The _Geophilus electricus_ (Plate XIII., Fig. 2) is a small, inconspicuous insect, about an inch and a half in length, and one tenth of an inch in diameter. Like others of its kind, it lives in holes in the ground, and, when discovered, makes off rapidly by the use of its one hundred and forty legs. The interesting fact that the luminous secretion could be separated from the insect was originally noticed by Macartney seventy years ago, who found that the fluid, as he terms it, could be communicated by the centipede to every portion of its integument. This author also claims that the insect is only luminous after exposure to the sun,--a peculiarity that is found in certain minerals described in a later chapter. The most remarkable exhibition of the luminosity of these insects has been recorded by Mr. B. E. Brodhurst, who saw it first twenty paces away, so vivid was its display. The light looked like moonlight, so bright was it through the trees. “It was a dark night, warm and sultry. Taking a letter, I could read it. It resembled an electric light, and proceeded from two centipedes and their trails. The light illuminated the entire body of the animal, and seemed to increase its diameter three times. It flashed along both sides of the creature in sections, there being about six from head to tail between which the light played. The light behaved precisely like the electric light; moving, as it were, perpetually in two streams, one on each side, and yet lighting up the whole body. The trail extended one and a half feet from each centipede over the grass and gravel walk, and it had the appearance of illuminated mucus. On securing one of the creatures for examination, I found, on touching it, the light was instantly extinguished.” This observer says that this phenomenon was frequently seen by others about his place. Mr. Brodhurst continues, “Professor Flower identified the centipede as _Geophilus subterraneus_. The published descriptions of the luminous properties of British centipedes differ considerably from what I observed in this instance; the latter attributing light to the creatures only when disturbed. I was never able to induce my centipede to shine while in captivity.” CHAPTER X. BY CRAB-LIGHT. In drifting over the calm waters of the ocean as night comes on, we notice in the depths below luminous forms of infinite variety. These are _medusæ_, as we have seen, moving here and there like veritable comets. They approach so near the unruffled surface, at times, as to expose the gleaming disk. The nets of the fishermen come up entangled in their golden trains, and along shore processions and columns of these wondrous shapes pass and repass.