The exact part that is played by the different components of these curious phosphorescent organs is not yet known, but sufficient has been said to indicate to the reader the degree of complexity that these organs may reach in the fish of the great depths of the ocean. [Illustration: FIG. 8.—Section of the anterior sub-orbital phosphorescent organ of _Pachystomias microdon_ (after Von Lendenfeld). L, lens; O, phosphorescent gland; P, pigment sheath.] But the power of emitting phosphorescent light is by no means confined to the group of fishes. Some of the Macrurous Decapoda among the Crustacea are known to be phosphorescent. In the case of _Heterocarpus Alphonsi_, for example, the naturalists of the ‘Investigator’ found that ‘clouds of a pale blue highly luminous substance, which not only illuminated the observers’ hands and surrounding objects in the vessel in which the creature was confined, but also finally communicated a luminosity to the water itself, were poured out apparently from the bases of the antennæ.’ ‘The _Willemoesia_, too, was luminous at two circumscribed points somewhere near the orifices of the genital glands.’ Again, all the Alcyonarians dredged by the ‘Challenger’ in deep water were found to be brilliantly phosphorescent when brought to the surface, the light consisting, according to Moseley, of red, yellow, and green rays only. Among the Echinoderms we have not many recorded instances of a phosphorescent light being emitted, but it is quite possible that many, if not all of them, may possess this power. The curious deep-sea form _Brisinga_, that was first discovered by Ch. Asbjörnsen, is known to be so brilliantly phosphorescent that it has been called a veritable _gloria maris_, and writing of the curious brittle-star _Ophiacantha spinulosa_ (dredged by the ‘Porcupine’ in 584 fathoms of water), Professor Wyville Thomson remarks that the light was of a ‘brilliant green, coruscating from the centre of the disc, now along one arm, now along another, and sometimes vividly illuminating the whole outline of the star-fish.’ According to Filhol many of the abysmal Annelid worms are in the habit of emitting a vivid phosphorescent light, and capable thereby of illuminating the medium in which they live.