454 THE POPULAR SCIENCE MONTHLY. 



1870, so many of the deep-sea animals were found to be phospliorescent, 

 that Prof. Thomson has suggested that tlie light necessary to the 

 development of the eyesight which some of the specimens possessed 

 may have had its origin in that source. In animal phosphorescence, 

 as in all her works, Nature exhibits an immense variety in the forms 

 in which she displays her power; in one case, the luminosity will be 

 visible in a fluid secretion ; in another, it will manifest itself through 

 the action of a minute and complicated organ ; one species of animal 

 will shine with a yellow light ; a second, with brilliant green ; a third, 

 with pale lilac ; and we are acquainted with one instance in which the 

 light changes successively to the chief colors of the solar spectrum. 

 The causes which produce these phenomena are still very obscure. 

 Although many forms of life are known in which the luminous quality 

 is present, scientific men are not yet agreed on what the quality 

 depends ; and the purposes which the light serves in the animal 

 economy are also little understood. But the phenomena themselves 

 are often very remarkable. 



Some strange theories were advanced to account for the j^hospho- 

 rescence of the sea, before the real cause was discovered. In 1686, an 

 ecclesiastic, named Tachard, suggested that the ocean absorbed the 

 sun's light by day, and emitted it again at night. About the same 

 time, a better-known philosopher, Robert Boyle, endeavored to account 

 for the same phenomenon by the friction which, he supposed, the 

 rotation of the earth upon its axis caused between the water and the 

 atmosphere. The problem was finally solved in 1V49, by the discovery 

 of luminous animalcules in the water of the Adriatic Sea; and a large 

 proportion of the lower classes of marine animals are now known 

 to be phosphorescent to a greater or less degree. Let us take the 

 invertebrate divisions of the animal kingdom in their regular order, 

 and briefly glance at one or two examples in each. Beginning with the 

 simplest forms of life, the Protozoa, we find, in addition to certain 

 Infusoria, the little jelly-like organism to which naturalists have given 

 the name of Noctiluca, the phosphorescence of which is largely demon- 

 strated around our coasts. 



The radiated class of sea-animals possess high phosphorescent 

 qualities. Star-fish, sea-pens, jelly-fish, sea-fans, sea-rushes, may be 

 mentioned as cases in which the luminous quality is present among 

 the radiata. We will take our examples from among the specimens 

 captured during the expeditions of the Porcupine. Op some occasions 

 when the dredge was hauled up late in the evening, the hempen tangles 

 which were attached to it came up sprinkled over with stars of the 

 most brilliant uranium green ; little stars, for the phosphorescent light 

 was much more vivid in the younger and smaller specimens. The light 

 was not constant, nor continuous all over the star, but sometimes it 

 struck out a line of fire all round the disk, flashing, or one might rather 

 say glowing, up to the centre ; then that would fade, and a defined 



