Dacrydium vitreum, dredged from 2,435 fathoms, a curious little mytiloïd shell-fish, which makes and inhabits a delicate flask-shaped tube of foraminifera and other foreign bodies cemented together by organic matter and lined by a delicate membrane, is of a fine reddish-brown colour dashed with green, and the animals of one or two species of Lima from extreme depths are of the usual vivid orange scarlet.
Some of the abyssal molluscs have even been found provided with organs of sight. A new species of Pleurotoma, from 2,090 fathoms, had a pair of well-developed eyes on short foot-stalks, and a Fusus from 1,207 fathoms was similarly provided. The presence of organs of sight at these great depths leaves little room to doubt that light must reach even these abysses from some source, and as from many considerations it can scarcely be sunlight, Professor Wyville Thomson throws out the suggestion "that the whole of the light beyond a certain depth may be due to phosphorescence, which is certainly very general, particularly among the larvæ and young of deep-sea animals."
Thus many of the creatures dredged in the Northern Atlantic, off the west coast of Ireland,[AA] in depths varying from 557 to 584 fathoms, were most brilliantly phosphorescent. In some places nearly everything brought up seemed to emit light, and the mud itself was perfectly full of luminous specks. The alcyonarians, the brittle-stars, and some annelids were the most brilliant. The Pennatidæ, the Virgulariæ, and the Gorgoniæ shone with a lambent white light, so bright that it showed quite distinctly the hour on a watch, while the light from Ophiacantha spinulosa was of a brilliant green, coruscating from the centre of the disk, now along one arm, now along another, and sometimes vividly illuminating the whole outline of the star-fish. While the Ophiacantha shines like a star of the most vivid uranium green, the sea-pen (Pavonaria quadrangularis) is resplendent with a pale lilac phosphorescence like the flame of cyanogen gas, not scintillating like the green light of Ophiacantha, but almost constant, sometimes flashing out at one point more vividly, and then dying gradually into comparative dimness, but still sufficiently bright to make every portion of the polyp visible.
[AA] Ibid., [Chapter III]. Cruise of the "Porcupine," pp. 98-149.
Such numbers of the Pavonaria were brought up at one haul of the dredge in the Sound of Skye, that the "Porcupine" had evidently passed over a forest of them. While the darkness of winter frowns over the surface of the Northern Atlantic, the animated shrubs at its bottom are thus glowing with light, and a kind of magical day prevails in depths which were supposed to be shrouded with perpetual night. But it might have been better for many of the luminous denizens of the abyss if a more obscure existence had been their lot; for in a sea swarming with predaceous crustaceans with great bright eyes phosphorescence must surely be a fatal gift.
Off the coast of Portugal there is a great fishery of sharks (Centroscymnus Cœlolepis), carried on at a depth of 500 fathoms. If an animal so highly organised as a shark can thus bear without inconvenience the enormous pressure of more than half a ton on the square inch existing at that depth, it is a sufficient proof that the pressure is applied under circumstances which prevent its affecting it to its prejudice, and there seems to be no reason why it should not tolerate equally well a pressure of one or two tons, or why many other fishes—though the dredge, in consequence of their facility of locomotion, will hardly ever be able to bring them to light—should not abound in the still waters of the abyssal deep.
The "Challenger" Exploring Expedition will no doubt reveal to us still many an unknown wonder of those interesting regions, and make us acquainted with a world of new animals which even the profundity of the ocean vainly strives to hide from the curiosity of man.
