As the night grows apace, and the wind rises, they sink into the deeper waters; yet the foam and crest of the waves still give out the curious light, though now from another source. Much of this is due to Crustaceans, minute creatures often almost invisible to the naked eye, yet possessing this wonderful gift of phosphorescence to a marked degree. Some species of the little _Gammarus_ are remarkable for their clear silvery light. They are familiarly known as water-fleas, attracting attention from their leaping powers, and are often found under seaweed above high-water mark, darting here and there in incredible numbers when their home is disturbed. These forms are extremely valuable as scavengers. That these interesting animals were light-givers, has long been known; Viviani observing it in a number of species in the beginning of the present century.[39] There is one peculiarity about many of these small animals; that is, the light has a more decided red tint than that of any other group of animals. This is especially true of many of the water-fleas, or _Entomostracans_, and the extremely transparent, ten-footed kinds. The light is often intense, but fitful and shortlived. It seems to start from the locality where the legs join the body, and rapidly spreads beneath the skin until the entire body appears to be suffused with light, and the little animal consumed with an internal fire. Yet if a bushelful of these gleaming living lights were confined, and a thermometer placed among them, it would not show the slightest variation or evidence of heat. The little Cyclops is very common in our freshwater ponds, and forms a beautiful object under the microscope. Along our sea-shores we may often see, under the rocks, clinging to the eel-grass, or among the thickly growing stems of _Coralina officinalis_, in some pool left by the tide, gleaming spots that move about in an erratic manner; now many collecting together, then breaking up into small patches of light, which in turn separate again. They are curious Crustaceans, known scientifically as the _Idotea phosphorea_. By day we shall find that they are usually spotted or entirely a bright yellow; at night emitting fitful gleams, perhaps as signals or as means of communication to their fellows.