and filial piety ought alike to secure our attention for the African mud-fish.  It lives its amphibious life among the rice-fields on the Nile, the Zambesi, and the Gambia, and is so greatly given to a terrestrial existence that its swim-bladder has become porous and cellular, so as to be modified into a pair of true and serviceable lungs.  In fact, the lungs themselves in all the higher animals are merely the swim-bladders of fish, slightly altered so as to perform a new but closely allied office.  The mud-fish is common enough in all the larger English aquariums, owing to a convenient habit in which it indulges, and which permits it to be readily conveyed to all parts of the globe on the same principle as the vans for furniture.  When the dry season comes on and the rice-fields are reduced to banks of baking mud, the mud-fish retire to the bottom of their pools, where they form for themselves a sort of cocoon of hardened clay, lined with mucus, and with a hole at each end to admit the air; and in this snug retreat they remain torpid till the return of wet weather.  As the fish usually reach a length of three or four feet, the cocoons are of course by no means easy to transport entire.  Nevertheless the natives manage to dig them up whole, fish and all; and if the capsules are not broken, the unconscious inmates can be sent across by steamer to Europe with perfect safety.  Their astonishment when they finally wake up after their long slumber, and find themselves inspecting the British public, as introduced to them by Mr. Farini, through a sheet of plate-glass, must be profound and interesting.

In England itself, on the other hand, we have at least one kind of fish which exemplifies the opposite or migratory solution of the dry pond problem, and that is our familiar friend the common eel.  The ways of eels are indeed mysterious, for nobody has ever yet succeeded in discovering where, when, or how they manage to spawn; nobody has ever yet seen an eel’s egg, or caught a female eel in the spawning condition, or even observed a really adult male or female specimen of perfect development.  All the eels ever found in fresh water are immature and undeveloped creatures.  But eels do certainly spawn somewhere or other in the deep sea, and every year, in the course of the summer, flocks of young ones, known as elvers, ascend the rivers in enormous quantities, like a vast army under numberless leaders.  At each tributary or affluent, be it river, brook, stream, or ditch, a proportionate detachment of the main body is given off to explore the various branches, while the central force wriggles its way up the chief channel, regardless of obstacles, with undiminished vigour.  When the young elvers come to a weir, a wall, a floodgate, or a lasher, they simply squirm their way up the perpendicular barrier with indescribable wrigglings, as if they were wholly unacquainted, physically as well as mentally, with Newton’s magnificent discovery of gravitation.  Nothing stops them; they go wherever water is to be found; and though millions perish hopelessly in the attempt, millions more survive in the end to attain their goal in the upper reaches.  They even seem to scent ponds or lakes mysteriously, at a distance, and will strike boldly straight across country, to sheets of water wholly cut off from communication with the river which forms their chief highway.