I called in at my neighbour Major Warren Pauncefote’s this afternoon, and found he was just engaged in draining the fishpond by his garden. He is going to deepen it and to puddle the bottom, so as to make it fit for his boys to swim in. Meanwhile he has transferred all the larger carp to a stone trough in the back yard, where I saw at once there was not half enough water for them. I’m sure he didn’t mean to be cruel, for he is the humanest soldier that ever spitted Fuzzy-wuzzy in the Soudan on his sword; but all the same, to any one who understands the prime needs of fish-life, the condition of those poor carp was most sad to look at. As every one knows, they breathe the oxygen dissolved in water; and as hundreds of them were confined in this Black Hole of Calcutta, the amount at their disposal was, of course, quite inadequate. Some of the poor things were dead or dying, turning on their lustreless sides in the pathetically helpless way of suffocating fish; the others kept coming up every now and then to the surface, gasping for breath, and gulping down great open-jawed mouthfuls of air, to relieve their misery. No doubt the oxygen they thus swallow enters the body-cavity, and slightly assists them in a?rating the blood, though much of it, also, may pass in the ordinary way through the gills, which are the regular and normal respiratory organs. It is always interesting to me, however, to watch fish when they come up thus to drink air at the surface, as goldfish often do when thoughtlessly confined in too small a glass basin; for in this instinctive act, as modern biologists now generally allow, we have the first faint beginnings of the evolution of lungs and the habit of air-breathing. Nay, more, terrestrial life itself, as a whole, depends in the last resort upon just such first feeble gaspings and gulpings. For lungs are nothing more, anatomically speaking, than developed swim-bladders, connected by a definite passage with the external air, and provided with a more or less perfect muscular mechanism for inhaling and expelling it.

In most fish, and in all the rudest types, the swim-bladder is merely a float or balloon, which can be filled with air, and compressed or expanded, so as to make the animal rise or sink at pleasure. But many fish exist in tropical ponds and shallow swamps to whom what has happened artificially to the carp in my friend’s ornamental water happens naturally every dry season; the marshy sheets in which they live evaporate altogether, and they are therefore compelled to lie dormant in the mud without food or drink for many weeks at a time. Under these peculiar circumstances, their air-bladder has gradually developed into a true lung; and, what is odder still, we possess in various countries distinct specimens at all the intermediate stages from air-bladder to lung in proportion as the ponds which they haunt become dry for longer or shorter periods. The bow-fin of the United States, for example, lives in turbid waters which do not quite dry up, but it has acquired the habit of rising to the surface every now and then, and gulping in large mouthfuls of air, which enter its swi............