Abstract
Thin and thick sections of both physiologically active and physiologically passive iridophores from a range of vertebrate species have been examined by electron microscopy at 60 kV and at 1,000 kV. All iridophores studied have been found to contain 65-A filaments linking successive crystals in their parallel stacks; their orientation in the cell is shown in stereo pairs of 0.25-microm sections obtained from high voltage microscopy. In addition, several of the physiologically passive iridophores contain 100-A filaments in varying numbers. It is suggested that the thin filaments might be iridophore actin and play a role in the movement of iridophore components, and that the 100-A filaments might play a cytoskeletal role in the iridophores in which they occur.