Occasionally mitochondria of Paramecium become filled with cristae that display a wavy or helical pattern. In thin sections these cristae are viewed as curved arcs as well as cross sectioned rows in different parts of the organelle. Stacks of decorated tubules of the contractile vacuole system are also seen in this micrograph. Cristae of mitochondria bear F1F0 ATP synthases while the decorated tubules bear the related V1V0 V-ATPase proton pump. The helical arrayed F1F0 and V1V0 units may be responsible for forming the tubular nature of the cristae and the tubular decorated spongiome (for discussion of this hypothesis see Allen, Protoplasma 189:1-8, 1995). TEM taken on 5/6/82 by R. Allen with Hitachi HU11A operating at 75kV. Neg. 14,250X. Bar = 0.5µm.