This species (_Pelagia cyanella_) is a characteristic oceanic discophorous medusa, common along the Atlantic coast of the United States; it is semi-transparent and lustrous pink.] This has recently (1897) been summed up very clearly by Prof. Arthur P. Crouch, in an article in “The Nineteenth Century,” from which it will be worth while to quote a paragraph or two: The conditions under which they [that is, deep-sea animals] have to live in the abysmal areas seem very unfavorable to animal existence. 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 thirty times more powerful than the steam pressure of a locomotive when drawing a train.[7] As late as 1880 a leading zoölogist 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 prey, 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 unusual accident of falling upwards, and no doubt meet with a violent death soon after leaving their accustomed level, and long before their bodies reach the surface....