Growth of Lobster Leg Muscle Fibers Over Intermolt and Molt

Growth of fibers in a small proximal bundle of the extensor muscle in the third walking leg of the lobster Homarus americanus was determined by comparing animals in the intermolt and immediate pre- and post-molt stages. The fibers grow in length immediately after molting by the addition of sarcomeres which remain relatively constant in size. The fibers grow in cross-sectional area by the splitting of large myofibrils upon molting and by their subsequent enlargement during the intermolt. Stretch applied to the muscle fibers as the animal expands its cuticle immediately after molting may be the stimulus for the splitting of myofibrils and the addition of sarcomeres.