WE have received a communication from Mr. Edward T. Dixon, of Billy Dun, Half Way Tree, Jamaica, regarding the luminosity of fire-flies in Jamaica. He mentions having observed large numbers of a species of fire-fly emitting flashes of light in rhythmic unison, a feature, it may be added, that has been noted in other lands. In the Jamaican species the flashes were emitted at intervals of just under three seconds duration. Mr. Dixon mentions having seen half an acre or more of a grass field lit up brilliantly by the flashes of fire-flies so that the shrubs and hedges were revealed. During the intervals between the flashes nothing was visible in the prevailing darkness. Little is known regarding the phenomenon, and experimental observations with reference to the coordination of light emission by these insects might prove of great interest.