THE FIBRILLAR SYSTEMS OF CILIATES AS REVEALED BY THE ELECTRON MICROSCOPE. II. TETRAHYMENA

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Abstract
1. Macronuclei, mitochondria, fragments of the pellicle and the oral apparatus of Tetrahymena may be isolated for electron microscopy by sonic dissection of osmium tetroxide fixed material. The fine morphology of the pellicle, the attached fibrillar structures and the oral apparatus are described. 2. The pellicle consists of a thin membrane which is sculptured to give a striated area immediately to the right of, and parallel to, each kinety, and two longitudinal ring-like thickenings, one at the level of and the other midway between the kinetics. 3. The kinetics of Tetrahymena, like those of Paramecium, are compound structures built up of discrete units. Each unit consists of three parts: (a) The cilium which passes through a ring-shaped thickening in the pellicle. (b) The ciliary basal body or kinetosome. This structure consists of two parts separated by a constriction. (c) A short, tapering, kinetodesmal fibril which arises from the kinetosome. These units of kinety structure are associated by their kinetodesmal fibrils. These fibrils overlap in shingle-like fashion to form the kinetodesma of the light microscopist. The individual kinetodesmal fibrils are highly polarized in this association. They all taper toward the anterior end of the animal. This mode of organization has now been demonstrated clearly in two ciliates, Tetrahymena and Paramecium. It will not be surprising if it is found to occur generally in ciliates. 4. The detailed structure of the oral apparatus, including the bases of the four membranelles and certain of their fibers, is revealed with new clarity. Prominent among the latter is a large fan-shaped group of fibers which arises from the first or undulating membranelle and probably extends deep into the interior of the animal. 5. The physical basis for some of the structures revealed to the light microscopist by silver impregnation is discussed.