0023-6152

AA00697606

23695

Unrefereed

0023-6152

AA00697606

From the viewpoint of adaptation for flight in bats, this report presented electron microscopic observations on the pectoral muscles during the growth period from the late embryo to the adult stage in the Japanese Lesser horseshoe bat, Rhino-lophus cornutus cornutus. Evidence obtained by examining the muscle fibers at different growth stages strongly indicated that their number was determined before birth, and that they remarkably increased in size to the flying stage probably because of the longitudinal splitting of the myofibrils when they attained a certain size. Furthermore, in the late embryo and newborn stages, a small number of longitudinally oriented T tubules occurred along the margin of the A-band although the predominant orientation of T tubules was transverse. In the flying stage which gave the first indication of differentiation into the adult muscle fiber types, however, almost all the T tubules ran in transverse direction near the A-I junction. Judging from the facts that the completion in orientation of the T tubules and the earliest sign of muscle-type differentiation were recognized in the flying stage, it was ultrastructurally concluded that the flying stage was the most important stage of the postnatal period in the bat from the standpoint of survival potential.