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Page:Popular Science Monthly Volume 21.djvu/400

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5. "With the Sunlight, Vegetable Life ceases in the Depths of the Sea.—All deep-sea fishes are therefore carnivorous; the most voracious feeding frequently on their own offspring, and the toothless kinds being nourished by the animalcules which live on the bottom, or which, 'like a constant rain,' settle down from the upper strata toward the bottom of the sea.

6. "The Perfect Quiet of the Water at Great Depths.—The agitation of the water, caused by the disturbances of the air, does not extend beyond the depth of a few fathoms; below this surface stratum there is no other movement except the quiet flow of ocean currents, and near the bottom of the deep sea the water is probably in a state of almost entire quiescence."

Now, the effect of these conditions on some part or parts of their structure is such that all deep-sea fishes are easily recognizable, without positive evidence of their having been caught at a great depth and in many of them the most striking characteristics relate to the pressure of the water they inhabit. Their bones and muscles are comparatively feebly developed; the former "have a fibrous, fissured, and cavernous texture, are light, with scarcely any calcareous matter, so that the point of a needle will readily penetrate them without breaking." They are loosely attached to each other—the vertebræ especially; and, unless carefully handled, the body will almost certainly fall to pieces. But that this is not the animal's normal condition we may be well assured. It is due simply to the absence of the pressure which keeps the whole organization compact; for, as has just been stated, most of these fishes are rapacious, and to indulge their enormous voracity they must execute rapid and powerful movements, to effect which their muscles must be as firm and their vertebræ as tautly braced as in their surface-swimming relatives. Marvelous as this is, it is far from being all that is marvelous in the structure of these dwellers in the profundities. Besides modifications of their eyes, such as are found in several other groups of animals, many of them are furnished with "more or less numerous, round, shining, mother-of-pearl colored bodies imbedded in the skin," of which Dr. Günther says: "These so-called phosphorescent or luminous organs are either large bodies of an oval or irregularly elliptical shape placed on the head, in the vicinity of the eye, or smaller round globular bodies arranged symmetrically in series along the sides of the body and tail, especially near the abdominal profile, less frequently along the back. . . . The organs of one kind consist of an anterior, biconvex, lens-like body, which is transparent during life, simple or composed of rods; and of a posterior chamber, which is filled with a transparent fluid, and coated with a dark membrane composed of hexagonal cells or of rods arranged as in a retina. . . . In the other kind the organ shows throughout a simple glandular structure, but apparently without an efferent duct. Branches of the spinal nerves run to each organ, and are distributed