The Plectognaths are mostly denizens of the warmer seas, but the pig-faced trigger-fish of the Mediterranean (_Balistes capriscus_) has been caught three times in the British waters since 1827, and the short sun-fish or molebut, though occurring but occasionally, may be said to have been taken from John o' Groat's to the Land's End. It grows to an immense size, often attaining the diameter of four feet, sometimes even double that size, and occasionally weighing from 300 to 500 pounds. When observed in our seas, the sun-fishes have generally appeared as though they were dead or dying, floating lazily along on one side and making little or no attempt to escape. It is to be presumed that in more congenial waters they evince a greater degree of liveliness. The order of the Lophobranchii is in many respects too curious and interesting to be passed over in silence. Here the gills, instead of being as usual ranged like the teeth of a comb, are clustered into small filamentous tufts placed by pairs along the branchial arches; the face projects into a long tubular snout, having the mouth either at its extremity, as in the Hippocampus and in the Pipe-fishes, or at its base, as in the Pegasus of the Indian seas; and the body is covered with shields or small plates, which often give it an angular form, and encase it as it were in jointed armour. But the most interesting feature of their economy is the pouches in which the males of the most characteristic genera carry the eggs until they are hatched. In the hippocampi this provision for the safety of the future generation, which strongly reminds one of the kangaroo or the opossum, forms a perfect sack, opening at its commencement only; in the pipe-fishes it is closed along its whole length by two soft flaps folding over each other. Another peculiarity of these interesting little fishes is the independent motion of their eyes, the one glancing hither and thither while its fellow remains motionless, or looks in different directions. This phenomenon of _double_ vision, which was long supposed to be peculiar to the chameleon, is, however, not confined to this singular reptile or to the hippocampi and pipe-fishes, but has been found by Mr. Gosse to exist likewise in the Little Weever (_Trachinus vipera_), in the Suckers (_Lepidogastri_), a small family remarkable for the power they possess of attaching themselves to stones or rocks by means of an adhesive disk on the under surface of their bodies, and in several other fishes. When imprisoned in an aquarium, few subjects of the deep display more intelligence or afford more entertainment than the little _Hippocampus brevirostris_, or Sea-Horse. [Illustration: Sea-Horse.]