442 DISTRIBUTION IN SPACE AND TLME 



THE ABYSMAL ZONE— LIFE IN DEEP WATER 



The Abysmal Zone includes that part of the sea into which 

 daylight penetrates but little, if at all. Even the average depth 

 of the ocean, taken as a whole, is about 2100 fathoms (12,600 

 feet), while the profoundest abysses may be more than double 

 this. The deepest patch at present known is off the coast of 

 New Zealand, where a sounding of over 5000 fathoms (30,000 

 feet) has been obtained. It was long supposed that the deep 

 sea was entirely devoid of life, but the numerous scientific in- 

 vestigations made during the last few decades have proved that 

 even at great depths there is a rich and varied fauna, closely 

 allied to that of the Neritic zone, but presenting many peculiar 

 features in relation to the entirely difterent physical conditions. 

 Except where this realm adjoins the Pelagic zone above it, it is 

 probably in complete darkness so far as daylight is concerned, 

 though it is more or less lit up by the phosphorescent glow given 

 out by many of its inhabitants. The pressure is enormous, and 

 the deep sea is also very cold, the temperature of its floor not 

 being far removed from freezing-point. There is a complete 

 absence of plants (except perhaps bacteria), and many of the 

 animals are consequently predaceous in a marked degree. The 

 requisite supply of food is maintained by the dead organisms 

 which rain down from the Pelagic zone, or get washed in at the 

 sides from the Neritic zone. Deep-sea animals present a great 

 variety of colours, though no one tint can be said to characterize 

 the fauna as a whole, and there is generally no blending of differ- 

 ent hues in the same animal, nor any complex patterns or mark- 

 ings. It would seem that the utilitarian explanations that are more 

 or less applicable to the colour-schemes of neritic forms fall short 

 here. Certain other features will best be explained by briefly 

 reviewing some of the chief groups of animals. 



Deep- Sea Fishes [Pisees). — Most of the fishes of the deep 

 sea are black or brown in colour, but some of them are purple, 

 pink, or red, and since these brighter hues are most prevalent 

 in the upper regions of the abyss, at depths of from 100 to 250 

 fathoms, it is not impossible that they may correspond to a dull 

 kind of sunset illumination due to light which has filtered down 

 from the surface. Many deep-sea fishes are also characterized by 

 the possession of variously arranged phosphorescent organs on 



