogen. The muscle elements are not syncytial, but separated from one another by intercalated discs. The inner and outer surfaces of the muscle wall are ensheathed by connective tissue membranes made up of long-period (700 Å with 9 subbands) collagen fibrils, very low polysaccharide content, and no elastin. Amoebocytes are frequently embedded in the collagen sheath.