If it were possible for human beings to penetrate to the abyssal depths of the ocean, finny torch-bearers would be found from the very surface to nearly four miles beneath it; existing in many cases under conditions almost incomprehensible when the enormous attendant pressure is considered. While it is extremely difficult to tell the exact depth from which a fish is taken by the dredge, sufficient data has been secured for naturalists to assume, though there is great difference of opinion, that, to a greater or less degree, the forms of certain depths have certain peculiarities. These are often seen in the organs of vision, which have been modified in many ways by the lack of light. Thus the eyes of forms that are found living five or six hundred feet below the surface are often extremely large, as in _Beryx_ (Plate XVIII., Fig. 1), as if to absorb the faintest beams of sunlight that may penetrate this distance. As we descend to twelve hundred feet, the eyes seem to grow larger; and beyond this, large and small eyed fishes are found indiscriminately. The former evidently use these organs; while those with small eyes are provided with remarkable organs of touch,--long feelers which can be thrown forward, or moved to a more or less extent, and used as the blind man uses his cane. An interesting, indeed remarkable, example of this is seen in the fish _Bathypterus longipes_, Günther found at a depth varying from one-half to three-quarters of a mile from the surface in the Atlantic. The eyes are extremely small, apparently useless; but the blind man’s cane is here, as the pectoral fins are modified to serve as feelers, two rays almost as long as the entire fish extending from the back of the head. As the fish swims freely, the fins are trailed behind; but, does it approach a prospective victim, the articulation of these wonderful feelers enables them to be thrown forward as a cane in advance of the fish. They are divided at the tip, and form a delicate sense-organ with which to explore the depths of this abyssal world. Upon the ventral fins, there are two similar rays, that serve a like purpose. Many fishes having remarkable feelers have quite recently been discovered, and among them _Eustomias obscurus_ (Plate XIX.), a fish found at a depth of twenty-seven hundred meters, which has a long tentacle dependent from the lower jaw.