WHILE studying the cytology of species of Epistylis, it was noticed that the nuclear apparatus of this ciliate presented certain interesting features. The macronucleus of Epistylis is a large and band-shaped body, staining deeply with all nuclear stains, and especially with Feulgen. The micronucleus is a small spherical structure situated in the neighbourhood of the macronucleus. The staining reactions of the micronucleus in two species of Epistylis show a significant difference. In Epistylis articulata From., the micronucleus is easily discernible as a deeply staining body. In E. plicatilis Ehrbg., on the other hand, the micronucleus gives a thoroughly negative reaction to Feulgen. Sometimes there are one or two minute granules which stain pink, but the rest of the nucleus is unstained. The difference is all the more striking because in the same mass culture both species were present, and they were treated together in the matter of fixation and staining.