By repeatedly filtering water taken up fresh from the sea, Ehrenberg succeeded in obtaining a fluid in which a greater number of these luminous creatures were concentrated. (Abhandlungen der Akad. der Wiss. zu Berlin aus dem J. 1833, S. 307; 1834, S. 537-575; 1838, S. 45 and 258.) This acute observer has found in the organs of the Photocaris, which emits flashes of light either at pleasure or when irritated or stimulated, a cellular structure with large cells and gelatinous interior resembling the electric organs of the Gymnotus and the Torpedo. “When the Photocaris is irritated, one sees in each cirrus a kindling and flickering of separate sparks, which gradually increase in intensity until the whole cirrus is illuminated; until at last the living fire runs also over the back of the small Nereis-like animal, so that it appears in the microscope like a thread of sulphur burning with a greenish-yellow light. It is a circumstance very deserving of attention, that in the Oceania (Thaumantias) hemisphærica the number and situation of the sparks correspond exactly with the thickened base of the larger cirri or organs which alternate with them. The exhibition of this wreath of fire is a vital act, and the whole development of light is an organic vital process which in the Infusoria shows itself as an instantaneous spark of light, and is repeated after short intervals of repose.” (Ehrenberg über das Leuchten des Meeres, 1836, S. 110, 158, 160, and 163.) According to these suppositions, the luminous creatures of the ocean show the existence of a magneto-electric light-evolving process in other classes of animals than fishes, insects, Mollusca, and Acalephæ. Is the secretion of the luminous fluid which is effused in some luminous creatures, and which continues to shine for some time _without any farther influence of the living animal_ (for example, in Lampyrides and Elaterides, in the German and Italian glow-worms, and in the South American Cucuyo which lives on the sugar-cane), only a consequence of the first electric discharge, or is it simply dependent on chemical mixture? The shining of insects surrounded by air has doubtless other physiological causes than those which occasion the luminosity of inhabitants of the water, fishes, Medusæ, and Infusoria. The small Infusoria of the ocean, being surrounded by strata of salt water which is a good conducting fluid, must be capable of an enormous electric tension of their light-flashing organs to enable them to shine so intensely in the water. They strike like Torpedos, Gymnoti, and the Tremola of the Nile, through the stratum of water; while electric fishes, in connexion with the galvanic circuit, decompose water and impart magnetism to steel bars, as I showed more than half a century ago (Versuche über die gereizte Muskel- und Nervenfaser, Bd. i. S. 438-441, and see also Obs. de Zoologie et d’Anatomie comparée, vol. i. p. 84); and as John Davy has since confirmed (Phil. Trans, for 1834, Part ii. p.