The Myxine, Glutinous Hag, or Borer, bears a near resemblance to the lamprey, but stands upon a much inferior degree of organisation, having no eyes--(the sole example of blindness among fishes), and a still softer skeleton, so that, when boiled, it almost entirely dissolves into mucus. In the lamprey and myxine, the branchial cells, which admit water, are lined by the delicate membrane through which the blood is aërated. In the former, however, the external apertures of the branchial cells are placed on the side of the neck; while in the myxine, which feeds on the internal parts of its prey, and buries its head and part of its body in the flesh, the openings of the respiratory organs are removed sufficiently far back to admit of the respiration going on while the animal's head is so inserted. Thus, even in this lowest and meanest of all vertebrate animals, we find a remarkable adaptation of its construction to its wants, and the proof that it has been as well taken care of by its Creator as the highest organised creatures of its class. [Illustration: Porcupine-Fish--(Diodon hystrix.)] [Illustration: Globe-Fish.] [Illustration: Short Sun-Fish.--(Orthagoriscus Mola.)] [Illustration: Trunk-Fish.--(Ostracion triqueter.)] [Illustration: File-Fish.--(Balistes erythropterus.)] One of the most remarkable orders of fishes is that of the Plectognaths, which are distinguished by having the superior maxillary bones and the intermaxillaries soldered together so as to render the upper jaw immovable, or incapable of projection. Among the Plectognaths, we find among others the prickly Globe-fishes and sea-porcupines; the curiously-shaped Sun-fishes, all head and no body; the Ostracions or Trunk-fishes, clothed like the armadillos in a defensive coat of mail, leaving only the tail, fins, mouth, and a small portion of the gill-opening, capable of motion; and the gorgeous Balistæ or File-fishes, which owe their family-name to the peculiar structure of their first dorsal fin. The first and strongest spine of this organ is studded up the front with numerous small projections, which, under the microscope, look like so many points of enamel or pearl arising from the surface of the bone and giving it the appearance of a file. The second smaller spine has in the fore part of its base a projection which, when the spines are elevated, locks into a corresponding notch in the posterior base of the first spine, and fixes it like the trigger of a gun-lock; from which the fish is called in Italy _pesce balestra_, or the cross-bow fish. The strong spine cannot be forced down till the small one has been first depressed and the catch disengaged.