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The problem of mitochondrial structure has been the subject of extensive research during the past few years. Since Palade (1) published his "crista" concept, several other workers have proposed various interpretations of structure.From sections of mouse pancreas and of guinea pig retinal rods, SjiSstrand (2) suggested that the mitochondria are surrounded by a double "membrane" and contain transverse double "membranes" rather than ridges described by Palade. This structure was also seen in the proximal convoluted tubule cells of the mouse kidney (3). Chapman (4), however, has been unable to substantiate presence of a double external "membrane" in insect muscle mitochondria, although the inner transverse double structures appear to have surface attachments which are interpreted as junctions with a limiting "membrane." Glimstedt and Lagerstedt (5) claim that their preparations of rat fiver mitochondria show "... cable-like dements consisting of equal sized granules piled in a string one after the other..." contained as a bundle within an external "membrane." A departure from the theories of transverse lamdlae was presented by Beams and Tahmisian (6) who worked on Hdix aspersa gonad and constructed a modal demonstrating "longitudinal coaxial lamella~." There are now two schooLs of thought concerning the presence or absence (7, 8) of double walled "membranes."Biochemical and phase microscopy studies in this laboratory (9-11) have adduced no conclusive proof for the presence of mitochondrial membranes. On the contrary, they give evidence for the probable existence of a gel structure. Therefore, this study was initiated for the purpose of correlating mitochondrial ultmstmcture with previous findings. Since the completion of this work Powers, Ehret, and Roth (8) have reported the lack of external mitochondrial "membranes" in Paramecium aurdia or P. bursaria.Some confusion still exists concerning the use of the terms mitockondria

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