While the Pholas conceals its luminosity in its dungeon, there are other molluscan light-givers which float about like light-ships astray. These are Pteropods, or wing-footed mollusks; delicate fairy ships of marvellous beauty. By some authorities they are said to represent the higher forms of the _Cephalophora_, while others consider them as degenerate or backsliding Cephalopods, of which the squids and octopi are representatives. They are pelagic, free-swimming mollusks, in which portions of the foot are modified into seeming wings, so that the little creature seems to fly through the water. They differ much in appearance. Some secrete a glassy, horny, cartilaginous or limey shell, which in some cases is only present in the larval forms, disappearing in the adult; while others, again, preserve it through their entire lives. The body is of various shapes: it is protected by the shell when present, and can be drawn into it. Though simple, helpless creatures, many have an armament which in a larger animal would be considered extremely effective. Thus in _Clio_ each tentacle bears nearly three thousand cylinders, each containing stalked suckers; and, as there are six tentacles, the little animal can grasp its microscopic prey with three hundred and sixty thousand hands. Besides this, it has a pair of many-toothed jaws and a toothed tongue. While extremely small, these animals exist in such vast multitudes, that they probably constitute an important food for certain whales. [Illustration: PLATE VI. APOLEMIA. CLEODORA. PRAYA.] One of the most interesting of the Pteropods, or wing-footed animals, as associated with our present subject, is the _Cleodora lanceolata_ (Plate VI., Fig. 1). It has a pyramidal shell, terminating in three sharp spines, the wing-like fins rising above. It is rarely over half an inch in length, almost transparent, and bears in its shell a small light, which, however, is distinctly seen through the transparent covering. A more beautiful living lamp it would be difficult to imagine; and when slowly flying through the ocean, in countless myriads, they must present a wondrous sight. One of this genus, observed by Giglioli, emitted a very livid red light; the luminous organ being at the summit of the shell. There are many different genera and species. _Hyalea_, an oceanic wing-foot, moves very rapidly, and looks not unlike a butterfly darting here and there, in erratic flight, in search of food; but the little _Cleodora_ moves in a regular and stately manner. In _Hyalea_ observed by Giglioli in the harbor of Anjer, Java, the light, which contributed largely to the general phosphorescence, was confined to the basal part of the shell.