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Page:Popular Science Monthly Volume 21.djvu/398

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two, the "Tropical Pacific" and the "Antarctic" region, the last including the Patagonian seas as well as those of New Zealand and Tasmania. The fishes of the second category (brackish water), owing to the fact of their living in salt-water equally with fresh, and thus being able to spread readily over the globe, can not help in any plan of parceling out the earth's surface into districts. The shore-fishes afford a somewhat better definition, and of them five groups are formed, which inhabit respectively the Arctic Ocean, the Northern Temperate Zone, the Equatorial Zone, the Southern Temperate Zone, and the Antarctic Ocean. The pelagic fishes seem to require separation, but as little can be deduced from them as from the inhabitants of brackish waters, and they insensibly mingle with the fishes of the deep sea.

Thirty years ago no one had the audacity to believe that the abysses of the ocean were tenanted with piscine life. Even animal life of any sort had been supposed to be impossible at a greater depth than that which has now been found to be but the portal of a new world of beings. The discovery of what has since been proved to be deep-sea forms of fishes began indeed long ago, but the abysmal nature of their haunts was hardly suspected, and certainly not recognized till much later, when the fact was established by Dr. Günther, conjointly with the late Mr. James Yate Johnson. On this subject Dr. Günther says: "The knowledge of the existence of deep-sea fishes is one of the recent discoveries of ichthyology. It was only twenty years ago, that, from the evidence afforded by the anatomical structure of a few singular fishes obtained in the North Atlantic, an opinion was expressed that these fishes inhabited great depths of the ocean, and that their organization was specially adapted for living under the physical abyssal conditions. These fishes agreed in the character of their connective tissue, which was so extremely weak as to yield to, and to break under, the slightest pressure, so that the greatest difficulty is experienced in preserving their body in its continuity. Another singular circumstance was, that some of the specimens were picked up floating on the surface of the water, having met their death while engaged in swallowing or digesting another fish not much inferior, or even superior, in size to themselves. The first peculiarity was accounted for by the fact that, if these fishes really inhabited the great depths supposed, their removal from the enormous pressure under which they lived would be accompanied by such an expansion of the gases within their tissues as to rupture them, and to cause a separation of the parts which had been held together by the pressure. The second circumstance was explained thus: a raptatorial fish, organized to live at a depth of between five hundred and eight hundred fathoms, seizes another usually inhabiting a depth of between three hundred and five hundred fathoms. In its struggles to escape, the fish seized, nearly as large or strong as the attacking fish, carries the latter out of its depth into a higher stratum, where the diminished pressure causes such an expansion of gases as