That birds should be luminous is not, perhaps, strange. Other vertebrates appear to possess this gift in an equally remarkable manner. Some years ago an English gentleman, a lover of sport, was travelling in South America; and among the tales that he heard from the natives was one that related to a monkey with fiery eyes, as they expressed it. It seemed that one season, when the tribe was far up the branch of a small river, a woman wandered off into the forest at night, and returned much alarmed, stating to the rest that an animal had appeared to her with eyes gleaming like coals. Several of the natives went to the spot designated, and were repaid with a glimpse of the strange creature. Such a tale was, of course, not received in good faith, being considered an example of the inventive fancy of these children of the forest; yet, curiously enough, Reninger the naturalist, who travelled extensively in Paraguay, states that he has seen the eyes of the monkey, _Nyctipithecus trivirgatus_, so brilliant in complete darkness that they illuminated objects at a distance of half a foot. In several instances I have referred to the phosphorescence of animals being used possibly as a warning; at least, this is the explanation given the phenomena by some observers, and one of the most interesting cases that may possibly come under this head is the luminosity of frogs’ eggs. This has been noticed in various parts of Europe; masses of luminous matter being found about ponds and damp places, and termed _mucilage atmosphérique_, as it was believed by the simple peasants to be part of the tail of comets. [Illustration: PLATE XX. LUMINOUS FISH. (_Stomias boa._)] On one occasion several peasants were travelling from one village to another at night, when suddenly a large meteor shot across the heavens, seeming to fall before them. A few miles farther on, in crossing a small swamp, they found several patches of a jelly-like matter, which gleamed as if at a white heat, which so alarmed them, that they ran into the next village, crying that a comet had fallen, and was burning up the earth. So much excitement was created that some scientific men visited the spot, finding the comet to be merely the mucus that had surrounded the eggs of a frog, and had become luminous. If the mucus was luminous when it surrounded the eggs, we may well imagine that birds would be deterred from eating them; but the luminosity probably precedes decomposition in the mass after the young have escaped.