PHOLAS LUCIFERASE.--_Pholas_ luciferase has all the properties of an enzyme, is destroyed at 60° C., is non-dialyzable, insoluble in fat solvents, but forms a colloidal solution in water. It is not affected by 1 per cent. NaF but its activity is suspended in saturated salt solutions, sugar or glycerine, and it may be preserved in this way, its activity returning on dilution. It is digested by trypsin and slowly destroyed by the fat solvent anæsthetics, such as chloroform. For this reason Dubois regards it as an oxidizing enzyme similar to the oxydones of Batelli and Stern. Because he found iron in an extract of _Pholas_ dialyzed for a long time against running water, Dubois considers that it is associated with iron, and reports that it will oxidize the ordinary oxidase reagents, such as pyrogallol, gum guaiac, a-naphthol and para-phenylene-diamine, etc. It remains to be proved, however, that luciferase and not the oxidizing systems such as occur in all cells are responsible for the coloration of these reagents. Dubois has found luciferases or substances capable of giving light with _Pholas_ luciferin in the blood of many non-luminous crustacea and mollusks (in _Barnea candida_, _Solen_, _Cardium edulis_, _Ostræa_ and _Mytilus_). CYPRIDINA LUCIFERIN.--Despite the large amount that has been written on luminous animals, Dubois' work on _Pholas_ and my own on _Cypridina_ and the firefly are the only truly chemical studies that give us any idea of the nature of the photogenic substances in any luminous animal. In many ways _Cypridina_ luciferin is similar to _Pholas_ luciferin, but the two differ in a sufficient number of points to make certain that they are not identical substances. As I have emphasized above, we should speak not of luciferin and luciferase but of the _luciferins_ and the _luciferases_. The luciferins, as the oxidizable substances, must claim first attention. They are more simple substances than the luciferases. If we are to produce light artificially in the same way that animals do, the luciferins must be synthesized. The luciferin of _Pholas_ will luminesce with KMnO_{4} and other oxidizing agents, and, although I have not yet succeeded in oxidizing _Cypridina_ luciferin with oxidizing agents, I have no doubt but that some inorganic catalyzer will be found to take the place of luciferase and accelerate oxidation of _Cypridina_ luciferin with light production.