1. 1. Porichthys luciferin gives an extensive series of luminescent cross-reactions with the luciferases of various other luminous organisms. 2. 2. The luminescence reaction of Porichthys is very similar to that of the marine ostracod crustacean, Cypridina hilgendorfii. 3. 3. A relatively high percentage of the stomachs of adult Porichthys contained the euphausiid, Euphausia pacifica. 4. 4. Theories regarding the origin of luciferin in Porichthys and some other shallow-water fishes are discussed. 5. 5. The discovery of luminescence in the marine teleosts, Apogon poecilopterus and Parapriacanthus dispar, is reported.