The contractile vacuole in A. p. contains at the surface a well differentiated membrane about 0.5[mu] thick. Adjoining this membrane on the outside there is usually a layer of substance in which numerous [beta] granules (Metcalf''s "excretory granules") are imbedded. This layer is more viscous and heavier than the adjoining cytoplasm. It is usually about 3[mu] thick when the vacuole is maximum in size and it becomes thicker during contraction. The [beta] granules around the contractile vacuole vary greatly in number and the layer of substance in which they are imbedded varies greatly in thickness, without any apparent variation in the function of the vacuole. These facts indicate that neither the [beta] granules nor the layer of substance is involved[long dash]at least directly[long dash]in the function of the contractile vacuole. The differentiation of a layer of substance on the surface of a contractile vacuole is probably due to the action of the fluid in the vacuole, on the adjoining cytoplasm. There is much confusion concerning the ideas held by different investigators in regard to the nomenclature, the structure and the function of the various granules and crystals in the cytoplasm of the protozoa. This matter is discussed.