Amphioxus photoreceptors were investigated with electron microscope. The visual cell of the Becherauge has the Stiftchensaum as the photoreceptoral structure which is composed of microvilli of the visual cell surface. Immediately underlying the Stiftchensaum is the tubular zone which is formed by the well-developed endoplasmic reticulum. Clumps of mitochondrial aggregations are found just inside of this zone, and numerous glycogen granules in the basal part of the cell.
The fine structures of other photoreceptoral organs (dorsal cells, ependymal sense cells and infundibular organ) were elucidated and discussed.