I. Specific Nature of Triggering Events.

The flash of Noctiluca miliaris occurs only in response to a characteristic all-or-none action potential, the polarity of which is opposite to that of metazoan action potentials, whether recorded internally or externally. Mechanical stimulation evokes a slow, generator-like graded potential which can give rise to the flash-triggering action potential. The flash is all-or-none; it facilitates, summates, and exhibits fatigue, each independently of changes in the amplitude of the action potential.