In contrast to many developing muscles which contain a spectrum of cells at different stages of differentiation, cell development in the locust abdominal intersegmental muscle tends to be synchronous, so that at any stage of development the cells are at the same stage of differentiation. This makes it feasible to relate the properties of the developing tissue as a whole to changes occurring within the cells.
Muscle contraction in the abdominal dorsal muscles of locust embryos and young hoppers has been related to ultrastructural changes within the muscle. Early in development both contraction and relaxation rates are very slow and the muscle shortens very little. The maximum registered tension is achieved relatively early while the rates of contraction and relaxation remain slow. Contraction and relaxation become more rapid as the embryo develops.
These changes can be related to the development of the reticular system, various components of which mature at different rates. When the muscle is first able to develop tension the myofibres contain scattered clusters of myofilaments while the transverse tubule system (T-system), the cisternae and the sarcoplasmic reticulum (SR) are not well developed. The myofibres reach their final size and the filaments are fully formed while the T-system is still irregular and the SR is sparse. The T-system and the cisternae become well developed before the SR. During the time that the relaxation time decreases the SR becomes increasingly prominent.