Correlated physiological and ultrastructural studies on specialised muscles. Ib. Ultrastructure of white and pink fibers of the levator of the eyestalk of Podophthalmus vigil (Weber)

The ultrastructure of the different kinds of muscle fiber found in the specialised eyestalk levator muscle of Podophthalmus vigil was determined by electron microscopy. Pink fibers have wide, 13 μ sarcomeres, an extensive cleft system, branching Z tubules and a thick layer of mitochondria. Their ratio of thin to thick filaments is 4–5:1. Two distinct kinds of white fiber were found, with sarcomere lengths of 7.9 μ and 9.8 μ. The former have a very well‐developed SR, few mitochondria, a thin: thick filament ratio of 3–5:1 and numerous diads. The second kind have a 7:1 ratio, the thin filaments not being in orbits around thick ones. Their SR is quite well developed, but the cleft system only moderately so. There are more mitochondria in them than in the other white fibers.