Because they have hitherto been unable to establish their mode of generation. Lacepede, the French naturalist, asserts, in the most unqualified way, that they are viviparous; but, says Sir H. Davy, " we do not remember any facts brought forward on the subject." Blumenbach says - " According to the most correct observations, the eel is certainly viviparous;" for which he quotes Voight's Neues Magazine. Sir Eve-rard Home, by a course of patient investigation, has ascertained that the common and conger eels, as well as lampreys, are hermaphrodites.
Because 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 courses of fresh water, - as the waters from the land, at this season, become warmer than those from the sea.
Sir H. Davy, in his Salmonia, has some interesting observations on this curious subject: - " Thus, it 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 in 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 which weigh from 10 to 15, or even 20 lbs. 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 Bally-shannon, 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. - Mr. J. Couch, in the Linncean Transactions, says, the little eels,|accord-ing 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 small brooks and rivers. When the cold water from the autumnal flood 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. Dr. Plot, in his History of Staffordshire, says: "eels pass in the night across meadows, from one pond to another;" and Mr. Anderson, in the Philosophical Transactions, distinctly states, that small eels have risen up the flood-gates and posts of the water-works of Norwich ; and then made their way to the water above, though the boards were smooth-planed, and 5 or 6 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. 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 Leuwenhoeck."
Because, as very large eels, after having migrated, never return to the river again, they must, (for it cannot be supposed that they all die immediately in the sea) remain in salt water. The conger eel, it may be added, is found from a few ounces to 100 lb. in weight.
Because its form is so entirely equal as to require little balance either one way or the other; the use of the ventral fins being to balance the fish in the water.
Because the skin in this and the greater number of fishes, passes directly over the eye without forming any fold; and in the above case it does not adhere very closely to the eye; the skin only exhibiting at that place a round transparent spot.
Because of the uniform opacity of the skin in passing over the eye.
Because of the coagulation of the albumen in which the skin is enveloped.