The Function and Metabolism of Certain Insect Muscles in Relation to their Structure

Electron microscopic observations on ultrathin sections of the red thoracic flightmuscles and white leg muscles of Hydrophilus and Dytiscus are reported. In red muscle-fibres with high values in frequency of contraction, oxygen consumption, and dehydrogenase activity, the single fibrils are completely surrounded by huge mitochondria. Tracheoles penetrate the sarcolemma and supply the mitochondria with oxygen by intracellular branches. In the less active white muscle fibres, mitochondria are found irregularly scattered between the fibrils or along the I band. The intracellular tracheolization is sparse but an endoplasmic reticulum is widely spread between the synfibrillar contractile material. The same muscles of the two insects differ considerably in detail.