Through these black abysses swim fishes with extraordinary adaptations to their conditions. No attempt at even brief descriptions would be worth making. All are small, often less than an inch, rarely as much as six inches long, yet they are armed to the teeth. This is especially true of the families Stomiatida• and Sternoptychidep, in which fishes of grotesque shape have big heads with a savage array of long sharp teeth.
All are voracious, and some, as Chiannodus, have mouths so capacious and stomachs so dis tensible that they can often swallow fishes as large as themselves, when their stretched stom ach with its load hangs beneath them like the yolk-sac of a newly-born trout. All are dark in color, brown, blue or violet marking the abyssal species. Some of them have light giving organs; and this was formerly regarded as a peculiar possession of deep-sea fishes, enabling them to see their prey in the Stygian gloom of the sunless abyss; but it is now known that light-organs are especially characteristic of pelagic fishes of the region between the surface and 250 fathoms of depth; and ichthyologists are uncertain what service they are to the fishes that carry them.
The eyes of most fishes, such as Macrotrus ormolus, that inhabit the deepest bottom-layers are very large and have the quality of nocturnal eyes generally — are "day-blind)); yet many fishes, squids, etc., hauled from great depths, have no visible eyes at all, or small and nearly useless ones; . and this puzzling contradiction applies to other fishes living at intermediate depths. Some of the blind abyssal fishes are provided with whiplike fin-rays or very long head-filaments that probably act as •f eelers,* and so serve the purpose of eyes in seeking food or taking warning of danger.
The general deductions to be made from this outline are that the waters of the ocean are everywhere inhabited, even to their uttermost depths, by living beings; and these are adapted to various circumstances and so form faunas of local extent and character.
Bibliography.— Goode and Bean, Ichthyology' (Washington 1885) ; Mosely, 'Notes of a Naturalist> (London 1878) ; Mur ray and Hjort, Depths of the (London 1912) ; Thomson, of the Challenger' (London 1877), and publications of sea-exploring expeditions and scientific insti tutions.