iv.) Eels migrate from the salt-water of different sizes, but I believe never when they are above a foot long—and the great mass of them are only from two and a half to four inches. They feed, grow, and fatten in fresh water. In small rivers they are seldom very large; but in large deep lakes they become as thick as a man’s arm, or even leg; and all those of a considerable size attempt to run to the sea in October or November, probably when they experience the cold of the first autumnal rains. Those that are not of the largest size, as I said before, pass the winter in the deepest parts of the mud of rivers and lakes, and do not seem to eat much, and remain, I believe, almost torpid. Their increase is not certainly known in any given time, but must depend upon the quantity of their food; but it is probable they do not become of the largest size from the smallest in one or even two seasons: but this, as well as many other particulars, can only be ascertained by new observations and experiments. Block states, that they grow slowly, and mentions, that some had been kept in the same pond for fifteen years. As very large eels, after having migrated, never return to the river again, they must (for it cannot be supposed they all die immediately in the sea) remain in salt water; and there is great probability, that they are then confounded with the conger, which is found of different colours and sizes, from the smallest to the largest, from a few ounces to one hundred pounds in weight. The colour of the conger is generally paler than that of the eel; but, in the Atlantic, it is said, that pale congers are found on one side of the Wolf Rock, and dark ones on the other. The conger has breathing tubes, which are said not to be found in the other eel; but to determine this, would require a more minute examination than has yet been made. Both the conger and common eel have fringes along the air-bladder, which are probably the ovaria; and Sir E. Home thinks them hermaphrodite, and that the seminal vessels are close to the kidneys. I hope this great comparative anatomist will be able to confirm his views by new dissections, and some chemical researches upon the nature of the fringes and the supposed melt. If viviparous, and the fringes contain the ova, one mother must produce tens of thousands, the ova being remarkably small; but it appears more probable, that they are oviparous, and that they deposit their ova in parts of the sea near deep basins, which remain warm in winter. This might be ascertained by experiment, particularly on the coast of the Mediterranean. I cannot find that they haunt the Arctic Ocean, which is probably of too low a temperature to suit their feelings or habits; and the Caspian and Black Sea are probably without them, from their not being found in the Volga or Danube; these being shallow seas, are perhaps too cold for them in winter. From the time (April) that small eels begin to migrate, it is