CHAPTER IV

STRUCTURE OF LUMINOUS ORGANS

The production of light is the converse of the detection of light. In the first case chemical energy is converted into radiant energy; in the second case radiant energy is converted into chemical energy. The lantern of the firefly is an organ of _chemi-photic_ change; the eye is an organ of _photo-chemical_ change. While it is theoretically probable that all reactions which proceed in one direction under the influence of light, will proceed in the opposite direction with the evolution of light, the formation of luciferin from oxyluciferin (described in