1. The general structure of Astasia harrisii Pringsheim is described.
2. The osmiophil material is well shown in Weigl preparations and resists bleaching by hydrogen peroxide or turpentine. In many individuals it consists roughly of an oval mass connected to the reservoir by what is considered to be a canal with osmiophilic walls.
3. The shape of this canal changes considerably, and in many specimens has a blebbed appearance. In others it consists of a number of small osmiophilic vacuoles placed end to end. A small vaeuole is often present at the tip of the canal.
4. In a few cases the reservoir is surrounded by an osmiophil cortex continuous with the walls of the canal.
5. It is suggested that the osmiophil material possibly represents the homologue of the Golgi apparatus in higher forms, and is concerned with the secretion or excretion of some liquid down the canal into the reservoir.
6. The possible evolution of the osmiophil material in Astasia is discussed.