THE NATURALIST.

Otago Witness, Issue 2325, 22 September 1898, Page 54

THE NATURALIST.

!n the Ocean's Depths. The temperature at the bottom of the ocean is nearly down to freezing point, and sometimes actually below it. There is a total absence of light, as far as sunlight is concerned, and there is an enormous pressure, reckoned at about one ton to the square inch in every 1000 fathoms, which is 160 times greater than that of the atmosphere we live in. At 2500 fathoms the pressure is 30 times more powerful than the steam pressure of a locomotive when drawing a train. As late as 1880 a leading zoologist explained the existence of deep-sea animals at such depths by assuming that their bodies were composed of solids and liquids of great density, and contained no air. This, however, is not the case with deep-sea fish, which are provided with air-inflated swimming bladders. If one of these fish, in full chase after its piey, happens to ascend beyond a certain level, its bladder becomes distended with the decreased pressure and carries it, in spite of all its efforts, still higher in its course. In fact, members of this unfortunate class are liable to become victims to the unl usual accident of falling upward, and no doubt meet with a violent death soon after leaving their accustomed level, and long before their bodies reach the surface in a distorted and unnatural state. Even ground sharks, brought up from a depth of no more than 500 fathoms, expire before they gain tbe surface. I The fauna of the deep blue sea — with a few exceptions hitherto only known as fossils — arc- new and specially modified forms of families and genera inhabiting shallow waters in modern times, and have been driven down to the depths of the ocean by their more powerful rivals in the battle of life, much as the ancient Britons were compelled to withdraw to the barren and inaccessible fastnesses of Wales. Some of their organs have undergone considerable modification in correspondence to the changed condition of their new habitats. Thus, down to 900 fathoms their eyes have generally become enlarged, to make the best of the faint light which may possibly penetrate there. After 1000 fathoms these organs are either still further enlarged, or so greatly reduced that in some species they disappear altogether and are replaced by enormously long feelers. The only light at gieat depths which would enable large eyes to be of any service is the phosphorescence of deep-sea animals. We know that at the surface this light is often very powerful, and Sir Wyville Thomson has recorded one occasion on which the sea at night was " a perfect blaze of phosphorescence, so strong that lights and shadows were thrown on the sails, and ie

was easy to read the smallest print." It" is thought possible by several naturalists that certain portions of the sea bottom bis,-" be as brilliantly illumined by this sort r.f fi^ht as the streets of a European city after sauset. Some deep-sea fish have two parade; rows of small circular phosphorescent organs running through the whole length of their bodies and as they glide through the dark waters of the profound abysses they must look likft model mail ships Arith rows of shining port holes. — Nineteenth Century.