One of the interesting experiences of NordenskiÖld in the Arctic Ocean was wading through the sludge, as the soft snow water along the beach is called, and seeing each footprint turn into a mass of light, caused by the phosphorescence of a small crustacean called Metridia. The light was bluish white, of great intensity, and although at times the cold was so severe that mercury would freeze, yet everywhere this marvelous light blazed. Even drops and splashes of the water seemed to be molten metal, but were merely alive with this minute light giver resembling Cyclops. In the Pacific, especially in summer, the exhibition of what might be called "crab light" is marvelous, and this is often true in the Atlantic. The light following the splash of an oar, the spray hurled aside by the cut water, the foaming water around a propeller, and the strange shifting specter which follows the rudder, are caused more or less by minute crustaceans which have the faculty of emitting light without heat.

Along the beach beneath seaweed, we shall find Gammarus, a long, very small, but mighty jumper, that at night emits a red light. Many of the near relatives of this little creature are phosphorescent, and perhaps the most beautiful of all is one named Idotea phosphorea. It is a yellowish spotted little creature found in pools alongshore. It darts about among the weed, and would rarely, if ever, be noticed during the day; but at night the entire animal seems permeated with a golden light which marks it in vivid lines against the dark bottom, and flashes and miniature meteors indicate it as it dashes across the little pool, its ocean world.

The most beautiful of all crustaceans is the one known as Sapphirina. I have seen the ocean filled with them; some red, others blue or yellow, purple or green, all known gems being imitated by these matchless gems of the sea, which in daylight vie with the most brilliant iridescence in producing wonderful displays. No more beautiful scene can be imagined than that embracing these living gems, standing out in brilliant tints against the deep blue of the ocean. These gems also have the gift of phosphorescence and at night appear in a new guise.

One of the singular long-legged spider crabs of the deep sea, Colossendeis, is said to be phosphorescent. Giglioli, the Italian naturalist, describes a crab which gives a golden purple light, the latter appearing from the thorax. The little shrimp, Mysis, which carries its young in a pouch, from which it is called the opossum shrimp, is not phosphorescent, but its young in what is called the zoËa stage are luminous. The odd-shaped little creature, which is the mantis shrimp in one of its stages, is brilliantly luminous, not over its entire body, but in the eyestalks. Some of the deep-sea crabs have luminous eyes, strange monsters wandering in the abysmal regions of the deep sea.

While most of these crabs have the light in only one place, one discovered by Sir Joseph Banks was luminous over its entire surface. Exactly what the luminous matter is, is not known, but in some instances it can be scraped off and will render the hands luminous when rubbed upon them. According to A. M. Norman, naturalist of the Porcupine expedition, the crustacean Ethusa, found at a depth of eighteen hundred feet, is blind, its eyestalk being spiny, and the eye replaced by a smooth, round termination which is supposed to be a light-emitting organ. Aristeus has phosphorescent eyes, which blaze with the yellow fire of a cat's eye, and this is true of many other crustaceans. Some have luminous backs; others have fiery bands upon the legs, while almost every portion of the body of some species is the seat of this wonderful light. That the lights are of some use there can be little doubt. In one little creature Dr. Gunther found a brilliant light stationed between its eyes, which certainly was a light to illumine its way in the deep, dark bed of the ocean.