TUBULAR MUSCLE-FIBERS IN ANTS AND OTHER INSECTS

Some insect muscles are composed of tubular fibers. Their walls contai n the contractile apparatus while their central cores comprise nuclei and mitochondria. Tubular fibers probably arose early in arthropod evo lution as suggested by their presence in some primitive insect and oth er arthropod taxa. No tubular muscle fibers seem to be present in lepi dopterans while muscles of beetles and of hemimetabolous insects featu re various proportions of tubular and non-tubular fibers. Tubular fibe rs are particularly well developed in Hymenoptera and Diptera where th ey compose all muscles but the fibrillar flight muscles. In several in sect orders, notably Diptera and Hymenoptera, certain muscles are comp osed of tubular fibers with particularly wide central cores. Some of t hese supposedly fast muscle fibers comprise the shortest sarcomeres ye t described. A correlation between the diameter of the central core of tubular fibers and their velocity of activation is thus suggested and for some ant muscles is corroborated by the expression of other struc tural properties and of enzyme activities.