Page:Popular Science Monthly Volume 7.djvu/471

Rh patch, a centimetre or so long, break out in the middle of an arm, and travel slowly out to the point, or the whole five rays would light up at the ends and spread the fire inward. Doubtless, in a sea swarming with active and predaceous crustaceans, with great bright eyes, phosphorescence must be a very fatal gift. On one occasion the dredge came up tangled with the long pink stems of a kind of sea-pen, which were resplendent with a pale lilac phosphorescence like the flame of cyanogen gas; not scintillating like the green light of the star-fish, but almost constant, sometimes flashing out at one point more brightly, and then dying into comparative dimness, but always sufficiently bright to make every portion of a stem caught in the tangles or sticking to the ropes distinctly visible. In some places, nearly everything brought up seemed to emit light, and the mud itself was perfectly full of luminous sparks. The sea-rushes, the sea-fans, and usually the seapens, shone with a lambent, white light, so bright that it showed distinctly the hour on a watch. In the neighborhood of the Madeiras, jelly-fish have been taken which emitted light in flashes, and the same phenomenon has been noticed in other parts, both in respect to jelly-fish, and, as we shall see, in respect to other animals.

Some of the most beautiful, luminous phenomena of the ocean are caused by animals belonging to the molluscous sub-kingdom, which is nearly as prolific in light-giving species as the Radiata. There is a shell-less mollusk which inhabits the Atlantic, in the neighborhood of the equator, and resembles a tiny cylinder of incandescent matter. It is microscopic in size, but prodigious numbers adhere together, until a tube from five or six to fourteen inches in length is formed, and the sea sometimes presents the appearance of a sheet of molten lava, from the number of these tubes which are floating in it. Moreover, a singular phenomenon is connected with this form of phosphorescence: the color of the light is constantly varying, passing instantaneously from red to brilliant crimson, to orange, to greenish, to blue, and finally to opaline yellow. Another highly phosphorescent species of Mollusca belongs to the family of the Salpidæ, which abounds in the Mediterranean and the warmer parts of the ocean. These individuals also swim adhering together in vast numbers, and produce the effect of long ribbons of fire, sometimes drawn straight in the direction of the currents, sometimes twisted and almost doubled by the action of the waves. In the Mediterranean their phosphorescence often resembles the light of the moon, giving rise to what the French term une mer de lait.

Luminosity is not so frequent a characteristic of the marine Articulata; nevertheless, it is exhibited by certain worm-like animals belonging to the class Annelida, and by a large number of the smaller Crustacea. In many instances the light takes the form of vivid scintillations similar to those emitted by the Medusæ, or jelly-fish, already mentioned. The appearance is sometimes very brilliant, when great