It is quite possible, however, that part of the fauna of the deep sea has been derived directly from the pelagic zone. The occurrence of bathybial Radiolaria, Foraminifera and Siphonophora, and among fishes genera and species of the pelagic families Sternoptychidæ and Scopelidæ, suggest that this zone may have contributed very largely to the fauna of the abyss. Much of course still remains to be done before we can consider any of these interesting problems connected with the deep-sea fauna to be definitely solved. All we can do at present is to speculate upon the direction in which the facts at our disposal seem to point, and by following up one clue after another hope that we may eventually arrive at the truth. The task may be a difficult one, but it will reward our efforts. If truth is hard to find when it lies at the bottom of a well, how much more inaccessible must it be when it lies hidden in the darkness of the sea’s abyss! CHAPTER IV THE CHARACTERS OF THE DEEP-SEA FAUNA The general characters presented by animals living in deep water may be considered under several headings. The most important are those that are directly or indirectly related to the fact that the animals live either in total darkness or in the faint and probably intermittent light emitted by phosphorescent animals; namely, the colour of the skin and the peculiarities of the eyes. The colours of the skin of the deep-sea animals vary to a very remarkable extent in the different groups. It cannot be said that there is any one colour at all predominant, and it is only in certain classes that black, white, or dull-coloured animals are more numerous than others. The colours are however usually very evenly distributed, and we find but few examples of animals with spots, stripes, or other pronounced markings. The majority of the fish are dark brown or black, but many other colours are represented. Thus _Ipnops Murrayi_, a typical deep-sea fish, is yellowish brown with colourless fins, and it exhibits a further character not uncommon in these abysmal forms, namely black buccal and branchial cavities. _Typhlonus nasus_, again, is said to be of a light brownish colour, with black fins. Many other examples could be given to show the prevalence in these regions of these black, dull, and pale uniform colours. But there are many exceptional cases. _Neoscopelus macrolepidotus_, for example—a form that according to Günther undoubtedly belongs to the bathybial region—is distinguished by its brilliant colours. It is bright red mixed with azure blue, the whole relieved by silver spots with circles of black on the abdomen. _Prorogadus nudus_ is of a pale rose colour, with the under and lateral sides of the head bluish black. _Rhodichthys regina_, found in 1,280 fathoms of water, is uniformly bright red in colour.