The property of emitting a phosphorescent light, sometimes spontaneously and sometimes on being stimulated, is likewise exemplified in the Ctenophora, a group resembling the Medusidæ in the jelly-like character of their bodies, but more closely allied in structure to the Actinozoa. But we will pass over these cases in order to dwell more particularly on the remarkable tunicate known as Pyrosoma, a name indicative of its phosphorescent property, being derived from two Greek words signifying fire-body. As shown in the illustration Pyrosoma is not a single creature, but is composed of a whole colony of individuals, each of which is represented by one of the projections on the surface of the tube, closed at one end, which they all combine to form. The free end on the exterior contains the mouth, while there is another opening in each individual toward the interior of the tube. Such colonies, which swim about by the alternate contraction and dilatation of the individuals composing them, are pretty common in the Mediterranean, where they may attain the length of perhaps fourteen inches, with a breadth of about three inches. In the ocean they may reach a much greater size. Mr. Moseley, in his "Notes of a Naturalist on the Challenger," mentions a giant specimen which he once caught in the deep-sea trawl, a specimen four feet in length and ten inches in diameter, with "walls of jelly about an inch in thickness." [Illustration: A. PYROSOMA. B. PONITON. (Magnified.)] The same naturalist states that the light emitted by this compound form is the most beautiful of all kinds of phosphorescence. When stimulated by a touch, or shake, or swirl of the water, it "gives out a globe of bluish light, which lasts for several seconds, as the animal drifts past several feet beneath the surface, and then suddenly goes out." He adds that on the giant specimen just referred to be wrote his name with his finger as it lay on the deck in a tub at night, and in a few seconds he had the gratification of seeing his name come out in "letters of fire." Among mollusks, the best known instance of phosphorescence is in the rock-boring Pholas, the luminosity of which after death is mentioned by Pliny. But it is not merely after death that Pholas becomes luminous--a phenomenon perfectly familiar even in the case of many fish, especially the herring and mackerel. It was long before the luminosity of the living animal was known, but this is now a well-ascertained fact; and Panceri, an Italian naturalist, recently dead, has been able to discover in this, as in several other marine phosphorescent forms, the precise seat of the light-giving bodies, which he has dissected out again and again for the sake of making experiments in connection with this subject.