Cytoplasts have been obtained from Acetabularia, and their substructure was examined after 3 and 11 days. After both periods of time, the chloroplasts display bundles of thylakoids; the latter are not inflated. The pseudograna vary in number according to the time of the daily cycle in the 11-day-old cytoplasts. The number of carbohydrate granules is variable, but the granules themselves are small; they have diffused limits after 3, but not after 11 days since the cytoplasts were obtained. The stroma is dense. The chloroplasts do not seem to be engaged in a process of division. Mitochondria contain a system of cristae abnormally developed. The Golgi apparatus is still present but has only few inflated vesicles; small granules are usually visible in the vicinity of the dictyosomes. The substructure of these organelles is compared with that in anucleate algae, and the possible significance of the observations is discussed.