HAL.—I will tell you all I know, which is not much. This is certain, that there are two migrations of eels,—one up and one down rivers, one _from_ and the other _to_ the sea; the first in spring and summer, the second in autumn or early winter. The first, of very small eels, which are sometimes not more than two or two and a half inches long; the second, of large eels, which sometimes are three or four feet long, and weigh from 10 to 15, or even 20lbs. There is great reason to believe, that all eels found in fresh water are the results of the first migration: they appear in millions in April and May, and sometimes continue to rise as late even as July and the beginning of August. I remember this was the case in Ireland, in 1823. It had been a cold backward summer, and when I was at Ballyshannon, about the end of July, the mouth of the river, which had been in flood all this month, under the fall, was blackened by millions of little eels, about as long as the finger, which were constantly urging their way up the moist rocks by the side of the fall. Thousands died, but their bodies remaining moist, served as the ladder for others to make their way; and I saw some ascending even perpendicular stones, making their road through wet moss, or adhering to some eels, that had died in the attempt. Such is the energy of these little animals, that they continue to find their way, in immense numbers, to Loch Erne. The same thing happens at the fall of the Bann, and Loch Neagh is thus peopled by them: even the mighty Fall of Shaffhausen does not prevent them from making their way to the Lake of Constance, where I have seen many very large eels. PHYS.—You have shown, that some eels come from the sea, but I do not think the facts prove, that all eels are derived from that source.