Figure 2. Nymphopsis spinosissima. High power view of a similar section as Figure 1. Sarcolemmal infoldings have become flattened tubules with distinctively dark walls, flanked by cisternae of the sarcoplasmic reticulum to form triads. At the right upper margin, the sectioning plane is entering the level of the I-band, indicated by tapering and termination of the thick myofilaments. Although the symmetry is a hexagonal one within the myofilament lattice, each myosin filament is surrounded by about 12 actin filaments, a characteristic of slow muscle. 45,000x