Fig. 9. Vertical parasagittal histological sections of medial (A) and lateral (B) edges of red muscle (RM) mass at 0.6L, illustrating the difference in development of lubricative sheath (LS). The lubricative sheath that surrounds the RM mass is thicker and more well-developed on the medial surface of the RM. Scale bar, 0.2 cm. WM, white muscle.