The lessons we learn from the study of the fishes of the deep sea are particularly instructive. It would take far more space than can be afforded here to fully illustrate all of the points that seem clear to us, but I hope I have said sufficient to show that the fish fauna is made up of genera and species belonging to several widely separate families of the Teleostei; that some of them show, in a very marked way, what may be looked upon as peculiarly bathybial characters, whilst others are but slightly modified from their shallow-water representatives. These facts by themselves lend support to the view that the fauna of the deep sea has been derived from the fauna of shallower water by successive migrations at different periods of the world’s history. Those that exhibit in a most marked degree the special bathybial characters are probably those whose immigration took place long ago, whilst those more closely related to shallow-water forms are, comparatively speaking, recent importations. The occurrence of Scopelidæ and Sternoptychidæ in deep water suggests, as Moseley pointed out many years ago, that the fauna is partly derived from the pelagic plankton. But while these points may seem clear to us, there are others that still require much more investigation and consideration. The whole question of the function and use of the phosphorescent organs, the mucous glands, the barbels and elongated fin rays, the mode of life, the deposition of ova and their development, afford problems which in the present state of our knowledge must remain unsolved. Let us hope that in the future there may be a new stimulus given to deep-sea research, and these problems may be again seriously studied and eventually solved. INDEX Actiniaria, 36, 93 —— two remarkable genera of, 15 _Aegir_, 15 Agassiz, A., —— on colour of Cœlentera, 65 —— on Echinoidea, 101, 103 Agassiz, L., on board the ‘Hassler,’ 12 ‘Albatross,’ American vessel, 15 Alcyonaria, 95 —— phosphorescence of, 81 Amphipoda, 124 Anemones —— of deep water, 36, 92 —— two remarkable genera of, 15 Annelida, 117 Ascidia compositæ, 146 —— salpiformes, 147 —— simplices, 142 Asteroidea, 104 Barriers of temperature, 32 _Bathynomus_, 129 Beddard, F. E., on Isopoda, 127 Benthos, 53 Berycidæ, 154 ‘Blake,’ American vessel, 12 Blue mud, 42 Brachiopoda, 115 Brachyura, 138 _Brisinga_, 9, 105 Buchanan’s experiment, 19 Carpenter, P. H., on Crinoidea, 100 _Cephalodiscus_, 113 Cephalopoda, 120 ‘Challenger,’ H.M.S., voyage of, 12 Cirripedia, 130 Cœlentera, —— colour of, 65 —— of deep sea, 91 Colour —— of the deep-sea fauna, 59, 66 —— of the deep-sea fish, 60 Copepoda, 124 Corals, 94 Crinoidea, 99 Crustacea, 123 —— colour of, 63 Darkness of the abyss, 22 Diatom ooze, 39 Dipnoi, 149 Echinoderma, 99 —— colour of, 64 Echinoidea, 101 Eels, 165 Elasipoda, 106 Elasmobranchii, 148, 153