The spawning of Ciona intestinalis with respect to light was studied, using both white light and monochromatic light. 2. A one-hour dark-adaption period followed by exposure to light resulted in spawning by 66.6% of the 884 animals tested. 3. Spawning occurs an average of 27.3 minutes after the onset of illumination. 4. Illumination need not be continuous until spawning occurs; the animals spawn when returned to the dark after a short illumination period, provided they have received enough energy. 5. The action spectrum for spawning suggests cytochrome c as a chromophore.
