The accelerating action of illumination in recovery of Arbacia eggs from exposure to ultraviolet radiation.

Light of wave lengths 0.30micro to 0.50micro, accelerates return of the cleavage rate of Arbacia eggs to normal, after delay by exposure to ultraviolet radiation (wave lengths 0.238micro to 0.31micro). Recovery is apparently complete. Wave lengths 0.30micro to 0.50micro have no effect on the cleavage rate of normal eggs, nor does such illumination previous to dosage with ultraviolet radiation influence subsequent recovery. Acceleration of recovery of the egg occurs before fertilization as well as after. The effects of ultraviolet radiation and recovery therefrom are essentially the same in nucleated "white halves" as in the intact eggs. This phenomenon in the Arbacia egg seems basically comparable to photoreactivation of bacteria and fungi.