HAL.—Pardon me—I have not concluded. There are eels in the Lake of Neufchatel, which communicates by a stream with the Rhine; but there are none in the Leman Lake, because the Rhone makes a subterraneous fall below Geneva; and though small eels can pass by moss or mount rocks, they cannot penetrate limestone, or move against a rapid descending current of water, passing, as it were, through a pipe. Again: no eels mount the Danube from the Black Sea; and there are none found in the great extent of lakes, swamps, and rivers communicating with the Danube,—though some of these lakes and morasses are wonderfully fitted for them, and though they are found abundantly in the same countries, in lakes and rivers connected with the ocean and the Mediterranean. Yet, when brought into confined water in the Danube, they fatten and thrive there. As to the instinct, which leads young eels to seek fresh water, it is difficult to reason;—probably they prefer warmth, and, swimming at the surface in the early summer, find the lighter water warmer, and likewise containing more insects, and so pursue the courses of fresh water, as the waters from the land, at this season, become warmer than those of the sea. Mr. J. Couch (Lin. Trans. T. xiv. p. 70) says, that the little eels, according to his observation, are produced within reach of the tide, and climb round falls to reach fresh water from the sea. I have sometimes seen them, in spring, swimming in immense shoals in the Atlantic, in Mount Bay, making their way to the mouths of small brooks and rivers. When the cold water from the autumnal floods begins to swell the rivers, this fish tries to return to the sea; but numbers of the smaller ones hide themselves during the winter in the mud, and many of them form, as it were, masses together. Various authors have recorded the migration of eels in a singular way,—such as Dr. Plot, who, in his History of Staffordshire, says, that they pass in the night, across meadows, from one pond to another: and Mr. Arderon (in Trans. Royal Soc.) gives a distinct account of small eels rising up the flood-gates and posts of the water-works of the city of Norwich; and they made their way to the water above, though the boards were smooth planed, and five or six feet perpendicular. He says, when they first rose out of the water upon the dry board, they rested a little—which seemed to be till their slime was thrown out, and sufficiently glutinous—and then they rose up the perpendicular ascent with the same facility as if they had been moving on a plane surface.—(Trans. Abr. vol. ix. p. 311.) There can, I think, be no doubt, that they are assisted by their small scales, which, placed like those of serpents, must facilitate their progressive motion: these scales have been microscopically observed by Lewenhoeck.—(Phil. Trans. vol. iv.) Eels migrate from the salt water of different sizes, but I believe never when they are above a foot long—and