Many beautiful phosphorescent jellies can be observed, as we drift along, by using a small glass cylinder. With the finger pressed upon the top, lower the open end near the little creature, then remove the finger, when the jelly will be drawn into the improvised aquarium. If the night is dark, the play about its delicate form will be found a rare study. Darwin refers to the beauties of the phosphorescent jellies observed on one of his collecting-tours. He says, “While sailing a little south of the Plata on one very dark night, the sea presented a wonderful and most beautiful spectacle. There was a fresh breeze, and every part of the surface which during the day is seen as foam now glowed with a pale light. The vessel drove before her bows two billows of liquid phosphorus, and in her wake she was followed by a milky train. As far as the eye reached, the crest of every wave was bright; and the sky above the horizon, from the reflected glare of these livid flames, was not so utterly obscure as over the vault of the heavens.... Having used the net during one night, I allowed it to become partially dry; and having occasion, twelve hours afterward, to employ it again, I found the whole surface sparkling as brightly as when first taken out of the water. It does not appear probable, in this case, that the particles could have remained so long alive. On one occasion, having kept a sea-jelly of the genus _Dianæa_ till it was dead, the water in which it was placed became luminous.... Near Fernando Do Norhona, the sea gave out light in flashes. The appearance was very similar to that which might be expected from a large fish moving rapidly through a luminous fluid. To this cause the sailors attributed it; at the time, however, I entertained some doubts, on account of the frequency and rapidity of the flashes.” To Spallanzani is due the credit of first calling attention to the phosphorescence of the jelly-fishes or sea-jellies; he having observed it in the Mediterranean jelly, _Pelagia phosphorea_, which is luminous over its entire surface. He subsequently made some interesting experiments with _Aurelia phosphorea_, a jelly-fish similar to one on our coast, and came to the conclusion that the _light-emitting_ organs lay in the arms, tentacles, and muscular zone of the body, and cavity of the stomach; the rest of the animal showing no luminosity. The light seemed to proceed from a viscous liquid, a secretion which oozed to the surface. One _Aurelia_ that he squeezed in twenty-seven ounces of milk rendered the whole so luminous that a letter was read by the light, this being one of the first practical results of the investigation of marine phosphorescence. Humboldt experimented with _Aurelia aurita_, and, having placed it upon a tin plate, observed, that, whenever he struck it with another metal, the slightest vibration of the tin rendered the animal completely luminous. He also observed that it emitted a greater light when in a galvanic circuit.